Editorial

3 pages, 396 KiB

Open AccessEditorial

Editorial: Special Issue on “Advanced Strategies for Catalyst Design”

by Laura Orian

Catalysts 2021, 11(1), 38; https://doi.org/10.3390/catal11010038 - 31 Dec 2020

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The word catalyst comes from the Greek κατα’λυσις, which means dissolution and was introduced in 1836 by the Swedish Berzelius [...] Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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Research

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23 pages, 4008 KiB

Open AccessArticle

Improved NOx Reduction Using C₃H₈ and H₂ with Ag/Al₂O₃ Catalysts Promoted with Pt and WOx

by Naomi N. González Hernández, José Luis Contreras, Marcos Pinto, Beatriz Zeifert, Jorge L. Flores Moreno, Gustavo A. Fuentes, María E. Hernández-Terán, Tamara Vázquez, José Salmones and José M. Jurado

Catalysts 2020, 10(10), 1212; https://doi.org/10.3390/catal10101212 - 19 Oct 2020

Cited by 7 | Viewed by 2455

Abstract

The addition of Pt (0.1 wt%Pt) to the 2 wt%Ag/Al₂O₃-WOx catalyst improved the C₃H₈– Selective Catalytic Reduction (SCR) of NO assisted by H₂ and widened the range of the operation window. During H₂ [...] Read more.

The addition of Pt (0.1 wt%Pt) to the 2 wt%Ag/Al₂O₃-WOx catalyst improved the C₃H₈– Selective Catalytic Reduction (SCR) of NO assisted by H₂ and widened the range of the operation window. During H₂–C₃H₈–SCR of NO, the bimetallic Pt–Ag catalyst showed two maxima in conversion: 80% (at 130 °C) and 91% (between 260 and 350 °C). This PtAg bimetallic catalyst showed that it could combine the catalytic properties of Pt at low temperature, with the properties of Ag/Al₂O₃ at high temperature. These PtAg catalysts were composed of Ag⁺, Ag_n^δ+ clusters, and PtAg nanoparticles. The catalysts were characterized by Temperature Programmed Reduction (TPR), Ultraviolet Visible Spectroscopy (UV-Vis), Scanning Electron Microscopy (SEM)/ Energy Dispersed X-ray Spectroscopy (EDS), x-ray Diffraction (XRD) and N₂ physisorption. The PtAg bimetallic catalysts were able to chemisorb H₂. The dispersion of Pt in the bimetallic catalysts was the largest for the catalyst with the lowest Pt/Ag atomic ratio. Through SEM, mainly spherical clusters smaller than 10 nm were observed in the PtAg catalyst. There were about 32% of particles with size equal or below 10 nm. The PtAg bimetallic catalysts produced NO₂ in the intermediate temperature range as well as some N₂O. The yield to N₂O was proportional to the Pt/Ag atomic ratio and reached 8.5% N₂O. WOx stabilizes Al₂O₃ at temperatures ≥650 °C, and also stabilizes Pt when it is reduced in H₂ at high temperature (800 °C). Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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15 pages, 3205 KiB

Open AccessArticle

Contact Glow Discharge Electrolysis: Effect of Electrolyte Conductivity on Discharge Voltage

by Giovanni Battista Alteri, Matteo Bonomo, Franco Decker and Danilo Dini

Catalysts 2020, 10(10), 1104; https://doi.org/10.3390/catal10101104 - 24 Sep 2020

Cited by 16 | Viewed by 3918

Abstract

Contact glow discharge electrolysis (CGDE) can be exploited in environmental chemistry for the degradation of pollutants in wastewater. This study focuses on the employment of cheap materials (e.g., steel and tungsten) as electrodes for experiments of CGDE conducted in electrochemical cells with variable [...] Read more.

Contact glow discharge electrolysis (CGDE) can be exploited in environmental chemistry for the degradation of pollutants in wastewater. This study focuses on the employment of cheap materials (e.g., steel and tungsten) as electrodes for experiments of CGDE conducted in electrochemical cells with variable electrolytic composition. A clear correlation between breakdown voltage (V_B)/discharge (or midpoint) voltage (V_D) and the conductivity of the electrolyte is shown. Regardless of the chemical nature of the ionogenic species (acid, base or salt), the higher the conductivity of the solution, the lower the applied potential required for the onset of the glow discharge. Concerning practical application, these salts could be added to poorly conductive wastewaters to increase their conductivity and thus reduce the ignition potential necessary for the development of the CGDE. Such an effect could render the process of chemical waste disposal from wastewaters more economical. Moreover, it is evidenced that both V_B and V_D are practically independent on the ratio anode area to cathode area if highly conductive solutions are employed. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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14 pages, 5110 KiB

Open AccessArticle

Asymmetric Cyanation of Activated Olefins with Ethyl Cyanoformate Catalyzed by Ti(IV)-Catalyst: A Theoretical Study

by Zhishan Su, Changwei Hu, Nasir Shahzad and Chan Kyung Kim

Catalysts 2020, 10(9), 1079; https://doi.org/10.3390/catal10091079 - 18 Sep 2020

Cited by 3 | Viewed by 2514

Abstract

The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed [...] Read more.

The reaction mechanism and origin of asymmetric induction for conjugate addition of cyanide to the C=C bond of olefin were investigated at the B3LYP-D3(BJ)/6-31+G**//B3LYP-D3(BJ)/6-31G**(SMD, toluene) theoretical level. The release of HCN from the reaction of ethyl cyanoformate (CNCOOEt) and isopropanol (HOiPr) was catalyzed by cinchona alkaloid catalyst. The cyanation reaction of olefin proceeded through a two-step mechanism, in which the C-C bond construction was followed by H-transfer to generate a cyanide adduct. For non-catalytic reaction, the activation barrier for the rate-determining C-H bond construction step was 34.2 kcal mol⁻¹, via a four-membered transition state. The self-assembly Ti(IV)-catalyst from tetraisopropyl titanate, (R)-3,3′-disubstituted biphenol, and cinchonidine accelerated the addition of cyanide to the C=C double bond by a dual activation process, in which titanium cation acted as a Lewis acid to activate the olefin and HNC was orientated by hydrogen bonding. The steric repulsion between the 9-phenanthryl at the 3,3′-position in the biphenol ligand and the Ph group in olefin raised the Pauli energy (ΔE^≠_Pauli) of reacting fragments at the re-face attack transition state, leading to the predominant R-product. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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14 pages, 5186 KiB

Open AccessArticle

Promoting Effect of the Core-Shell Structure of MnO₂@TiO₂ Nanorods on SO₂ Resistance in Hg⁰ Removal Process

by Xiaopeng Zhang, Xiangkai Han, Chengfeng Li, Xinxin Song, Hongda Zhu, Junjiang Bao, Ning Zhang and Gaohong He

Catalysts 2020, 10(1), 72; https://doi.org/10.3390/catal10010072 - 03 Jan 2020

Cited by 11 | Viewed by 2500

Abstract

Sorbent of αMnO₂ nanorods coating TiO₂ shell (denoted as αMnO₂-NR@TiO₂) was prepared to investigate the elemental mercury (Hg⁰) removal performance in the presence of SO₂. Due the core-shell structure, αMnO₂-NR@TiO₂ [...] Read more.

Sorbent of αMnO₂ nanorods coating TiO₂ shell (denoted as αMnO₂-NR@TiO₂) was prepared to investigate the elemental mercury (Hg⁰) removal performance in the presence of SO₂. Due the core-shell structure, αMnO₂-NR@TiO₂ has a better SO₂ resistance when compared to αMnO₂ nanorods (denoted as αMnO₂-NR). Kinetic studies have shown that both the sorption rates of αMnO₂-NR and αMnO₂-NR@TiO₂, which can be described by pseudo second-order models and SO₂ treatment, did not change the kinetic models for both the two catalysts. In contrast, X-ray photoelectron spectroscopy (XPS) results showed that, after reaction in the presence of SO₂, S concentration on αMnO₂-NR@TiO₂ surface is lower than on αMnO₂-NR surface, which demonstrated that TiO₂ shell could effectively inhibit the SO₂ diffusion onto MnO₂ surface. Thermogravimetry-differential thermosgravimetry (TG-DTG) results further pointed that SO₂ mainly react with TiO₂ forming Ti(SO₄)O in αMnO₂-NR@TiO₂, which will protect Mn from being deactivated by SO₂. These results were the reason for the better SO₂ resistance of αMnO₂-NR@TiO₂. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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12 pages, 1308 KiB

Open AccessCommunication

A Four Coordinated Iron(II)-Digermyl Complex as an Effective Precursor for the Catalytic Dehydrogenation of Ammonia Borane

by Yoshinao Kobayashi and Yusuke Sunada

Catalysts 2020, 10(1), 29; https://doi.org/10.3390/catal10010029 - 25 Dec 2019

Cited by 7 | Viewed by 2856

Abstract

A coordinatively unsaturated iron(II)-digermyl complex, Fe[Ge(SiMe₃)₃]₂(THF)₂ (1), was synthesized in one step by the reaction of FeBr₂ with 2 equiv of KGe(SiMe₃)₃. Complex 1 shows catalytic activity comparable to [...] Read more.

A coordinatively unsaturated iron(II)-digermyl complex, Fe[Ge(SiMe₃)₃]₂(THF)₂ (1), was synthesized in one step by the reaction of FeBr₂ with 2 equiv of KGe(SiMe₃)₃. Complex 1 shows catalytic activity comparable to that of its silicon analogue in reduction reactions. In addition, 1 acts as an effective precursor for the catalytic dehydrogenation of ammonia borane. Catalytically active species can also be generated in situ by simple mixing of the easy-to-handle precursors FeBr₂, Ge(SiMe₃)₄, KO^tBu, and phenanthroline. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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11 pages, 2060 KiB

Open AccessArticle

Benchmarking Acidic and Basic Catalysis for a Robust Production of Biofuel from Waste Cooking Oil

by Claudia Carlucci, Michael Andresini, Leonardo Degennaro and Renzo Luisi

Catalysts 2019, 9(12), 1050; https://doi.org/10.3390/catal9121050 - 10 Dec 2019

Cited by 7 | Viewed by 2921

Abstract

The production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting [...] Read more.

The production of biodiesel at the industrial level is mainly based on the use of basic catalysts. Otherwise, also acidic catalysis allowed high conversion and yields, as this method is not affected by the percentage of free fatty acids present in the starting sample. This work has been useful in assessing the possible catalytic pathways in the production of fatty acid methyl esters (FAMEs), starting from different cooking waste oil mixtures, exploring particularly acidic catalysis. It was possible to state that the optimal experimental conditions required concentrated sulfuric acid 20% w/w as a catalyst, a reaction time of twelve hours, a temperature of 85 °C and a molar ratio MeOH/oil of 6:1. The role of silica in the purification method was also explored. By evaluating the parameters, type of catalyst, temperature, reaction time and MeOH/oil molar ratios, it has been possible to develop a robust method for the production of biodiesel from real waste mixtures with conversions up to 99%. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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14 pages, 3305 KiB

Open AccessArticle

The Role of Iodine Catalyst in the Synthesis of 22-Carbon Tricarboxylic Acid and Its Ester: A Case Study

by Yanxia Liu, Yagang Zhang, Lulu Wang, Xingjie Zan and Letao Zhang

Catalysts 2019, 9(12), 972; https://doi.org/10.3390/catal9120972 - 20 Nov 2019

Cited by 3 | Viewed by 3272

Abstract

Here, 22-carbon tricarboxylic acid (C22TA) and its ester (C22TAE) were prepared via the Diels–Alder reaction of polyunsaturated fatty acids (PUFAs) and their esters (PUFAEs) as dienes with fumaric acid (FA) and dimethyl fumarate (DF) as dienophiles, respectively. The role of an iodine catalyst [...] Read more.

Here, 22-carbon tricarboxylic acid (C22TA) and its ester (C22TAE) were prepared via the Diels–Alder reaction of polyunsaturated fatty acids (PUFAs) and their esters (PUFAEs) as dienes with fumaric acid (FA) and dimethyl fumarate (DF) as dienophiles, respectively. The role of an iodine catalyst for the synthesis of C22TA and C22TAE in the Diels–Alder type reaction was investigated using a spectroscopic approach. The chemical structures of the products were characterized using proton nuclear magnetic resonance (¹H-NMR) and electrospray ionization mass spectrometry (ESI-MS) analysis. Results showed that nonconjugated dienes can react with dienophiles through a Diels–Alder reaction with an iodine catalyst, and that iodine transformed the nonconjugated double bonds of dienes into conjugated double bonds via a radical process. DF was more favorable for the Diels–Alder reaction than FA. This was mainly because the dienophile DF contained an electron-withdrawing substituent, which reduced the highest and lowest occupied molecular orbital (HOMO–LUMO) energy gap and accelerated the Diels–Alder reaction. By transforming nonconjugated double bonds into conjugated double bonds, iodine as a Lewis acid increased the electron-withdrawing effect of the carbonyl group on the carbon–carbon double bond and reduced the energy difference between the HOMO of diene and the LUMO of dienophile, thus facilitating the Diels–Alder reaction. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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13 pages, 3732 KiB

Open AccessArticle

Synthesis of GO-SalenMn and Asymmetric Catalytic Olefin Epoxidation

by Fengqin Wang, Tiankui Huang, Shurong Rao, Qian Chen, Cheng Huang, Zhiwen Tan, Xiyue Ding and Xiaochuan Zou

Catalysts 2019, 9(10), 824; https://doi.org/10.3390/catal9100824 - 30 Sep 2019

Cited by 2 | Viewed by 3247

Abstract

Graphene oxide (GO) was used as a catalyst carrier, and after the hydroxyl group in GO was modified by 3-aminopropyltrimethoxysilane (MPTMS), axial coordination and immobilization with homogeneous chiral salenMnCl catalyst were carried out. The immobilized catalysts were characterized in detail by FT–IR, TG–DSC, [...] Read more.

Graphene oxide (GO) was used as a catalyst carrier, and after the hydroxyl group in GO was modified by 3-aminopropyltrimethoxysilane (MPTMS), axial coordination and immobilization with homogeneous chiral salenMnCl catalyst were carried out. The immobilized catalysts were characterized in detail by FT–IR, TG–DSC, XPS, EDS, SEM, X-ray, and AAS, and the successful preparation of GO-salenMn was confirmed. Subsequently, the catalytic performance of GO-salenMn for asymmetric epoxidation of α-methyl-styrene, styrene, and indene was examined, and it was observed that GO-salenMn could efficiently catalyze the epoxidation of olefins under an m-CPBA/NMO oxidation system. In addition, α-methyl-styrene was used as a substrate to investigate the recycling performance of GO-salenMn. After repeated use for three times, the catalytic activity and enantioselectivity did not significantly change, and the conversion was still greater than 99%. As the number of cycles increased, the enantioselectivity and chemoselectivity gradually decreased, but even after 10 cycles, the enantiomeric excess was 52%, which was higher than that of the homogeneous counterpart under the same conditions. However, compared to fresh catalysts, the yield decreased from 96.9 to 55.6%. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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20 pages, 14640 KiB

Open AccessFeature PaperArticle

In Silico Acetylene [2+2+2] Cycloadditions Catalyzed by Rh/Cr Indenyl Fragments

by Shah Masood Ahmad, Marco Dalla Tiezza and Laura Orian

Catalysts 2019, 9(8), 679; https://doi.org/10.3390/catal9080679 - 09 Aug 2019

Cited by 7 | Viewed by 3793

Abstract

Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)₃IndRh] (Ind = (C₉H₇) [...] Read more.

Metal-catalyzed alkyne [2+2+2] cycloadditions provide a variety of substantial aromatic compounds of interest in the chemical and pharmaceutical industries. Herein, the mechanistic aspects of the acetylene [2+2+2] cycloaddition mediated by bimetallic half-sandwich catalysts [Cr(CO)₃IndRh] (Ind = (C₉H₇)⁻, indenyl anion) are investigated. A detailed exploration of the potential energy surfaces (PESs) was carried out to identify the intermediates and transition states, using a relativistic density functional theory (DFT) approach. For comparison, monometallic parent systems, i.e., CpRh (Cp = (C₅H₅)⁻, cyclopentadienyl anion) and IndRh, were included in the analysis. The active center is the rhodium nucleus, where the [2+2+2] cycloaddition occurs. The coordination of the Cr(CO)₃ group, which may be in syn or anti conformation, affects the energetics of the catalytic cycle as well as the mechanism. The reaction and activation energies and the turnover frequency (TOF) of the catalytic cycles are rationalized, and, in agreement with the experimental findings, our computational analysis reveals that the presence of the second metal favors the catalysis. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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17 pages, 5517 KiB

Open AccessArticle

Pd₄S/SiO₂: A Sulfur-Tolerant Palladium Catalyst for Catalytic Complete Oxidation of Methane

by Lei Ma, Shiyan Yuan, Taotao Jiang, Xiangming Zhu, Chunshan Lu and Xiaonian Li

Catalysts 2019, 9(5), 410; https://doi.org/10.3390/catal9050410 - 30 Apr 2019

Cited by 9 | Viewed by 3970

Abstract

Sulfur species (e.g. H₂S or SO₂) are the natural enemies of most metal catalysts, especially
palladium catalysts. The previously reported methods of improving sulfur-tolerance were to
effectively defer the deactivation of palladium catalysts, but could not prevent PdO and [...] Read more.

Sulfur species (e.g. H₂S or SO₂) are the natural enemies of most metal catalysts, especially
palladium catalysts. The previously reported methods of improving sulfur-tolerance were to
effectively defer the deactivation of palladium catalysts, but could not prevent PdO and carrier
interaction between sulfur species. In this report, novel sulfur-tolerant SiO₂ supported Pd4S
catalysts (5 wt. % Pd loading) were prepared by H₂S–H₂ aqueous bubble method and applied to
catalytic complete oxidation of methane. The catalysts were characterization by X-ray diffraction,
Transmission electron microscopy, X-ray photoelectron Spectroscopy, temperature-programmed
oxidation, and temperature-programmed desorption techniques under identical conditions. The
structural characterization revealed that Pd4S and metallic Pd0 were found on the surface of freshly
prepared catalysts. However, Pd4S remained stable while most of metallic Pd0 was converted to
PdO during the oxidation reaction. When coexisting with PdO, Pd₄S not only protected PdO from
sulfur poisoning, but also determined the catalytic activity. Moreover, the content of Pd4S could be
adjusted by changing H₂S concentration of H₂S–H₂ mixture. When H₂S concentration was 7 %, the
Pd₄S/SiO₂ catalyst was effective in converting 96% of methane at the 400 °C and also exhibited
long-term stability in the presence of 200 ppm H₂S. A Pd₄S/SiO₂ catalyst that possesses excellent
sulfur-tolerance, oxidation stability, and catalytic activity has been developed for catalytic
complete oxidation of methane. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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Review

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29 pages, 12891 KiB

Open AccessReview

Progress and Challenges of Mercury-Free Catalysis for Acetylene Hydrochlorination

by Yanxia Liu, Lin Zhao, Yagang Zhang, Letao Zhang and Xingjie Zan

Catalysts 2020, 10(10), 1218; https://doi.org/10.3390/catal10101218 - 20 Oct 2020

Cited by 13 | Viewed by 4217

Abstract

Activated carbon-supported HgCl₂ catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl₂ is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis [...] Read more.

Activated carbon-supported HgCl₂ catalyst has been used widely in acetylene hydrochlorination in the chlor-alkali chemical industry. However, HgCl₂ is an extremely toxic pollutant. It is not only harmful to human health but also pollutes the environment. Therefore, the design and synthesis of mercury-free and environmentally benign catalysts with high activity has become an urgent need for vinyl chloride monomer (VCM) production. This review summarizes research progress on the design and development of mercury-free catalysts for acetylene hydrochlorination. Three types of catalysts for acetylene hydrochlorination in the chlor-alkali chemical industry are discussed. These catalysts are a noble metal catalyst, non-noble metal catalyst, and non-metallic catalyst. This review serves as a guide in terms of the catalyst design, properties, and catalytic mechanism of mercury-free catalyst for the acetylene hydrochlorination of VCM. The key problems and issues are discussed, and future trends are envisioned. Full article

(This article belongs to the Special Issue Advanced Strategies for Catalyst Design)

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