Catalysts

379 KiB

Open AccessArticle

Investigation of the Deactivation Phenomena Occurring in the Cyclohexane Photocatalytic Oxidative Dehydrogenation on MoO_x/TiO₂ through Gas Phase and in situ DRIFTS Analyses

by Vincenzo Vaiano, Diana Sannino, Ana Rita Almeida, Guido Mul and Paolo Ciambelli

Catalysts 2013, 3(4), 978-997; https://doi.org/10.3390/catal3040978 - 13 Dec 2013

Cited by 11 | Viewed by 6708

Abstract

In this work, the results of gas phase cyclohexane photocatalytic oxidative dehydrogenation on MoO_x/SO₄/TiO₂ catalysts with DRIFTS analysis are presented. Analysis of products in the gas-phase discharge of a fixed bed photoreactor was coupled with in situ monitoring [...] Read more.

In this work, the results of gas phase cyclohexane photocatalytic oxidative dehydrogenation on MoO_x/SO₄/TiO₂ catalysts with DRIFTS analysis are presented. Analysis of products in the gas-phase discharge of a fixed bed photoreactor was coupled with in situ monitoring of the photocatalyst surface during irradiation with an IR probe. An interaction between cyclohexane and surface sulfates was found by DRIFTS analysis in the absence of UV irradiation, showing evidence of the formation of an organo-sulfur compound. In particular, in the absence of irradiation, sulfate species initiate a redox reaction through hydrogen abstraction of cyclohexane and formation of sulfate (IV) species. In previous studies, it was concluded that reduction of the sulfate (IV) species via hydrogen abstraction during UV irradiation may produce gas phase SO₂ and thereby loss of surface sulfur species. Gas phase analysis showed that the presence of MoO_x species, at same sulfate loading, changes the selectivity of the photoreaction, promoting the formation of benzene. The amount of surface sulfate influenced benzene yield, which decreases when the sulfate coverage is lower. During irradiation, a strong deactivation was observed due to the poisoning of the surface by carbon deposits strongly adsorbed on catalyst surface. Full article

(This article belongs to the Special Issue Advances in Catalyst Deactivation)

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333 KiB

Open AccessArticle

Influence of Gold on Hydrotalcite-like Compound Catalysts for Toluene and CO Total Oxidation

by Eric Genty, Renaud Cousin, Sylvie Capelle and Stéphane Siffert

Catalysts 2013, 3(4), 966-977; https://doi.org/10.3390/catal3040966 - 12 Dec 2013

Cited by 11 | Viewed by 8344

Abstract

X₆Al₂HT500 hydrotalcites, where X represents Mg, Fe, Cu or Zn were synthetized and investigated before and after gold deposition for toluene and CO total oxidation reactions. The samples have been characterized by specific areas, XRD measurements and Temperature Programmed [...] Read more.

X₆Al₂HT500 hydrotalcites, where X represents Mg, Fe, Cu or Zn were synthetized and investigated before and after gold deposition for toluene and CO total oxidation reactions. The samples have been characterized by specific areas, XRD measurements and Temperature Programmed Reduction. Concerning the toluene total oxidation, the best activity was obtained with Au/Cu₆Al₂HT500 catalyst with T₅₀ at 260 °C. However, catalytic behavior of Au/X₆Al₂HT500 sample in both reactions depends mainly on the nature of the support. Full article

(This article belongs to the Special Issue New Trends in Gold Catalysts)

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234 KiB

Open AccessArticle

Facile and Efficient Acetylation of Primary Alcohols and Phenols with Acetic Anhydride Catalyzed by Dried Sodium Bicarbonate

by Fulgentius Nelson Lugemwa, Koonj Shaikh and Edwin Hochstedt

Catalysts 2013, 3(4), 954-965; https://doi.org/10.3390/catal3040954 - 03 Dec 2013

Cited by 42 | Viewed by 22597

Abstract

A variety of primary alcohols and phenols were reacted with acetic anhydride at room temperature in the presence of sodium bicarbonate to produce corresponding esters in good to excellent yields. The acetylation of 4-nitrobenzyl alcohol was also carried out using other bicarbonates and [...] Read more.

A variety of primary alcohols and phenols were reacted with acetic anhydride at room temperature in the presence of sodium bicarbonate to produce corresponding esters in good to excellent yields. The acetylation of 4-nitrobenzyl alcohol was also carried out using other bicarbonates and carbonates. The reaction in the presence of cesium bicarbonate and lithium carbonate gave 4-nitrobenzyl acetate in excellent yield, while in the presence of Na₂CO₃, K₂CO₃, Cs₂CO₃, or KHCO₃ the yield was in the range of 80%–95%. Calcium carbonate and cobaltous carbonate did not promote the acetylation of 4-ntirobenzyl alcohol using acetic anhydride. The acetylation of 4-nitrobenzyl alcohol was carried out using ethyl acetate, THF, toluene, diethyl ether, dichloromethane and acetonitrile, and gave good yields ranging from 75%–99%. Toluene was the best solvent for the reaction, while diethyl ether was the poorest. Full article

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242 KiB

Open AccessReview

Titania Photocatalysis beyond Recombination: A Critical Review

by Bunsho Ohtani

Catalysts 2013, 3(4), 942-953; https://doi.org/10.3390/catal3040942 - 15 Nov 2013

Cited by 172 | Viewed by 14330

Abstract

This short review paper shows the significance of recombination of a photoexcited electron and a hole in conduction and valence bands, respectively, of a titania photocatalyst, since recombination has not yet been fully understood and has not been evaluated adequately during the past [...] Read more.

This short review paper shows the significance of recombination of a photoexcited electron and a hole in conduction and valence bands, respectively, of a titania photocatalyst, since recombination has not yet been fully understood and has not been evaluated adequately during the past several decades of research on heterogeneous photocatalysis. Full article

(This article belongs to the Special Issue Photocatalysts)

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661 KiB

Open AccessArticle

Rate Parameter Distributions for Isobutane Dehydrogenation and Isobutene Dimerization and Desorption over HZSM-5

by Trevor C. Brown, David J. Miron, Abdullah K. Alanazi and Cam Le Minh

Catalysts 2013, 3(4), 922-941; https://doi.org/10.3390/catal3040922 - 15 Nov 2013

Cited by 3 | Viewed by 6155

Abstract

Deconvolution of the evolved isobutene data obtained from temperature-programmed, low-pressure steady-state conversion of isobutane over HZSM-5 has yielded apparent activation energies for isobutane dehydrogenation, isobutene dimerization and desorption. Intrinsic activation energies and associated isobutane collision frequencies are also estimated. A combination of wavelet [...] Read more.

Deconvolution of the evolved isobutene data obtained from temperature-programmed, low-pressure steady-state conversion of isobutane over HZSM-5 has yielded apparent activation energies for isobutane dehydrogenation, isobutene dimerization and desorption. Intrinsic activation energies and associated isobutane collision frequencies are also estimated. A combination of wavelet shrinkage denoising, followed by time-varying flexible least squares of the evolved mass-spectral abundance data over the temperature range 150 to 450 °C, provides accurate, temperature-dependent, apparent rate parameters. Intrinsic activation energies for isobutane dehydrogenation range from 86 to 235.2 kJ mol⁻¹ (average = 150 ± 42 kJ mol⁻¹) for isobutene dimerization from 48.3 to 267 kJ mol⁻¹ (average = 112 ± 74 kJ mol⁻¹) and for isobutene desorption from 64.4 to 97.8 kJ mol⁻¹ (average = 77 ± 12 kJ mol⁻¹). These wide ranges reflect the heterogeneity and acidity of the zeolite surface and structure. Seven distinct locations and sites, including Lewis and Brønsted acid sites can be identified in the profiles. Isobutane collision frequencies range from 10^−0.4 to 10^22.2 s⁻¹ and are proportional to the accessibility of active sites, within the HZSM-5 micropores or on the external surface. Full article

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199 KiB

Open AccessArticle

An Ionic Liquid Solution of Chitosan as Organocatalyst

by Tatjana Heckel, Dagny Dagmara Konieczna and René Wilhelm

Catalysts 2013, 3(4), 914-921; https://doi.org/10.3390/catal3040914 - 11 Nov 2013

Cited by 19 | Viewed by 8679

Abstract

Chitosan, which is derived from the biopolymer chitin, can be readily dissolved in different ionic liquids. The resulting homogeneous solutions were applied in an asymmetric Aldol reaction. Depending on the type of ionic liquid used, high asymmetric inductions were found. The influence of [...] Read more.

Chitosan, which is derived from the biopolymer chitin, can be readily dissolved in different ionic liquids. The resulting homogeneous solutions were applied in an asymmetric Aldol reaction. Depending on the type of ionic liquid used, high asymmetric inductions were found. The influence of different additives was also studied. The best results were obtained in [BMIM][Br] without an additive. Full article

(This article belongs to the Special Issue Ionic Liquids in Catalysis)

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578 KiB

Open AccessArticle

Formic Acid Oxidation over Hierarchical Porous Carbon Containing PtPd Catalysts

by Angélica M. Baena-Moncada, Gustavo M. Morales, Cesar Barbero, Gabriel A. Planes, Jonathan Florez-Montaño and Elena Pastor

Catalysts 2013, 3(4), 902-913; https://doi.org/10.3390/catal3040902 - 31 Oct 2013

Cited by 8 | Viewed by 6773

Abstract

The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that [...] Read more.

The use of high surface monolithic carbon as support for catalysts offers important advantage, such as elimination of the ohmic drop originated in the interparticle contact and improved mass transport by ad-hoc pore design. Moreover, the approach discussed here has the advantage that it allows the synthesis of materials having a multimodal porous size distribution, with each pore size contributing to the desired properties. On the other hand, the monolithic nature of the porous support also imposes new challenges for metal loading. In this work, the use of Hierarchical Porous Carbon (HPC) as support for PtPd nanoparticles was explored. Three hierarchical porous carbon samples (denoted as HPC-300, HPC-400 and HPC-500) with main pore size around 300, 400 and 500 nm respectively, are used as porous support. PtPd nanoparticles were loaded by impregnation and subsequent chemical reduction with NaBH₄. The resulting material was characterized by EDX, XRD and conventional electrochemical techniques. The catalytic activity toward formic acid and methanol electrooxidation was evaluated by electrochemical methods, and the results compared with commercial carbon supported PtPd. The Hierarchical Porous Carbon support discussed here seems to be promising for use in DFAFC anodes. Full article

(This article belongs to the Special Issue Carbon Catalysts)

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669 KiB

Open AccessReview

Ionic Liquids: The Synergistic Catalytic Effect in the Synthesis of Cyclic Carbonates

by Weiguo Cheng, Qian Su, Jinquan Wang, Jian Sun and Flora T.T. Ng

Catalysts 2013, 3(4), 878-901; https://doi.org/10.3390/catal3040878 - 22 Oct 2013

Cited by 68 | Viewed by 10047

Abstract

This review presents the synergistic effect in the catalytic system of ionic liquids (ILs) for the synthesis of cyclic carbonate from carbon dioxide and epoxide. The emphasis of this review is on three aspects: the catalytic system of metal-based ionic liquids, the catalytic [...] Read more.

This review presents the synergistic effect in the catalytic system of ionic liquids (ILs) for the synthesis of cyclic carbonate from carbon dioxide and epoxide. The emphasis of this review is on three aspects: the catalytic system of metal-based ionic liquids, the catalytic system of hydrogen bond-promoted ionic liquids and supported ionic liquids. Metal and ionic liquids show a synergistic effect on the cycloaddition reactions of epoxides. The cations and anions of ionic liquids show a synergistic effect on the cycloaddition reactions. The functional groups in cations or supports combined with the anions have a synergistic effect on the cycloaddition reactions. Synergistic catalytic effects of ILs play an important role of promoting the cycloaddition reactions of epoxides. The design of catalytic system of ionic liquids will be possible if the synergistic effect on a molecular level is understood. Full article

(This article belongs to the Special Issue Ionic Liquids in Catalysis)

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695 KiB

Open AccessReview

Catalysts Supported on Carbon Materials for the Selective Hydrogenation of Citral

by Esther Bailón-García, Francisco J. Maldonado-Hódar, Agustín F. Pérez-Cadenas and Francisco Carrasco-Marín

Catalysts 2013, 3(4), 853-877; https://doi.org/10.3390/catal3040853 - 22 Oct 2013

Cited by 65 | Viewed by 12191

Abstract

The heterogeneously catalyzed selective-hydrogenation of citral is one of the more feasible ways for obtaining its appreciated unsaturated-alcohols, nerol and geraniol, which are present in over 250 essential oils. Thus, citral has very recently come to be produced petro-chemically in very large quantities, [...] Read more.

The heterogeneously catalyzed selective-hydrogenation of citral is one of the more feasible ways for obtaining its appreciated unsaturated-alcohols, nerol and geraniol, which are present in over 250 essential oils. Thus, citral has very recently come to be produced petro-chemically in very large quantities, and so partial hydrogenation of citral has become a very economical route for the production of these compounds. However, the selective hydrogenation of citral is not easy, because citral is an α,β-unsaturated aldehyde which possesses three double bonds that can be hydrogenated: an isolated C=C bond and the conjugated C=O and C=C bonds. For this reason, in catalyst selection there are several important issues which affect the product selectivity, for example, the active metal and metal particle size which are factors related to the catalyst preparation method, catalyst precursor, or support surface area, as well as other factors such as porosity, the addition of a second catalytic metal, and, of course, the type of catalyst support. About this last one, carbon materials are very interesting supports for this type of hydrogenation reaction due to their unique chemical and textural properties. This review collects and analyzes the results obtained in the selective hydrogenation of citral catalyzed by carbon material supported metals. Full article

(This article belongs to the Special Issue Carbon Catalysts)

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259 KiB

Open AccessArticle

Palladium-Catalyzed Polyfluorophenylation of Porphyrins with Bis(polyfluorophenyl)zinc Reagents

by Noriaki Sugita, Satoshi Hayashi, Sawa Ishii and Toshikatsu Takanami

Catalysts 2013, 3(4), 839-852; https://doi.org/10.3390/catal3040839 - 22 Oct 2013

Cited by 11 | Viewed by 6152

Abstract

A facile and efficient method for the synthesis of pentafluorophenyl- and related polyfluorophenyl-substituted porphyrins has been achieved via palladium-catalyzed cross-coupling reactions of brominated porphyrins with bis(polyfluorophenyl)zinc reagents. The reaction is applicable to a variety of free-base bromoporphyrins, their metal complexes, and a number [...] Read more.

A facile and efficient method for the synthesis of pentafluorophenyl- and related polyfluorophenyl-substituted porphyrins has been achieved via palladium-catalyzed cross-coupling reactions of brominated porphyrins with bis(polyfluorophenyl)zinc reagents. The reaction is applicable to a variety of free-base bromoporphyrins, their metal complexes, and a number of bis(polyfluorophenyl)zinc reagents. Full article

(This article belongs to the Special Issue Palladium Catalysts for Cross-Coupling Reaction)

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1868 KiB

Open AccessReview

Carbon-Supported PtRuMo Electrocatalysts for Direct Alcohol Fuel Cells

by María V. Martínez-Huerta, Nikolaos Tsiouvaras, Gonzalo García, Miguel A. Peña, Elena Pastor, José L. Rodriguez and José L.G. Fierro

Catalysts 2013, 3(4), 811-838; https://doi.org/10.3390/catal3040811 - 21 Oct 2013

Cited by 9 | Viewed by 8047

Abstract

The review article discusses the current status and recent findings of our investigations on the synthesis and characterization of carbon-supported PtRuMo electrocatalysts for direct alcohol fuel cells. In particular, the effect of the carbon support and the composition on the structure, stability and [...] Read more.

The review article discusses the current status and recent findings of our investigations on the synthesis and characterization of carbon-supported PtRuMo electrocatalysts for direct alcohol fuel cells. In particular, the effect of the carbon support and the composition on the structure, stability and the activity of the PtRuMo nanoparticles for the electrooxidation of CO, methanol and ethanol have been studied. Different physicochemical techniques have been employed for the analysis of the catalysts structures: X-ray analytical methods (XRD, XPS, TXRF), thermogravimetry (TGA) and transmission electron microscopy (TEM), as well as a number of electrochemical techniques like CO adsorption studies, current-time curves and cyclic voltammetry measurements. Furthermore, spectroscopic methods adapted to the electrochemical systems for in situ studies, such as Fourier transform infrared spectroscopy (FTIRS) and differential electrochemical mass spectrometry (DEMS), have been used to evaluate the oxidation process of CO, methanol and ethanol over the carbon-supported PtRuMo electrocatalysts. Full article

(This article belongs to the Special Issue Carbon Catalysts)

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719 KiB

Open AccessReview

Palladium-Catalyzed Intermolecular Oxidative Amination of Alkenes with Amines, Using Molecular Oxygen as Terminal Oxidant

by Yasushi Obora and Yasutaka Ishii

Catalysts 2013, 3(4), 794-810; https://doi.org/10.3390/catal3040794 - 16 Oct 2013

Cited by 28 | Viewed by 10303

Abstract

In this review, we summarize recent progress from our group with regard to Pd-catalyzed oxidative amination of alkenes with amines. Intermolecular oxidative amination of alkenes with secondary anilines was induced using a palladium-complex catalyst combined with molybdovanadophosphate as a co-catalyst under dioxygen, leading [...] Read more.

In this review, we summarize recent progress from our group with regard to Pd-catalyzed oxidative amination of alkenes with amines. Intermolecular oxidative amination of alkenes with secondary anilines was induced using a palladium-complex catalyst combined with molybdovanadophosphate as a co-catalyst under dioxygen, leading to allylic amines and enamines in good yields with high selectivities. The reaction proceeded efficiently, using molecular oxygen as the terminal oxidant. In addition, palladium-catalyzed oxidative amination of alkenes with anilines as primary amines was achieved using molecular oxygen as the sole oxidant, producing (Z)-N-alkenyl-substituted anilines in high yields. Full article

(This article belongs to the Special Issue Palladium Catalysts for Cross-Coupling Reaction)

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2817 KiB

Open AccessReview

Mesoporous Silica Based Gold Catalysts: Novel Synthesis and Application in Catalytic Oxidation of CO and Volatile Organic Compounds (VOCs)

by Hongjing Wu, Giuseppe Pantaleo, Anna M. Venezia and Leonarda F. Liotta

Catalysts 2013, 3(4), 774-793; https://doi.org/10.3390/catal3040774 - 15 Oct 2013

Cited by 29 | Viewed by 9677

Abstract

Gold nanoparticles, particularly with the particle size of 2–5 nm, have attracted increasing research attention during the past decades due to their surprisingly high activity in CO and volatile organic compounds (VOCs) oxidation at low temperatures. In particular, CO oxidation below room temperature [...] Read more.

Gold nanoparticles, particularly with the particle size of 2–5 nm, have attracted increasing research attention during the past decades due to their surprisingly high activity in CO and volatile organic compounds (VOCs) oxidation at low temperatures. In particular, CO oxidation below room temperature has been extensively studied on gold nanoparticles supported on several oxides (TiO₂, Fe₂O₃, CeO₂, etc.). Recently, mesoporous silica materials (such as SBA-15, MCM-41, MCM-48 and HMS) possessing ordered channel structures and suitable pore diameters, large internal surface areas, thermal stabilities and excellent mechanical properties, have been investigated as suitable hosts for gold nanoparticles. In this review we highlight the development of novel mesoporous silica based gold catalysts based on examples, mostly from recently reported results. Several synthesis methods are described herein. In detail we report: the modification of silica with organic functional groups; the one-pot synthesis with the incorporation of both gold and coupling agent containing functionality for the synthesis of mesoporous silica; the use of cationic gold complexes; the synthesis of silica in the presence of gold colloids or the dispersion of gold colloids protected by ligands or polymers onto silica; the modification of silica by other metal oxides; other conventional preparation methods to form mesoporous silica based gold catalysts. The gold based catalysts prepared as such demonstrate good potential for use in oxidation of CO and VOCs at low temperatures. From the wide family of VOCs, the oxidation of methanol and dimethyldisulfide has been addressed in the present review. Full article

(This article belongs to the Special Issue Catalytic Combustion)

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775 KiB

Open AccessArticle

Sulfonate Ionic Liquid as a Stable and Active Catalyst for Levoglucosenone Production from Saccharides via Catalytic Pyrolysis

by Shinji Kudo, Zhenwei Zhou, Kento Yamasaki, Koyo Norinaga and Jun-ichiro Hayashi

Catalysts 2013, 3(4), 757-773; https://doi.org/10.3390/catal3040757 - 30 Sep 2013

Cited by 42 | Viewed by 10233

Abstract

In this study, various types of ionic liquids (ILs) were examined for catalytic activity in the pyrolysis of cellulose for the production of levoglucosenone, which is a valuable and versatile compound for the synthesis of a variety of novel compounds. Cellulose was simply [...] Read more.

In this study, various types of ionic liquids (ILs) were examined for catalytic activity in the pyrolysis of cellulose for the production of levoglucosenone, which is a valuable and versatile compound for the synthesis of a variety of novel compounds. Cellulose was simply mixed with the ILs and subjected for the pyrolysis, typically at 300 °C, to produce volatile products, including levoglucosenone, separated from the ILs phase. The type of IL anion significantly affected the catalysis, and the use of ILs bearing sulfonate anion resulted in distinguished yields of levoglucosenone and IL recoveries for the reutilization. Detailed thermogravimetric analysis and discussion on properties of ILs revealed the active and thermally stable nature of the sulfonate ILs. Catalytic pyrolysis with those ILs was applied to the conversion of other saccharides composed of glucose molecules, resulting in a preferential formation of levoglucosenone but at low yields as compared to that from cellulose. Full article

(This article belongs to the Special Issue Ionic Liquids in Catalysis)

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Catalysts, Volume 3, Issue 4 (December 2013) – 14 articles , Pages 757-997

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