Catalysts

1156 KiB

Open AccessArticle

Structural Evolution under Reaction Conditions of Supported (NH₄)₃HPMo₁₁VO₄₀ Catalysts for the Selective Oxidation of Isobutane

by Fangli Jing, Benjamin Katryniok, Elisabeth Bordes-Richard, Franck Dumeignil and Sébastien Paul

Catalysts 2015, 5(1), 460-477; https://doi.org/10.3390/catal5010460 - 23 Mar 2015

Cited by 17 | Viewed by 7810

Abstract

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH₄ [...] Read more.

When using heteropolycompounds in the selective oxidation of isobutane to methacrolein and methacrylic acid, both the keeping of the primary structure (Keggin units) and the presence of acidic sites are necessary to obtain the desired products. The structural evolution of supported (NH₄)₃HPMo₁₁VO₄₀ (APMV) catalysts under preliminary thermal oxidizing and reducing treatments was investigated. Various techniques, such as TGA/DTG (Thermo-Gravimetric Analysis/Derivative Thermo-Gravimetry), H₂-TPR (Temperature Programed Reduction), in situ XRD (X-Ray Diffraction) and XPS (X-ray Photoelectron Spectroscopy), were applied. It was clearly evidenced that the thermal stability and the reducibility of the Keggin units are improved by supporting 40% APMV active phase on Cs₃PMo₁₂O₄₀ (CPM). The partial degradation of APMV takes place depending on temperature and reaction conditions. The decomposition of ammonium cations (releasing NH₃) leads to the formation of vacancies favoring cationic exchanges between vanadium coming from the active phase and cesium coming from the support. In addition, the vanadium expelled from the Keggin structure is further reduced to V⁴⁺, species, which contributes (with Mo⁵⁺) to activate isobutane. The increase in reducibility of the supported catalyst is assumed to improve the catalytic performance in comparison with those of unsupported APMV. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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10957 KiB

Open AccessArticle

Design of Cobalt Nanoparticles with Tailored Structural and Morphological Properties via O/W and W/O Microemulsions and Their Deposition onto Silica

by Gabriella Di Carlo, Matteo Lualdi, Anna M. Venezia, Magali Boutonnet and Margarita Sanchez-Dominguez

Catalysts 2015, 5(1), 442-459; https://doi.org/10.3390/catal5010442 - 19 Mar 2015

Cited by 17 | Viewed by 7601

Abstract

Cobalt nanostructures with different size and morphology, i.e., spherical nanoparticles, nanorods, and particles arranged into elongated structures, were prepared using micelles and microemulsions as confined reaction media. The syntheses were carried out using three types of systems: aqueous surfactant solutions, oil-in water [...] Read more.

Cobalt nanostructures with different size and morphology, i.e., spherical nanoparticles, nanorods, and particles arranged into elongated structures, were prepared using micelles and microemulsions as confined reaction media. The syntheses were carried out using three types of systems: aqueous surfactant solutions, oil-in water (O/W), and water-in-oil (W/O) microemulsions. The influence of the surfactant and the precipitating agent used for synthesis was also investigated. For this purpose, cobalt nanostructures were prepared using different non-ionic surfactants, namely Synperonic^® 10/6, Pluronic^® P123 and a mixture of SPAN 20–TWEEN 80. Three different precipitating agents were used: sodium borohydride, sodium hydroxide, and oxalic acid. Our findings revealed that by changing the type of reaction media as well as the precipitating agent it is possible to modify the shape and size of the cobalt nanostructures. Moreover, the use of O/W microemulsion generates better results in terms of colloidal stability and uniformity of particle size with respect to W/O microemulsion. The different cobalt nanostructures were supported on commercial and mesoporous silica; transmission electron microscopy (TEM) images showed that after deposition the Co nanocrystals remain well dispersed on the silica supports. This behavior suggests their great potential in catalytic applications. Full article

(This article belongs to the Special Issue Synthesis of Nanostructured Catalytic Materials from Microemulsions)

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4980 KiB

Open AccessArticle

Activated Carbon, Carbon Nanofiber and Carbon Nanotube Supported Molybdenum Carbide Catalysts for the Hydrodeoxygenation of Guaiacol

by Eduardo Santillan-Jimenez, Maxime Perdu, Robert Pace, Tonya Morgan and Mark Crocker

Catalysts 2015, 5(1), 424-441; https://doi.org/10.3390/catal5010424 - 16 Mar 2015

Cited by 66 | Viewed by 8665

Abstract

Molybdenum carbide was supported on three types of carbon support—activated carbon; multi-walled carbon nanotubes; and carbon nanofibers—using ammonium molybdate and molybdic acid as Mo precursors. The use of activated carbon as support afforded an X-ray amorphous Mo phase, whereas crystalline molybdenum carbide phases [...] Read more.

Molybdenum carbide was supported on three types of carbon support—activated carbon; multi-walled carbon nanotubes; and carbon nanofibers—using ammonium molybdate and molybdic acid as Mo precursors. The use of activated carbon as support afforded an X-ray amorphous Mo phase, whereas crystalline molybdenum carbide phases were obtained on carbon nanofibers and, in some cases, on carbon nanotubes. When the resulting catalysts were tested in the hydrodeoxygenation (HDO) of guaiacol in dodecane, catechol and phenol were obtained as the main products, although in some instances significant amounts of cyclohexane were produced. The observation of catechol in all reaction mixtures suggests that guaiacol was converted into phenol via sequential demethylation and HDO, although the simultaneous occurrence of a direct demethoxylation pathway cannot be discounted. Catalysts based on carbon nanofibers generally afforded the highest yields of phenol; notably, the only crystalline phase detected in these samples was Mo₂C or Mo₂C-ζ, suggesting that crystalline Mo₂C is particularly selective to phenol. At 350 °C, carbon nanofiber supported Mo₂C afforded near quantitative guaiacol conversion, the selectivity to phenol approaching 50%. When guaiacol HDO was performed in the presence of acetic acid and furfural, guaiacol conversion decreased, although the selectivity to both catechol and phenol was increased. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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1439 KiB

Open AccessArticle

Structural Evolution of Molybdenum Carbides in Hot Aqueous Environments and Impact on Low-Temperature Hydroprocessing of Acetic Acid

by Jae-Soon Choi, Viviane Schwartz, Eduardo Santillan-Jimenez, Mark Crocker, Samuel A. Lewis, Sr., Michael J. Lance, Harry M. Meyer III and Karren L. More

Catalysts 2015, 5(1), 406-423; https://doi.org/10.3390/catal5010406 - 13 Mar 2015

Cited by 15 | Viewed by 6685

Abstract

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites [...] Read more.

We investigated the structural evolution of molybdenum carbides subjected to hot aqueous environments and their catalytic performance in low-temperature hydroprocessing of acetic acid. While bulk structures of Mo carbides were maintained after aging in hot liquid water, a portion of carbidic Mo sites were converted to oxidic sites. Water aging also induced changes to the non-carbidic carbon deposited during carbide synthesis and increased surface roughness, which in turn affected carbide pore volume and surface area. The extent of these structural changes was sensitive to the initial carbide structure and was lower under actual hydroprocessing conditions indicating the possibility of further improving the hydrothermal stability of Mo carbides by optimizing catalyst structure and operating conditions. Mo carbides were active in acetic acid conversion in the presence of liquid water, their activity being comparable to that of Ru/C. The results suggest that effective and inexpensive bio-oil hydroprocessing catalysts could be designed based on Mo carbides, although a more detailed understanding of the structure-performance relationships is needed, especially in upgrading of more complex reaction mixtures or real bio-oils. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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5229 KiB

Open AccessArticle

Influence of the Synthesis Method for Pt Catalysts Supported on Highly Mesoporous Carbon Xerogel and Vulcan Carbon Black on the Electro-Oxidation of Methanol

by Cinthia Alegre, María Elena Gálvez, Rafael Moliner and María Jesús Lázaro

Catalysts 2015, 5(1), 392-405; https://doi.org/10.3390/catal5010392 - 13 Mar 2015

Cited by 29 | Viewed by 7038

Abstract

Platinum catalysts supported on carbon xerogel and carbon black (Vulcan) were synthesized with the aim of investigating the influence of the characteristics of the support on the electrochemical performance of the catalysts. Three synthesis methods were compared: an impregnation method with two different [...] Read more.

Platinum catalysts supported on carbon xerogel and carbon black (Vulcan) were synthesized with the aim of investigating the influence of the characteristics of the support on the electrochemical performance of the catalysts. Three synthesis methods were compared: an impregnation method with two different reducing agents, sodium borohydride and formic acid, and a microemulsion method, in order to study the effect of the synthesis method on the physico-chemical properties of the catalysts. X-ray diffraction and transmission electron microscopy were applied. Cyclic voltammetry and chronoamperometry were used for studying carbon monoxide and methanol oxidation. Catalysts supported on carbon xerogel presented higher catalytic activities towards CO and CH₃OH oxidation than catalysts supported on Vulcan. The higher mesoporosity of carbon xerogel was responsible for the favored diffusion of reagents towards catalytic centers. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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3358 KiB

Open AccessReview

B-Site Metal (Pd, Pt, Ag, Cu, Zn, Ni) Promoted La_1−xSr_xCo_1−yFe_yO_3–_δPerovskite Oxides as Cathodes for IT-SOFCs

by Shaoli Guo, Hongjing Wu, Fabrizio Puleo and Leonarda F. Liotta

Catalysts 2015, 5(1), 366-391; https://doi.org/10.3390/catal5010366 - 12 Mar 2015

Cited by 52 | Viewed by 12701

Abstract

Perovskite oxides La_1−xSr_xCo_1−yFe_yO_3–δ (LSCF) have been extensively investigated and developed as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to mixed ionic–electronic conductivity and high electrooxygen reduction activity for [...] Read more.

Perovskite oxides La_1−xSr_xCo_1−yFe_yO_3–δ (LSCF) have been extensively investigated and developed as cathode materials for intermediate temperature solid oxide fuel cells (IT-SOFCs) due to mixed ionic–electronic conductivity and high electrooxygen reduction activity for oxygen reduction. Recent literature investigations show that cathode performances can be improved by metal surface modification or B-site substitution on LSCF. Although the specific reaction mechanism needs to be further investigated, the promoting effect of metal species in enhancing oxygen surface exchange and oxygen bulk diffusion is well recognized. To our knowledge, no previous reviews dealing with the effect of metal promotion on the cathodic performances of LSCF materials have been reported. In the present review, recent progresses on metal (Pd, Pt, Ag, Cu, Zn, Ni) promotion of LSCF are discussed focusing on two main aspects, the different synthesis approaches used (infiltration, deposition, solid state reaction, one pot citrate method) and the effects of metal promotion on structural properties, oxygen vacancies content and cathodic performances. The novelty of the work lies in the fact that the metal promotion at the B-site is discussed in detail, pointing at the effects produced by two different approaches, the LSCF surface modification by the metal or the metal ion substitution at the B-site of the perovskite. Moreover, for the first time in a review article, the importance of the combined effects of oxygen dissociation rate and interfacial oxygen transfer rate between the metal phase and the cathode phase is addressed for metal-promoted LSCF and compared with the un-promoted oxides. Perspectives on new research directions are shortly given in the conclusion. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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6340 KiB

Open AccessArticle

A Mechanistic Study of Direct Activation of Allylic Alcohols in Palladium Catalyzed Amination Reactions

by Yasemin Gumrukcu, Bas De Bruin and Joost N. H. Reek

Catalysts 2015, 5(1), 349-365; https://doi.org/10.3390/catal5010349 - 11 Mar 2015

Cited by 15 | Viewed by 8442

Abstract

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative [...] Read more.

We here report a computational approach on the mechanism of allylicamination reactions using allyl-alcohols and amines as the substrates and phosphoramidite palladium catalyst 1a, which operates in the presence of catalytic amount of 1,3-diethylurea as a co-catalyst. DFT calculations showed a cooperative hydrogen-bonding array between the urea moiety and the hydroxyl group of the allyl alcohol, which strengthens the hydrogen bond between the O-H moiety of the coordinated allyl-alcohol and the carbonyl-moiety of the ligand. This hydrogen bond pattern facilitates the (rate-limiting) C-O oxidative addition step and leads to lower energy isomers throughout the catalytic cycle, clarifying the role of the urea-moiety. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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22504 KiB

Open AccessReview

Recent Advances in Carbon Supported Metal Nanoparticles Preparation for Oxygen Reduction Reaction in Low Temperature Fuel Cells

by Yaovi Holade, Nihat Ege Sahin, Karine Servat, Teko W. Napporn and Kouakou B. Kokoh

Catalysts 2015, 5(1), 310-348; https://doi.org/10.3390/catal5010310 - 6 Mar 2015

Cited by 99 | Viewed by 23280

Abstract

The oxygen reduction reaction (ORR) is the oldest studied and most challenging of the electrochemical reactions. Due to its sluggish kinetics, ORR became the major contemporary technological hurdle for electrochemists, as it hampers the commercialization of fuel cell (FC) technologies. Downsizing the metal [...] Read more.

The oxygen reduction reaction (ORR) is the oldest studied and most challenging of the electrochemical reactions. Due to its sluggish kinetics, ORR became the major contemporary technological hurdle for electrochemists, as it hampers the commercialization of fuel cell (FC) technologies. Downsizing the metal particles to nanoscale introduces unexpected fundamental modifications compared to the corresponding bulk state. To address these fundamental issues, various synthetic routes have been developed in order to provide more versatile carbon-supported low platinum catalysts. Consequently, the approach of using nanocatalysts may overcome the drawbacks encountered in massive materials for energy conversion. This review paper aims at summarizing the recent important advances in carbon-supported metal nanoparticles preparation from colloidal methods (microemulsion, polyol, impregnation, Bromide Anion Exchange…) as cathode material in low temperature FCs. Special attention is devoted to the correlation of the structure of the nanoparticles and their catalytic properties. The influence of the synthesis method on the electrochemical properties of the resulting catalysts is also discussed. Emphasis on analyzing data from theoretical models to address the intrinsic and specific electrocatalytic properties, depending on the synthetic method, is incorporated throughout. The synthesis process-nanomaterials structure-catalytic activity relationships highlighted herein, provide ample new rational, convenient and straightforward strategies and guidelines toward more effective nanomaterials design for energy conversion. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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613 KiB

Open AccessArticle

Ni-CeO₂/C Catalysts with Enhanced OSC for the WGS Reaction

by Laura Pastor-Pérez, Tomás Ramírez Reina, Svetlana Ivanova, Miguel Ángel Centeno, José Antonio Odriozola and Antonio Sepúlveda-Escribano

Catalysts 2015, 5(1), 298-309; https://doi.org/10.3390/catal5010298 - 6 Mar 2015

Cited by 25 | Viewed by 8492

Abstract

In this work, the WGS performance of a conventional Ni/CeO₂ bulk catalyst is compared to that of a carbon-supported Ni-CeO₂ catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO₂ [...] Read more.

In this work, the WGS performance of a conventional Ni/CeO₂ bulk catalyst is compared to that of a carbon-supported Ni-CeO₂ catalyst. The carbon-supported sample resulted to be much more active than the bulk one. The higher activity of the Ni-CeO₂/C catalyst is associated to its oxygen storage capacity, a parameter that strongly influences the WGS behavior. The stability of the carbon-supported catalyst under realistic operation conditions is also a subject of this paper. In summary, our study represents an approach towards a new generation of Ni-ceria based catalyst for the pure hydrogen production via WGS. The dispersion of ceria nanoparticles on an activated carbon support drives to improved catalytic skills with a considerable reduction of the amount of ceria in the catalyst formulation. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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4705 KiB

Open AccessArticle

Downhole Upgrading of Orinoco Basin Extra-Heavy Crude Oil Using Hydrogen Donors under Steam Injection Conditions. Effect of the Presence of Iron Nanocatalysts

by Cesar Ovalles, Victor Rivero and Arelys Salazar

Catalysts 2015, 5(1), 286-297; https://doi.org/10.3390/catal5010286 - 5 Mar 2015

Cited by 25 | Viewed by 7292

Abstract

An extra-heavy crude oil underground upgrading concept and laboratory experiments are presented which involve the addition of a hydrogen donor (tetralin) to an Orinoco Basin extra-heavy crude oil under steam injection conditions (280–315 °C and residence times of at least 24-h). Three iron-containing [...] Read more.

An extra-heavy crude oil underground upgrading concept and laboratory experiments are presented which involve the addition of a hydrogen donor (tetralin) to an Orinoco Basin extra-heavy crude oil under steam injection conditions (280–315 °C and residence times of at least 24-h). Three iron-containing nanocatalysts (20 nm, 60 nm and 90 nm) were used and the results showed increases of up to 8° in API gravity, 26% desulfurization and 27% reduction in the asphaltene content of the upgraded product in comparison to the control reaction using inert sand. The iron nanocatalysts were characterized by SEM, XPS, EDAX, and Mössbauer spectroscopy before and after the upgrading reactions. The results indicated the presence of hematite (Fe₂O₃) as the predominant iron phase. The data showed that the catalysts were deactivating by particle sintering (~20% increase in particle size) and also by carbon deposition. Probable mechanisms of reactions are proposed. Full article

(This article belongs to the Special Issue Upgrading Tar Sands and Heavy Crude)

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1370 KiB

Open AccessArticle

CNT-TiO_2−δ Composites for Improved Co-Catalyst Dispersion and Stabilized Photocatalytic Hydrogen Production

by Peirong Chen, Lidong Wang, Ping Wang, Aleksander Kostka, Michael Wark, Martin Muhler and Radim Beranek

Catalysts 2015, 5(1), 270-285; https://doi.org/10.3390/catal5010270 - 2 Mar 2015

Cited by 19 | Viewed by 8148

Abstract

Composites consisting of carbon nanotubes (CNTs) grown directly on oxygen-deficient anatase TiO₂ (TiO_2−δ) were synthesized by a two-step chemical vapor deposition (CVD) method and applied in photocatalytic hydrogen production from aqueous methanol solutions using photodeposited Pt as the co-catalyst. Thermogravimetry [...] Read more.

Composites consisting of carbon nanotubes (CNTs) grown directly on oxygen-deficient anatase TiO₂ (TiO_2−δ) were synthesized by a two-step chemical vapor deposition (CVD) method and applied in photocatalytic hydrogen production from aqueous methanol solutions using photodeposited Pt as the co-catalyst. Thermogravimetry coupled with mass spectroscopy, X-ray diffraction, scanning electron microscopy, photocurrent analysis, X-ray photoelectron spectroscopy, and (scanning) transmission electron microscopy were performed to investigate the physical and (photo)chemical properties of the synthesized CNT-TiO_2−δ composites before and after photocatalytic methanol reforming. The initial photocatalytic activity of TiO₂ was found to be significantly improved in the presence of oxygen vacancies. An optimized amount (~7.2 wt%) of CNTs grown on the TiO_2−δ surface led to a highly effective stabilization of the photocatalytic performance of TiO_2−δ, which is attributed to the improved dispersion and stability of the photodeposited Pt co-catalyst nanoparticles and enhanced separation efficiency of photogenerated electron-hole pairs, rendering the photocatalysts less prone to deactivation. Full article

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6228 KiB

Open AccessReview

Heterogeneous Catalyst Deactivation and Regeneration: A Review

by Morris D. Argyle and Calvin H. Bartholomew

Catalysts 2015, 5(1), 145-269; https://doi.org/10.3390/catal5010145 - 26 Feb 2015

Cited by 1334 | Viewed by 99354

Abstract

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid [...] Read more.

Deactivation of heterogeneous catalysts is a ubiquitous problem that causes loss of catalytic rate with time. This review on deactivation and regeneration of heterogeneous catalysts classifies deactivation by type (chemical, thermal, and mechanical) and by mechanism (poisoning, fouling, thermal degradation, vapor formation, vapor-solid and solid-solid reactions, and attrition/crushing). The key features and considerations for each of these deactivation types is reviewed in detail with reference to the latest literature reports in these areas. Two case studies on the deactivation mechanisms of catalysts used for cobalt Fischer-Tropsch and selective catalytic reduction are considered to provide additional depth in the topics of sintering, coking, poisoning, and fouling. Regeneration considerations and options are also briefly discussed for each deactivation mechanism. Full article

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

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1048 KiB

Open AccessArticle

Selective Oxidation of Raw Glycerol Using Supported AuPd Nanoparticles

by Carine E. Chan-Thaw, Sebastiano Campisi, Di Wang, Laura Prati and Alberto Villa

Catalysts 2015, 5(1), 131-144; https://doi.org/10.3390/catal5010131 - 13 Feb 2015

Cited by 29 | Viewed by 7285

Abstract

Bimetallic AuPd supported on different carbonaceous materials and TiO₂ was tested in the liquid phase oxidation of commercial grade and raw glycerol. The latter was directly obtained from the base-catalyzed transesterification of edible rapeseed oil using KOH. The best catalytic results were [...] Read more.

Bimetallic AuPd supported on different carbonaceous materials and TiO₂ was tested in the liquid phase oxidation of commercial grade and raw glycerol. The latter was directly obtained from the base-catalyzed transesterification of edible rapeseed oil using KOH. The best catalytic results were obtained using activated carbon and nitrogen-functionalized carbon nanofibers as supports. In fact, the catalysts were more active using pure glycerol instead of the one obtained from rapeseed, where strong deactivation phenomena were present. Fourier transform infrared (FT-IR) and TEM were utilized to investigate the possible reasons for the observed loss of activity. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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156 KiB

Open AccessArticle

Guanidine Hydrochloride/ZnI₂ as Heterogeneous Catalyst for Conversion of CO₂ and Epoxides to Cyclic Carbonates under Mild Conditions

by Bo Liu, Mengshuai Liu, Lin Liang and Jianmin Sun

Catalysts 2015, 5(1), 119-130; https://doi.org/10.3390/catal5010119 - 11 Feb 2015

Cited by 15 | Viewed by 10217

Abstract

In this article, the combination of guanidine hydrochloride with co-catalyst ZnI₂ proved to be a highly efficient heterogeneous catalyst for the environmentally benign, solvent-free synthesis of cyclic carbonates under mild reaction conditions. The effects of different co-catalysts as well as reaction parameters [...] Read more.

In this article, the combination of guanidine hydrochloride with co-catalyst ZnI₂ proved to be a highly efficient heterogeneous catalyst for the environmentally benign, solvent-free synthesis of cyclic carbonates under mild reaction conditions. The effects of different co-catalysts as well as reaction parameters including catalyst loadings, CO₂ pressure, reaction temperature, and reaction time on the coupling reaction of CO₂ to propylene oxide were thoroughly investigated. With the molar ratio of guanidine hydrochloride to ZnI₂ at 5:1, excellent yield (94%) and selectivity (≥99%) of propylene carbonate were obtained under 100 °C and at 1 MPa for 1.5 h. Additionally, ZnI₂ could be recycled, but because of the washing loss of guanidine hydrochloride, there was a slight decrease in the yield of propylene carbonate. Gratifyingly, the activity of the catalytic system could be restored by adding additional 20 mol% of fresh guanidine hydrochloride, thus exhibiting excellent recyclability of the ZnI₂ catalyst. Moreover, the binary catalysts were also versatile when using other epoxides for CO₂ cycloaddition. A possible reaction mechanism was proposed wherein guanidine hydrochloride plays a dual role in activating CO₂ and epoxide, and ZnI₂ activated epoxide, simultaneously. The synergistic effect of guanidine hydrochloride and ZnI₂ ensure the reaction proceeds effectively. Full article

(This article belongs to the Special Issue Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis)

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14316 KiB

Open AccessArticle

Application of “Boomerang” Linear Polystyrene-Stabilized Pd Nanoparticles to a Series of C-C Coupling Reactions in Water

by Atsushi Ohtaka, Toshiyuki Okagaki, Go Hamasaka, Yasuhiro Uozumi, Tsutomu Shinagawa, Osamu Shimomura and Ryôki Nomura

Catalysts 2015, 5(1), 106-118; https://doi.org/10.3390/catal5010106 - 9 Feb 2015

Cited by 27 | Viewed by 7985

Abstract

The application of a catch-and-release system for soluble Pd species between water (reaction medium) and polystyrene (polymer support) was examined in the Suzuki coupling reaction with 2-bromothiophene and the Heck reaction with styrene or bromobenzene. Although a slight increase in particle size was [...] Read more.

The application of a catch-and-release system for soluble Pd species between water (reaction medium) and polystyrene (polymer support) was examined in the Suzuki coupling reaction with 2-bromothiophene and the Heck reaction with styrene or bromobenzene. Although a slight increase in particle size was observed by TEM after re-stabilization of the Pd species on linear polystyrene, no agglomeration was observed. Full article

(This article belongs to the Special Issue Metal Catalysts Recycling and Heterogeneous/Homogeneous Catalysis)

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5585 KiB

Open AccessArticle

Preparation for Pt-Loaded Zeolite Catalysts Using w/o Microemulsion and Their Hydrocracking Behaviors on Fischer-Tropsch Product

by Toshiaki Hanaoka, Tomohisa Miyazawa, Katsuya Shimura and Satoshi Hirata

Catalysts 2015, 5(1), 88-105; https://doi.org/10.3390/catal5010088 - 6 Feb 2015

Cited by 7 | Viewed by 8096

Abstract

Pt-loaded β-type zeolite catalysts with constant Pt content (0.11 wt.%) and similar pore structure were prepared using a water-in-oil (w/o) microemulsion. The effect of Pt particle synthesis conditions using microemulsion (a type of Pt complex-forming agents and the molar ratio of complex-forming agent [...] Read more.

Pt-loaded β-type zeolite catalysts with constant Pt content (0.11 wt.%) and similar pore structure were prepared using a water-in-oil (w/o) microemulsion. The effect of Pt particle synthesis conditions using microemulsion (a type of Pt complex-forming agents and the molar ratio of complex-forming agent to Pt⁴⁺) on loaded Pt particle size was investigated. The Pt particle size of the Pt catalyst using tetraethylammonium chloride (TEAC) as a complex-forming agent with the molar TEAC/Pt ratio 10 was the minimum value (3.8 nm), and was much smaller than that (6.7 nm) prepared by the impregnation method. The utilization of the complex-forming agent of which hydrophobic groups occupied a small volume and the appropriate complex-forming agent/Pt ratio were favorable for synthesis of small Pt particles. The effect of loaded Pt particle size on the hydrocracking of the Fischer-Tropsch (FT) product was investigated using the Pt-loaded zeolite catalysts at 250 °C with an initial H₂ pressure of 0.5 MPa, and reaction time of 1 h. The Pt catalyst with a Pt particle size of 4.2 nm prepared using the microemulsion exhibited the maximum corresponding jet fuel yield (30.0%), which was higher than that of the impregnated catalyst. Full article

(This article belongs to the Special Issue Synthesis of Nanostructured Catalytic Materials from Microemulsions)

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6499 KiB

Open AccessArticle

Supported Photocatalyst for Removal of Emerging Contaminants from Wastewater in a Continuous Packed-Bed Photoreactor Configuration

by Mª Emma Borges, Dulce María García, Tania Hernández, Juan Carlos Ruiz-Morales and Pedro Esparza

Catalysts 2015, 5(1), 77-87; https://doi.org/10.3390/catal5010077 - 2 Feb 2015

Cited by 54 | Viewed by 8992

Abstract

Water pollution from emerging contaminants (ECs) or emerging pollutants is an important environmental problem. Heterogeneous photocatalytic treatment, as advanced oxidation treatment of wastewater effluents, has been proposed to solve this problem. In this paper, a heterogeneous photocatalytic process was studied for emergent contaminants [...] Read more.

Water pollution from emerging contaminants (ECs) or emerging pollutants is an important environmental problem. Heterogeneous photocatalytic treatment, as advanced oxidation treatment of wastewater effluents, has been proposed to solve this problem. In this paper, a heterogeneous photocatalytic process was studied for emergent contaminants removal using paracetamol as a model contaminant molecule. TiO₂ photocatalytic activity was evaluated using two photocatalytic reactor configurations: Photocatalyst solid suspension in wastewater in a stirred photoreactor and TiO₂ supported on glass spheres (TGS) configuring a packed bed photoreactor. The surface morphology and texture of the TGS were monitored by scanning electron microscope (SEM). The influence of photocatalyst amount and wastewater pH were evaluated in the stirred photoreactor and the influence of wastewater flowrate was tested in the packed bed photoreactor, in order to obtain the optimal operation conditions. Moreover, results obtained were compared with those obtained from photolysis and adsorption studies, using the optimal operation conditions. Good photocatalytic activities have been observed and leads to the conclusion that the heterogeneous photocatalytic system in a packed bed is an effective method for removal of emerging pollutants. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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11807 KiB

Open AccessArticle

Effect of Ce and Zr Addition to Ni/SiO2 Catalysts for Hydrogen Production through Ethanol Steam Reforming

by Jose Antonio Calles, Alicia Carrero, Arturo Javier Vizcaíno and Montaña Lindo

Catalysts 2015, 5(1), 58-76; https://doi.org/10.3390/catal5010058 - 30 Jan 2015

Cited by 37 | Viewed by 10037

Abstract

A series of Ni/Ce\(_{x}\)Zr\(_{1-x}\)O\(_{2}\)/SiO\(_{2}\) catalysts with different Zr/Ce mass ratios were prepared by incipient wetness impregnation. Ni/SiO\(_{2}\), Ni/CeO\(_{2}\) and Ni/ZrO\(_{2}\) were also prepared as reference materials to compare. Catalysts' performances were tested in ethanol steam reforming for hydrogen production and characterized by XRD, [...] Read more.

A series of Ni/Ce\(_{x}\)Zr\(_{1-x}\)O\(_{2}\)/SiO\(_{2}\) catalysts with different Zr/Ce mass ratios were prepared by incipient wetness impregnation. Ni/SiO\(_{2}\), Ni/CeO\(_{2}\) and Ni/ZrO\(_{2}\) were also prepared as reference materials to compare. Catalysts' performances were tested in ethanol steam reforming for hydrogen production and characterized by XRD, H\(_{2}\)-temperature programmed reduction (TPR), NH\(_{3}\)-temperature programmed desorption (TPD), TEM, ICP-AES and N\(_{2}\)-sorption measurements. The Ni/SiO\(_{2}\) catalyst led to a higher hydrogen selectivity than Ni/CeO\(_{2}\) and Ni/ZrO\(_{2}\), but it could not maintain complete ethanol conversion due to deactivation. The incorporation of Ce or Zr prior to Ni on the silica support resulted in catalysts with better performance for steam reforming, keeping complete ethanol conversion over time. When both Zr and Ce were incorporated into the catalyst, Ce\(_{x}\)Zr\(_{1-x}\)O\(_{2}\) solid solution was formed, as confirmed by XRD analyses. TPR results revealed stronger Ni-support interaction in the Ce\(_{x}\)Zr\(_{1-x}\)O\(_{2}\)-modified catalysts than in Ni/SiO\(_{2}\) one, which can be attributed to an increase of the dispersion of Ni species. All of the Ni/Ce\(_{x}\)Zr\(_{1-x}\)O\(_{2}\)/SiO\(_{2}\) catalysts exhibited good catalytic activity and stability after 8 h of time on stream at 600°. The best catalytic performance in terms of hydrogen selectivity was achieved when the Zr/Ce mass ratio was three. Full article

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

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3434 KiB

Open AccessReview

Design of Pt/Carbon Xerogel Catalysts for PEM Fuel Cells

by Nathalie Job, Stéphanie D. Lambert, Anthony Zubiaur, Chongjiang Cao and Jean-Paul Pirard

Catalysts 2015, 5(1), 40-57; https://doi.org/10.3390/catal5010040 - 28 Jan 2015

Cited by 17 | Viewed by 9338

Abstract

The design of efficient catalytic layers of proton exchange membrane fuel cells (PEMFCs) requires the preparation of highly-loaded and highly-dispersed Pt/C catalysts. During the last few years, our work focused on the preparation of Pt/carbon xerogel electrocatalysts, starting from simple impregnation techniques that [...] Read more.

The design of efficient catalytic layers of proton exchange membrane fuel cells (PEMFCs) requires the preparation of highly-loaded and highly-dispersed Pt/C catalysts. During the last few years, our work focused on the preparation of Pt/carbon xerogel electrocatalysts, starting from simple impregnation techniques that were further optimized via the strong electrostatic adsorption (SEA) method to reach high dispersion and a high metal weight fraction. The SEA method, which consists of the optimization of the precursor/support electrostatic impregnation through an adequate choice of the impregnation pH with regard to the support surface chemistry, leads to very well-dispersed Pt/C samples with a maximum 8 wt.% Pt after drying and reduction under H₂. To increase the metal loading, the impregnation-drying-reduction cycle of the SEA method can be repeated several times, either with fresh Pt precursor solution or with the solution recycled from the previous cycle. In each case, a high dispersion (Pt particle size ~3 nm) is obtained. Finally, the procedure can be simplified by combination of the SEA technique with dry impregnation, leading to no Pt loss during the procedure. Full article

(This article belongs to the Special Issue Electrocatalysis in Fuel Cells)

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216 KiB

Open AccessEditorial

Palladium Catalysts for Cross-Coupling Reaction

by Kei Manabe

Catalysts 2015, 5(1), 38-39; https://doi.org/10.3390/catal5010038 - 22 Jan 2015

Cited by 9 | Viewed by 5557

Abstract

Palladium-catalyzed cross-coupling reactions constitute one of the most important and useful transformations in transition metal-catalyzed reactions [1–3]. Although this research field emerged in the 1970s, it is still attracting considerable attention in synthetic and organometallic chemistry. New catalysts and catalytic systems are being [...] Read more.

Palladium-catalyzed cross-coupling reactions constitute one of the most important and useful transformations in transition metal-catalyzed reactions [1–3]. Although this research field emerged in the 1970s, it is still attracting considerable attention in synthetic and organometallic chemistry. New catalysts and catalytic systems are being developed to further expand the utility of the reactions. This Special Issue on “Palladium Catalysts for Cross-Coupling Reaction” covers the diverse aspects of the ever-evolving field of palladium catalysts in cross coupling chemistry.[...] Full article

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

1246 KiB

Open AccessArticle

Ruthenium Modification on Mn and Zr-Modified Co/SiO₂ Catalysts for Slurry-Phase Fischer-Tropsch Synthesis

by Tomohisa Miyazawa, Toshiaki Hanaoka, Katsuya Shimura and Satoshi Hirata

Catalysts 2015, 5(1), 26-37; https://doi.org/10.3390/catal5010026 - 12 Jan 2015

Cited by 6 | Viewed by 6596

Abstract

The addition of Ru to Mn and Zr-modified Co/SiO₂ catalysts, while applying different preparation orders and loading amounts, was investigated as a means of enhancing the Fischer-Tropsch synthesis reaction. The coimpregnation of Zr/SiO₂ with Co, Mn and Ru gave the most [...] Read more.

The addition of Ru to Mn and Zr-modified Co/SiO₂ catalysts, while applying different preparation orders and loading amounts, was investigated as a means of enhancing the Fischer-Tropsch synthesis reaction. The coimpregnation of Zr/SiO₂ with Co, Mn and Ru gave the most attractive catalytic properties. This can be attributed to the higher dispersion of Co metal resulting from the coimpregnation of Co and Mn as well as enhanced reducibility due to the presence of Ru. The addition of a moderate amount of Ru together with the appropriate order of addition affected both the Co reducibility and the catalytic activity, primarily because of increased reducibility. The addition of even 0.1 wt.% Ru resulted in an obvious enhancement of Fischer-Tropsch synthesis activity. Full article

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99 KiB

Open AccessArticle

Palladium on Carbon-Catalyzed Suzuki-Miyaura Coupling Reaction Using an Efficient and Continuous Flow System

by Tomohiro Hattori, Aya Tsubone, Yoshinari Sawama, Yasunari Monguchi and Hironao Sajiki

Catalysts 2015, 5(1), 18-25; https://doi.org/10.3390/catal5010018 - 12 Jan 2015

Cited by 42 | Viewed by 11375

Abstract

The continuous flow Suzuki-Miyaura reaction between various haloarenes and arylboronic acids was successfully achieved within only ca. 20 s during the single-pass through a cartridge filled with palladium on carbon (Pd/C). No palladium leaching was observed in the collected reaction solution by atomic [...] Read more.

The continuous flow Suzuki-Miyaura reaction between various haloarenes and arylboronic acids was successfully achieved within only ca. 20 s during the single-pass through a cartridge filled with palladium on carbon (Pd/C). No palladium leaching was observed in the collected reaction solution by atomic absorption spectrometry (detection limit: 1 ppm). Full article

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

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2230 KiB

Open AccessReview

Fischer-Tropsch Synthesis on Multicomponent Catalysts: What Can We Learn from Computer Simulations?

by José L. C. Fajín, M. Natália D. S. Cordeiro and José R. B. Gomes

Catalysts 2015, 5(1), 3-17; https://doi.org/10.3390/catal5010003 - 9 Jan 2015

Cited by 20 | Viewed by 15007

Abstract

In this concise review paper, we will address recent studies based on the generalized-gradient approximation (GGA) of the density functional theory (DFT) and on the periodic slab approach devoted to the understanding of the Fischer-Tropsch synthesis process on transition metal catalysts. As it [...] Read more.

In this concise review paper, we will address recent studies based on the generalized-gradient approximation (GGA) of the density functional theory (DFT) and on the periodic slab approach devoted to the understanding of the Fischer-Tropsch synthesis process on transition metal catalysts. As it will be seen, this computational combination arises as a very adequate strategy for the study of the reaction mechanisms on transition metal surfaces under well-controlled conditions and allows separating the influence of different parameters, e.g., catalyst surface morphology and coverage, influence of co-adsorbates, among others, in the global catalytic processes. In fact, the computational studies can now compete with research employing modern experimental techniques since very efficient parallel computer codes and powerful computers enable the investigation of more realistic molecular systems in terms of size and composition and to explore the complexity of the potential energy surfaces connecting reactants, to intermediates, to products of reaction. In the case of the Fischer-Tropsch process, the calculations were used to complement experimental work and to clarify the reaction mechanisms on different catalyst models, as well as the influence of additional components and co-adsorbate species in catalyst activity and selectivity. Full article

(This article belongs to the Special Issue Feature Papers to Celebrate the Landmarks of Catalysts)

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138 KiB

Open AccessEditorial

Acknowledgement to Reviewers of Catalysts in 2014

by Catalysts Editorial Office

Catalysts 2015, 5(1), 1-2; https://doi.org/10.3390/catal5010001 - 8 Jan 2015

Viewed by 3447

Abstract

The editors of Catalysts would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2014:[...] Full article

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Catalysts, Volume 5, Issue 1 (March 2015) – 24 articles , Pages 1-477

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