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BACKGROUND The selective conversion of cellulose to gluconic acid under mild conditions is challenging as it has abundant intra-and inter-molecular hydrogen bonds that protect the β-1,4-glycosidic bonds and make it intrinsically recalcitrant to deploymerize. RESULTS Au-Pd/TiO2 and Au-Pt/TiO2 catalysts prepared by sol immobilization method without pre-treatment are active and selective for the oxidation of glucose and cellobiose to gluconic acid under base-free conditions. Important preparation parameters are the pre-treatment of the catalyst and the metal ratio. CONCLUSION The optimized catalyst provided a good yield of gluconic acid from cellobiose and has opened up a new catalyst system for cellobiose conversion in terms of a heterogeneous catalyst.

Cu–ZrO2 catalysts were synthesized by the methanothermal (Me) and oxalate gel precipitation (Og) methods. Detailed characterization of the catalysts synthesized by the Me method shows that these contain only Cu substituted into the tetragonal ZrO2 lattice. For catalysts prepared using the Og method Cu is found not only in the tetragonal ZrO2 lattice but also in the form of CuO particles on the zirconia surface. When these materials were tested for the hydrogenation of levulinic acid (LA) to γ-valerolactone (GVL) it was found that Me materials show no catalytic activity, whereas GVL was formed using Og catalysts. A reduction treatment of the Og catalysts prior to use resulted in a marked increase in the catalytic activity, however, no activity increase was observed when the Me material was exposed to a similar treatment before testing. Based on these results and characterization data, we conclude that the catalytically active component of Cu–ZrO2 catalysts for the hydrogenation of LA is reduced Cu particles dispersed on the catalyst surface with strong interaction with the Cu incorporated zirconia support, while the role of Cu in the zirconia lattice is to improve the adhesion of these particles and maintain their dispersion.

By combining nanocatalysis and base-catalysis, a novel one-pot multistep process was found for the synthesis of substituted heterocycles of biological relevance from simple substrates. It is based on an initial Au/O2 oxidation of allylic alcohols followed by a base-catalysed tandem hetero-Michael/aldolisation/crotonisation with ortho-hydroxy or ortho-amino benzaldehydes. The flexibility of the reaction even allowed the benzaldehyde partner to be prepared in situ in an example of one-pot/5-steps process.

In this review we discuss the history of research into the use of gold for the acetylene hydrochlorination reaction, and describe the recent developments which have led to its commercialisation. We discuss the use of different precursors and the addition to gold of a secondary metal as methods which attempt to improve these catalysts, and consider the nature of the active gold species. The vast majority of poly vinyl chloride (PVC) produced globally still uses a mercuric chloride as a catalyst, despite the environmental problems associated with it. Due to the agreement by the Chinese government to remove mercury usage in the PVC industry over the course of the next few years there is an obvious need to find a replacement catalyst; the potential use of gold for this process has been well known for several decades and to date gold seems to be the best candidate for this, primarily due to its superior selectivity when compared to other metals.

A series of ruthenium catalysts supported on two different carbons were tested for the hydrogenation of lactic acid to 1,2-propanediol and butanone to 2-butanol. The properties of the carbon supports were investigated by inelastic neutron scattering and correlated with the properties of the ruthenium deposited onto the carbons by wet impregnation or sol-immobilisation. It was noted that the rate of butanone hydrogenation was highly dependent on the carbon support, while no noticeable difference in rates was observed between different catalysts for the hydrogenation of lactic acid.

In this study, we examine autoxidation and its role on the catalytic aerobic oxidation of cinnamyl alcohol using supported AuPd nanoparticles. We further report the crucial role of reaction conditions in the reaction pathway. Close attention is paid to the mechanism of the formation of benzaldehyde, a by-product formed in large quantities from the process of autoxidation. The activity of the catalysts depends on the preparation method with different sizes of nanoparticles obtained by the two methods of preparation. The catalysts can inhibit the autoxidation process or the two processes, namely catalytic oxidation and autoxidation, can coexist. In the case of oxidation of cinnamyl alcohol, 0.5%(wt) Au–0.5%(wt) Pd/TiO2 catalysts prepared by various methods allow different product distributions to be obtained. The catalyst prepared by the sol-immobilisation method seems to prevent autoxidation, leaving the catalytic process dominant. Catalysts prepared by the impregnation method seem to enable both the catalytic process and autoxidation to occur at the same time. We show that using the optimum catalyst for this reaction, the autoxidation process can be mitigated.

Precious metal nanoparticles supported on magnesium-aluminum hydrotalcite (HT), TiO2 , and MgO were prepared by sol immobilization and assessed for the catalytic oxidation of octanol, which is a relatively unreactive aliphatic alcohol, with molecular oxygen as the oxidant under solvent- and base-free conditions. Compared with the TiO2 - and MgO-supported catalysts, platinum HT gave the highest activity and selectivity towards the aldehyde. The turnover number achieved for the platinum HT catalyst was3700 after 180 min under mild reaction conditions. Moreover, the results for the oxidation of different substrates indicate that a specific interaction of octanal with the platinum HT catalyst could lead to deactivation of the catalyst.

The selective hydrogenation of furfuryl alcohol was investigated at room temperature by using supported palladium catalysts. The catalysts are very selective to the formation of 2-methylfuran. Furthermore, the addition of tin to palladium showed similar catalytic activity, but was more selective to tetrahydrofurfuryl alcohol. Variation of the Sn/Pd ratio has shown a considerable and interesting effect on the selectivity pattern. Addition of a small amount of Sn (1 wt %) shifted the selectivity towards tetrahydrofurfuryl alcohol and methyltetrahydrofuran, which are ring-saturated molecules. Increasing the tin ratio further decreased the catalytic activity and also showed very poor selectivity to either of these products.

Catalysts containing bimetallic gold–palladium nanoparticles are extremely active and selective for the oxidation of alcohols to aldehydes and the direct synthesis of hydrogen peroxide from molecular hydrogen and oxygen. We show that the oxidation of benzyl alcohol can be carried out at 50 °C and below by generating hydrogen peroxide in situ. The oxidation of benzyl alcohol to benzaldehyde has been achieved with high selectivity (>85%) at temperatures where no reaction is observed with only molecular oxygen in an autoclave. The effect of temperature, catalyst support, and solvent are studied in an autoclave system and reactions were carried out in a fixed bed reactor at a range of gas flow rates where the catalysts demonstrated stable conversion and selectivity.

The oxidation of four butanediols under base-free conditions has been investigated using a set of Au, Pd and Pt catalysts prepared using sol-immobilization. The supported nanoparticles are found to be active with bimetallic alloys having much higher activity when compared with the monometallic counterparts. In general the AuPt catalysts are the most active and in all cases the corresponding C4 oxidation products were observed with high selectivity; sequential reaction of these products leads to the formation of acetic acid as an undesired by-product.

The selective hydrogenation of furfuryl alcohol into 2-methylfuran was investigated at room temperature using palladium supported catalysts. We have shown that Pd–TiO2 catalysts can be very effective for the synthesis of 2-methylfuran at room temperature and low pressure of hydrogen (1–3 bar). The effect of various reaction conditions (pressure, catalyst amount, and solvent) was studied.

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.

The oxidation of 1,4-butanediol and butyrolactone have been investigated by using supported gold, palladium and gold-palladium nanoparticles. The products of such reactions are valuable chemical intermediates and, for example, can present a viable pathway for the sustainable production of polymers. If both gold and palladium were present, a significant synergistic effect on the selective formation of dimethyl succinate was observed. The support played a significant role in the reaction, with magnesium hydroxide leading to the highest yield of dimethyl succinate. Based on structural characterisation of the fresh and used catalysts, it was determined that small gold-palladium nanoalloys supported on a basic Mg(OH)2 support provided the best catalysts for this reaction.

In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO2 catalyst in the aerobic oxidation of 1,4-butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3-propanediol and its two methyl-substituted homologues, 2-methyl-1,3-propanediol and 2,2-dimethyl-1,3-propanediol, over a Au/TiO2 catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed-field gradient nuclear magnetic resonance (PFG-NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non-invasive characterisation tools for catalytic materials, which complement conventional reaction data.

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. © 2012 Elsevier B.V. All rights reserved.

The effect of water on the catalytic oxidation of 1,4-butanediol in methanol over Au/TiO(2) has been investigated by catalytic reaction studies and NMR diffusion and relaxation studies. The addition of water to the dry catalytic system led to a decrease of both conversion and selectivity towards dimethyl succinate. Pulsed-field gradient (PFG)-NMR spectroscopy was used to assess the effect of water addition on the effective self-diffusivity of the reactant within the catalyst. NMR relaxation studies were also carried out to probe the strength of surface interaction of the reactant in the absence and presence of water. PFG-NMR studies revealed that the addition of water to the initial system, although increasing the dilution of the system, leads to a significant decrease of effective diffusion rate of the reactant within the catalyst. From T(1) and T(2) relaxation measurements it was possible to infer the strength of surface interaction of the reactant with the catalyst surface. The addition of water was found to inhibit the adsorption of the reactant over the catalyst surface, with the T(1)/T(2) ratio of 1,4-butanediol decreasing significantly when water was added. The results overall suggest that both the decrease of diffusion rate and adsorption strength of the reactant within the catalyst, due to water addition, limits the access of reactant molecules to the catalytic sites, which results in a decrease of reaction rate and conversion.

We report the solvent-free oxidation of 1-hexene with air by using supported gold catalysts with a catalytic amount of tert-butyl hydroperoxide (TBHP) as initiator. We confirm that gold supported on graphite is an effective catalyst for such oxidations and that graphite was the preferred support. Preparation of catalysts using modified sol-immobilisation was found to be effective, particularly when the PVA stabiliser was removed by a solvent treatment prior to the reaction.

The oxidative esterification of a homologous series of diols (1,3-propanediol,2-methyl-propanediol and 2,2-dimethyl-1,3-propanediol) with methanol has been investigated using titania-supported gold, palladium and gold–palladium catalysts using molecular oxygen. The gold– palladium catalysts showed the highest activity and 1,3-propanediol was the most reactive while the additional methyl groups decreased the reactivity. However, it is possible to achieve high selectivity to methyl 3-hydroxypropionate and 2-methyl-3-hydroxyisobutyrate by mono-oxidations.

Gold–palladium nanoparticles either in the form of colloids or supported nanoparticles have been extensively used as redox catalysts in recent years. These materials are very effective for the transformation of organic compounds to highly useful chemical products. The catalytic materials are usually prepared either using deposition-precipitation or impregnation techniques, but recently significant attention has been focused on the use of colloidal methods. Here we compare and contrast the preparation and catalytic reactivity of Au–Pd supported nanoparticles synthesised by impregnation, deposition-precipitation and colloidal methods. The catalyst materials have been evaluated for the oxidation of benzyl alcohol, as a model reaction. In addition, we have focused our attention on the utilisation of different types of reactors (autoclave versus glass reactors) and we now emphasise the possibility of using simplified types of reactors which have the advantage of significant cost savings and ease of application.

Trimetallic Au-Pd-Pt nanoparticles have been supported on activated carbon by the sol-immobilisation method. They are found to be highly active and selective catalysts for the solvent-free aerobic oxidation of benzyl alcohol. The addition of Pt promotes the selectivity to the desired product benzaldehyde at the expense of toluene formation. Detailed aberration corrected STEM-XEDS analysis confirmed that the supported particles are indeed Au-Pd-Pt ternary alloys, but also identified composition fluctuations from particle-to-particle which vary systematically with nanoparticle size. © 2013 The Royal Society of Chemistry.

The oxidative esterification of 1,2-propanediol to methyl lactate and methyl pyruvate was investigated using gold and gold palladium nanoparticles supported on a variety of supports. Methyl lactate can be used in cosmetics and personal care products, whereas methyl pyruvate is useful in the treatment of diseases of the nervous system. We show that gold-palladium alloy catalysts can be very effective for the oxidative esterification of 1,2-propanediol to methyl lactate and methyl pyruvate. Five supports, titania, carbon, silica, iron oxide and ceria are contrasted. The addition of palladium to gold significantly enhances the activity and retains the high selectivity to methyl lactate using O 2 as oxidant. Using ceria as support a significant improvement in the selectivity to methyl lactate was observed, whereas using silica as support high selectivity to methyl pyruvate was achieved. The use of colloidal methods and the effect of support and Au/Pd molar ratio are discussed.

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. © 2012 Springer Science+Business Media New York.

The oxidation of 2-hexen-1-ol and 1-hexen-3-ol with air has been studied using supported gold, palladium and gold–palladium catalysts. The main aim was to determine if either the alcohol or alkene functional group can be oxidised selectively. However, based on the reaction products observed (2-hexen-1-ol forms 2-hexene, hexanal, (E)-2-hexenal, (E)-3-hexen-1-ol, 4-hexen-1-ol and (E)-2-hexanoic acid. 1-Hexen-3-ol forms 1-hexene, 3-hexanone, 1-hexen-3-one and 3-hexenol), the main pathway in these reactions is isomerisation and, in addition, significant yields of the products are due to a disproportionation reaction. Controlling the selectivity in molecules with multiple function groups by manipulating the catalyst composition and reaction conditions can promote or hinder the various reaction pathways, thereby increasing the selectivity to the desired oxidation products.

In this paper, we demonstrate a facile route to carbon-supported nanoparticles of a gold/palladium alloy which exhibit catalytic activity for the oxidation of benzylic alcohols, using the biopolymer chitosan. The biomolecule acts triply as a structure-directing agent, anti-sintering matrix and in situ source of carbon in which the catalytically active nanoparticles are dispersed. The catalyst works without the need for environmentally harmful bases and solvents.