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Open AccessEditorial

Emissions Control Catalysis

by

Ioannis V. Yentekakis

and

Philippe Vernoux

Catalysts 2019, 9(11), 912; https://doi.org/10.3390/catal9110912 - 31 Oct 2019

Cited by 2 | Viewed by 2315

Abstract

Important advances have been achieved over the past years in agriculture, industrial technology, energy, and health, which have contributed to human well-being [...] Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

Research

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Open AccessFeature PaperArticle

Catalytic Properties of Double Substituted Lanthanum Cobaltite Nanostructured Coatings Prepared by Reactive Magnetron Sputtering

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Mohammad Arab Pour Yazdi

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Catalysts 2019, 9(4), 381; https://doi.org/10.3390/catal9040381 - 23 Apr 2019

Cited by 5 | Viewed by 2574

Abstract

Lanthanum perovskites are promising candidates to replace platinum group metal (PGM), especially regarding catalytic oxidation reactions. We have prepared thin catalytic coatings of Sr and Ag doped lanthanum perovskite by using the cathodic co-sputtering magnetron method in reactive condition. Such development of catalytic [...] Read more.

Lanthanum perovskites are promising candidates to replace platinum group metal (PGM), especially regarding catalytic oxidation reactions. We have prepared thin catalytic coatings of Sr and Ag doped lanthanum perovskite by using the cathodic co-sputtering magnetron method in reactive condition. Such development of catalytic films may optimize the surface/bulk ratio to save raw materials, since a porous coating can combine a large exchange surface with the gas phase with an extremely low loading. The sputtering deposition process was optimized to generate crystallized and thin perovskites films on alumina substrates. We found that high Ag contents has a strong impact on the morphology of the coatings. High Ag loadings favor the growth of covering films with a porous wire-like morphology showing a good catalytic activity for CO oxidation. The most active composition displays similar catalytic performances than those of a Pt film. In addition, this porous coating is also efficient for CO and NO oxidation in a simulated Diesel exhaust gas mixture, demonstrating the promising catalytic properties of such nanostructured thin sputtered perovskite films. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

H₂O and/or SO₂ Tolerance of Cu-Mn/SAPO-34 Catalyst for NO Reduction with NH₃ at Low Temperature

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Catalysts 2019, 9(3), 289; https://doi.org/10.3390/catal9030289 - 21 Mar 2019

Cited by 18 | Viewed by 3333

Abstract

A series of molecular sieve catalysts (Cu–Mn/SAPO-34) with different loadings of Cu and Mn components were prepared by the impregnation method. The deNO_x activity of the catalyst was investigated during the selective catalytic reduction (SCR) of NO with NH₃ in the [...] Read more.

A series of molecular sieve catalysts (Cu–Mn/SAPO-34) with different loadings of Cu and Mn components were prepared by the impregnation method. The deNO_x activity of the catalyst was investigated during the selective catalytic reduction (SCR) of NO with NH₃ in the temperature range of 120 °C to 330 °C, including the effects of H₂O vapors and SO₂. In order to understand the poisoning mechanism by the injection of H₂O and/or SO₂ into the feeding gas, the characteristics of the fresh and spent catalyst were identified by means of Brunner−Emmet−Teller (BET), X-ray Diffraction (XRD), Scanning Electronic Microscopy (SEM) and Thermal Gravity- Differential Thermal Gravity (TG-DTG). The conversion of NO by the catalyst can achieve at 72% under the reaction temperature of 120 °C, while the value reached more than 90% under the temperature between 180 °C and 330 °C. The deNO_x activity test shows that the H₂O has a reversible negative effect on NO conversion, which is mainly due to the competitive adsorption of H₂O and NH₃ on Lewis acid sites. When the reaction temperature increases to 300 °C, the poisoning effect of H₂O can be negligible. The poisoning effect of SO₂ on deNO_x activity is dependent on the reaction temperature. At low temperature, the poisoning effect of SO₂ is permanent with no recovery of deNO_x activity after the elimination of SO₂. The formation of (NH4)₂SO₄, which results in the plug of active sites and a decrease of surface area, and the competitive adsorption of SO₂ and NO should be responsible for the loss of deNO_x activity over Cu/SAPO-34. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Optimization of Ammonia Oxidation Using Response Surface Methodology

by

Marek Inger

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Agnieszka Dobrzyńska-Inger

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Jakub Rajewski

and

Marcin Wilk

Catalysts 2019, 9(3), 249; https://doi.org/10.3390/catal9030249 - 09 Mar 2019

Cited by 13 | Viewed by 3274

Abstract

In this paper, the design of experiments and response surface methodology were proposed to study ammonia oxidation process. The following independent variables were selected: the reactor’s load, the temperature of reaction and the number of catalytic gauzes, whereas ammonia oxidation efficiency and N [...] Read more.

In this paper, the design of experiments and response surface methodology were proposed to study ammonia oxidation process. The following independent variables were selected: the reactor’s load, the temperature of reaction and the number of catalytic gauzes, whereas ammonia oxidation efficiency and N₂O concentration in nitrous gases were assumed as dependent variables (response). Based on the achieved results, statistically significant mathematical models were developed which describe the effect of independent variables on the analysed responses. In case of ammonia oxidation efficiency, its achieved value depends on the reactor’s load and the number of catalytic gauzes, whereas the temperature in the studied range (870–910 °C) has no effect on this dependent variable. The concentration of nitrous oxide in nitrous gases depends on all three parameters. The developed models were used for the multi-criteria optimization with the application of desirability function. Sets of parameters were achieved for which optimization assumptions were met: maximization of ammonia oxidation efficiency and minimization of the N₂O amount being formed in the reaction. Full article

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Open AccessArticle

Investigation of Various Pd Species in Pd/BEA for Cold Start Application

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Catalysts 2019, 9(3), 247; https://doi.org/10.3390/catal9030247 - 07 Mar 2019

Cited by 21 | Viewed by 3261

Abstract

A series of Pd/BEA catalysts with various Pd loadings were synthesized. Two active Pd²⁺ species, Z⁻-Pd²⁺-Z⁻ and Z⁻-Pd(OH)⁺, on exchanged sites of zeolites, were identified by in situ FTIR using CO and NH [...] Read more.

A series of Pd/BEA catalysts with various Pd loadings were synthesized. Two active Pd²⁺ species, Z⁻-Pd²⁺-Z⁻ and Z⁻-Pd(OH)⁺, on exchanged sites of zeolites, were identified by in situ FTIR using CO and NH₃ respectively. Higher NO_x storage capacity of Z⁻-Pd²⁺-Z⁻ was demonstrated compared with that of Z⁻-Pd(OH)⁺, which was caused by the different resistance to H₂O. Besides, lower Pd loading led to a sharp decline of Z⁻-Pd(OH)⁺, which was attributed to the ‘exchange preference’ for Z⁻-Pd²⁺-Z⁻ in BEA. Based on this research, the atom utilization of Pd can be improved by decreasing Pd loading. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessFeature PaperArticle

Effect of Preparation Method of Co-Ce Catalysts on CH₄ Combustion

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Catalysts 2019, 9(3), 219; https://doi.org/10.3390/catal9030219 - 27 Feb 2019

Cited by 15 | Viewed by 3136

Abstract

Transition metal oxides have recently attracted considerable attention as candidate catalysts for the complete oxidation of methane, the main component of the natural gas, used in various industrial processes or as a fuel in turbines and vehicles. A series of novel Co-Ce mixed [...] Read more.

Transition metal oxides have recently attracted considerable attention as candidate catalysts for the complete oxidation of methane, the main component of the natural gas, used in various industrial processes or as a fuel in turbines and vehicles. A series of novel Co-Ce mixed oxide catalysts were synthesized as an effort to enhance synergistic effects that could improve their redox behavior, oxygen storage ability and, thus, their activity in methane oxidation. The effect of synthesis method (hydrothermal or precipitation) and Co loading (0, 2, 5, and 15 wt.%) on the catalytic efficiency and stability of the derived materials was investigated. Use of hydrothermal synthesis results in the most efficient Co/CeO₂ catalysts, a fact related with their improved physicochemical properties, as compared with the materials prepared via precipitation. In particular, a CeO₂ support of smaller crystallite size and larger surface area seems to enhance the reducibility of the Co₃O₄/CeO₂ materials, as evidenced by the blue shift of the corresponding reduction peaks (H₂-TPR, H₂-Temperature Programmed Reduction). The limited methane oxidation activity over pure CeO₂ samples is significantly enhanced by Co incorporation and further improved by higher Co loadings. The optimum performance was observed over a 15 wt% Co/CeO₂ catalyst, which also presented sufficient tolerance to water presence. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Comprehensive Comparison between Nanocatalysts of Mn−Co/TiO₂ and Mn−Fe/TiO₂ for NO Catalytic Conversion: An Insight from Nanostructure, Performance, Kinetics, and Thermodynamics

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Catalysts 2019, 9(2), 175; https://doi.org/10.3390/catal9020175 - 13 Feb 2019

Cited by 29 | Viewed by 3372

Abstract

The nanocatalysts of Mn−Co/TiO₂ and Mn−Fe/TiO₂ were synthesized by hydrothermal method and comprehensively compared from nanostructures, catalytic performance, kinetics, and thermodynamics. The physicochemical properties of the nanocatalysts were analyzed by N₂ adsorption, transmission electron microscope (TEM), X-ray diffraction (XRD), H [...] Read more.

The nanocatalysts of Mn−Co/TiO₂ and Mn−Fe/TiO₂ were synthesized by hydrothermal method and comprehensively compared from nanostructures, catalytic performance, kinetics, and thermodynamics. The physicochemical properties of the nanocatalysts were analyzed by N₂ adsorption, transmission electron microscope (TEM), X-ray diffraction (XRD), H₂-temperature-programmed reduction (TPR), NH₃-temperature-programmed desorption (TPD), and X-ray photoelectron spectroscopy (XPS). Based on the multiple characterizations performed on Mn−Co/TiO₂ and Mn−Fe/TiO₂ nanocatalysts, it can be confirmed that the catalytic properties were decidedly dependent on the phase compositions of the nanocatalysts. The Mn−Co/TiO₂ sample presented superior structure characteristics than Mn−Fe/TiO₂, with the increased surface area, the promoted active components distribution, the diminished crystallinity, and the reduced nanoparticle size. Meanwhile, the Mn⁴⁺/Mnⁿ⁺ ratios in the Mn−Co/TiO₂ nanocatalyst were higher than Mn−Fe/TiO₂, which further confirmed the better oxidation ability and the larger amount of Lewis acid sites and Bronsted acid sites on the sample surface. Compared to Mn−Fe/TiO₂ nanocatalyst, Mn−Co/TiO₂ nanocatalyst displayed the preferable catalytic property with higher catalytic activity and stronger selectivity in the temperature range of 75–250 °C. The results of mechanism and kinetic study showed that both Eley-Rideal mechanism and Langmuir-Hinshelwood mechanism reactions contributed to selective catalytic reduction of NO with NH₃ (NH₃-SCR) over Mn−Fe/TiO₂ and Mn−Co/TiO₂ nanocatalysts. In this test condition, the NO conversion rate of Mn−Co/TiO₂ nanocatalyst was always higher than that of Mn−Fe/TiO₂. Furthermore, comparing the reaction between doping transition metal oxides and NH₃, the order of temperature−Gibbs free energy under the same reaction temperature is as follows: Co₃O₄ < CoO < Fe₂O₃ < Fe₃O₄, which was exactly consistent with nanostructure characterization and NH₃-SCR performance. Meanwhile, the activity difference of MnO_x exhibited in reducibility properties and Ellingham Diagrams manifested the promotion effects of cobalt and iron dopings. Generally, it might offer a theoretical method to select superior doping metal oxides for NO conversion by comprehensive comparing the catalytic performance with the insight from nanostructure, catalytic performance, reaction kinetics, and thermodynamics. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Experimental Clarification of the RWGS Reaction Effect in H₂O/CO₂ SOEC Co-Electrolysis Conditions

by

Evangelia Ioannidou

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Stylianos Neophytides

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Dimitrios K. Niakolas

Catalysts 2019, 9(2), 151; https://doi.org/10.3390/catal9020151 - 02 Feb 2019

Cited by 20 | Viewed by 3961

Abstract

In the present investigation, modified X-Ni/GDC electrodes (where X = Au, Mo, and Fe) are studied, in the form of half-electrolyte supported cells, for their performance in the RWGS through catalytic-kinetic measurements. The samples were tested at open circuit potential conditions in order [...] Read more.

In the present investigation, modified X-Ni/GDC electrodes (where X = Au, Mo, and Fe) are studied, in the form of half-electrolyte supported cells, for their performance in the RWGS through catalytic-kinetic measurements. The samples were tested at open circuit potential conditions in order to elucidate their catalytic activity towards the production of CO (r_co), which is one of the products of the H₂O/CO₂ co-electrolysis reaction. Physicochemical characterization is also presented, in which the samples were examined in the form of powders and as half cells with BET, H₂-TPR, Air-TPO and TGA re-oxidation measurements in the presence of H₂O. In brief, it was found that the rate of the produced CO (r_co) increases by increasing the operating temperature and the partial pressure of H₂ in the reaction mixture. In addition, the first results revealed that Fe and Mo modification enhances the catalytic production of CO, since the 2wt% Fe-Ni/GDC and 3wt% Mo-Ni/GDC electrodes were proven to perform better compared to the other samples, in the whole studied temperature range (800–900 °C), reaching thermodynamic equilibrium. Furthermore, carbon formation was not detected. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Tuning the Catalytic Properties of Copper-Promoted Nanoceria via a Hydrothermal Method

by

Konstantinos Kappis

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Christos Papadopoulos

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Joan Papavasiliou

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John Vakros

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Yiannis Georgiou

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Yiannis Deligiannakis

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George Avgouropoulos

Catalysts 2019, 9(2), 138; https://doi.org/10.3390/catal9020138 - 01 Feb 2019

Cited by 23 | Viewed by 4930

Abstract

Copper-cerium mixed oxide catalysts have gained ground over the years in the field of heterogeneous catalysis and especially in CO oxidation reaction due to their remarkable performance. In this study, a series of highly active, atomically dispersed copper-ceria nanocatalysts were synthesized via appropriate [...] Read more.

Copper-cerium mixed oxide catalysts have gained ground over the years in the field of heterogeneous catalysis and especially in CO oxidation reaction due to their remarkable performance. In this study, a series of highly active, atomically dispersed copper-ceria nanocatalysts were synthesized via appropriate tuning of a novel hydrothermal method. Various physicochemical techniques including electron paramagnetic resonance (EPR) spectroscopy, X-ray diffraction (XRD), N₂ adsorption, scanning electron microscopy (SEM), Raman spectroscopy, and ultraviolet-visible diffuse reflectance spectroscopy (UV-Vis DRS) were employed in the characterization of the synthesized materials, while all the catalysts were evaluated in the CO oxidation reaction. Moreover, discussion of the employed mechanism during hydrothermal route was provided. The observed catalytic activity in CO oxidation reaction was strongly dependent on the nanostructured morphology, oxygen vacancy concentration, and nature of atomically dispersed Cu²⁺ clusters. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Mechanism and Performance of the SCR of NO with NH₃ over Sulfated Sintered Ore Catalyst

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Catalysts 2019, 9(1), 90; https://doi.org/10.3390/catal9010090 - 16 Jan 2019

Cited by 15 | Viewed by 2838

Abstract

A sulfated sintered ore catalyst (SSOC) was prepared to improve the denitration performance of the sintered ore catalyst (SOC). The catalysts were characterized by X-ray Fluorescence Spectrometry (XRF), Brunauer–Emmett–Teller (BET) analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy [...] Read more.

A sulfated sintered ore catalyst (SSOC) was prepared to improve the denitration performance of the sintered ore catalyst (SOC). The catalysts were characterized by X-ray Fluorescence Spectrometry (XRF), Brunauer–Emmett–Teller (BET) analyzer, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and diffuse reflectance infrared spectroscopy (DRIFTS) to understand the NH₃-selective catalytic reduction (SCR) reaction mechanism. Moreover, the denitration performance and stability of SSOC were also investigated. The experimental results indicated that there were more Brønsted acid sites at the surface of SSOC after the treatment by sulfuric acid, which lead to the enhancement of the adsorption capacity of NH₃ and NO. Meanwhile, Lewis acid sites were also observed at the SSOC surface. The reaction between −NH₂,

{NH}_{4}^{+}

and NO (E-R mechanism) and the reaction of the coordinated ammonia with the adsorbed NO₂ (L-H mechanism) were attributed to NO_x reduction. The maximum denitration efficiency over the SSOC, which was about 92%, occurred at 300 °C, with a 1.0 NH₃/NO ratio, and 5000 h⁻¹ gas hourly space velocity (GHSV). Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

“PdO vs. PtO”—The Influence of PGM Oxide Promotion of Co₃O₄ Spinel on Direct NO Decomposition Activity

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Gunugunuri K. Reddy

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Torin C. Peck

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Charles A. Roberts

Catalysts 2019, 9(1), 62; https://doi.org/10.3390/catal9010062 - 09 Jan 2019

Cited by 11 | Viewed by 4283

Abstract

Direct decomposition of NO into N₂ and O₂ (2NO→N₂ + O₂) is recognized as the “ideal” reaction for NOx removal because it needs no reductant. It was reported that the spinel Co₃O₄ is one of [...] Read more.

Direct decomposition of NO into N₂ and O₂ (2NO→N₂ + O₂) is recognized as the “ideal” reaction for NOx removal because it needs no reductant. It was reported that the spinel Co₃O₄ is one of the most active single-element oxide catalysts for NO decomposition at higher reaction temperatures, however, activity remains low below 650 °C. The present study aims to investigate new promoters for Co₃O₄, specifically PdO vs. PtO. Interestingly, the PdO promoter effect on Co₃O₄ was much greater than the PtO effect, yielding a 4 times higher activity for direct NO decomposition at 650 °C. Also, Co₃O₄ catalysts with the PdO promoter exhibit higher selectivity to N₂ compared to PtO/Co₃O₄ catalysts. Several characterization measurements, including X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR), and in situ FT-IR, were performed to understand the effect of PdO vs. PtO on the properties of Co₃O₄. Structural and surface analysis measurements show that impregnation of PdO on Co₃O₄ leads to a greater ease of reduction of the catalysts and an increased thermal stability of surface adsorbed NOx species, which contribute to promotion of direct NO decomposition activity. In contrast, rather than remaining solely as a surface species, PtO enters the Co₃O₄ structure, and it promotes neither redox properties nor NO adsorption properties of Co₃O₄, resulting in a diminished promotional effect compared to PdO. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Electrochemical Promotion of Nanostructured Palladium Catalyst for Complete Methane Oxidation

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Yasmine M. Hajar

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Balaji Venkatesh

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Elena A. Baranova

Catalysts 2019, 9(1), 48; https://doi.org/10.3390/catal9010048 - 06 Jan 2019

Cited by 6 | Viewed by 4536

Abstract

Electrochemical promotion of catalysis (EPOC) was investigated for methane complete oxidation over palladium nano-structured catalysts deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. The catalytic rate was evaluated at different temperatures (400, 425 and 450 °C), reactant ratios and polarization values. The electrophobic behavior [...] Read more.

Electrochemical promotion of catalysis (EPOC) was investigated for methane complete oxidation over palladium nano-structured catalysts deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. The catalytic rate was evaluated at different temperatures (400, 425 and 450 °C), reactant ratios and polarization values. The electrophobic behavior of the catalyst, i.e., reaction rate increase upon anodic polarization was observed for all temperatures and gas compositions with an apparent Faradaic efficiency as high as 3000 (a current application as low as 1 μA) and maximum rate enhancement ratio up to 2.7. Temperature increase resulted in higher enhancement ratios under closed-circuit conditions. Electrochemical promotion experiments showed persistent behavior, where the catalyst remained in the promoted state upon current or potential interruption for a long period of time. An increase in the polarization time resulted in a longer-lasting persistent promotion (p-EPOC) and required more time for the reaction rate to reach its initial open-circuit value. This was attributed to continuous promotion by the stored oxygen in palladium oxide, which was formed during the anodic polarization in agreement with p-EPOC mechanism reported earlier. Full article

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Open AccessArticle

A CeO₂/ZrO₂-TiO₂ Catalyst for the Selective Catalytic Reduction of NO_x with NH₃

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Catalysts 2018, 8(12), 592; https://doi.org/10.3390/catal8120592 - 30 Nov 2018

Cited by 18 | Viewed by 3022

Abstract

In this study, CeZr_0.5Ti_aO_x (with a = 0, 1, 2, 5, 10) catalysts were prepared by a stepwise precipitation approach for the selective catalytic reduction of NO_x with NH₃. When Ti was added, all of [...] Read more.

In this study, CeZr_0.5Ti_aO_x (with a = 0, 1, 2, 5, 10) catalysts were prepared by a stepwise precipitation approach for the selective catalytic reduction of NO_x with NH₃. When Ti was added, all of the Ce-Zr-Ti oxide catalysts showed much better catalytic performances than the CeZr_0.5O_x. Particularly, the CeZr_0.5Ti₂O_x catalyst showed excellent activity for broad temperature range under high space velocity condition. Through the control of pH value and precipitation time during preparation, the function of the CeZr_0.5Ti₂O_x catalyst could be controlled and the structure with highly dispersed CeO₂ (with redox functions) on the surface of ZrO₂-TiO₂ (with acidic functions) could be obtained. Characterizations revealed that the superior catalytic performance of the catalyst is associated with its outstanding redox properties and adsorption/activation functions for the reactants. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

Low-Temperature Electrocatalytic Conversion of CO₂ to Liquid Fuels: Effect of the Cu Particle Size

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Antonio De Lucas-Consuegra

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Juan Carlos Serrano-Ruiz

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Nuria Gutiérrez-Guerra

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José Luis Valverde

Catalysts 2018, 8(8), 340; https://doi.org/10.3390/catal8080340 - 20 Aug 2018

Cited by 15 | Viewed by 3791

Abstract

A novel gas-phase electrocatalytic system based on a low-temperature proton exchange membrane (Sterion) was developed for the gas-phase electrocatalytic conversion of CO₂ to liquid fuels. This system achieved gas-phase electrocatalytic reduction of CO₂ at low temperatures (below 90 °C) over a [...] Read more.

A novel gas-phase electrocatalytic system based on a low-temperature proton exchange membrane (Sterion) was developed for the gas-phase electrocatalytic conversion of CO₂ to liquid fuels. This system achieved gas-phase electrocatalytic reduction of CO₂ at low temperatures (below 90 °C) over a Cu cathode by using water electrolysis-derived protons generated in-situ on an IrO₂ anode. Three Cu-based cathodes with varying metal particle sizes were prepared by supporting this metal on an activated carbon at three loadings (50, 20, and 10 wt %; 50% Cu-AC, 20% Cu-AC, and 10% Cu-AC, respectively). The cathodes were characterized by N₂ adsorption–desorption, temperature-programmed reduction (TPR), and X-ray diffraction (XRD) and their performance towards the electrocatalytic conversion of CO₂ was subsequently studied. The membrane electrode assembly (MEA) containing the cathode with the largest Cu particle size (50% Cu-AC, 40 nm) showed the highest CO₂ electrocatalytic activity per mole of Cu, with methyl formate being the main product. This higher electrocatalytic activity was attributed to the lower Cu–CO bonding strength over large Cu particles. Different product distributions were obtained over 20% Cu-AC and 10% Cu-AC, with acetaldehyde and methanol being the main reaction products, respectively. The CO₂ consumption rate increased with the applied current and reaction temperature. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Promotional Effect of Cerium and/or Zirconium Doping on Cu/ZSM-5 Catalysts for Selective Catalytic Reduction of NO by NH₃

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Catalysts 2018, 8(8), 306; https://doi.org/10.3390/catal8080306 - 28 Jul 2018

Cited by 17 | Viewed by 3230

Abstract

The cerium and/or zirconium-doped Cu/ZSM-5 catalysts (CuCe_xZr_1−xO_y/ZSM-5) were prepared by ion exchange and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H₂-TPR). Activities of the [...] Read more.

The cerium and/or zirconium-doped Cu/ZSM-5 catalysts (CuCe_xZr_1−xO_y/ZSM-5) were prepared by ion exchange and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), temperature-programmed reduction by hydrogen (H₂-TPR). Activities of the catalysts obtained on the selective catalytic reduction (SCR) of nitric oxide (NO) by ammonia were measured using temperature programmed reactions. Among all the catalysts tested, the CuCe_0.75Zr_0.25O_y/ZSM-5 catalyst presented the highest catalytic activity for the removal of NO, corresponding to the broadest active window of 175–468 °C. The cerium and zirconium addition enhanced the activity of catalysts, and the cerium-rich catalysts exhibited more excellent SCR activities as compared to the zirconium-rich catalysts. XRD and TEM results indicated that zirconium additions improved the copper dispersion and prevented copper crystallization. According to XPS and H₂-TPR analysis, copper species were enriched on the ZSM-5 grain surfaces, and part of the copper ions were incorporated into the zirconium and/or cerium lattice. The strong interaction between copper species and cerium/zirconium improved the redox abilities of catalysts. Furthermore, the introduction of zirconium abates N₂O formation in the tested temperature range. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Hydrogen Production from Chemical Looping Reforming of Ethanol Using Ni/CeO₂ Nanorod Oxygen Carrier

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Catalysts 2018, 8(7), 257; https://doi.org/10.3390/catal8070257 - 25 Jun 2018

Cited by 25 | Viewed by 4467

Abstract

Chemical looping reforming (CLR) technique is a prospective option for hydrogen production. Improving oxygen mobility and sintering resistance are still the main challenges of the development of high-performance oxygen carriers (OCs) in the CLR process. This paper explores the performance of Ni/CeO₂ [...] Read more.

Chemical looping reforming (CLR) technique is a prospective option for hydrogen production. Improving oxygen mobility and sintering resistance are still the main challenges of the development of high-performance oxygen carriers (OCs) in the CLR process. This paper explores the performance of Ni/CeO₂ nanorod (NR) as an OC in CLR of ethanol. Various characterization methods such as N₂ adsorption-desorption, X-ray diffraction (XRD), Raman spectra, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), H₂ temperature-programmed reduction (TPR), and H₂ chemisorption were utilized to study the properties of fresh OCs. The characterization results show the Ni/CeO₂-NR possesses high Ni dispersion, abundant oxygen vacancies, and strong metal-support interaction. The performance of prepared OCs was tested in a packed-bed reactor. H₂ selectivity of 80% was achieved by Ni/CeO₂-NR in 10-cycle stability test. The small particle size and abundant oxygen vacancies contributed to the water gas shift reaction, improving the catalytic activity. The covered interfacial Ni atoms closely anchored on the underlying surface oxygen vacancies on the (111) facets of CeO₂-NR, enhancing the anti-sintering capability. Moreover, the strong oxygen mobility of CeO₂-NR also effectively eliminated surface coke on the Ni particle surface. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Synthesis of Sulfur-Resistant TiO₂-CeO₂ Composite and Its Catalytic Performance in the Oxidation of a Soluble Organic Fraction from Diesel Exhaust

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Catalysts 2018, 8(6), 246; https://doi.org/10.3390/catal8060246 - 14 Jun 2018

Cited by 16 | Viewed by 3425

Abstract

Sulfur poisoning is one of the most important factors deteriorating the purification efficiency of diesel exhaust after-treatment system, thus improving the sulfur resistibility of catalysts is imperative. Herein, ceria oxygen storage material was introduced into a sulfur-resistant titania by a co-precipitation method, and [...] Read more.

Sulfur poisoning is one of the most important factors deteriorating the purification efficiency of diesel exhaust after-treatment system, thus improving the sulfur resistibility of catalysts is imperative. Herein, ceria oxygen storage material was introduced into a sulfur-resistant titania by a co-precipitation method, and the sulfur resistibility and catalytic activity of prepared TiO₂-CeO₂ composite in the oxidation of diesel soluble organic fraction (SOF) were studied. Catalytic performance testing results show that the CeO₂ modification significantly improves the catalytic SOF purification efficiency of TiO₂-CeO₂ catalyst. SO₂ uptake and energy-dispersive X-ray (EDX) results suggest that the ceria doping does not debase the excellent sulfur resistibility of bare TiO₂, the prepared TiO₂-CeO₂ catalyst exhibits obviously better sulfur resistibility than the CeO₂ and commercial CeO₂-ZrO₂-Al₂O₃. X-ray powder diffraction (XRD) and Raman spectra indicate that cerium ions can enter into the TiO₂ lattice and not form complete CeO₂ crystals. X-ray photoelectron spectroscopy (XPS), H₂-temperature programmed reduction (H₂-TPR) and oxygen storage capacity (OSC) testing results imply that the addition of CeO₂ in TiO₂-CeO₂ catalyst can significantly enhance the surface oxygen concentration and oxygen storage capacity of TiO₂-CeO₂. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessArticle

CuO Nanoparticles Supported on TiO₂ with High Efficiency for CO₂ Electrochemical Reduction to Ethanol

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Catalysts 2018, 8(4), 171; https://doi.org/10.3390/catal8040171 - 21 Apr 2018

Cited by 87 | Viewed by 8448

Abstract

Non-noble metal oxides consisting of CuO and TiO₂ (CuO/TiO₂ catalyst) for CO₂ reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO₂ catalyst, which could efficiently [...] Read more.

Non-noble metal oxides consisting of CuO and TiO₂ (CuO/TiO₂ catalyst) for CO₂ reduction were fabricated using a simple hydrothermal method. The designed catalysts of CuO could be in situ reduced to a metallic Cu-forming Cu/TiO₂ catalyst, which could efficiently catalyze CO₂ reduction to multi-carbon oxygenates (ethanol, acetone, and n-propanol) with a maximum overall faradaic efficiency of 47.4% at a potential of −0.85 V vs. reversible hydrogen electrode (RHE) in 0.5 M KHCO₃ solution. The catalytic activity for CO₂ electroreduction strongly depends on the CuO contents of the catalysts as-prepared, resulting in different electrochemistry surface areas. The significantly improved CO₂ catalytic activity of CuO/TiO₂ might be due to the strong CO₂ adsorption ability. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessFeature PaperEditor’s ChoiceArticle

Gas-Phase Phosphorous Poisoning of a Pt/Ba/Al₂O₃ NO_x Storage Catalyst

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Catalysts 2018, 8(4), 155; https://doi.org/10.3390/catal8040155 - 11 Apr 2018

Cited by 6 | Viewed by 3845

Abstract

The effect of phosphorous exposure on the NO_x storage capacity of a Pt/Ba/Al₂O₃ catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H₂O [...] Read more.

The effect of phosphorous exposure on the NO_x storage capacity of a Pt/Ba/Al₂O₃ catalyst coated on a ceramic monolith substrate has been studied. The catalyst was exposed to phosphorous by evaporating phosphoric acid in presence of H₂O and O₂. The NO_x storage capacity was measured before and after the phosphorus exposure and a significant loss of the NO_x storage capacity was detected after phosphorous exposure. The phosphorous poisoned samples were characterized by X-ray photoelectron spectroscopy (XPS), environmental scanning electron microscopy (ESEM), N₂-physisorption and inductive coupled plasma atomic emission spectroscopy (ICP-AES). All characterization methods showed an axial distribution of phosphorous ranging from the inlet to the outlet of the coated monolith samples with a higher concentration at the inlet of the samples. Elemental analysis, using ICP-AES, confirmed this distribution of phosphorous on the catalyst surface. The specific surface area and pore volume were significantly lower at the inlet section of the monolith where the phosphorous concentration was higher, and higher at the outlet where the phosphorous concentration was lower. The results from the XPS and scanning electron microscopy (SEM)-energy dispersive X-ray (EDX) analyses showed higher accumulation of phosphorus towards the surface of the catalyst at the inlet of the monolith and the phosphorus was to a large extent present in the form of P₄O₁₀. However, in the middle section of the monolith, the XPS analysis revealed the presence of more metaphosphate (PO₃⁻). Moreover, the SEM-EDX analysis showed that the phosphorous to higher extent had diffused into the washcoat and was less accumulated at the surface close to the outlet of the sample. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Review

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Open AccessFeature PaperEditor’s ChoiceReview

A Review of Low Temperature NH₃-SCR for Removal of NO_x

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Devaiah Damma

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Padmanabha R. Ettireddy

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Benjaram M. Reddy

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Panagiotis G. Smirniotis

Catalysts 2019, 9(4), 349; https://doi.org/10.3390/catal9040349 - 10 Apr 2019

Cited by 188 | Viewed by 15502

Abstract

The importance of the low-temperature selective catalytic reduction (LT-SCR) of NO_x by NH₃ is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, [...] Read more.

The importance of the low-temperature selective catalytic reduction (LT-SCR) of NO_x by NH₃ is increasing due to the recent severe pollution regulations being imposed around the world. Supported and mixed transition metal oxides have been widely investigated for LT-SCR technology. However, these catalytic materials have some drawbacks, especially in terms of catalyst poisoning by H₂O or/and SO₂. Hence, the development of catalysts for the LT-SCR process is still under active investigation throughout seeking better performance. Extensive research efforts have been made to develop new advanced materials for this technology. This article critically reviews the recent research progress on supported transition and mixed transition metal oxide catalysts for the LT-SCR reaction. The review covered the description of the influence of operating conditions and promoters on the LT-SCR performance. The reaction mechanism, reaction intermediates, and active sites are also discussed in detail using isotopic labelling and in situ FT-IR studies. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessReview

Hydrogenation of Carbon Dioxide to Value-Added Chemicals by Heterogeneous Catalysis and Plasma Catalysis

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Catalysts 2019, 9(3), 275; https://doi.org/10.3390/catal9030275 - 18 Mar 2019

Cited by 117 | Viewed by 10654

Abstract

Due to the increasing emission of carbon dioxide (CO₂), greenhouse effects are becoming more and more severe, causing global climate change. The conversion and utilization of CO₂ is one of the possible solutions to reduce CO₂ concentrations. This can [...] Read more.

Due to the increasing emission of carbon dioxide (CO₂), greenhouse effects are becoming more and more severe, causing global climate change. The conversion and utilization of CO₂ is one of the possible solutions to reduce CO₂ concentrations. This can be accomplished, among other methods, by direct hydrogenation of CO₂, producing value-added products. In this review, the progress of mainly the last five years in direct hydrogenation of CO₂ to value-added chemicals (e.g., CO, CH₄, CH₃OH, DME, olefins, and higher hydrocarbons) by heterogeneous catalysis and plasma catalysis is summarized, and research priorities for CO₂ hydrogenation are proposed. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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Open AccessFeature PaperReview

Electropositive Promotion by Alkalis or Alkaline Earths of Pt-Group Metals in Emissions Control Catalysis: A Status Report

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Ioannis V. Yentekakis

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Philippe Vernoux

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Grammatiki Goula

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Angel Caravaca

Catalysts 2019, 9(2), 157; https://doi.org/10.3390/catal9020157 - 05 Feb 2019

Cited by 22 | Viewed by 4260

Abstract

Recent studies have shown that the catalytic performance (activity and/or selectivity) of Pt-group metal (PGM) catalysts for the CO and hydrocarbons oxidation as well as for the (CO, HCs or H₂)-SCR of NO_x or N₂O can be remarkably [...] Read more.

Recent studies have shown that the catalytic performance (activity and/or selectivity) of Pt-group metal (PGM) catalysts for the CO and hydrocarbons oxidation as well as for the (CO, HCs or H₂)-SCR of NO_x or N₂O can be remarkably affected through surface-induced promotion by successful application of electropositive promoters, such as alkalis or alkaline earths. Two promotion methodologies were implemented for these studies: the Electrochemical Promotion of Catalysis (EPOC) and the Conventional Catalysts Promotion (CCP). Both methodologies were in general found to achieve similar results. Turnover rate enhancements by up to two orders of magnitude were typically achievable for the reduction of NO_x by hydrocarbons or CO, in the presence or absence of oxygen. Subsequent improvements (ca. 30–60 additional percentage units) in selectivity towards N₂ were also observed. Electropositively promoted PGMs were also found to be significantly more active for CO and hydrocarbons oxidations, either when these reactions occur simultaneously with deNO_x reactions or not. The aforementioned direct (via surface) promotion was also found to act synergistically with support-mediated promotion (structural promotion); the latter is typically implemented in TWCs through the complex (Ce–La–Zr)-modified γ-Al₂O₃ washcoats used. These attractive findings prompt to the development of novel catalyst formulations for a more efficient and cost-effective control of the emissions of automotives and stationary combustion processes. In this report the literature findings in the relevant area are summarized, classified and discussed. The mechanism and the mode of action of the electropositive promoters are consistently interpreted with all the observed promoting phenomena, by means of indirect (kinetics) and direct (spectroscopic) evidences. Full article

(This article belongs to the Special Issue Emissions Control Catalysis)

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