Research

17 pages, 4430 KiB

Open AccessFeature PaperArticle

Exploring the Effect of Sn Addition to Supported Au Nanoparticles on Reducible/Non-Reducible Metal Oxides Supports for Alkane Oxidation

by Marta Stucchi, Alessandro Vomeri, Sándor Stichleutner, Károly Lázár, Emanuela Pitzalis, Claudio Evangelisti and Laura Prati

Chemistry 2023, 5(3), 1560-1576; https://doi.org/10.3390/chemistry5030107 - 21 Jul 2023

Viewed by 1194

Abstract

Acetone-stabilized Au- and Sn-solvated metal atoms (SMAs) were used as to obtain Au- and AuSn-supported catalysts by simple impregnation on a reducible (TiO₂) and a non-reducible (Al₂O₃) metal-oxide. Their catalytic behaviour was investigated for cyclohexane oxidation to [...] Read more.

Acetone-stabilized Au- and Sn-solvated metal atoms (SMAs) were used as to obtain Au- and AuSn-supported catalysts by simple impregnation on a reducible (TiO₂) and a non-reducible (Al₂O₃) metal-oxide. Their catalytic behaviour was investigated for cyclohexane oxidation to cyclohexanol and cyclohexanone (KA oil), and their morphological and physical properties were studied by TEM, STEM-EDS and ¹¹⁹Sn-Mössbauer spectroscopy. The catalytic results firstly demonstrated that the bare supports played a role on the reaction mechanism, slowing down the formation of the oxidation products and directing the radical formation. Hereinafter, the comparison between the monometallic Au-supported catalysts and the corresponding bimetallic Au-Sn catalysts allowed for the understanding of the potential role of Sn. ¹¹⁹Sn-Mössbauer characterization analyses showed the presence of SnO_2, which was recognized to favour the electrons’ exchange to form radicals, interacting with oxygen. Such interaction, in particular, could be favoured by the co-presence of Au. Moreover, the same metal composition on the catalyst surface resulted in a different catalytic behaviour depending on the support. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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17 pages, 6208 KiB

Open AccessArticle

Catalytic Performances of Co/TiO₂ Catalysts in the Oxidative Dehydrogenation of Ethane to Ethylene: Effect of CoTiO₃ and Co₂TiO₄ Phase Formation

by Hanane Mahir, Younes Brik, Abdallah Benzaouak, Eleonora La Greca, Luca Consentino, Mohamed Kacimi, Adnane El Hamidi and Leonarda Francesca Liotta

Chemistry 2023, 5(3), 1518-1534; https://doi.org/10.3390/chemistry5030104 - 06 Jul 2023

Cited by 1 | Viewed by 1250

Abstract

Co/TiO₂ catalysts with different cobalt loadings (3.8, 7.5 and 15 wt%) were prepared by impregnation method of Co(NO₃)₂ 6H₂O over titania. Samples containing Co(NO₃)₂·6H₂O and TiO₂ in stoichiometric proportions in [...] Read more.

Co/TiO₂ catalysts with different cobalt loadings (3.8, 7.5 and 15 wt%) were prepared by impregnation method of Co(NO₃)₂ 6H₂O over titania. Samples containing Co(NO₃)₂·6H₂O and TiO₂ in stoichiometric proportions in order to obtain CoTiO₃ and Co₂ TiO₄ phases were also synthesized. The effect of the calcination treatment at two different temperatures, 550 and 1150 °C, was investigated. Characterizations by several techniques, such as XRD, UV–vis–NIR, DRS, Raman and XPS, were carried out. XRD showed the coexistence of three phases: CoTiO₃; Co₂TiO₄ and Co₃O₄ after calcination at 550 °C, while calcination at high temperature (1150 °C) led to single-phase systems (CoTiO₃ or Co₂TiO₄). Diffuse reflection and XPS spectroscopy showed that divalent cobalt occupies octahedral sites in the ilmenite phase, and both tetrahedral and octahedral sites in the spinel phase. The catalytic performances of the prepared catalysts were evaluated in the oxidative dehydrogenation reaction (ODH) of ethane to ethylene, as a function of the Co content for Co/TiO₂ catalysts and as a function of the calcination temperatures for the CoTiO₃ and Co₂TiO₄ phases. Co(7.5)/TiO₂ was the most active, although the conversion of ethane decreased in the first 150 min of the reaction, reaching values comparable to those of Co₂TiO₄ and CoTiO₃; however, Co(7.5)/TiO₂ was confirmed as having the best selectivity to ethylene in comparison with the bulk phases, CoTiO₃ and Co₂TiO₄. The influence of the reaction mixture composition, specifically the presence of water, at different percentages, was investigated. There is a decrease in the overall ethane conversion and an increase in the ethylene selectivity when the percentage of water increases. This behavior can likely be attributed to an increase in the surface concentration of hydroxyl species (OH), resulting in heightened surface acidity. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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12 pages, 1890 KiB

Open AccessArticle

Au Single Metal Atom for Carbon Dioxide Reduction Reaction

by Anna Vidal-López, Sergio Posada-Pérez, Miquel Solà and Albert Poater

Chemistry 2023, 5(2), 1395-1406; https://doi.org/10.3390/chemistry5020095 - 05 Jun 2023

Cited by 2 | Viewed by 1782

Abstract

CO₂ is the gas that contributes the most to the greenhouse effect and, therefore, to global warming. One of the greatest challenges facing humanity is the reduction of the concentration of CO₂ in the air. Here, we analyze the possible use [...] Read more.

CO₂ is the gas that contributes the most to the greenhouse effect and, therefore, to global warming. One of the greatest challenges facing humanity is the reduction of the concentration of CO₂ in the air. Here, we analyze the possible use of Au₁@g-C₃N₄ electrocatalyst to transform CO₂ into added-value products. We use density functional theory (DFT) to determine the reaction Gibbs energies for eight electron–proton transfer reaction paths of the electrochemical carbon dioxide reduction reaction (CO2RR) using a single Au atom supported on 2D carbon nitride support. Our simulations classify the Au₁@g-C₃N₄ electrocatalysts as “beyond CO” since their formation is energetically favored, although their strong binding with a Au single atom does not allow the desorption process. DFT calculations revealed that the lowest energy pathway is CO₂ (g) → COOH* → CO* → HCO* → HCOH* → CH₂OH* → CH₂* → CH₃* → CH₄ (g), where the first hydrogenation of CO to HCO is predicted as the rate-limiting step of the reaction with slightly lower potential than predicted for Cu electrodes, the most effective catalysts for CO2RR. Methane is predicted to be the main reaction product after eight proton–electron transfers (CO₂ + 8 H⁺ + 8e⁻ → CH₄ + 2H₂O). The generation of formaldehyde is discarded due to the large formation energy of the adsorbed moiety and the production of methanol is slightly less favorable than methane formation. Our computational study helps to identify suitable electrocatalysts for CO2RR by reducing the amount of metal and using stable and low-cost supports. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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12 pages, 1777 KiB

Open AccessArticle

Probing Low-Temperature OCM Performance over a Dual-Domain Catalyst Bed

by Baoting Huang, Jin Wang, Dina Shpasser and Oz M. Gazit

Chemistry 2023, 5(2), 1101-1112; https://doi.org/10.3390/chemistry5020075 - 08 May 2023

Cited by 1 | Viewed by 1474

Abstract

The Mn-Na₂WO₄/SiO₂ catalyst is regarded as the most promising catalyst for the oxidative coupling of methane (OCM). Despite its remarkable performance, the Mn-Na₂WO₄/SiO₂ catalyst requires a high reaction temperature (>750 °C) to show [...] Read more.

The Mn-Na₂WO₄/SiO₂ catalyst is regarded as the most promising catalyst for the oxidative coupling of methane (OCM). Despite its remarkable performance, the Mn-Na₂WO₄/SiO₂ catalyst requires a high reaction temperature (>750 °C) to show significant activity, a temperature regime that simultaneously causes quick deactivation. In the current work, we show that the benefits of this catalyst can be leveraged even at lower reaction temperatures by a using a stacked catalyst bed, which includes also a small amount of 5% La₂O₃/MgO on-top- of the Mn-Na₂WO₄/SiO₂ catalyst. The simple stacking of the two catalysts provides >7-fold higher activity and ~1.4-fold higher C₂ yield at 705 °C compared to Mn-Na₂WO₄/SiO₂ and La₂O₃/MgO, respectively. We specifically show that the enhanced OCM performance is associated with synergistic interactions between the two catalyst domains and study their origin. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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13 pages, 7345 KiB

Open AccessArticle

Production of Alkyl Levulinates from Carbohydrate-Derived Chemical Intermediates Using Phosphotungstic Acid Supported on Humin-Derived Activated Carbon (PTA/HAC) as a Recyclable Heterogeneous Acid Catalyst

by Nivedha Vinod and Saikat Dutta

Chemistry 2023, 5(2), 800-812; https://doi.org/10.3390/chemistry5020057 - 06 Apr 2023

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Abstract

This work reports a straightforward and high-yielding synthesis of alkyl levulinates (ALs), a class of promising biofuel, renewable solvent, and chemical feedstock of renewable origin. ALs were prepared by the acid-catalyzed esterification of levulinic acid (LA) and by the alcoholysis of carbohydrate-derived chemical [...] Read more.

This work reports a straightforward and high-yielding synthesis of alkyl levulinates (ALs), a class of promising biofuel, renewable solvent, and chemical feedstock of renewable origin. ALs were prepared by the acid-catalyzed esterification of levulinic acid (LA) and by the alcoholysis of carbohydrate-derived chemical platforms, such as furfuryl alcohol (FAL) and α-angelica lactone (α-AGL). Phosphotungstic acid (PTA) was chosen as the solid acid catalyst for the transformation, which was heterogenized on humin-derived activated carbon (HAC) for superior recyclability. Using HAC as catalyst support expands the scope of valorizing humin, a complex furanic resin produced inevitably as a side product (often considered waste) during the acid-catalyzed hydrolysis/dehydration of sugars and polymeric carbohydrates. Under optimized conditions (150 °C, 7 h, 25 wt.% of 20%PTA/HAC-600 catalyst), ethyl levulinate (EL) was obtained in an 85% isolated yield starting from FAL. Using the general synthetic protocol, EL was isolated in 88% and 84% yields from LA and α-AGL, respectively. The 20%PTA/HAC-600 catalyst was successfully recovered from the reaction mixture and recycled for five cycles. A marginal loss in the yield of ALs was observed in consecutive catalytic cycles due to partial leaching of PTA from the HAC support. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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9 pages, 2987 KiB

Open AccessCommunication

Defective PrO_x for Efficient Electrochemical NO₂⁻-to-NH₃ in a Wide Potential Range

by Shunhan Jia, Xingxing Tan, Limin Wu, Jiaqi Feng, Libing Zhang, Liang Xu, Ruhan Wang, Xiaofu Sun and Buxing Han

Chemistry 2023, 5(2), 753-761; https://doi.org/10.3390/chemistry5020053 - 29 Mar 2023

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Abstract

Electrocatalytic reduction of nitrite (NO₂⁻) is a sustainable and carbon-neutral approach to producing green ammonia (NH₃). We herein report the first work on building defects on PrO_x for electrochemical NO₂⁻ reduction to NH₃, [...] Read more.

Electrocatalytic reduction of nitrite (NO₂⁻) is a sustainable and carbon-neutral approach to producing green ammonia (NH₃). We herein report the first work on building defects on PrO_x for electrochemical NO₂⁻ reduction to NH₃, and demonstrate a high NH₃ yield of 2870 μg h⁻¹ cm⁻² at the optimal potential of –0.7 V with a faradaic efficiency (FE) of 97.6% and excellent FEs of >94% at a wide given potential range (−0.5 to −0.8 V). The kinetic isotope effect (KIE) study suggested that the reaction involved promoted hydrogenation. Theoretical calculations clarified that there was an accelerated rate-determining step of NO₂⁻ reduction on PrO_x. The results also indicated that PrO_x could be durable for long-term electrosynthesis and cycling tests. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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23 pages, 5972 KiB

Open AccessArticle

Synthesis and Structure of COE-11, a New Borosilicate Zeolite with a Two-Dimensional Pore System of 12-Ring Channels

by Bernd Marler, Hermann Gies, Trees De Baerdemaeker, Ulrich Müller, Andrei-Nicolae Parvulescu, Weiping Zhang, Toshiyuki Yokoi, Feng-Shou Xiao, Xiangju Meng, Dirk De Vos and Ute Kolb

Chemistry 2023, 5(2), 730-752; https://doi.org/10.3390/chemistry5020052 - 28 Mar 2023

Cited by 1 | Viewed by 1609

Abstract

The new zeolite, COE-11, was synthesized at 155 °C to 168 °C by hydrothermal synthesis from a reaction mixture of SiO₂/tetraethylammonium hydroxide/H₃BO₃/NaOH/H₂O. Because tetraethylammonium is an unspecific structure directing agent, COE-11 crystallizes in all cases [...] Read more.

The new zeolite, COE-11, was synthesized at 155 °C to 168 °C by hydrothermal synthesis from a reaction mixture of SiO₂/tetraethylammonium hydroxide/H₃BO₃/NaOH/H₂O. Because tetraethylammonium is an unspecific structure directing agent, COE-11 crystallizes in all cases together with at least one impurity phase from a selection of phases: zeolite types *BEA, CHA, FER, MFI, MOR, MTW; the layered silicates magadiite and kenyaite; and searlsite and silica polymorph quartz. The crystal structure was solved from 3D electron diffraction (3D ED) data. Subsequent structure refinements of X-ray powder diffraction (PXRD) data and single crystal electron diffraction data converged to residual values of R_F = 0.039, chi² = 3.6 (PXRD) and R_F = 21.81% (3D ED) confirming the structure model. COE-11 crystallizes in space group C2 with unit cell dimensions of a₀ = 17.3494(11) Å, b₀ = 17.3409(11) Å, c₀ = 14.2789(4) Å and β = 113.762(2) °. The structure of COE-11 is characterized by a microporous borosilicate framework with intersecting, highly elliptical 12-ring channels running parallel (110) and (1–10) and forming a two-dimensional pore system. The Rietveld refinement provided a hint that boron partly substitutes silicon on three specific T sites of the framework. The idealized chemical composition of as-made COE-11 is [(CH₃CH₂)₄N]₄[B₄Si₆₂O₁₃₂] per unit cell. Physico-chemical characterization using solid-state NMR spectroscopy, SEM, TG-DTA, and ATR-FTIR spectroscopy confirmed that COE-11 is a microporous borosilicate zeolite. COE-11 is structurally closely related to zeolite beta polymorph B but differs concerning the dimensionality of the pore system, which is 2D instead of 3D. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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10 pages, 2354 KiB

Open AccessArticle

UiO-66 MOF-Derived Ru@ZrO₂ Catalysts for Photo-Thermal CO₂ Hydrogenation

by Fernando Almazán, Marta Lafuente, Amaya Echarte, Mikel Imizcoz, Ismael Pellejero and Luis M. Gandía

Chemistry 2023, 5(2), 720-729; https://doi.org/10.3390/chemistry5020051 - 25 Mar 2023

Cited by 3 | Viewed by 2016

Abstract

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived [...] Read more.

The use of metal–organic frameworks (MOFs) as templates or precursors in the manufacture of heterogeneous catalysts is highly attractive due to the transfer of MOFs’ inherent porosity and homogeneous metallic distribution to the derived structure. Herein, we report on the preparation of MOF-derived Ru@ZrO₂ catalysts by controlled thermal treatment of zirconium-based MOF UiO-66 with ruthenium moieties. Ru³⁺ (3 or 10 mol%) precursor was added to UiO-66 synthesis and, subsequently, the as-synthesized hybrid structure was calcined in flowing air at different temperatures (400–600 °C) to obtain ZrO₂-derived oxides doped with highly dispersed Ru metallic clusters. The materials were tested for the catalytic photo-thermal conversion of CO₂ to CH₄. Methanation experiments were conducted in a continuous flow (feed flow rate of 5 sccm and 1:4 CO₂ to H₂ molar ratio) reactor at temperatures from 80 to 300 °C. Ru_0.10@ZrO₂ catalyst calcined at 600 °C was able to hydrogenate CO₂ to CH₄ with production rates up to 65 mmol_CH4·g_cat.^–1·h^–1, CH₄ yield of 80% and nearly 100% selectivity at 300 °C. The effect of the illumination was investigated with this catalyst using a high-power visible LED. A CO₂ conversion enhancement from 18% to 38% was measured when 24 sun of visible LED radiation was applied, mainly due to the increase in the temperature as a result of the efficient absorption of the radiation received. MOF-derived Ru@ZrO₂ catalysts have resulted to be noticeably active materials for the photo-thermal hydrogenation of CO₂ for the purpose of the production of carbon-neutral methane. A remarkable effect of the ZrO₂ crystalline phase on the CH₄ selectivity has been found, with monoclinic zirconia being much more selective to CH₄ than its cubic allotrope. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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14 pages, 3086 KiB

Open AccessArticle

Comparison of Cu-CHA-Zeolites in the Hybrid NSR-SCR Catalytic System for NO_x Abatement in Mobile Sources

by Sergio Molina-Ramírez, Marina Cortés-Reyes, Concepción Herrera, María Ángeles Larrubia and Luis José Alemany

Chemistry 2023, 5(1), 602-615; https://doi.org/10.3390/chemistry5010043 - 10 Mar 2023

Viewed by 1583

Abstract

DeNO_x activity in a NSR–SCR hybrid system of two copper-containing chabazite-type zeolitic catalysts was addressed. A Pt-Ba-K/Al₂O₃ model catalyst was used as the NSR (NO_x storage and reduction) catalyst. For the SCR (selective catalytic reduction) system, two Cu-CHA [...] Read more.

DeNO_x activity in a NSR–SCR hybrid system of two copper-containing chabazite-type zeolitic catalysts was addressed. A Pt-Ba-K/Al₂O₃ model catalyst was used as the NSR (NO_x storage and reduction) catalyst. For the SCR (selective catalytic reduction) system, two Cu-CHA zeolites were synthesized employing a single hydrothermal synthesis method assisted with ultrasound and incorporating Cu in a 2 wt.%, 2Cu-SAPO-34 and 2Cu-SSZ-13. The prepared catalysts were characterized, and the crystallinity, surface area, pore size, HR-TEM and EDX mapping, coordination of Cu ions and acidity were compared. The NH₃ storage capacity of the SCR catalysts was 1890 and 837

{μ mol NH}_{3} {\cdot g}_{cat}^{- 1}

for 2Cu-SAPO-34 and 2Cu-SSZ-13, respectively. DeNO_x activity was evaluated for the single NSR system and the double-bed NSR–SCR by employing alternating lean (3%O₂) and rich (1%H₂) cycles, maintaining a concentration of 600 ppm NO, 1.5% H₂O and 0.3% CO₂ between 200 and 350 °C. The addition of the SCR system downstream of the NSR catalyst significantly improved NO_x conversion mainly at low temperature, maintaining the selectivity to N₂ above 80% and reaching values above 90% at 250 °C when the 2Cu-SSZ-13 catalyst was located. The total reduction in the production of NH₃ and ~2% of N₂O was observed when comparing the NSR–SCR configuration with the single NSR catalyst. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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13 pages, 2525 KiB

Open AccessArticle

Selective Styrene Oxidation Catalyzed by Phosphate Modified Mesoporous Titanium Silicate

by Rupak Chatterjee, Avik Chowdhury, Sudip Bhattacharjee, Rajaram Bal and Asim Bhaumik

Chemistry 2023, 5(1), 589-601; https://doi.org/10.3390/chemistry5010042 - 10 Mar 2023

Cited by 2 | Viewed by 1662

Abstract

Selective oxidation of organics over an efficient heterogeneous catalyst under mild liquid phase conditions is a very demanding chemical reaction. Herein, we first report the modification of the surface of mesoporous silica MCM-41 material by phosphate for the efficient incorporation of Ti(IV) in [...] Read more.

Selective oxidation of organics over an efficient heterogeneous catalyst under mild liquid phase conditions is a very demanding chemical reaction. Herein, we first report the modification of the surface of mesoporous silica MCM-41 material by phosphate for the efficient incorporation of Ti(IV) in the silica framework to obtain highly ordered 2D hexagonal mesoporous material STP-1. STP-1 has been synthesized by using tetraethyl orthosilicate, triethyl phosphate, and titanium isopropoxide as Si, P, and Ti precursors, respectively, in the presence of cationic surfactant cetyltrimethylammonium bromide (CTAB) under hydrothermal conditions. The observed specific surface area and pore volume of STP-1 were 878 m²g⁻¹ and 0.75 ccg⁻¹, respectively. Mesoporous STP-1 has been thoroughly characterized by XRD, FT-IR, Raman spectroscopy, SEM, and TEM analyses. Titanium incorporation (Ti/Si = 0.006) was confirmed from the EDX analysis. This mesoporous STP-1 was used as a heterogeneous catalyst for the selective oxidation of styrene into benzaldehye in the presence of dilute aqueous H₂O₂ as an oxidizing agent. Various reaction parameters such as the reaction time, the reaction temperature, and the styrene/H₂O₂ molar ratio were systematically studied in this article. Under optimized reaction conditions, the selectivity of benzaldehyde could reach up to 93.8% from styrene over STP-1. Further, the importance of both titanium and phosphate in the synthesis of STP-1 for selective styrene oxidation was examined by comparing the catalytic result with only a phosphate-modified mesoporous silica material, and it suggests that both titanium and phosphate synergistically play an important role in the high selectivity of benzaldehyde in the liquid phase oxidation of styrene. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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18 pages, 5995 KiB

Open AccessArticle

Ni-Mg/Al Mixed Oxides Prepared from Layered Double Hydroxides as Catalysts for the Conversion of Furfural to Tetrahydrofurfuryl Alcohol

by Abdulaziz Aldureid, Daniel Montané, Jordi Llorca and Francesc Medina

Chemistry 2023, 5(1), 571-588; https://doi.org/10.3390/chemistry5010041 - 09 Mar 2023

Cited by 1 | Viewed by 1489

Abstract

Ni-Mg/Al mixed oxide catalysts (Ni₂A_l, Ni₂Mg₁Al, and Ni₁Mg₁Al) obtained from layered double hydroxides (LDHs) were tested on the one-pot production of tetrahydrofurfuryl alcohol (TFA) from furfural (FF). Upon calcination at 400 [...] Read more.

Ni-Mg/Al mixed oxide catalysts (Ni₂A_l, Ni₂Mg₁Al, and Ni₁Mg₁Al) obtained from layered double hydroxides (LDHs) were tested on the one-pot production of tetrahydrofurfuryl alcohol (TFA) from furfural (FF). Upon calcination at 400 °C and reduction at 500 °C, the LDHs gave catalysts containing small nickel crystallites (<4 nm) dispersed on mixtures of metal oxides and spinel structures. Complete conversion of FF (>99.5%) was achieved on all the catalysts after 4 h at 190 °C and 5.0 MPa of H₂ using 5 wt.% FF in ethanol and a furfural-to-catalyst mass ratio of 7.44 g/g. TFA evolved from the sequential hydrogenation of FF to furfuryl alcohol (FA) to TFA. Competing reaction routes involved decarbonylation of FF to furan (FUR) followed by hydrogenation to tetrahydrofuran (THF) or hydrogenolysis to n-butane (BU) and the hydrogenation of the carbonyl group in FF to form 2-methyl furan (mFUR) and its hydrogenation to 2-methyltetrahydrofuran (mTHF). A third competing route consisted of the nucleophilic addition of FF with ethanol and with FA to form acetals (such as 2-(diethoxymethyl)furan, FDA), which were later converted to difurfuryl ether (DFE) and tetrahydrofurfuryl ethyl ether (TFEE) as final products. Hydrogen pressure favored the production of TFA and diminished the formation of acetals, while temperature reduced the capacity of the catalyst to hydrogenate the furan ring, thus reducing TFA and increasing FA and FUR. An 80% yield to TFA was achieved with the Ni₂Mg₁Al catalysts after 6 h at 190 °C and 50 bar H₂, but a variety of coproducts were present at low concentration. Testing of the catalysts in gas-phase hydrogenation conditions at atmospheric pressure revealed a poorer performance, with FA as the main product. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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15 pages, 3864 KiB

Open AccessArticle

Conversion of Ethanol to Butadiene over Binary MgO-SiO₂ Mixed Oxides Prepared by the Ammonia Evaporation Method

by Ismail Bin Samsudin, Stephan Jaenicke and Gaik-Khuan Chuah

Chemistry 2023, 5(1), 544-558; https://doi.org/10.3390/chemistry5010039 - 07 Mar 2023

Viewed by 1593

Abstract

The ammonia evaporation method, originally applied for the preparation of highly dispersed silica-supported copper catalysts, was used to synthesize magnesia-silica for the one-step conversion of ethanol to 1,3-butadiene. The MgO-SiO₂ catalysts obtained by this method contained a high fraction of magnesium silicate [...] Read more.

The ammonia evaporation method, originally applied for the preparation of highly dispersed silica-supported copper catalysts, was used to synthesize magnesia-silica for the one-step conversion of ethanol to 1,3-butadiene. The MgO-SiO₂ catalysts obtained by this method contained a high fraction of magnesium silicate hydrates, which are associated with enhanced butadiene selectivity. These catalysts were benchmarked against those prepared by a conventional wet-kneading method. A Mg/Si molar ratio of 4 was optimal, forming butadiene with 37% yield, which is far superior to the 15% yield obtained with MgO-SiO₂ formed by wet-kneading. At 475 °C and a WHSV of 3.2 h⁻¹, a productivity of 0.612 g_BD g_cat⁻¹ h⁻¹ was measured without the catalyst suffering from deactivation, even after 52 h TOS. The catalysts were characterized by spectroscopic and thermal techniques to elucidate their physicochemical properties and explain the differences in the catalytic performance. The presence of magnesium silicate hydrates gave a balance of surface acidity and basicity, which greatly improved butadiene formation. The open morphology of MgO-SiO₂ with vertically arranged platelets and the presence of large pores are proposed to contribute to the stability of the catalyst. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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18 pages, 4009 KiB

Open AccessArticle

Gold Clusters Immobilized by Post-Synthesis Methods on Thiol-Containing SBA-15 Mesoporous Materials for the Aerobic Oxidation of Cyclohexene: Influence of Light and Hydroperoxide

by Rafael Delgado, Carlos Márquez-Álvarez, Álvaro Mayoral, Ramón de la Serna, Javier Agúndez and Joaquín Pérez-Pariente

Chemistry 2023, 5(1), 526-543; https://doi.org/10.3390/chemistry5010038 - 07 Mar 2023

Viewed by 1431

Abstract

Gold nanospecies produced by a historically inspired two-liquid phase system were immobilized on plate-like mesoporous silica, SBA-15, functionalized with mercaptopropyl groups by a post-synthesis method, and the resulting materials were tested in the oxidation of cyclohexene with molecular oxygen at atmospheric pressure. The [...] Read more.

Gold nanospecies produced by a historically inspired two-liquid phase system were immobilized on plate-like mesoporous silica, SBA-15, functionalized with mercaptopropyl groups by a post-synthesis method, and the resulting materials were tested in the oxidation of cyclohexene with molecular oxygen at atmospheric pressure. The main purpose of this approach was to compare the physicochemical properties and catalytic performance of these materials with those of previously reported related materials functionalized by in situ methods during synthesis. In addition, catalytic tests under ambient lighting and darkness and also in the presence and absence of the initiator tert-butyl hydroperoxide (TBHP) were carried out. The samples were characterized by chemical analysis, N₂ adsorption/desorption, TGA, SEM, HRTEM, UV-vis spectroscopy and XPS. Gold nanoclusters and isolated gold atoms but no AuNPs were found in the catalysts (0.31–2.69 wt.% of gold). The XPS shows that nearly 60% of the -SH groups (1.33 wt.% of S) were oxidized to sulphonic groups upon gold immobilization. The AuNCs and isolated gold atoms evolved in the the reaction medium to form AuNPs. The activity of the samples was lower than that of the catalysts supported on related S-bearing SBA-15 functionalized in situ, which was attributed to their different Au/S ratios, which in turn regulated the evolutionary process of the gold species during the reaction. The catalysts turned out to be inactive in darkness, which evidences that the cyclohexene oxidation carried out at ambient illumination is actually photocatalyzed by the AuNPs formed in situ during the reaction. The TBHP initiator is required to obtain the activity in order to counteract the inhibitors of cyclohexene auto-oxidation present in the commercial reagent. On the other hand, no major differences in the selectivity among the different catalysts and reactions were observed, with 2-cyclohexen-1-one and 2-cyclohexen-1-ol resulting from the allylic oxidation as main products (selectivity of (one + ol) ~80% at a conversion ≥ 35%; one/ol~2). Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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15 pages, 4126 KiB

Open AccessArticle

Kinetic and Spectroscopic Studies of Methyl Ester Promoted Methanol Dehydration to Dimethyl Ether on ZSM-5 Zeolite

by Zhiqiang Yang, Benjamin J. Dennis-Smither, Zhuoran Xu, Zhenchao Zhao, Meiling Guo, Neil Sainty, Guangjin Hou, Xuebin Liu and Glenn J. Sunley

Chemistry 2023, 5(1), 511-525; https://doi.org/10.3390/chemistry5010037 - 06 Mar 2023

Viewed by 1625

Abstract

Methyl carboxylate esters have been shown to be potent promoters of low-temperature methanol dehydration to dimethyl ether (DME) using various zeolite catalysts. In the present work, catalytic kinetic studies, in-situ Fourier-transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (NMR) techniques were [...] Read more.

Methyl carboxylate esters have been shown to be potent promoters of low-temperature methanol dehydration to dimethyl ether (DME) using various zeolite catalysts. In the present work, catalytic kinetic studies, in-situ Fourier-transform infrared spectroscopy (FT-IR) and solid-state nuclear magnetic resonance spectroscopy (NMR) techniques were used to elucidate the promotional mechanism of methyl carboxylate esters on methanol dehydration to DME, using the medium pore zeolite H-ZSM-5 (MFI) as the catalyst. Kinetic studies were performed using the very potent methyl n-hexanoate promoter. The DME yield was dependent on both the methanol and methyl n-hexanoate partial pressures across the temperature ranges used in this study (110 to 130 °C). This is consistent with the promoted reaction being a bimolecular reaction between methanol and ester species adsorbed at the catalyst active sites, via an S_N2 type reaction, as previously postulated. The in-situ FT-IR studies reveal that the Brønsted acid (BA) sites on H-ZSM-5 were very rapidly titrated by ester carbonyl group adsorption and bonded more strongly with esters than with methanol. Upon methanol addition, an even lower DME formation temperature (30 °C) was observed with methyl n-hexanoate pretreated H-ZSM-5 samples in the in-situ NMR studies, further confirming the strong promotion of this methyl ester on methanol dehydration to DME. The adsorption and reactivity of different methyl esters on H-ZSM-5 indicates that while methyl formate more easily dissociates into a surface methoxy species, [Si(OMe)Al], and carboxylic acid, it is a less potent promoter than alkyl-chain-containing methyl esters in methanol dehydration to DME, which in turn did not show this dissociative behavior in the low-temperature NMR studies. This indicates that methyl alkyl carboxylates do not need to be dissociated to a surface methoxy species to promote the methanol dehydration reaction and that a bimolecular associative mechanism plays an important role in promoting DME formation. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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13 pages, 997 KiB

Open AccessArticle

Conversion of Sugar Di-Ketals to Bio-Hydrocarbons through Catalytic Cracking over Beta Catalysts in Fixed and Fluidized Catalytic Beds

by Cristiane Cardoso, Yiu L. Lam, Marlon B. B. de Almeida and Marcelo Maciel Pereira

Chemistry 2023, 5(1), 479-491; https://doi.org/10.3390/chemistry5010035 - 04 Mar 2023

Cited by 1 | Viewed by 1360

Abstract

Second-generation biomass (BM) can be produced in amounts that meet worldwide fuel demands. However, BM favors parallel and undesirable reactions in its transformation chain. We circumvent this problem by first modifying BM by ketalization, giving a user-friendly liquid we named BP (bio-petroleum). This [...] Read more.

Second-generation biomass (BM) can be produced in amounts that meet worldwide fuel demands. However, BM favors parallel and undesirable reactions in its transformation chain. We circumvent this problem by first modifying BM by ketalization, giving a user-friendly liquid we named BP (bio-petroleum). This study converted a representative compound of BP, DX (1,2:3,5-di-O-isopropylidene-α-D-xylofuranose), mixed with n-hexane by beta zeolites and catalysts containing beta zeolite. Beta zeolite showed low coke and high liquid product yields in converting this mixture (having 30 wt. % DX) into hydrocarbons in a fixed-bed reactor at 500 °C with a space velocity of 16 h⁻¹ (0.3 catalyst/feed). Its performance was further improved by steam treatment (lowering the coke yield by lowering the acid site density) or incorporation into a catalyst (improving DX participation due to the active sites in the matrix). Further, by changing the conversion process from a fixed bed to a fluidized cracking unit, a much larger amount of the deactivated catalyst could be used (catalyst/feed = 3), remarkably reducing oxygenates and fully converting DX. Additionally, the green hydrocarbon efficiency (olefin, aromatics, furans, and cyclo-alkanes) of DX was approximately 77%. Hence, beta catalysts were shown to have a great potential to provide green fuels for future bio-refineries. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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16 pages, 4394 KiB

Open AccessArticle

Crotonaldehyde Adsorption on Cu-Pt Surface Alloys: A Quantum Mechanics Study

by Ricardo Ruvalcaba, Jonathan Guerrero-Sanchez, Noboru Takeuchi and Francisco Zaera

Chemistry 2023, 5(1), 463-478; https://doi.org/10.3390/chemistry5010034 - 03 Mar 2023

Cited by 2 | Viewed by 1679

Abstract

The adsorption of crotonaldehyde on Cu-Pt alloy surfaces was characterized by density functional theory (DFT). Two surfaces were considered: Cu₂Pt/Cu(111) and Cu₃Pt/Cu(111). It was determined that the presence of Pt on the surface, even when isolated as single atoms [...] Read more.

The adsorption of crotonaldehyde on Cu-Pt alloy surfaces was characterized by density functional theory (DFT). Two surfaces were considered: Cu₂Pt/Cu(111) and Cu₃Pt/Cu(111). It was determined that the presence of Pt on the surface, even when isolated as single atoms fully surrounded by Cu, provides additional stability for the adsorbates, increasing the magnitude of the adsorption energy by as much as 40 kJ/mol. The preferred bonding on both surfaces is via multiple coordination, with the most stable configuration being a cis arrangement with di-σ bonding of the C=O bond across a Cu–Cu bridge and an additional π bonding to a Pt atom. The fact that Pt significantly affects the adsorption of unsaturated aldehydes such as crotonaldehyde explains why the kinetics of their hydrogenation using single-atom alloy (SAA) catalysts vary with alloy composition, as we previously reported, and brings into question the simple model in which the role of Pt is only to promote the dissociation of H₂. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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16 pages, 4109 KiB

Open AccessFeature PaperArticle

How Topological Differences between Two Oxide Surfaces Determine Selectivity—The Case of the Dehydra-Decyclization of Tetrahydrofuran

by Sai Praneet Batchu, Stavros Caratzoulas and Dionisios G. Vlachos

Chemistry 2023, 5(1), 422-437; https://doi.org/10.3390/chemistry5010031 - 01 Mar 2023

Cited by 1 | Viewed by 1378

Abstract

Production of butadiene from biomass-based tetrahydrofuran (THF) is explored as an alternative to the existing petroleum-based processes. Metal oxide catalysts have been shown to exhibit varying product selectivities when reacted with THF. Among those oxides, ZrO₂ showed the highest selectivity for butadiene. [...] Read more.

Production of butadiene from biomass-based tetrahydrofuran (THF) is explored as an alternative to the existing petroleum-based processes. Metal oxide catalysts have been shown to exhibit varying product selectivities when reacted with THF. Among those oxides, ZrO₂ showed the highest selectivity for butadiene. In contrast, Al₂O₃ showed the highest selectivity for the competing retro-Prins products, C₃H₆ and HCHO. The reasons behind the varying selectivity across oxides are unclear. In this work, we employ periodic density functional theory and mean-field microkinetic modeling to investigate the mechanism of the reaction of THF to butadiene and retro-Prins products on t-ZrO₂ (101) (dry and hydrous) and on γ-Al₂O₃ (110). Our simulations reproduce the experimental selectivity trends. High selectivity for butadiene is promoted by the presence of neighboring Lewis acid metal sites that facilitate E1cB hydroxyl elimination from a 3-butenoxide intermediate; on hydrous Al₂O₃; where such neighboring Lewis acid centers are not available, the butenoxide undergoes E2 elimination and retro-Prins products ensue. The THF ring opening is rate-determining on ZrO₂, whereas the γ-proton elimination that yields the 3-butenoxide intermediate is rate controlling on hydroxylated Al₂O₃. We conclude that the local topology around the active site greatly influences the mechanism and selectivity. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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16 pages, 3813 KiB

Open AccessArticle

Vapor-Phase Oxidant-Free Dehydrogenation of 2,3- and 1,4-Butanediol over Cu/SiO₂ Catalyst Prepared by Crown-Ether-Assisted Impregnation

by Enggah Kurniawan, Shuya Hosaka, Masayuki Kobata, Yasuhiro Yamada and Satoshi Sato

Chemistry 2023, 5(1), 406-421; https://doi.org/10.3390/chemistry5010030 - 28 Feb 2023

Cited by 9 | Viewed by 2203 | Correction

Abstract

A silica-supported copper (Cu/SiO₂) catalyst containing highly dispersed Cu nanoparticles was prepared via a crown-ether-assisted impregnation method. A 12-crown-4-ether-assisted Cu/SiO₂ catalyst outperformed several Cu/SiO₂ catalysts prepared with various organic additives in the dehydrogenation of 2,3- and 1,4-butanediol. It was [...] Read more.

A silica-supported copper (Cu/SiO₂) catalyst containing highly dispersed Cu nanoparticles was prepared via a crown-ether-assisted impregnation method. A 12-crown-4-ether-assisted Cu/SiO₂ catalyst outperformed several Cu/SiO₂ catalysts prepared with various organic additives in the dehydrogenation of 2,3- and 1,4-butanediol. It was found that the catalytic activity, i.e., the formation rate of acetoin from 2,3-butanediol and that of γ-butyrolactone from 1,4-butanediol, was proportional to the copper surface area. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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13 pages, 1755 KiB

Open AccessArticle

Gold(III) Chloride-Mediated Transformation of Furfural to the trans-N,N-4,5-Diaminocyclopent-2-enones in the Presence of Anilines

by Marina A. Tzani and Ioannis N. Lykakis

Chemistry 2023, 5(1), 393-405; https://doi.org/10.3390/chemistry5010029 - 27 Feb 2023

Viewed by 1663

Abstract

We investigated the efficient approach of a series of trans-N,N-4,5-substituted-diaminocyclopent-2-enones (trans-DACPs) from furfural and anilines mediated by Gold(III) chloride (HAuCl₄). The present protocol required a low amount of the catalysts, 1.5 mol%, open air [...] Read more.

We investigated the efficient approach of a series of trans-N,N-4,5-substituted-diaminocyclopent-2-enones (trans-DACPs) from furfural and anilines mediated by Gold(III) chloride (HAuCl₄). The present protocol required a low amount of the catalysts, 1.5 mol%, open air conditions, the absence of any additives, and short reaction times. The desired trans-DACPs were isolated in good to high yields. The protocol was also applied to secondary amines, leading to the corresponding 4,5-diamino-cyclopent-2-enones in good yields. To the best of our knowledge, this is the first gold-mediated paradigm as an efficient catalyst for the formation of the cyclopentenones core-bearing C-N bonds under mild reaction conditions. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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12 pages, 2128 KiB

Open AccessArticle

Solvent-Assisted Adsorption of Cellulose on a Carbon Catalyst as a Pretreatment Method for Hydrolysis to Glucose

by Abhijit Shrotri, Kiko Eguchi, Lina Mahardiani, Hirokazu Kobayashi, Masakuni Yamashita, Hiroshi Yagita and Atsushi Fukuoka

Chemistry 2023, 5(1), 381-392; https://doi.org/10.3390/chemistry5010028 - 24 Feb 2023

Viewed by 1804

Abstract

Cellulose hydrolysis to glucose using a heterogeneous catalyst is a necessary step in producing bio-based chemicals and polymers. The requirement for energy-intensive pretreatments, such as ball milling, to increase the reactivity of cellulose is one of the major issues in this area. Here, [...] Read more.

Cellulose hydrolysis to glucose using a heterogeneous catalyst is a necessary step in producing bio-based chemicals and polymers. The requirement for energy-intensive pretreatments, such as ball milling, to increase the reactivity of cellulose is one of the major issues in this area. Here, we show that by using solvent-assisted adsorption as a pretreatment step, cellulose can be adsorbed on the surface of a carbon catalyst. For adsorption pretreatment, phosphoric acid (H₃PO₄) performed better than other solvents such as sulfuric acid (H₂SO₄), tetrabutylammonium fluoride/dimethyl sulfoxide (TBAF/DMSO) and 1-butyl-3-methylimidazolium chloride ([BMMI]Cl). Hydrolysis after the adsorption of cellulose and the removal of H₃PO₄ produced a 73% yield of glucose. Partial hydrolysis of cellulose in H₃PO₄ before adsorption increased the final glucose yield. The glucose yield was proportional to the number of weakly acidic functional groups on the carbon catalyst, indicating the reaction was heterogeneously catalyzed. In a preliminary lab-scale life-cycle analysis (LCA), greenhouse gas (GHG) emissions per kg of glucose produced through the hydrolysis of cellulose were calculated. The H₃PO₄-assisted adsorption notably reduces GHG emissions compared to the previously reported ball milling pretreatment. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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17 pages, 3017 KiB

Open AccessArticle

Steering the Metal Precursor Location in Pd/Zeotype Catalysts and Its Implications for Catalysis

by Luc C. J. Smulders, Johan H. van de Minkelis, Johannes D. Meeldijk, Min Tang, Anna Liutkova, Kang Cheng, S. Tegan Roberts, Glenn J. Sunley, Emiel J. M. Hensen, Petra E. de Jongh and Krijn P. de Jong

Chemistry 2023, 5(1), 348-364; https://doi.org/10.3390/chemistry5010026 - 23 Feb 2023

Cited by 2 | Viewed by 2206

Abstract

Bifunctional catalysts containing a dehydrogenation–hydrogenation function and an acidic function are widely applied for the hydroconversion of hydrocarbon feedstocks obtained from both fossil and renewable resources. It is well known that the distance between the two functionalities is important for the performance of [...] Read more.

Bifunctional catalysts containing a dehydrogenation–hydrogenation function and an acidic function are widely applied for the hydroconversion of hydrocarbon feedstocks obtained from both fossil and renewable resources. It is well known that the distance between the two functionalities is important for the performance of the catalyst. In this study, we show that the heat treatment of the catalyst precursor can be used to steer the location of the Pd precursor with respect to the acid sites in SAPO-11 and ZSM-22 zeotype materials when ions are exchanged with Pd(NH₃)₄(NO₃)₂. Two sets of catalysts were prepared based on composite materials of alumina with either SAPO-11 or ZSM-22. Pd was placed on/in the zeotype, followed by a calcination-reduction (CR) or direct reduction (DR) treatment. Furthermore, catalysts with Pd on the alumina binder were prepared. CR results in having more Pd nanoparticles inside the zeotype crystals, whereas DR yields more particles on the outer surface of the zeotype crystals as is confirmed using HAADF-STEM and XPS measurements. The catalytic performance in both n-heptane and n-hexadecane hydroconversion of the catalysts shows that having the Pd nanoparticles on the alumina binder is most beneficial for maximizing the isomer yields. Pd-on-zeotype catalysts prepared using the DR approach show intermediate performances, outperforming their Pd-in-zeotype counterparts that were prepared with the CR approach. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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14 pages, 2644 KiB

Open AccessArticle

Environmental Applications of Zeolites: Hydrophobic Sn-BEA as a Selective Gas Sensor for Exhaust Fumes

by Martin Jendrlin, Julien Grand, Louwanda Lakiss, Florent Dubray, Philippe Bazin, Jaafar El Fallah, Svetlana Mintova and Vladimir Zholobenko

Chemistry 2023, 5(1), 334-347; https://doi.org/10.3390/chemistry5010025 - 21 Feb 2023

Cited by 3 | Viewed by 1995

Abstract

Environmental monitoring of pollutants, such as NO_x and CO_x, which can be facilitated by a range of gas sensors, is of considerable fundamental and practical importance. This work has been focused on the synthesis and evaluation of zeolite β with [...] Read more.

Environmental monitoring of pollutants, such as NO_x and CO_x, which can be facilitated by a range of gas sensors, is of considerable fundamental and practical importance. This work has been focused on the synthesis and evaluation of zeolite β with tin (Sn-BEA) and dealuminated β (DeAl-BEA) zeolites. The zeolite samples have been extensively investigated by IR, UV-VIS and NMR spectroscopy, XRD, TGA, and N₂ adsorption-desorption. The prepared Sn-BEA sample is characterised by the submicron particle size, an almost defect-free structure, and high hydrophobicity. Sensors containing selective microporous layers based on Sn-BEA and DeAl-BEA zeolites have been prepared and extensively tested. Both the Sn-BEA and DeAl-BEA zeolites have been deposited in thin films and evaluated as gas sensors for CO, CO₂, NO, and NO₂ in the presence of water vapour at room temperature. The Sn-BEA zeolite-based sensor showed high selectivity towards NO₂, while the DeAl-BEA is selective towards CO₂ and NO₂. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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20 pages, 4183 KiB

Open AccessArticle

Environmental Applications of Zeolites: Preparation and Screening of Cu-Modified Zeolites as Potential CO Sensors

by Martin Jendrlin, Julien Grand, Louwanda Lakiss, Philippe Bazin, Svetlana Mintova and Vladimir Zholobenko

Chemistry 2023, 5(1), 314-333; https://doi.org/10.3390/chemistry5010024 - 20 Feb 2023

Cited by 1 | Viewed by 1616

Abstract

This work is focused on the application of Cu-containing zeolites as potential environmental sensors for monitoring carbon monoxide. A number of commercial zeolites with different structural properties (NaX, NaY, MOR, FER, BEA and ZSM-5) were modified using CuSO₄, Cu(NO₃) [...] Read more.

This work is focused on the application of Cu-containing zeolites as potential environmental sensors for monitoring carbon monoxide. A number of commercial zeolites with different structural properties (NaX, NaY, MOR, FER, BEA and ZSM-5) were modified using CuSO₄, Cu(NO₃)₂ and Cu(OAc)₂ solutions as copper sources to prepare Cu⁺-containing zeolites, since Cu⁺ forms stable complexes with CO at room temperature that can be monitored by infrared spectroscopy. Zeolite impregnation with Cu(NO₃)₂ resulted in the highest total Cu-loadings, while the Cu(OAc)₂-treated samples had the highest Cu⁺/Cu_total ratio. Cu(NO₃)₂-impregnated MOR, which displayed the highest concentration of Cu⁺, was subjected to a number of tests to evaluate its performance as a potential CO sensor. The working temperature and concentration ranges of the sensor were determined to be from 20 to 300 °C and from 10 to 10,000 ppm, respectively. The stepwise CO desorption experiments indicated that the sensor can be regenerated at 400 °C if required. Additional analyses under realistic flow conditions demonstrated that for hydrophilic zeolites, the co-adsorption of water can compromise the sensor’s performance. Therefore, a hydrophobic Sn-BEA was utilised as a parent material for the preparation of an impregnated Cu-Sn-BEA zeolite, which exhibited superior resistance to interfering water while maintaining its sensing properties. Overall, the prepared Cu-modified zeolites showed promising potential as environmental CO sensors, displaying high sensitivity and selectivity under representative testing conditions. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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20 pages, 5604 KiB

Open AccessArticle

Revisiting the Impact of Tungsten on the Catalytic Properties of Ammonia-SCR V₂O₅-WO₃/TiO₂ Catalysts: Geometric vs. Electronic Effects

by Hermann Wilfried Siaka, Christophe Dujardin, Alain Moissette and Pascal Granger

Chemistry 2023, 5(1), 294-313; https://doi.org/10.3390/chemistry5010023 - 20 Feb 2023

Viewed by 1389

Abstract

The SCR performance of V₂O₅-WO₃/TiO₂ SCR-catalysts characterized by different surface W density (2.1W/nm² and 9.5W/nm²) and different surface V density varying in the range 1–8V/nm² has been investigated in order to clarify [...] Read more.

The SCR performance of V₂O₅-WO₃/TiO₂ SCR-catalysts characterized by different surface W density (2.1W/nm² and 9.5W/nm²) and different surface V density varying in the range 1–8V/nm² has been investigated in order to clarify existing controversies on the preferential involvement of electronic and geometric effects in the catalytic properties. It was found that tungsten has a weak effect on the VO_x cluster size distribution through contraction of dilution effect. In contrast, the optimal interaction between W and V, when both reach their highest composition, appears to be a relevant parameter that can enhance their acidic properties and improve the catalytic efficiency in dry conditions. On the other hand, an absence of significant interaction leads to discontinuity due to deactivation. In the presence of steam, acidic properties are averaged, lowering the impact of the V to W ratio. Finally, the critical importance of acidic properties which outperform redox properties in the definition of active site is pointed out in the light of this study. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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18 pages, 4873 KiB

Open AccessArticle

Operando NAP-XPS Studies of a Ceria-Supported Pd Catalyst for CO Oxidation

by Xènia Garcia, Lluís Soler, Xavier Vendrell, Isabel Serrano, Facundo Herrera, Jordi Prat, Eduardo Solano, Massimo Tallarida, Jordi Llorca and Carlos Escudero

Chemistry 2023, 5(1), 1-18; https://doi.org/10.3390/chemistry5010001 - 20 Dec 2022

Cited by 3 | Viewed by 3425

Abstract

Supported Pd/CeO₂ catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to the unique oxygen storage capacity and redox properties of the ceria support, which highly influence the structural, chemical and electronic state of Pd species. [...] Read more.

Supported Pd/CeO₂ catalytic systems have been widely investigated in the low-temperature oxidation of CO (LTO CO) due to the unique oxygen storage capacity and redox properties of the ceria support, which highly influence the structural, chemical and electronic state of Pd species. Herein, operando near-ambient pressure XPS (NAP-XPS) technique has allowed the study of a conventional Pd/CeO₂ catalyst surface during the CO oxidation reaction under experimental conditions closer to the actual catalytic reaction, unfeasible with other surface science techniques that demand UHV conditions. SEM, HRTEM and XRD analyses of the powder catalyst, prepared by conventional incipient wetness impregnation, reveal uniformly CeO₂-loaded Pd NPs of less than 2 nm size, which generated an increase in oxygen vacancies with concomitant ceria reduction, as indicated by H₂-TPR and Raman measurements. Adsorbed peroxide (O₂²⁻) species on the catalyst surface could also be detected by Raman spectra. Operando NAP-XPS results obtained at the ALBA Synchrotron Light Source revealed two kinds of Pd species under reaction conditions, namely PdO_x and Pd^II ions in a Pd_xCe_1−xO_2−δ solution, the latter one appearing to be crucial for the CO oxidation. By means of a non-destructive depth profile analysis using variable synchrotron excitation energies, the location and the role of these palladium species in the CO oxidation reaction could be clarified: PdO_x was found to prevail on the upper surface layers of the metallic Pd supported NPs under CO, while under reaction mixture it was rapidly depleted from the surface, leaving a greater amount in the subsurface layers (7% vs. 12%, respectively). On the contrary, the Pd_xCe_1−xO_2−δ phase, which was created at the Pd–CeO₂ interface in contact with the gas environment, appeared to be predominant on the surface of the catalyst. Its presence was crucial for CO oxidation evolution, acting as a route through which active oxygen species could be transferred from ceria to Pd species for CO oxidation. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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15 pages, 1729 KiB

Open AccessArticle

Acid Site Density as a Kinetic Descriptor of Catalytic Reactions over Zeolites

by Dmitry Yu. Murzin

Chemistry 2022, 4(4), 1609-1623; https://doi.org/10.3390/chemistry4040105 - 23 Nov 2022

Cited by 4 | Viewed by 1406

Abstract

A mathematical framework for the quantitative description of site density dependence of catalytic data (activity and selectivity) was developed considering that changes in the electrostatic contribution to the Gibbs energy of an elementary reaction on the acid sites in zeolites depend on the [...] Read more.

A mathematical framework for the quantitative description of site density dependence of catalytic data (activity and selectivity) was developed considering that changes in the electrostatic contribution to the Gibbs energy of an elementary reaction on the acid sites in zeolites depend on the proximity of these sites. For the two-step sequence with the most abundant surface intermediate, an expression for turnover frequency explicitly containing the acid site density was derived. The treatment was extended to linear sequences of elementary reaction and analysis of the acid site density on selectivity in parallel and consecutive reactions, allowing to quantitatively relate the ratio between products for such reactions. Experimental data on Prins condensation of isopulegol with acetone and transformations of syngas over mesoporous H-ZSM-5 supported cobalt nanoparticles to a mixture of iso- and normal hydrocarbons were used as a show case. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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Review

Jump to: Research, Other

14 pages, 4192 KiB

Open AccessReview

Hydrogen Evolution upon Ammonia Borane Solvolysis: Comparison between the Hydrolysis and Methanolysis Reactions

by Naixin Kang, Changlong Wang and Didier Astruc

Chemistry 2023, 5(2), 886-899; https://doi.org/10.3390/chemistry5020060 - 13 Apr 2023

Cited by 4 | Viewed by 1837

Abstract

Hydrogen (H₂) production is a key challenge for green carbon-free sustainable energy. Among the H₂ evolution methods from H-rich materials, ammonia borane (AB) solvolysis stands as a privileged source under ambient and sub-ambient conditions given its stability, non-toxicity, and solubility [...] Read more.

Hydrogen (H₂) production is a key challenge for green carbon-free sustainable energy. Among the H₂ evolution methods from H-rich materials, ammonia borane (AB) solvolysis stands as a privileged source under ambient and sub-ambient conditions given its stability, non-toxicity, and solubility in protic solvents, provided suitable and optimized nanocatalysts are used. In this paper dedicated to Prof. Avelino Corma, we comparatively review AB hydrolysis and alcoholysis (mostly methanolysis) in terms of nanocatalyst performances and discuss the advantages and inconveniences of these two AB solvolysis methods including AB regeneration. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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29 pages, 15587 KiB

Open AccessReview

Cesium Heteropolyacid Salts: Synthesis, Characterization and Activity of the Solid and Versatile Heterogeneous Catalysts

by Marcio Jose da Silva, Alana Alves Rodrigues and Neide Paloma Gonçalves Lopes

Chemistry 2023, 5(1), 662-690; https://doi.org/10.3390/chemistry5010047 - 21 Mar 2023

Cited by 4 | Viewed by 2294

Abstract

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through [...] Read more.

Keggin-type heteropolyacid cesium salts have been regarded as potential candidates for heterogeneous catalytic reactions. This review describes the success of Keggin-type heteropolyacids cesium salts (Cs-HPA salts) as efficient catalysts in various synthesis processes. The Cs-HPA catalysts can be synthesized as solid salts through the metathesis of a solution containing precursor HPA and another solution containing soluble Cs salt, which will give Cs-HPA salt as a solid precipitate. Alternatively, they can be also obtained from the commercial precursor HPA. In this review, all the routes to prepare the different cesium salts (i.e., saturated, lacunar, metal-doped) were described. These salts can be used in acid-catalyzed reactions (i.e., esterification, etherification, acetalization, dehydration) or oxidative transformations (oxidative esterification, oxidation, epoxidation). All of these reactions were addressed herein. Aspects related to the synthesis and characterization of these catalyst salts were discussed. This review aims to discuss the most pertinent heterogeneous catalytic systems based on Keggin HPA Cs salts. The focus was to correlate the physicochemical properties of these salts with their catalytic activity. Ultimately, the most recent advances achieved in the applications of these Cs-HPA salts as catalysts in the synthesis of industrial interest compounds were discussed. Cesium heteropoly salts are an alternative to the traditional soluble mineral acids as well as to solid-supported catalysts. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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19 pages, 3864 KiB

Open AccessReview

Niche Applications of MXene Materials in Photothermal Catalysis

by Zhiyi Wu, Jiahui Shen, Chaoran Li, Chengcheng Zhang, Chunpeng Wu, Zimu Li, Xingda An and Le He

Chemistry 2023, 5(1), 492-510; https://doi.org/10.3390/chemistry5010036 - 06 Mar 2023

Cited by 7 | Viewed by 3041

Abstract

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing [...] Read more.

MXene materials have found emerging applications as catalysts for chemical reactions due to their intriguing physical and chemical applications. In particular, their broad light response and strong photothermal conversion capabilities are likely to render MXenes promising candidates for photothermal catalysis, which is drawing increasing attention in both academic research and industrial applications. MXenes are likely to satisfy all three criteria of a desirable photothermal catalyst: strong light absorption, effective heat management, and versatile surface reactivity. However, their specific functionalities are largely dependent on their structure and composition, which makes understandings of the structure–function relationship of crucial significance. In this review, we mainly focus on the recent progress of MXene–based photothermal catalysts, emphasizing the functionalities and potential applications of MXene materials in fields of photothermal catalysis, and provide insights on design principles of highly efficient MXene–based photothermal catalysts from the atomic scale. This review provides a relatively thorough understanding of MXene–based materials for photothermal catalysis, as well as an in–depth investigation of emerging high-prospect applications in photothermal catalysis. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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14 pages, 1728 KiB

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Advancements in Basic Zeolites for Biodiesel Production via Transesterification

by Guoju Yang and Jihong Yu

Chemistry 2023, 5(1), 438-451; https://doi.org/10.3390/chemistry5010032 - 03 Mar 2023

Cited by 4 | Viewed by 2145

Abstract

The excessive utilization of petroleum diesel has led to the depletion of fossil resources and severe environmental pollution. Biodiesel produced from renewable triglycerides (TGs) or waste lipids is a low-emission fuel substitute for diesel. Biodiesel is mainly produced by transesterification reactions over homogeneous [...] Read more.

The excessive utilization of petroleum diesel has led to the depletion of fossil resources and severe environmental pollution. Biodiesel produced from renewable triglycerides (TGs) or waste lipids is a low-emission fuel substitute for diesel. Biodiesel is mainly produced by transesterification reactions over homogeneous base catalysts with excellent activity and low cost. In comparison, solid base catalysts are more attractive due to their lower environmental impact and simpler production and purification processes. It remains a challenge to further improve the stability and activity of solid base catalysts. Because of the high surface area, superior stability, and tunable basicity, basic zeolites, especially two-dimensional zeolites, have emerged as promising solid basic catalysts for the transesterification of TGs. In this review, we present recent advancements in the synthesis, characterization, and catalytic performance of basic zeolites for the transesterification of TGs. Challenges and development prospects of basic zeolites for biodiesel production via transesterification are also pointed out. We expect that this review will inspire the more efficient and rational design of zeolites for sustainable fuel production. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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31 pages, 4552 KiB

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Development of Power-to-X Catalytic Processes for CO₂ Valorisation: From the Molecular Level to the Reactor Architecture

by Luis F. Bobadilla, Lola Azancot, Ligia A. Luque-Álvarez, Guillermo Torres-Sempere, Miriam González-Castaño, Laura Pastor-Pérez, Jie Yu, Tomás Ramírez-Reina, Svetlana Ivanova, Miguel A. Centeno and José A. Odriozola

Chemistry 2022, 4(4), 1250-1280; https://doi.org/10.3390/chemistry4040083 - 08 Oct 2022

Cited by 4 | Viewed by 2882

Abstract

Nowadays, global climate change is likely the most compelling problem mankind is facing. In this scenario, decarbonisation of the chemical industry is one of the global challenges that the scientific community needs to address in the immediate future. Catalysis and catalytic processes are [...] Read more.

Nowadays, global climate change is likely the most compelling problem mankind is facing. In this scenario, decarbonisation of the chemical industry is one of the global challenges that the scientific community needs to address in the immediate future. Catalysis and catalytic processes are called to play a decisive role in the transition to a more sustainable and low-carbon future. This critical review analyses the unique advantages of structured reactors (isothermicity, a wide range of residence times availability, complex geometries) with the multifunctional design of efficient catalysts to synthesise chemicals using CO₂ and renewable H₂ in a Power-to-X (PTX) strategy. Fine-chemistry synthetic methods and advanced in situ/operando techniques are essential to elucidate the changes of the catalysts during the studied reaction, thus gathering fundamental information about the active species and reaction mechanisms. Such information becomes crucial to refine the catalyst’s formulation and boost the reaction’s performance. On the other hand, reactors architecture allows flow pattern and temperature control, the management of strong thermal effects and the incorporation of specifically designed materials as catalytically active phases are expected to significantly contribute to the advance in the valorisation of CO₂ in the form of high added-value products. From a general perspective, this paper aims to update the state of the art in Carbon Capture and Utilisation (CCU) and PTX concepts with emphasis on processes involving the transformation of CO₂ into targeted fuels and platform chemicals, combining innovation from the point of view of both structured reactor design and multifunctional catalysts development. Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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3 pages, 610 KiB

Open AccessCorrection

Correction: Kurniawan et al. Vapor-Phase Oxidant-Free Dehydrogenation of 2,3- and 1,4-Butanediol over Cu/SiO₂ Catalyst Prepared by Crown-Ether-Assisted Impregnation. Chemistry 2023, 5, 406–421

by Enggah Kurniawan, Shuya Hosaka, Masayuki Kobata, Yasuhiro Yamada and Satoshi Sato

Chemistry 2023, 5(3), 1719-1721; https://doi.org/10.3390/chemistry5030117 - 07 Aug 2023

Cited by 1 | Viewed by 650

Abstract

In the published article “Vapor-Phase Oxidant-Free Dehydrogenation of 2,3- and 1,4-Butanediol over Cu/SiO₂ Catalyst Prepared by Crown-Ether-Assisted Impregnation“ [...] Full article

(This article belongs to the Special Issue Heterogeneous Catalysis — A Themed Issue in Honor of Prof. Dr. Avelino Corma)

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