Gold-based Catalysts Research Articles

Gold-Based Nanoparticulate Catalysts for the Oxidative Esterification of 1,4-Butanediol to Dimethyl Succinate

The effect of the reaction conditions and catalyst composition on the oxidation of 1,4-butanediol has been investigated. We have shown that gold and gold–palladium nanoparticles supported on titania can be effective catalysts for this oxidation reaction. We have demonstrated that the formation of butyrolactone, methyl-4-hydroxybutyrate and dimethyl succinate follow a sequential reaction pathway. We have also investigated the role of acid/base on the reaction and have shown a beneficial synergistic effect of alloying gold with palladium on both the conversion and selectivity towards dimethyl succinate.

Oxidative esterification of renewable furfural on gold-based catalysts: Which is the best support?

Gold-based catalysts over different supports were investigated in the oxidative esterification of furfural by employing an efficient and sustainable process. The catalytic performances follow the trend: Zirconia–Au>Ceria–Au≫Titania–Au. Zirconia came out to be the best support option to promote activity, selectivity and also stability. The chemical and morphological properties observed for zirconia-supported sample seem to fulfill a good compromise between high gold dispersion and the presence of suitable acid–base properties, for good selectivity. Moreover, stability and recycling of the catalysts were also investigated.

An electrochemical study of carbon dioxide electroreduction on gold-based nanoparticle catalysts

We report here on an electrochemical study of carbon dioxide electroreduction (CO2ER) employing electrochemical impedance spectroscopy (EIS) and a rotating ring-disk electrode (RRDE) on different gold based catalysts, namely bulk polycrystalline gold, gold nanoparticles (Au NPs) and Au@Ag core–shell nanoparticles. RRDE measurements allowed the identification of the reduction potential of CO2 to CO and the characterisation of NPs based on their selectivity for CO2ER with respect to hydrogen evolution. Gold–silver combined catalysts were found to be more selective than Au NPs although at higher overpotential. One gold–silver catalyst exhibits a constant selectivity over a wide potential range. For the first time, EIS data showed the existence of two charge transfers during the reduction of CO2. These are attributed to two surface confined reactions that involve an adsorbed intermediate which is correlated with a proposed mechanism. The potential range of these reactions is specific for each catalyst with gold–silver catalysts exhibiting a slower electron transfer than Au NPs, Au and Ag polycrystalline electrodes.

Strategies for Designing Supported Gold–Palladium Bimetallic Catalysts for the Direct Synthesis of Hydrogen Peroxide

Hydrogen peroxide is a widely used chemical but is not very efficient to make in smaller than industrial scale. It is an important commodity chemical used for bleaching, disinfection, and chemical manufacture. At present, manufacturers use an indirect process in which anthraquinones are sequentially hydrogenated and oxidized in a manner that hydrogen and oxygen are never mixed. However, this process is only economic at a very large scale producing a concentrated product. For many years, the identification of a direct process has been a research goal because it could operate at the point of need, producing hydrogen peroxide at the required concentration for its applications. Research on this topic has been ongoing for about 100 years. Until the last 10 years, catalyst design was solely directed at using supported palladium nanoparticles. These catalysts require the use of bromide and acid to arrest peroxide decomposition, since palladium is a very active catalyst for hydrogen peroxide hydrogenation. Recently, chemists have shown that supported gold nanoparticles are active when gold is alloyed with palladium because this leads to a significant synergistic enhancement in activity and importantly selectivity. Crucially, bimetallic gold-based catalysts do not require the addition of bromide and acids, but with carbon dioxide as a diluent its solubility in the reaction media acts as an in situ acid promoter, which represents a greener approach for peroxide synthesis. The gold catalysts can operate under intrinsically safe conditions using dilute hydrogen and oxygen, yet these catalysts are so active that they can generate peroxide at commercially significant rates. The major problem associated with the direct synthesis of hydrogen peroxide concerns the selectivity of hydrogen usage, since in the indirect process this factor has been finely tuned over decades of operation. In this Account, we discuss how the gold-palladium bimetallic catalysts have active sites for the synthesis and hydrogenation of hydrogen peroxide that are different, in contrast to monometallic palladium in which synthesis and hydrogenation operate at the same sites. Through treatment of the support with acids prior to the deposition of the gold-palladium bimetallic particles, we can obtain a catalyst that can make hydrogen peroxide at a very high rate without decomposing or hydrogenating the product. This innovation opens up the way to design improved catalysts for the direct synthesis process, and these possibilities are described in this Account.

O2 Adsorption and Oxidative Activity on Gold-Based Catalysts with and without a Ceria Support

Understanding the O2 adsorption and oxidative activity on gold-based catalysts is of great significance for gold catalysis. According to the adsorption behaviors of O2 on Au(111)+, 3Au/Au(111)+, Au19+, and Au9/CeO2(111), the electronic nature of why O2 weakly interacts with free positively charged Au substrate while it strongly interacts with Au cluster supported on ceria is well-explained herein. The ceria support serves as an electronic repository, where it gains and stores electrons from the supported metal cluster and releases them when the metal cluster interacts with molecular O2. The possible oxygen species on gold-based catalysts have been systematically confirmed for the first time. On the Au9/CeO2 modeling catalyst, a peroxide species forms when O2 locates at the hollow site of Au9, while a superoxide forms for O2 at the top site of a Ce atom. It is very interesting to find that Ce3+ ion distributions in Aun/CeO2 catalysts have diverse possibilities. The superoxide close to Au9 has the highest oxidative activity. The interface between the Au cluster and ceria surface is the active site for Aun/CeO2 catalysts. The present work sheds light on understanding the oxidative mechanism of metal/support catalysts, as well as the development of new catalysts with high performance at relatively low temperature.

Heterogeneous Catalysis by Gold-based Bimetallic Catalysts

This critical review summarizes recent advances on the preparation, characterization and application of Aubased bimetallic Au-M catalysts. Particularly bimetallic Au-Pd, Au-Pt and Au-Ag catalysts have been emphasized. The diversity of the structure and combination of these bimetallic Au-M catalysts leads to various catalytic performances in, i.e., oxidation, hydrogenation, electrocatalytic, and photocatalytic reactions. The promotional effects of Au have been discussed by its electronic and geometric modifications of active metals. Efforts on controlling the structure (morphology, particle size and growth of crystalline) of supported bimetallic Au-M catalysts via advanced synthetic approaches have been elaborated. An overview on the challenges and opportunities for future research toward the understanding of catalytic chemistry of gold-based bimetallic systems has also been presented along with the descrption of few of the recent patents. Keywords: Bimetallic catalyst, nanoalloy, gold-based catalysts, Au-Pd, Au-Cu, Au-Ag.

The effect of MnO2 loading on the glycerol electrooxidation activity of Au/MnO2/C catalysts

Manganese oxides have shown promise as co-catalysts for platinum- and palladium-based alcohol electrooxidation catalysts. In this investigation, the effect of adding MnO2 to a gold-based catalyst system was explored for the glycerol electrooxidation reaction. It was found that modification of the carbon support with MnO2 had the effect of stabilising gold nanoparticles, giving rise to smaller gold particles with a more uniform particle size distribution than on the carbon alone. All gold-based catalysts gave very high currents for glycerol oxidation (1–5Amg−1cat) and catalysts with MnO2 contents of 5 and 9wt% yielded the highest mass activities (35–37Amg−1Au). This is believed to be partly due to MnO2 preventing gold agglomeration, creating a larger gold surface area for reaction. In addition, it is believed that MnO2 may act as an active co-catalyst, especially at higher potentials, by means of oxygen spillover onto gold – leading to higher activities and lower peak potentials. MnO2 was also found to activate the glycerol oxidation reaction earlier, giving lower onset potentials. Stability and impedance studies showed that MnO2-modified catalysts were less stable at a low potential (0V) than Au/C. This could be due to blocking of mixed-valence manganese oxide sites or poisoning of the smaller gold particles on these catalysts. However, at a higher potential of 0.2V, Au/5% MnO2/C demonstrated the best activity and stability overall. All our catalysts are more active than the palladium- and platinum-based catalysts reported in literature, with our best-performing catalyst on a mass activity basis (Au/9% MnO2/C) being at least 12 times more active. This effectively demonstrates the advantage of using a gold-based catalyst for glycerol oxidation, especially when supported by MnO2 which aids in lowering the overpotential for glycerol oxidation over gold.

After the gold rush?

I always look forward to the quarterly publication of Platinum Metals Review; for anyone with even a passing interest in platinum group metals (PGMs), it is a leading source of insight with excellent contributions from academia and industry alike. January’s issue carried a fascinating “final analysis” article from the University of Cardiff ’s Professor Stan Golunski. It is entitled “Catalysis after the gold rush” and details a new EU grant awarded to Cardiff University which “aims to explore the implications of discoveries made over the last 25 years of intensive research into catalysis by gold and so accelerate the discovery and development of other catalytic materials such as those based on PGMs which may hold the key to solving many of the pressing challenges facing us now and in the future” [1]. The article made me think about gold catalysis in a slightly different way, I must admit. The enormous wave of interest in the metal’s use as a catalyst, driven primarily from the work of Haruta and Hutchings in the 1980s, really has laid down an incredibly strong foundation of understanding to build upon. The Cardiff team are correct to seek to exploit this and believe that the learning from 25 years of intensive research into one metal will help drive progress elsewhere, whether that be with precious metals, cheaper base metals or combinations thereof. However, I truly believe we are not quite at the end of the gold rush just yet. Professor Golunski makes fair points regarding economics and commercialisation of gold-based catalyst systems. It is somewhat ironic that just as certain new solutions were poised to break into the market, the gold price reached record levels making those technologies uncompetitive financially, a situation barely even considered feasible a few short years ago. The gold–palladium catalyst utilised in the vinyl acetate monomer process is certainly the best known example of a commercialised process, but there are a number of others currently (or previously) active in plants around the world. Granted, these are smaller in scale but are all adding to the understanding of gold-based catalysis in an industrial setting. Other processes are currently in the pipeline, but of course, only time (and the financial markets!) will tell if they reach full commercialisation. So, I for one do not believe the best years have yet passed for gold in catalysis. The metal continues to surprise scientifically, and new opportunities are bound to arise. In the meantime, I hope you will all continue to communicate advances in the field through Gold Bulletin. I have been particularly busy over the last few months dealing with many excellent papers. Of course, my ongoing thanks to those of you that submit your work to us and our diligent referees. This issue contains the usual spread of interesting subjects, ranging from gold metallurgy to surface plasmon resonance and everything in between. Enjoy.

Promising Stability of Gold-Based Catalysts Prepared by Direct Anionic Exchange for DeNO x Applications in Lean Burn Conditions

Supported gold catalysts on γ-Al2O3 have been investigated in the catalytic reduction of NO x in simulated Diesel exhaust gas conditions. Different parameters have been examined essentially the mode of gold incorporation via classical deposition–precipitation and anionic exchange methods and the nature of the pre-activation thermal treatment. The resistance to thermal ageing under reactive conditions at 500 °C was found completely different with a significant rate enhancement on anionic-exchange samples. Further comparisons also show that the nature of the pre-activation thermal treatment influences the extent of surface reconstructions during thermal ageing with a detrimental effect of reductive pre-treatment on the catalytic performances.

Progress in controlling the size, composition and nanostructure of supported gold–palladium nanoparticles for catalytic applications

This review article gives an overview of the recent developments in the synthesis strategies of supported gold-based bimetallic nanoparticle catalysts. The catalytic efficiency of these supported bimetallic nanoparticles, similar to monometallic nanoparticles, depends on their structural characteristics, but with added complexities because of the presence of the second metal. We discuss three major structural features of supported bimetallic nanoparticles, namely (a) size, (b) composition and (c) nanostructure, all of which play a crucial role in the resulting overall catalytic performances of the materials. Selected literature examples, where these three parameters have been extensively studied and controlled by changing the synthesis strategies, are analyzed and presented. A specific objective of this article is to motivate researchers to characterize these supported nanoparticles more thoroughly to investigate their structural features in detail and design based on this knowledge suitable and innovative synthesis strategies to control these properties. Because of the sheer number of examples in this field of research, this paper focuses only on gold–palladium bimetallic nanoparticles; however we are convinced that the broader scientific message could be extended to other bimetallic catalyst compositions.

Gold catalysts in environmental remediation and water-gas shift technologies

This review presents studies and investigations of the use of gold catalysts in environmental applications, from the oxidation of CO and volatile organic compounds (VOCs) in environmental technologies to the production of hydrogen, a non-polluting energy source, in the water-gas shift (WGS) reaction. It summarizes a variety of results, from the discovery made by Haruta et al. about the catalytic behaviour of gold in CO oxidation, to the use of gold-based catalysts in environmental remediation, by the catalytic removal of different types of VOC using a wide variety of oxide supports and finally to the use of this highly active noble metal in WGS applications. It also discusses gold loading methods, comparing them in terms of simplicity, efficiency and the resultant particle size and dispersion of Au over various supports. The application of different types of supporting materials is also presented, with a critical discussion of the parameters affecting the choice and use of such materials, i.e. how the support interacts with gold particles and with pollutant molecules along with the advantages a support offers to VOC oxidation and WGS reactions. It ends by highlighting the potential of gold catalyts in the future.

Non-mercury catalytic acetylene hydrochlorination over bimetallic Au–Co(iii)/SAC catalysts for vinyl chloride monomer production

Several gold-based catalysts including Au, Au–La(III), Au–Co(II), and Au–Co(III) were prepared and assessed for acetylene hydrochlorination, combining with characterizations of low-temperature N2 adsorption/desorption, thermogravimetric analysis, X-ray diffraction, temperature-programmed reduction, inductively coupled plasma-atomic emission spectroscopy, transmission electron microscopy, and X-ray photoelectron spectroscopy. The best catalytic performance was obtained over Au1Co(III)3/SAC catalysts with an acetylene conversion of 92% and a selectivity to VCM of 99.9%. It is indicated that the additives of Co(III), Co(II) and La(III) are preferential to stabilize the catalytic active Au+ species and inhibit the reduction of Au3+ to Au0 in the preparation process of Au-based/SAC catalysts. The addition of these additives can greatly inhibit the occurrence of coke deposition on the catalyst surface, and also inhibit the catalyst sintering, thereby improving the activity and long-term stability of the Au-based catalysts.

Highly Selective, Facile NO2 Reduction to NO at Cryogenic Temperatures on Hydrogen Precovered Gold

We have discovered that NO(2) is reduced to NO at 77 K by hydrogen precovered gold in vacuum. Here, we investigate the partial reduction of NO(2) to NO on an atomic-hydrogen populated model gold catalyst for a more fundamental understanding of the surface chemistry of hydrogenation. Gold-based catalysts have been found to be active for many hydrogenation reactions, but few related fundamental studies have been conducted. Our experimental results reveal a high catalytic activity for gold: indeed, NO(2) is reduced to NO with 100% conversion and 100% selectivity at temperatures lower than 120 K. Density functional theory calculations and reflection-absorption infrared spectroscopy measurements indicate that HNO(2) and N(2)O(3) are intermediates which are highly dependent on surface hydrogen concentrations; subsequent hydrogenation of HNO(2) and dissociation of N(2)O(3) upon annealing induces the production of NO and H(2)O.

The Selective Oxidation of 1,2-Propanediol by Supported Gold-Based Nanoparticulate Catalysts

The oxidation of 1,2-propanediol to form lactic acid and hydroxyacetone has been investigated using supported metal nanoparticles. A series of supported gold, palladium, platinum and combinations of these metals have been investigated. In the presence of base the major product formed is lactate, often in excellent yields as, under these conditions the terminal hydroxyl group is oxidised. In the absence of base, more vigorous conditions are required to elicit high conversions; surprisingly, a major product from such reactions is a mono-oxidation product hydroxyacetone, along with lactate.

Conversion of Synthesis Gas to Dimethylether Over Gold-based Catalysts

It is shown that Au–zinc oxide–alumina catalysts are suitable for the water–gas shift reaction and for methanol (MeOH) and DME synthesis, indicating their use in a direct single-stage process for converting syngas to a DME + methanol mixture. Temperatures above 340 °C were required in order to obtain reasonable catalytic activity. A 67 % DME selectivity was achieved at 380 °C with a low space velocity 0.75 dm3 h−1 g−1 and 50 bar. The lower CO conversions at the higher temperature of 460 °C was probably due to the MeOH equilibrium limitation in the range of temperatures 340 to 460 °C, but deactivation is observed as well, above 460 °C. Au/ZnO/γ-Al2O3 is more stable than traditional copper-based catalysts, which are stable below about 300 °C, and then only in the absence of water. The gold composite catalyst was mainly selective toward DME, MeOH and CH4, and to C2 to C5 hydrocarbons. An analysis of the main reactions involved indicates that only the methanol synthesis reaction reaches a near-equilibrium situation, with the other reactions being under kinetic control.

The selective oxidation of 1,2-propanediol to lactic acid using mild conditions and gold-based nanoparticulate catalysts

The use of bio-renewable resources for the generation of materials and chemicals continues to attract significant research attention. It is well established that glycerol is an excellent starting material for the production of 1,2-propanediol by dehydration/hydrogenation and that this can subsequently be oxidised to lactic acid, which has the potential to be used as a major chemical in the production of biodegradable polymers. Previous studies using gold catalysts for the oxidation of 1,2-propanediol have used elevated temperatures and pressures. We now show that the oxidation of 1,2-propanediol to form lactic acid can be carried out selectively under mild reaction conditions with gold–platinum catalysts prepared using a sol-immobilisation method, with activated carbon as the support. Carrying out the reaction at ambient temperature with air significantly improves the reaction in terms of its environmental impact and its industrial attractiveness, as lactic acid can be obtained with high selectivity.

Origin of the selectivity in the gold-mediated oxidation of benzyl alcohol

Benzyl alcohol has received substantial attention as a probe molecule to test the selectivity and efficiency of novel metallic gold catalysts. Herein, the mechanisms of benzyl alcohol oxidation on a gold surface covered with atomic oxygen are elucidated; the results show direct correspondence to the reaction on gold-based catalysts. The selective, partial oxidation of benzyl alcohol to benzaldehyde is achieved with low oxygen surface concentrations and takes place through dehydrogenation of the alcohol to form benzaldehyde via a benzyloxy (C6H5–CH2O) intermediate. While in this case atomic oxygen plays solely a dehydrogenating role, at higher concentrations it leads to the formation of intermediates from benzaldehyde, producing benzoic acid and CO2. Facile ester (benzyl benzoate) formation also occurs at low oxygen concentrations, which indicates that benzoic acid is not a precursor of further oxidation of the ester; instead, the ester is produced by the coupling of adsorbed benzyloxy and benzaldehyde. Key to the high selectivity seen at low oxygen concentrations is the fact that the production of the aldehyde (and esters) is kinetically favored over the production of benzoic acid.

Correction to Structure and Surface Chemistry of Gold-Based Model Catalysts

ADVERTISEMENT RETURN TO ISSUEPREVAddition/CorrectionORIGINAL ARTICLEThis notice is a correctionCorrection to Structure and Surface Chemistry of Gold-Based Model CatalystsJinlong Gong*Cite this: Chem. Rev. 2012, 112, 5, 3055Publication Date (Web):March 29, 2012Publication History Published online29 March 2012Published inissue 9 May 2012https://doi.org/10.1021/cr300102eCopyright © 2012 American Chemical SocietyRIGHTS & PERMISSIONSArticle Views1645Altmetric-Citations1LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (106 KB) Get e-Alerts Get e-Alerts

Hydrochlorination of acetylene to vinyl chloride monomer over bimetallic Au–La/SAC catalysts

Gold and gold-based bimetallic catalysts for acetylene hydrochlorination were prepared with HAuCl 4·4H 2O and LaCl 3·7H 2O as precursors and analyzed by the characterization methods of BET, XRD, SEM, TG and ICP-AES. The results indicate that pitch-based spherical activated carbon SAC is the optimal carrier; Au/C catalyst deactivates easily for coke deposition and the valence change of Au in the reaction, the addition of lanthanum to gold can weaken the occurrence of coke deposition and inhibit the valence change of gold to improve the stability of the catalyst; Under the reaction conditions of temperature 423 K, C 2H 2 hourly space velocity (GHSV) 360 h −1, feed volume ratio V (HCl)/V (C 2H 2) = 1.15 and Au loading of 1 wt%, the optimal atomic ratio of Au, La (a/a) was 1:3, the conversion of acetylene was up to 98% and the selectivity to VCM was more than 99.8%.

In situ XPS study of the adsorption and reactions of NO and O 2 on gold nanoparticles deposited on TiO 2 and SiO 2

Ambient pressure photoelectron spectroscopy (APPES) has been used to study the adsorption of nitric oxide (NO) and molecular oxygen (O 2) over gold-based model catalysts consisting of mono-dispersed gold nanoparticles with different diameters (2–5 nm) and oxide supports (including polycrystalline silica and titania thin films). APPES is an in situ technique that makes possible to monitor via XPS chemical changes occurring on the catalyst surface and to identify adsorbed species under reaction conditions. In our experiments, no changes were observed on the Au/SiO 2 samples during exposure to 0.5 Torr of NO, while adsorbed NO and several N-containing species were detected on Au/TiO 2 model catalysts under the same conditions. In addition, shifts in the Ti 3p and O 1s peaks in TiO 2 were observed relative to the Au 4f peak. Similar behavior, although to a lesser extent, was observed on Au/TiO 2 samples when O 2 was used. In both cases, the shifts of the Ti 3p and O 1s peaks could be attributed to band bending effects on the TiO 2 substrate caused by chemisorption of the gases.