Catalysts

2023

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14 pages, 2441 KiB

Open AccessFeature PaperArticle

Gold(I)-Catalyzed Direct Alkyne Hydroarylation in Ionic Liquids: Mechanistic Insights

by Sara Bonfante, Pietro Bax, Marco Baron and Andrea Biffis

Catalysts 2023, 13(5), 822; https://doi.org/10.3390/catal13050822 - 29 Apr 2023

Cited by 1 | Viewed by 1352

Abstract

The factors determining the catalytic performance of a recently discovered system for direct intermolecular alkyne hydroarylations, comprising a gold(I) complex of general formula LAuX (L = neutral ligand; X = weakly coordinating counteranion) and an ionic liquid as solvent, have been investigated. In [...] Read more.

The factors determining the catalytic performance of a recently discovered system for direct intermolecular alkyne hydroarylations, comprising a gold(I) complex of general formula LAuX (L = neutral ligand; X = weakly coordinating counteranion) and an ionic liquid as solvent, have been investigated. In particular, the effect of the ionic liquid anion, cation, and of the electronic and steric properties of the neutral ligand L have been considered. The results of the investigation shed some light in particular on the role of the anion, which is multiform and can potentially influence the catalytic performance in many respects, and on the role of the neutral ligand, which should be a relatively poor electron donor but not so much as to compromise the stability of the catalyst. Knowledge of the factors affecting catalytic performance will speed up the optimization of this catalytic system, in the case of direct alkyne hydroarylations with different substrates, and will also facilitate the extension of its application to other reactions. Full article

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18 pages, 5902 KiB

Open AccessArticle

Gold and Ceria Modified NiAl Hydrotalcite Materials as Catalyst Precursors for Dry Reforming of Methane

by Valeria La Parola, Giuseppe Pantaleo, Leonarda Francesca Liotta, Anna Maria Venezia, Margarita Gabrovska, Dimitrinka Nikolova and Tatyana Tabakova

Catalysts 2023, 13(3), 606; https://doi.org/10.3390/catal13030606 - 16 Mar 2023

Cited by 3 | Viewed by 1911

Abstract

Structured hydrotalcite NiAl-HT material with Ni/Al atomic ratio of 2.5 was prepared by co-precipitation of Ni and Al nitrate precursors and then modified by the addition of 1 wt% Ce and/or 3 wt% Au species. The obtained materials, after calcination at 600 °C, [...] Read more.

Structured hydrotalcite NiAl-HT material with Ni/Al atomic ratio of 2.5 was prepared by co-precipitation of Ni and Al nitrate precursors and then modified by the addition of 1 wt% Ce and/or 3 wt% Au species. The obtained materials, after calcination at 600 °C, were characterized by XRD, XPS and TPR. Their catalytic performance was tested through dry reforming of methane (DRM) and by the temperature-programmed surface reaction of methane (TPSR-CH₄). Thermal gravimetry analysis (TGA) of the spent catalysts was performed to determine the amount of carbon accumulated during the reaction. The effects of the addition of cerium as a support promoter and gold as nickel promoter and the sequential addition of cerium and gold on the structural properties and on the catalytic efficiency were investigated. Under the severe condition of high space velocity (600,000 mL g⁻¹ h⁻¹), all the catalysts were quite active, with values of CH₄ conversion between 67% and 74% at 700 °C. In particular, the combination of cerium and gold enhanced the CH₄ conversion up to 74%. Both additives, individually and simultaneously, enhanced the nickel dispersion with respect to the unpromoted NiAl and favored the reducibility of the nickel. During DRM all the catalysts formed graphitic carbon, contributing to their deactivation. The lower carbon gasification temperature of the promoted catalysts confirmed a positive effect played by Ce and Au in assisting the formation of an easier-to-remove carbon. The positive effect was testified by the better stability of the Ce/NiAl with respect to the other catalysts. In the gold-containing samples, this effect was neutralized by Au diffusing towards the catalyst surface during DRM, masking the nickel active sites. TPSR-CH₄ test highlighted different CH₄ activation capability of the catalysts. Furthermore, the comparison of the deposited carbon features (amount and removal temperature) of the DRM and TPSR spent catalysts indicated a superior activation of CO₂ by the Au/Ce/NiAl, to be related to the close interaction of gold and ceria enhancing the oxygen mobility in the catalyst lattice. Full article

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24 pages, 6649 KiB

Open AccessArticle

The Impact of Functionality and Porous System of Nanostructured Carriers Based on Metal–Organic Frameworks of UiO-66-Type on Catalytic Performance of Embedded Au Nanoparticles in Hydroamination Reaction

by Vera I. Isaeva, Vladimir V. Chernyshev, Vadim V. Vergun, Danil A. Arkhipov, Grigory S. Deyko, Lev M. Glukhov, Gennady I. Kapustin, Olga P. Tkachenko and Leonid M. Kustov

Catalysts 2023, 13(1), 133; https://doi.org/10.3390/catal13010133 - 6 Jan 2023

Cited by 2 | Viewed by 2221

Abstract

New methods for the preparation of metal–organic frameworks UiO-66 and NH₂-UiO-66 with a hierarchical porous structure were developed using the MW-assisted technique under atmospheric pressure. The synthesized nanostructured meso-UiO-66 and meso-NH₂-UiO-66 matrices were utilized as Au nanoparticle carriers. The [...] Read more.

New methods for the preparation of metal–organic frameworks UiO-66 and NH₂-UiO-66 with a hierarchical porous structure were developed using the MW-assisted technique under atmospheric pressure. The synthesized nanostructured meso-UiO-66 and meso-NH₂-UiO-66 matrices were utilized as Au nanoparticle carriers. The resulting Au@meso-UiO-66 and Au@NH₂-UiO-66 nanohybrids were studied in the reaction of phenylacetylene hydroamination with aniline into imine ([phenyl-(1-phenylethylydene)amine]) for the first time. Their catalytic behavior is significantly determined by a combination of factors, such as a small crystal size, micro–mesoporous structure, and functionality of the UiO-66 and NH₂-UiO-66 carriers, as well as a high dispersion of embedded gold nanoparticles. The Au@meso-UiO-66 and Au@NH₂-UiO-66 nanocatalysts demonstrate high activities (TOF), with conversion and selectivity values over 90. This excellent catalytic performance is comparable or even better than that demonstrated by heterogeneous systems based on conventional inorganic and inorganic supports known from the literature. Full article

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2022

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12 pages, 3985 KiB

Open AccessArticle

Highly Active Large Au Clusters and Even More Active Ag Nanoparticles Supported on Ceria-Zirconia: Impact of Particle Size and Potassium Ion Loading on Activity in Catalytic Transfer Hydrogenation

by Ewa M. Iwanek (nee Wilczkowska), Marek Gliński, Aleksandra Siwiec, Sylwia Siennicka, Magdalena Zybert and Zbigniew Kaszkur

Catalysts 2022, 12(9), 974; https://doi.org/10.3390/catal12090974 - 30 Aug 2022

Cited by 2 | Viewed by 1505

Abstract

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, [...] Read more.

Although heterogeneous monometallic gold catalysts are commonly more active when the gold particles are smaller, this study shows that the reverse is true in the case of liquid phase catalytic transfer hydrogenation of acetophenone with 2-pentanol. Higher catalytic activity of larger gold particles, i.e., over 30 nm in diameter, than of smaller particles of average 4 nm in size was observed. Moreover, this effect was contradictory to that observed for supported monometallic silver catalysts in which the interaction with the support and hence particle size was shown to cause drastic changes in the activity in this reaction, with the large particles being completely inactive and tiny ones being the most active system studied. In this reaction, the ceria-zirconia solid solutions were used as the supports for the catalysts and both zirconium doped ceria, as well as cerium doped zirconia carriers were tested. The supports themselves exhibited little activity in this reaction. It was shown that the activity of the supports and catalysts depends on the Ce/Zr ratio and potassium content. Both types of catalysts showed excellent selectivity to 1-phenylethanol and conversion of acetophenone, although it was noted that a high loading of potassium carbonate in the gold catalysts propelled undesired reactions, thereby reducing the selectivity to 1-phenylethanol. Full article

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19 pages, 2936 KiB

Open AccessArticle

Gold-Based Catalysts for Complete Formaldehyde Oxidation: Insights into the Role of Support Composition

by Lyuba Ilieva, Dimitar Dimitrov, Elitsa Kolentsova, Anna Maria Venezia, Daniela Karashanova, Georgi Avdeev, Petya Petrova, Razvan State and Tatyana Tabakova

Catalysts 2022, 12(7), 705; https://doi.org/10.3390/catal12070705 - 27 Jun 2022

Cited by 2 | Viewed by 1818

Abstract

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, [...] Read more.

Formaldehyde (HCHO) is recognized as one of the most emitted indoor air pollutants with high detrimental effect on human health. Significant research efforts are focused on HCHO removal to meet emission regulations in an effective and economically profitable way. For over three decades, the unique electronic properties and catalytic abilities of nano-gold catalysts continue to be an attractive research area for the catalytic community. Recently, we reported that mechanochemical mixing is a relevant approach to the preparation of Co-Ce mixed oxides with high activity in complete benzene oxidation. A trend of higher surface defectiveness, in particular, oxygen vacancies, caused by close interaction between cobalt oxide and cerium oxide phases, was observed for a mixed oxide composition of 70 wt.% Co₃O₄ and 30 wt.% CeO₂. These results directed further improvement by promotion with gold and optimization of mixed oxide composition, aiming for the development of an efficient catalyst for room temperature HCHO abatement. Support modification with potassium was studied; however, the K addition caused less enhancement of HCHO oxidation activity than expected. This motivated the preparation of new carrier material. In addition to Co₃O₄-CeO₂ mixed metal oxides with preset ratio, γ-Al₂O₃ intentionally containing 33% boehmite and shortly named Al₂O₃-b was used for synthesis. Analysis of the role of support composition in HCHO oxidation was based on the characterization of nano-gold catalysts by textural measurements, XRD, HRTEM, XPS, and TPR techniques. Gold supported on mechanochemically treated Co₃O₄-CeO₂-Al₂O₃-b (50 wt.% Al₂O₃-b) exhibited superior activity owing to high Ce³⁺ and Co³⁺ surface amounts and the most abundant oxygen containing species with enhanced mobility. This catalyst achieved oxidation to CO₂ and H₂O by 95% HCHO conversion at room temperature and 100% at 40 °C, thus implying the potential of this composition in developing efficient catalytic materials for indoor air purification. Full article

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2018

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15 pages, 3527 KiB

Open AccessReview

Recent Advances in the Gold-Catalysed Low-Temperature Water–Gas Shift Reaction

by James H. Carter and Graham J. Hutchings

Catalysts 2018, 8(12), 627; https://doi.org/10.3390/catal8120627 - 5 Dec 2018

Cited by 31 | Viewed by 6249

Abstract

The low-temperature water–gas shift reaction (LTS: CO + H₂O ⇌ CO₂ + H₂) is a key step in the purification of H₂ reformate streams that feed H₂ fuel cells. Supported gold catalysts were originally identified as [...] Read more.

The low-temperature water–gas shift reaction (LTS: CO + H₂O ⇌ CO₂ + H₂) is a key step in the purification of H₂ reformate streams that feed H₂ fuel cells. Supported gold catalysts were originally identified as being active for this reaction twenty years ago, and since then, considerable advances have been made in the synthesis and characterisation of these catalysts. In this review, we identify and evaluate the progress towards solving the most important challenge in this research area: the development of robust, highly active catalysts that do not deactivate on-stream under realistic reaction conditions. Full article

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13 pages, 3222 KiB

Open AccessArticle

Selective Hydrogenation of Cinnamaldehyde Catalyzed by ZnO-Fe₂O₃ Mixed Oxide Supported Gold Nanocatalysts

by Wei Wang, Yan Xie, Shaohua Zhang, Xing Liu, Masatake Haruta and Jiahui Huang

Catalysts 2018, 8(2), 60; https://doi.org/10.3390/catal8020060 - 3 Feb 2018

Cited by 24 | Viewed by 5700

Abstract

ZnO-Fe₂O₃ mixed oxides and supported gold nanocatalysts were prepared by using coprecipitation and deposition–precipitation methods, respectively. Cinnamaldehyde hydrogenation over various ZnO-Fe₂O₃ mixed oxides supported gold nanocatalysts have been investigated at 140 °C and a hydrogen pressure of [...] Read more.

ZnO-Fe₂O₃ mixed oxides and supported gold nanocatalysts were prepared by using coprecipitation and deposition–precipitation methods, respectively. Cinnamaldehyde hydrogenation over various ZnO-Fe₂O₃ mixed oxides supported gold nanocatalysts have been investigated at 140 °C and a hydrogen pressure of 1.0 MPa. The molar ratio of Fe to Zn was found to greatly affect the selective hydrogenation catalytic activity of ZnO-Fe₂O₃ mixed oxide supported gold nanocatalysts. Among these supported gold nanocatalysts in this work, Au/Zn_0.7Fe_0.3O_x (Au loading of 1.74 wt %) exhibited the highest conversion of cinnamaldehyde and high selectivity to cinnamal alcohol. The excellent catalytic activity of Au/Zn_0.7Fe_0.3O_x was tightly associated with a large surface area, small gold nanoparticles, and good H₂ dissociation ability at low temperature. Full article

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2017

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16832 KiB

Open AccessFeature PaperReview

Dynamic Processes on Gold-Based Catalysts Followed by Environmental Microscopies

by Eric Genty, Luc Jacobs, Thierry Visart de Bocarmé and Cédric Barroo

Catalysts 2017, 7(5), 134; https://doi.org/10.3390/catal7050134 - 1 May 2017

Cited by 12 | Viewed by 7165

Abstract

Since the early discovery of the catalytic activity of gold at low temperature, there has been a growing interest in Au and Au-based catalysis for a new class of applications. The complexity of the catalysts currently used ranges from single crystal to 3D [...] Read more.

Since the early discovery of the catalytic activity of gold at low temperature, there has been a growing interest in Au and Au-based catalysis for a new class of applications. The complexity of the catalysts currently used ranges from single crystal to 3D structured materials. To improve the efficiency of such catalysts, a better understanding of the catalytic process is required, from both the kinetic and material viewpoints. The understanding of such processes can be achieved using environmental imaging techniques allowing the observation of catalytic processes under reaction conditions, so as to study the systems in conditions as close as possible to industrial conditions. This review focuses on the description of catalytic processes occurring on Au-based catalysts with selected in situ imaging techniques, i.e., PEEM/LEEM, FIM/FEM and E-TEM, allowing a wide range of pressure and material complexity to be covered. These techniques, among others, are applied to unravel the presence of spatiotemporal behaviours, study mass transport and phase separation, determine activation energies of elementary steps, observe the morphological changes of supported nanoparticles, and finally correlate the surface composition with the catalytic reactivity. Full article

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2016

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5166 KiB

Open AccessArticle

Au Capping Agent Removal Using Plasma at Mild Temperature

by Indra Puspitasari, Emmanuel Skupien, Freek Kapteijn and Patricia J. Kooyman

Catalysts 2016, 6(11), 179; https://doi.org/10.3390/catal6110179 - 17 Nov 2016

Cited by 5 | Viewed by 6439

Abstract

To prevent sintering, ozone treatment at mild temperature is used to remove the capping agent from supported Au nanoparticles. The Au nanoparticles are first synthesized as a colloidal solution and then supported on alumina. Fourier Transform Infra Red (FTIR) shows the capping agent [...] Read more.

To prevent sintering, ozone treatment at mild temperature is used to remove the capping agent from supported Au nanoparticles. The Au nanoparticles are first synthesized as a colloidal solution and then supported on alumina. Fourier Transform Infra Red (FTIR) shows the capping agent is removed completely. Transmission Electron Microscopy (TEM) and catalytic test reactions show the Au does not sinter significantly upon low temperature ozone treatment. Full article

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3283 KiB

Open AccessFeature PaperReview

Au/CeO₂ Catalysts: Structure and CO Oxidation Activity

by Miguel Angel Centeno, Tomás Ramírez Reina, Svetlana Ivanova, Oscar Hernando Laguna and José Antonio Odriozola

Catalysts 2016, 6(10), 158; https://doi.org/10.3390/catal6100158 - 18 Oct 2016

Cited by 60 | Viewed by 12985

Abstract

In this comprehensive review, the main aspects of using Au/CeO₂ catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface [...] Read more.

In this comprehensive review, the main aspects of using Au/CeO₂ catalysts in oxidation reactions are considered. The influence of the preparation methods and synthetic parameters, as well as the characteristics of the ceria support (presence of doping cations, oxygen vacancies concentration, surface area, redox properties, etc.) in the dispersion and chemical state of gold are revised. The proposed review provides a detailed analysis of the literature data concerning the state of the art and the applications of gold–ceria systems in oxidation reactions. Full article

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6554 KiB

Open AccessFeature PaperArticle

Au/TiO₂-CeO₂ Catalysts for Photocatalytic Water Splitting and VOCs Oxidation Reactions

by Roberto Fiorenza, Marianna Bellardita, Luisa D’Urso, Giuseppe Compagnini, Leonardo Palmisano and Salvatore Scirè

Catalysts 2016, 6(8), 121; https://doi.org/10.3390/catal6080121 - 10 Aug 2016

Cited by 68 | Viewed by 10027

Abstract

Photocatalytic water splitting for H₂ production and photocatalytic oxidation of 2-propanol, an example of volatile organic compounds, were investigated over TiO₂ catalysts loaded with gold and/or ceria. In the water splitting reaction the presence of gold only slightly affected the performance [...] Read more.

Photocatalytic water splitting for H₂ production and photocatalytic oxidation of 2-propanol, an example of volatile organic compounds, were investigated over TiO₂ catalysts loaded with gold and/or ceria. In the water splitting reaction the presence of gold only slightly affected the performance of TiO₂ whereas the presence of CeO₂ had a more remarkable positive effect. In the 2-propanol oxidation Au/TiO₂ was the most active sample in terms of alcohol conversion whereas Au/TiO₂-CeO₂ exhibited the highest CO₂ yield. On the basis of characterization experiments (X-Ray Diffraction (XRD), Energy Dispersive X-ray Analysis EDX, surface area measurements, Diffuse Reflectance Spectroscopy (DRS) and Raman spectroscopy), it was suggested that the interaction of Au with TiO₂ causes an increase in the charge separation between the photo-excited electron/hole pairs, leading to an enhanced photocatalytic activity (to acetone over Au/TiO₂ and to CO₂ over Au/TiO₂-CeO₂), whereas the presence of ceria, acting as a hole trap, positively mainly affects the formation of hydrogen by water splitting. Full article

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4525 KiB

Open AccessFeature PaperReview

Biomass Derived Chemicals: Furfural Oxidative Esterification to Methyl-2-furoate over Gold Catalysts

by Maela Manzoli, Federica Menegazzo, Michela Signoretto and Damiano Marchese

Catalysts 2016, 6(7), 107; https://doi.org/10.3390/catal6070107 - 20 Jul 2016

Cited by 44 | Viewed by 10332

Abstract

The use of heterogeneous catalysis to upgrade biomass wastes coming from lignocellulose into higher value-added chemicals is one of the most explored subjects in the prospective vision of bio-refinery. In this frame, a lot of interest has been driven towards biomass-derived building block [...] Read more.

The use of heterogeneous catalysis to upgrade biomass wastes coming from lignocellulose into higher value-added chemicals is one of the most explored subjects in the prospective vision of bio-refinery. In this frame, a lot of interest has been driven towards biomass-derived building block molecules, such as furfural. Gold supported catalysts have been successfully proven to be highly active and selective in the furfural oxidative esterification to methyl-2-furoate under mild conditions by employing oxygen as benign oxidant. Particular attention has been given to the studies in which the reaction occurs even without base as co-catalyst, which would lead to a more green and economically advantageous process. The Au catalysts are also stable and quite easily recovered and represent a feasible and promising route to efficiently convert furfural to methyl-2-furoate to be scaled up at industrial level. Full article

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2911 KiB

Open AccessFeature PaperArticle

Gold Catalysts on Y-Doped Ceria Supports for Complete Benzene Oxidation

by Lyuba Ilieva, Petya Petrova, Leonarda F. Liotta, Janusz W. Sobczak, Wojciech Lisowski, Zbigniew Kaszkur, Gabriel Munteanu and Tatyana Tabakova

Catalysts 2016, 6(7), 99; https://doi.org/10.3390/catal6070099 - 8 Jul 2016

Cited by 14 | Viewed by 6127

Abstract

Gold (3 wt. %) catalysts on Y-doped (1, 2.5, 5 and 7.5 wt. % Y₂O₃) ceria supports prepared by coprecipitation (CP) or impregnation (IM) were studied in complete benzene oxidation (CBO). A low-extent Y modification was chosen to avoid [...] Read more.

Gold (3 wt. %) catalysts on Y-doped (1, 2.5, 5 and 7.5 wt. % Y₂O₃) ceria supports prepared by coprecipitation (CP) or impregnation (IM) were studied in complete benzene oxidation (CBO). A low-extent Y modification was chosen to avoid ordering of oxygen vacancies. The samples were characterized by XRD, TGA, XPS and TPR techniques. A positive role of air pretreatment at 350 °C as compared to 200 °C was established for all Y-containing catalysts and it was explained by cleaning the active sites from carbonates. The oxygen supply cannot be considered as a limiting step for benzene oxidation except for the high 7.5%-doped samples, as suggested by TGA and TPR data. On the basis of XPS results of fresh and used in CBO catalysts, the presence of cationic gold species does not seem important for high CBO activity. The gold catalyst on an IM support with 1% Y-doping exhibited the best performance. A 100% benzene conversion was achieved only over this catalyst and Au/ceria, while it was not reached even at 300 °C over all other studied catalysts. Gold and ceria particle agglomeration or coke formation should be excluded as a possible reason, and the most probable explanation could be associated with the importance of the benzene activation stage. Full article

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7168 KiB

Open AccessArticle

Effects of Support and Synthetic Procedure for Sol-Immobilized Au Nanoparticles

by Michela Signoretto, Federica Menegazzo, Alessandro Di Michele and Ermelinda Fioriniello

Catalysts 2016, 6(6), 87; https://doi.org/10.3390/catal6060087 - 20 Jun 2016

Cited by 14 | Viewed by 6959

Abstract

New gold catalysts supported on CeO₂, ZrO₂ and TiO₂ were synthesized by two different techniques: deposition-precipitation and colloidal method. The role of the surfactant (PVA, PVP, THPC) was also investigated. The catalysts were tested in the oxidation of glucose [...] Read more.

New gold catalysts supported on CeO₂, ZrO₂ and TiO₂ were synthesized by two different techniques: deposition-precipitation and colloidal method. The role of the surfactant (PVA, PVP, THPC) was also investigated. The catalysts were tested in the oxidation of glucose to gluconic acid, in aqueous environment and under mild conditions (60 °C and atmospheric pressure). TEM and SEM analyses have shown that the small size of gold nanoparticles is a necessary condition, but not sufficient for a good conversion. In fact, for an active sample, we have verified that the excess of surfactant must be removed because it would coat the surface of the catalyst. The surfactant, however, should not be completely eliminated, since it has the fundamental role of stabilizing the sample preventing nanoparticles from aggregation. It was evidenced that both the synthetic approach and the kind of support affect the catalysts’ activity. In fact, by focusing on the three different supports, with all the preparation methods, the ceria has proved to be the best support. This is due to its ability to obtain small gold nanoparticles and to its ability to accumulate oxygen. The most appropriate synthesis methodology proved to be the colloidal method with PVA. Recyclability issue was investigated too. Full article

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2014

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991 KiB

Open AccessEditorial

New Trends in Gold Catalysts

by Leonarda F. Liotta

Catalysts 2014, 4(3), 299-304; https://doi.org/10.3390/catal4030299 - 16 Jul 2014

Cited by 8 | Viewed by 6352

Abstract

Gold is an element that has fascinated mankind for millennia. The catalytic properties of gold have been a source of debate, due to its complete chemical inertness when in a bulk form, while it can oxidize CO at temperatures as low as ~200 [...] Read more.

Gold is an element that has fascinated mankind for millennia. The catalytic properties of gold have been a source of debate, due to its complete chemical inertness when in a bulk form, while it can oxidize CO at temperatures as low as ~200 K when in a nanocrystalline state, as discovered by Haruta in the late 1980s [1]. Since then, extensive activity in both applied and fundamental research on gold has been initiated. The importance of the catalysis by gold represents one of the fasted growing fields in science and is proven by the promising applications in several fields, such as green chemistry and environmental catalysis, in the synthesis of single-walled carbon nanotubes, as modifiers of Ni catalysts for methane steam and dry reforming reactions and in biological and electrochemistry applications. The range of reactions catalyzed by gold, as well as the suitability of different supports and the influence of the preparation conditions have been widely explored and optimized in applied research [2]. Gold catalysts appeared to be very different from the other noble metal-based catalysts, due to their marked dependence on the preparation method, which is crucial for the genesis of the catalytic activity. Several methods, including deposition-precipitation, chemical vapor deposition and cation adsorption, have been applied for the preparation of gold catalysts over reducible oxides, like TiO₂. Among these methods, deposition-precipitation has been the most frequently employed method for Au loading, and it involves the use of tetrachloroauric (III) acid as a precursor. On the other hand, the number of articles dealing with Au-loaded acidic supports is smaller than that on basic supports, possibly because the deposition of [AuCl₄]⁻ or [AuOH_xCl₄_−x]⁻ species on acidic supports is difficult, due to their very low point of zero charge. Despite this challenge, several groups have reported the use of acidic zeolites as supports for gold. Zeolites are promising supports for Au stabilization, because of the presence of ion-exchange sites, such as NH⁴⁺, that can be substituted by Au⁺ ions through the elimination of NH₄Cl [3]. Moreover, zeolites, due to their high thermal stability, the presence of a large surface area and micropores, may hinder Au sintering. [...] Full article

530 KiB

Open AccessReview

Gold Nanoparticles as the Catalyst of Single-Walled Carbon Nanotube Synthesis

by Yoshikazu Homma

Catalysts 2014, 4(1), 38-48; https://doi.org/10.3390/catal4010038 - 5 Mar 2014

Cited by 20 | Viewed by 8808

Abstract

Gold nanoparticles have been proven to act as efficient catalysts for chemical reactions, such as oxidation and hydrogen production. In this review we focus on a different aspect of the catalysis of gold nanoparticles; single-walled carbon nanotube (SWCNT) synthesis. This is not a [...] Read more.

Gold nanoparticles have been proven to act as efficient catalysts for chemical reactions, such as oxidation and hydrogen production. In this review we focus on a different aspect of the catalysis of gold nanoparticles; single-walled carbon nanotube (SWCNT) synthesis. This is not a traditional meaning of catalytic reaction, but SWCNTs cannot be synthesized without nanoparticles. Previously, gold was considered as unsuitable metal species as the catalyst of SWCNT synthesis. However, gold nanoparticles with diameters smaller than 5 nm were found to effectively produce SWCNTs. We discuss the catalysis of gold and related metals for SWCNT synthesis in comparison with conventional catalysts, such as iron, cobalt, and nickel. Full article

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2013

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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 14 | Viewed by 8631

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

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2603 KiB

Open AccessReview

Gold Nanoparticle-Biological Molecule Interactions and Catalysis

by Jonathan G. Heddle

Catalysts 2013, 3(3), 683-708; https://doi.org/10.3390/catal3030683 - 3 Sep 2013

Cited by 32 | Viewed by 13423

Abstract

This review gives a brief summary of the field of gold nanoparticle interactions with biological molecules, particularly those with possible catalytic relevance. Gold nanoparticles are well known as catalysts in organic chemistry but much is unknown regarding their potential as catalysts of reactions [...] Read more.

This review gives a brief summary of the field of gold nanoparticle interactions with biological molecules, particularly those with possible catalytic relevance. Gold nanoparticles are well known as catalysts in organic chemistry but much is unknown regarding their potential as catalysts of reactions involving biological molecules such as protein and nucleic acids. Biological molecules may be the substrate for catalysis or, if they are the ligand coating the gold particle, may be the catalyst itself. In other cases biological molecules may form a template upon which gold nanoparticles can be precisely arrayed. As relatively little is currently known about the catalytic capabilities of gold nanoparticles in this area, this review will consider templating in general (including, but not restricted to, those which result in structures having potential as catalysts) before going on to consider firstly catalysis by the gold nanoparticle itself followed by catalysis by ligands attached to gold nanoparticles, all considered with a focus on biological molecules. Full article

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4520 KiB

Open AccessArticle

Investigation on the Stability of Supported Gold Nanoparticles

by Michela Signoretto, Federica Menegazzo, Valentina Trevisan, Francesco Pinna, Maela Manzoli and Flora Boccuzzi

Catalysts 2013, 3(3), 656-670; https://doi.org/10.3390/catal3030656 - 21 Aug 2013

Cited by 12 | Viewed by 8618

Abstract

The procedures leading to the preservation of catalytic performances of Au/ZrO₂ samples have been investigated. The three potential causes of deactivation, namely the particle growth by sintering of gold nanoparticles, the metal leaching and the formation of un-reactive species which inhibit the [...] Read more.

The procedures leading to the preservation of catalytic performances of Au/ZrO₂ samples have been investigated. The three potential causes of deactivation, namely the particle growth by sintering of gold nanoparticles, the metal leaching and the formation of un-reactive species which inhibit the reaction, have been evaluated. In particular, this paper deals with the stability of gold nanoparticles: (1) under storage conditions; (2) with time on stream for a gas phase reaction (LT-WGSR); (3) with time on stream for a liquid phase reaction (furfural oxidative esterification). Full article

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1231 KiB

Open AccessArticle

Fabrication and Catalytic Activity of Thermally Stable Gold Nanoparticles on Ultrastable Y (USY) Zeolites

by Takashi Sanada, Chika Murakami, Kinga Góra-Marek, Keiko Iida, Naonobu Katada and Kazu Okumura

Catalysts 2013, 3(3), 599-613; https://doi.org/10.3390/catal3030599 - 9 Jul 2013

Cited by 12 | Viewed by 8622

Abstract

Au was deposited on ultrastable Y (USY) zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH₄-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, [...] Read more.

Au was deposited on ultrastable Y (USY) zeolites using an ion-exchange method. Up to 5.5 wt% Au was introduced into the NH₄-form of USY zeolites. In contrast, deposition of Au hardly took place on the H- and Na-forms of Y-type zeolites, NH₄-forms of mordenite, and ZSM-5. Treatment of the Au-loaded USY zeolite in a H₂ atmosphere, afforded Au⁰ nanoparticles. These particles were thermally stable even at 973 K, where their mean particle diameter was 3.7 nm. In contrast, highly aggregated Au particles were observed after thermal treatment at temperatures lower than 523 K, followed by storage in air for a month. The resulting particle sizes were in good correlation with the IR band intensity of the adsorbed CO and the catalytic activity of Au in the aerobic oxidation of benzyl alcohol. The Au nanoparticles showed highest activity when the Au/USY zeolite was thermally treated at 673–973 K. A negligible deactivation was observed after repeating the reaction at least 12 times. In the case of Au/TiO₂ catalyst prepared by the deposition-precipitation method, the highest activity was observed at 573 K, which was lower than the temperature used for the Au/USY zeolites. This study demonstrated the potential use of the NH₄-form of USY zeolites for supporting Au. Full article

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1439 KiB

Open AccessArticle

Ni-Based Catalysts for Low Temperature Methane Steam Reforming: Recent Results on Ni-Au and Comparison with Other Bi-Metallic Systems

by Hongjing Wu, Valeria La Parola, Giuseppe Pantaleo, Fabrizio Puleo, Anna M. Venezia and Leonarda F. Liotta

Catalysts 2013, 3(2), 563-583; https://doi.org/10.3390/catal3020563 - 5 Jun 2013

Cited by 141 | Viewed by 18264

Abstract

Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious [...] Read more.

Steam reforming of light hydrocarbons provides a promising method for hydrogen production. Ni-based catalysts are so far the best and the most commonly used catalysts for steam reforming because of their acceptably high activity and significantly lower cost in comparison with alternative precious metal-based catalysts. However, nickel catalysts are susceptible to deactivation from the deposition of carbon, even when operating at steam-to-carbon ratios predicted to be thermodynamically outside of the carbon-forming regime. Reactivity and deactivation by carbon formation can be tuned by modifying Ni surfaces with a second metal, such as Au through alloy formation. In the present review, we summarize the very recent progress in the design, synthesis, and characterization of supported bimetallic Ni-based catalysts for steam reforming. The progress in the modification of Ni with noble metals (such as Au and Ag) is discussed in terms of preparation, characterization and pretreatment methods. Moreover, the comparison with the effects of other metals (such as Sn, Cu, Co, Mo, Fe, Gd and B) is addressed. The differences of catalytic activity, thermal stability and carbon species between bimetallic and monometallic Ni-based catalysts are also briefly shown. Full article

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5075 KiB

Open AccessArticle

Electron Transfer at Gold Nanostar Assemblies: A Study of Shape Stability and Surface Density Influence

by Mariana Chirea

Catalysts 2013, 3(1), 288-309; https://doi.org/10.3390/catal3010288 - 12 Mar 2013

Cited by 26 | Viewed by 11847

Abstract

Gold nanostars of ~70 nm tip to tip distances were synthesized by a seed mediated method and covalently self-assembled on 1,5-pentanedithiol modified electrodes. Electron transfer kinetics at the AuNS/dithiol modified electrodes were studied as a function of AuNS surface density which was varied [...] Read more.

Gold nanostars of ~70 nm tip to tip distances were synthesized by a seed mediated method and covalently self-assembled on 1,5-pentanedithiol modified electrodes. Electron transfer kinetics at the AuNS/dithiol modified electrodes were studied as a function of AuNS surface density which was varied by increasing their self-assembly time from 8 h, 16 h, 24 h to 32 h. Excellent electrocatalytic properties of AuNSs were observed toward electrochemistry of [Fe(CN)₆]^4−/3− redox couple. The apparent heterogeneous electron transfer constant, k_et, has progressively increased with the surface density of AuNSs bonded to the electrodes from 0.65 × 10⁻⁵ cm s⁻¹ (8 h), 1.47 × 10⁻⁵ cm s⁻¹ (16 h), 3.95 × 10⁻⁵ cm s⁻¹ (24 h) to an excellent 85.0 × 10⁻⁵cm s⁻¹ (32 h). Electrochemical charging of nanostars was confirmed, for the first time, by 79 times increase of double layer capacitance, C_dl, from 0.34 µF (8 h) to 27 µF (32 h). The electrochemical charging of AuNSs had also a strong influence on the electron tunneling process through the 1,5PDT molecules being more efficient at dense layers of AuNSs. The tunneling parameter, β, has decreased from 1.13 Å⁻¹ (16 h) to 0.50 Å⁻¹ (32 h). The AuNSs were chemically stable toward [Fe(CN)₆]^4−/3− showing no change in shape after electrochemical measurements. Full article

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1868 KiB

Open AccessArticle

Defect-Driven Restructuring of TiO₂ Surface and Modified Reactivity Toward Deposited Gold Atoms

by Kenneth Park, Vincent Meunier, Minghu Pan and Ward Plummer

Catalysts 2013, 3(1), 276-287; https://doi.org/10.3390/catal3010276 - 8 Mar 2013

Cited by 5 | Viewed by 7016

Abstract

A partially reduced TiO2 surface exhibits increasingly complex nature when forming various defects, whose stoichiometry, structure and properties are markedly different from those of bulk TiO2. Using scanning tunneling microscopy and density functional theory, we investigate different types of surface defects formed by [...] Read more.

A partially reduced TiO2 surface exhibits increasingly complex nature when forming various defects, whose stoichiometry, structure and properties are markedly different from those of bulk TiO2. Using scanning tunneling microscopy and density functional theory, we investigate different types of surface defects formed by Ti interstitials on TiO2 (110) and their reactivity toward deposited gold atoms. Sub-stoichiometric strands greatly enhance bonding of Au by transferring the excess charges from the reduced Ti3+ onto the strands. Thus the sub-stoichiometric strands behave as strong electron donor sites toward reactants. On the contrary, fully stoichiometric nanoclusters provide increased Au bonding through its 1-coordinated oxygen, which acts as a strong electron acceptor site. Specific interactions between Au and defects as well as the implication of electron donor/acceptor complexes for catalytic reactions are discussed. Full article

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2012

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76 KiB

Open AccessEditorial

New Frontiers in Gold Catalyzed Reactions

by Leonarda F. Liotta

Catalysts 2012, 2(2), 299-302; https://doi.org/10.3390/catal2020299 - 29 May 2012

Cited by 4 | Viewed by 6470

Abstract

For many years, gold has been regarded as a poor catalyst due to its chemical inertness towards reactive molecules such as oxygen and hydrogen. The interest in using gold in catalysis has increased during the last 20 years, since Haruta reported the surprisingly [...] Read more.

For many years, gold has been regarded as a poor catalyst due to its chemical inertness towards reactive molecules such as oxygen and hydrogen. The interest in using gold in catalysis has increased during the last 20 years, since Haruta reported the surprisingly high activity in CO oxidation at low temperature for small (3–5 nm) gold particles supported on various oxides. [...] Full article

494 KiB

Open AccessArticle

Influence of Gold on Ce-Zr-Co Fluorite-Type Mixed Oxide Catalysts for Ethanol Steam Reforming

by Julio Cesar Vargas, Svetlana Ivanova, Sébastien Thomas, Anne-Cécile Roger and Véronique Pitchon

Catalysts 2012, 2(1), 121-138; https://doi.org/10.3390/catal2010121 - 3 Feb 2012

Cited by 12 | Viewed by 8937

Abstract

The effect of gold presence on carbon monoxide oxidation and ethanol steam reforming catalytic behavior of two Ce-Zr-Co mixed oxides catalysts with a constant Co charge and different Ce/Zr ratios was investigated. The Ce-Zr-Co mixed oxides were obtained by the pseudo sol-gel like [...] Read more.

The effect of gold presence on carbon monoxide oxidation and ethanol steam reforming catalytic behavior of two Ce-Zr-Co mixed oxides catalysts with a constant Co charge and different Ce/Zr ratios was investigated. The Ce-Zr-Co mixed oxides were obtained by the pseudo sol-gel like method, based on metallic propionates polymerization and thermal decomposition, whereas the gold-supported Ce-Zr-Co mixed oxides catalysts were prepared using the direct anionic exchange. The catalysts were characterized using XRD, TPR, and EDXS-TEM. The presence of Au in doped Ce-Zr-Co oxide catalyst decreases the temperature necessary to reduce the cobalt and the cerium loaded in the catalyst and favors a different reaction pathway, improving the acetaldehyde route by ethanol dehydrogenation, instead of the ethylene route by ethanol dehydration or methane re-adsorption, thus increasing the catalytic activity and selectivity into hydrogen. Full article

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970 KiB

Open AccessReview

Monometallic Supported Gold Catalysts in Organic Transformations: Ring Making and Ring Breaking

by Krisztián Csankó, Pál Sipos and István Pálinkó

Catalysts 2012, 2(1), 101-120; https://doi.org/10.3390/catal2010101 - 1 Feb 2012

Cited by 3 | Viewed by 8732

Abstract

Supported gold catalysts are highly active in oxidation reactions. Beside the most frequently studied CO oxidation, they are readily applied in the epoxidation of more or less complex olefinic compounds using air or oxygen directly or other oxidants like peroxides of various kinds. [...] Read more.

Supported gold catalysts are highly active in oxidation reactions. Beside the most frequently studied CO oxidation, they are readily applied in the epoxidation of more or less complex olefinic compounds using air or oxygen directly or other oxidants like peroxides of various kinds. Less frequently though, the reverse reaction, ring opening with single or double C–O scission is also investigated. These and other ring making and breaking reactions are reviewed, and the catalytic roles of gold species are described. Full article

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2011

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1072 KiB

Open AccessArticle

The Influence of Base Metal (M) Oxidation State in Au-M-O/TiO₂ Systems on Their Catalytic Activity in Carbon Monoxide Oxidation

by Jan Mizera, Nika Spiridis, Robert P. Socha, Małgorzata Zimowska, Ryszard Grabowski, Katarzyna Samson and Józef Korecki

Catalysts 2012, 2(1), 38-55; https://doi.org/10.3390/catal2010038 - 22 Dec 2011

Cited by 8 | Viewed by 8405

Abstract

Base metal promoted gold/titania catalysts were synthesized, characterized and tested in CO oxidation reaction. Catalysts containing dopant metals in higher oxidation states exhibited higher activity than catalysts containing dopants in reduced states. The activity of fresh catalysts promoted by Cu, Fe and Ni [...] Read more.

Base metal promoted gold/titania catalysts were synthesized, characterized and tested in CO oxidation reaction. Catalysts containing dopant metals in higher oxidation states exhibited higher activity than catalysts containing dopants in reduced states. The activity of fresh catalysts promoted by Cu, Fe and Ni was similar to the unpromoted one, but treatment in reducing and oxidizing atmospheres revealed the supremacy of the copper promoted catalyst. The sequential deposition method proved to be better than the co-deposition—precipitation method. An attempt to explain these differences using XPS, FTIR and H₂ TPR was performed. Full article

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1600 KiB

Open AccessReview

The Art of Manufacturing Gold Catalysts

by Laura Prati and Alberto Villa

Catalysts 2012, 2(1), 24-37; https://doi.org/10.3390/catal2010024 - 21 Dec 2011

Cited by 51 | Viewed by 9531

Abstract

Gold has been considered as an active catalyst only when suitable techniques of preparation provided high metal dispersion. A comprehensive survey of the different methods now available for preparing active gold catalysts is reported with particular attention to the role of the supporting [...] Read more.

Gold has been considered as an active catalyst only when suitable techniques of preparation provided high metal dispersion. A comprehensive survey of the different methods now available for preparing active gold catalysts is reported with particular attention to the role of the supporting material in determining catalyst characteristics. Full article

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1617 KiB

Open AccessArticle

Gold/Iron Carbonyl Clusters for Tailored Au/FeO_x Supported Catalysts

by Rosa Bonelli, Stefano Zacchini and Stefania Albonetti

Catalysts 2012, 2(1), 1-23; https://doi.org/10.3390/catal2010001 - 21 Dec 2011

Cited by 17 | Viewed by 7569

Abstract

A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt₄]₄[Au₄Fe₄(CO)₁₆] and [NEt₄][AuFe₄(CO)₁₆] as precursors of highly [...] Read more.

A novel preparation method was developed for the preparation of gold/iron oxide supported catalysts using the bimetallic carbonyl cluster salts [NEt₄]₄[Au₄Fe₄(CO)₁₆] and [NEt₄][AuFe₄(CO)₁₆] as precursors of highly dispersed nanoparticles over different supports. A series of catalysts with different metal loadings were prepared and tested in the complete oxidation of dichlorobenzene, toluene, methanol and in the preferential oxidation of CO in the presence of H₂ (PROX) as model reactions. The characterization by BET, XRD, TEM, H₂-TPR, ICP-AES and XPS point out the way the nature of the precursors and the thermal treatment conditions affected the dispersion of the active phase and their catalytic activity in the studied reactions. Full article

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Graphical abstract

907 KiB

Open AccessArticle

Pre-Reduction of Au/Iron Oxide Catalyst for Low-Temperature Water-Gas Shift Reaction Below 150 °C

by Shinji Kudo, Taisuke Maki, Takashi Fukuda and Kazuhiro Mae

Catalysts 2011, 1(1), 175-190; https://doi.org/10.3390/catal1010175 - 9 Dec 2011

Cited by 9 | Viewed by 9217

Abstract

Low-temperature water-gas shift reaction (WGS) using gold catalyst is expected to be an attractive technique to realize an efficient on-site hydrogen production process. In this paper, Au/Fe₃O₄ catalysts for promoting the WGS below 150 °C were developed by a preliminary [...] Read more.

Low-temperature water-gas shift reaction (WGS) using gold catalyst is expected to be an attractive technique to realize an efficient on-site hydrogen production process. In this paper, Au/Fe₃O₄ catalysts for promoting the WGS below 150 °C were developed by a preliminary reduction of Au/iron oxide (Fe³⁺) catalyst utilizing high reactivity of Au nano-particles. The reduction was conducted under a CO, H₂, or CO/H₂O stream at either 140 or 200 °C, and the effect of reduction conditions on the characteristics of the Au/Fe₃O₄ catalyst and on the catalytic activity in WGS at 80 °C was investigated. The reaction progress during the pre-reduction treatment was qualitatively analyzed, and it was found that the iron oxide in Au/Fe₂O₃ calcined at 200 °C was easily reduced to Fe₃O₄ phase in all reduction conditions. The reduction conditions affected the characteristics of both Au and iron oxide, but all of the reduced catalysts had small Fe₃O₄ particles of less than 20 nm with Au particles on the surface. The surface area and content of cationic Au were high in the order of CO, H₂, CO/H₂O, and 140, 200 °C. In the WGS test at 80 °C using the developed catalysts, the activities of the catalysts pre-reduced by CO at 140 or 200 °C and by H₂ at 140 °C were very high with 100% CO conversion even at such a low temperature. These results indicated that factors such as higher surface area, crystallized Fe₃O₄, and cationic Au content contributed to the catalytic activity. Full article

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6721 KiB

Open AccessArticle

Nano-Scale Au Supported on Carbon Materials for the Low Temperature Water Gas Shift (WGS) Reaction

by Sonia Gil, Amaya Romero, Antonio de Lucas, Paula Sánchez, Fernando Dorado, Ana Raquel de la Osa, Jesús Manuel García-Vargas and Jose Luis Valverde

Catalysts 2011, 1(1), 155-174; https://doi.org/10.3390/catal1010155 - 9 Dec 2011

Cited by 7 | Viewed by 8470

Abstract

Au-based catalysts supported on carbon materials with different structures such as graphite (G) and fishbone type carbon nanofibers (CNF-F) were prepared using two different methods (impregnation and gold-sol) to be tested in the water gas shift (WGS) reaction. Atomic absorption spectrometry, transmission electron [...] Read more.

Au-based catalysts supported on carbon materials with different structures such as graphite (G) and fishbone type carbon nanofibers (CNF-F) were prepared using two different methods (impregnation and gold-sol) to be tested in the water gas shift (WGS) reaction. Atomic absorption spectrometry, transmission electron microscopy (TEM), temperature-programmed oxidation (TPO), X-ray diffraction (XRD), Raman spectroscopy, elemental analyses (CNH), N₂ adsorption-desorption analysis, temperature-programmed reduction (TPR) and temperature-programmed decomposition were employed to characterize both the supports and catalysts. Both the crystalline nature of the carbon supports and the method of gold incorporation had a strong influence on the way in which Au particles were deposited on the carbon surface. The higher crystallinity and the smaller and well dispersed Au particle size were, the higher activity of the catalysts in the WGS reaction was noted. Finally, catalytic activity showed an important dependence on the reaction temperature and steam-to-CO molar ratio. Full article

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1316 KiB

Open AccessReview

Synthesis of Gold Catalysts Supported on Mesoporous Silica Materials: Recent Developments

by Luis-Felipe Gutiérrez, Safia Hamoudi and Khaled Belkacemi

Catalysts 2011, 1(1), 97-154; https://doi.org/10.3390/catal1010097 - 2 Dec 2011

Cited by 97 | Viewed by 17805

Abstract

Mesoporous silica materials (MSM) with ordered and controllable porous structure, high surface area, pore volume and thermal stability are very suitable catalyst supports, because they provide high dispersion of metal nanoparticles and facilitate the access of the substrates to the active sites. Since [...] Read more.

Mesoporous silica materials (MSM) with ordered and controllable porous structure, high surface area, pore volume and thermal stability are very suitable catalyst supports, because they provide high dispersion of metal nanoparticles and facilitate the access of the substrates to the active sites. Since the conventional wet-impregnation and deposition-precipitation methods are not appropriate for the incorporation of gold nanoparticles (AuNPs) into MSM, considerable efforts have been made to develop suitable methods to synthesize Au/MSM catalysts, because the incorporation of AuNPs into the channel system can prevent their agglomeration and leaching. In this review, we summarize the main methods to synthesize active gold catalysts supported on MSM. Examples and details of the preparative methods, as well as selected applications are provided. We expect this article to be interesting to researchers due to the wide variety of chemical reactions that can be catalyzed by gold supported catalysts. Full article

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1124 KiB

Open AccessArticle

Synthesis and Catalytic Features of Hybrid Metal Nanoparticles Supported on Cellulose Nanofibers

by Akihiro Azetsu, Hirotaka Koga, Akira Isogai and Takuya Kitaoka

Catalysts 2011, 1(1), 83-96; https://doi.org/10.3390/catal1010083 - 25 Nov 2011

Cited by 82 | Viewed by 13612

Abstract

The structural and functional design of metal nanoparticles has recently allowed remarkable progress in the development of high-performance catalysts. Gold nanoparticles (AuNPs) are among the most innovative catalysts, despite bulk Au metal being regarded as stable and inactive. The hybridization of metal NPs [...] Read more.

The structural and functional design of metal nanoparticles has recently allowed remarkable progress in the development of high-performance catalysts. Gold nanoparticles (AuNPs) are among the most innovative catalysts, despite bulk Au metal being regarded as stable and inactive. The hybridization of metal NPs has attracted major interest in the field of advanced nanocatalysts, due to electro-mediated ligand effects. In practical terms, metal NPs need to be supported on a suitable matrix to avoid any undesirable aggregation; many researchers have reported the potential of polymer-supported AuNPs. However, the use of conventional polymer matrices make it difficult to take full advantage of the inherent properties of the metal NPs, since most of active NPs are imbedded inside the polymer support. This results in poor accessibility for the reactants. Herein, we report the topochemical synthesis of Au and palladium (Pd) bimetallic NPs over the surfaces of 2,2,6,6-tetramethylpiperidine-1-oxyl (TEMPO)-oxidized cellulose nanofibers (TOCNs), and their exceptional catalytic performance. Highly-dispersed AuPdNPs were successfully synthesized in situ on the crystal surfaces of TOCNs with a very high density of carboxylate groups. The AuPdNPs^@TOCN nanocomposites exhibit excellent catalytic efficiencies in the aqueous reduction of 4-nitrophenol to 4-aminophenol, depending on the molar ratios of Au and Pd. Full article

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1236 KiB

Open AccessArticle

In Situ Synthesis of Bimetallic Hybrid Nanocatalysts on a Paper-Structured Matrix for Catalytic Applications

by Hirotaka Koga, Yuuka Umemura and Takuya Kitaoka

Catalysts 2011, 1(1), 69-82; https://doi.org/10.3390/catal1010069 - 25 Nov 2011

Cited by 17 | Viewed by 8458

Abstract

Bimetallic nanoparticles have attracted significant attention as their electrochemical and catalytic properties being superior to those of the individual component nanoparticles. In this study, gold-silver hybrid nanoparticles (AuAgNPs) with an Au_core-Ag_shell nanostructure were successfully synthesized on zinc oxide (ZnO) whiskers. [...] Read more.

Bimetallic nanoparticles have attracted significant attention as their electrochemical and catalytic properties being superior to those of the individual component nanoparticles. In this study, gold-silver hybrid nanoparticles (AuAgNPs) with an Au_core-Ag_shell nanostructure were successfully synthesized on zinc oxide (ZnO) whiskers. The as-prepared nanocatalyst, denoted AuAgNPs^@ZnO whisker, exhibits an excellent catalytic efficiency in the aqueous reduction of 4-nitrophenol to 4-aminophenol; the turnover frequency was up to 40 times higher than that of each component nanoparticle. Their unique features were attributed to the electronic ligand effect at the bimetallic interface. In addition, the AuAgNPs were synthesized on a ZnO whisker-containing paper with a fiber-network microstructure, which was prepared via a papermaking technique. The paper-structured AuAgNPs composite possessed both a paper-like practical utility and a good catalytic performance. Furthermore, the on-paper synthesis process for these bimetallic nanocatalysts is facile. These easy-to-handle nanocatalyst hybrid composites are expected to find a wide range of applications in various chemical and catalytic processes. Full article

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755 KiB

Open AccessArticle

Gold Functionalized Supported Ionic Liquids Catalyst for CO Oxidation

by Svetlana Ivanova, Luis Francisco Bobadilla, Anna Penkova, Francisca Romero Sarria, Miguel Angel Centeno and Jose Antonio Odriozola

Catalysts 2011, 1(1), 52-68; https://doi.org/10.3390/catal1010052 - 25 Nov 2011

Cited by 5 | Viewed by 8258

Abstract

The present study tries to give an insight to the combination of the homogeneous and heterogeneous catalytic properties in a new class of materials. Well dispersed gold nanoparticles on an ionic liquid layer supported on a mineral carrier have been prepared. This work [...] Read more.

The present study tries to give an insight to the combination of the homogeneous and heterogeneous catalytic properties in a new class of materials. Well dispersed gold nanoparticles on an ionic liquid layer supported on a mineral carrier have been prepared. This work is concentrated on the characterizations and understanding of the interactions between all the components of the catalytic system. The application of the materials in the reaction of oxidation of carbon monoxide shows rather unexpected results—a good catalytic activity completely independent of the temperature. Full article

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443 KiB

Open AccessReview

Catalytic Reactions on Model Gold Surfaces: Effect of Surface Steps and of Surface Doping

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

Catalysts 2011, 1(1), 40-51; https://doi.org/10.3390/catal1010040 - 21 Nov 2011

Cited by 8 | Viewed by 7782

Abstract

The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT) based calculations were considered to clarify the role of the low coordinated gold atoms and the role of [...] Read more.

The adsorption energies and the activation energy barriers for a series of reactions catalyzed by gold surfaces and obtained theoretically through density functional theory (DFT) based calculations were considered to clarify the role of the low coordinated gold atoms and the role of doping in the catalytic activity of gold. The effect of the surface steps was introduced by comparison of the activation energy barriers and of the adsorption energies on flat gold surfaces such as the Au(111) surface with those on stepped surfaces such as the Au(321) or the Au(110) surfaces. It is concluded that the presence of low coordinated atoms on the latter surfaces increases the adsorption energies of the reactants and decreases the activation energy barriers. Furthermore, the increasing of the adsorption energy of the reaction products can lead to lower overall reaction rates in the presence of low gold coordinated atoms due to desorption limitations. On the other hand, the effect of doping gold surfaces with other transition metal atoms was analyzed using the dissociation reaction of molecular oxygen as a test case. The calculations showed that increasing the silver content in some gold surfaces was related to a considerable increment of the reactivity of bimetallic systems toward the oxygen dissociation. Importantly, that increment in the reactivity was enhanced by the presence of low coordinated atoms in the catalytic surface models considered. Full article

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4231 KiB

Open AccessArticle

Role of the Support Effects on the Catalytic Activity of Gold Clusters: A Density Functional Theory Study

by Min Gao, Andrey Lyalin and Tetsuya Taketsugu

Catalysts 2011, 1(1), 18-39; https://doi.org/10.3390/catal1010018 - 17 Nov 2011

Cited by 40 | Viewed by 11735

Abstract

It is demonstrated that the support effects play a crucial role in the gold nanocatalysis. Two types of support are considered—the “inert” support of hexagonal boron nitride (h-BN) with the N and B vacancy defects and the “active” support of rutile TiO₂ [...] Read more.

It is demonstrated that the support effects play a crucial role in the gold nanocatalysis. Two types of support are considered—the “inert” support of hexagonal boron nitride (h-BN) with the N and B vacancy defects and the “active” support of rutile TiO₂(110). It is demonstrated that Au and Au₂ can be trapped effectively by the vacancy defects in h-BN. In that case, the strong adsorption on the surface defects is accompanied by the charge transfer to/from the adsorbate. The excess of the positive or negative charge on the supported gold clusters can considerably promote their catalytic activity. Therefore gold clusters supported on the defected h-BN surface can not be considered as pseudo-free clusters. We also demonstrate that the rutile TiO₂(110) support energetically promotes H₂ dissociation on gold clusters. We show that the formation of the OH group near the supported gold cluster is an important condition for H₂ dissociation. We demonstrate that the active sites towards H₂ dissociation on the supported Au_n are located at corners and edges of the gold cluster in the vicinity of the low coordinated oxygen atoms on TiO₂(110). Thus catalytic activity of a gold nanoparticle supported on the rutile TiO₂(110) surface is proportional to the length of the perimeter interface between the nanoparticle and the support. Full article

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1206 KiB

Open AccessReview

Atomically Monodisperse Gold Nanoclusters Catalysts with Precise Core-Shell Structure

by Yan Zhu, Rongchao Jin and Yuhan Sun

Catalysts 2011, 1(1), 3-17; https://doi.org/10.3390/catal1010003 - 7 Sep 2011

Cited by 39 | Viewed by 11585

Abstract

The emphasis of this review is atomically monodisperse Au_n nanoclusters catalysts (n = number of metal atom in cluster) that are ideally composed of an exact number of metal atoms. Au_n which range in size from a dozen to a [...] Read more.

The emphasis of this review is atomically monodisperse Au_n nanoclusters catalysts (n = number of metal atom in cluster) that are ideally composed of an exact number of metal atoms. Au_n which range in size from a dozen to a few hundred atoms are particularly promising for nanocatalysis due to their unique core-shell structure and non-metallic electronic properties. Au_n nanoclusters catalysts have been demonstrated to exhibit excellent catalytic activity in hydrogenation and oxidation processes. Such unique properties of Au_n significantly promote molecule activation by enhancing adsorption energy of reactant molecules on catalyst surface. The structural determination of Au_n nanoclusters allows for a precise correlation of particle structure with catalytic properties and also permits the identification of catalytically active sites on the gold particle at an atomic level. By learning these fundamental principles, one would ultimately be able to design new types of highly active and highly selective gold nanocluster catalysts for a variety of catalytic processes. Full article

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