[Show abstract][Hide abstract] ABSTRACT: The selective oxidation of methane to methanol has been studied using trimetallic AuPdCu/TiO2 catalysts prepared by incipient wetness impregnation. They are able to catalyse the selective oxidation of methane to methanol under mild aqueous reaction conditions using H2O2 as the oxidant. When compared with bimetallic, Au–Pd/TiO2 analogues, the new trimetallic catalysts present productivities which are up to 5 times greater under the same test conditions, and this is coupled with methanol selectivity of up to 83%. Characterisation shows that whilst Au–Pd is present as Au-core–Pd-shell nanoparticles, copper is present as either Cu or Cu2O in <5 nm particles.
No preview · Article · Dec 2015 · Catalysis Science & Technology
[Show abstract][Hide abstract] ABSTRACT: The selective hydrogenation of furfural at ambient temperature has been investigated using a Pd/TiO2 catalyst. The effect of the solvent was studied and high activity and selectivity to 2-methylfuran and furfuryl alcohol was observed using octane as solvent but a number of byproducts were observed. The addition of Ru to the PdTiO2 catalyst decreased the catalytic activity but improved the selectivity towards 2-methylfuran and furfuryl alcohol with decreased byproduct formation. Variation of the Ru/Pd ratio has shown an interesting effect on the selectivity. The addition of a small amount of Ru (1 wt%) shifted the selectivity towards furfuryl alcohol and 2-methylrofuran. Further increasing the Ru ratio decreased the catalytic activity and also showed a very poor selectivity to 2-methylfuran.
No preview · Article · Dec 2015 · Catalysis Science & Technology
[Show abstract][Hide abstract] ABSTRACT: A ceramic membrane reactor was investigated for the continuous catalytic oxidation of benzyl alcohol with oxygen. The reactor had a concentric configuration. An inner tube created an annulus for the catalyst packed-bed (0.9 wt % Au-Pd/TiO2, particle size 90-125 μm) through which the liquid phase (benzyl alcohol, neat or dissolved in o-xylene) flowed. This was followed by the tubular ceramic membrane, which consisted of layers of alumina and a zirconia top layer with a nominal average pore size of 50 nm. The role of the membrane was to provide an interface for gas and liquid to come in contact. Pure oxygen was fed to the opposite side of the membrane in the outer shell of the reactor. Temperature affected conversion but not selectivity, possibly because of insufficient supply of oxygen. However, increasing catalyst contact time or decreasing benzyl alcohol concentration improved selectivity and conversion, indicating that a key parameter was the balance between oxygen supply by the membrane vs oxygen demand by the reaction. By adjusting the operating parameters, reaction performance improved. Selectivity to benzaldehyde 88% and conversion of benzyl alcohol 75% were obtained at 3.2 bara of gas pressure, 24444 gcat·s/galcohol catalyst contact time, 0.5 M benzyl alcohol concentration, and temperature of 120 °C. This performance was comparable to simulated trickle bed operation, where oxygen and substrate were premixed before entering the catalyst packed bed. The membrane reactor offers safer operation, since flammable oxygen/organic mixtures formed in the trickle bed are avoided.
No preview · Article · Dec 2015 · Organic Process Research & Development
[Show abstract][Hide abstract] ABSTRACT: Molybdenum blue (MB), is a polyoxometalate with a nanoring structure comprising Mo5+–O–Mo6+ bridges, which is active for the catalytic oxidation of cyclohexane to cyclohexanol and cyclohexanone. However, little is known about the mechanistic features responsible of this catalytic activity. In the present work, the Mo5+–O–Mo6+ moieties embedded in the MB nanoring structure were characterized using diffuse reflectance-UV–Visible spectroscopy and solid state EPR spectroscopy. The amount of Mo5+ centres was then varied by thermal treatment of the polyoxometalate in the absence of oxygen, and the resultant effect on the catalytic activity was investigated. It was observed that, an increased amount of Mo5+ centres preserved the conversion of cyclohexane (ca. 6 %) but led to a loss of selectivity to cyclohexanol giving cyclohexanone as the major product, and the simultaneous formation of adipic acid. To rationalise these results the catalysts were studied using EPR spin trapping to investigate the decomposition of cyclohexyl hydroperoxide (CHHP), a key intermediate in the oxidation process of cyclohexane. This analysis showed that CHHP has to be bound to the MB surface in order to explain its catalytic activity and product distribution.
No preview · Article · Dec 2015 · Catalysis Letters
[Show abstract][Hide abstract] ABSTRACT: In this work, we show that the introduction of acidic oxygen functionalities to the surface of carbon nanofibers serves to depress the hydrogenation and the decomposition of hydrogen peroxide during the direct synthesis of H2O2. Moreover, the presence of acidic groups enhances the H2O2 productivity in the case of supported AuPd nanoparticles.
No preview · Article · Dec 2015 · Catalysis Science & Technology
[Show abstract][Hide abstract] ABSTRACT: MAXNET Energy is an initiative of the Max Planck society in which eight Max Planck institutes and two external partner institutions form a research consortium aiming at a deeper understanding of the electrocatalytic conversion of small molecules. We give an overview of the activities within the MAXNET Energy research consortium. The main focus of research is the electrocatalytic water splitting reaction with an emphasis on the anodic oxygen evolution reaction (OER). Activities span a broad range from creation of novel catalysts by means of chemical or material synthesis, characterization and analysis applying innovative electrochemical techniques, atomistic simulations of state-of-the-art x-ray spectroscopy up to model-based systems analysis of coupled reaction and transport mechanisms. Synergy between the partners in the consortium is generated by two modes of cooperation – one in which instrumentation, techniques and expertise are shared, and one in which common standard materials and test protocols are used jointly for optimal comparability of results and to direct further development. We outline the special structure of the research consortium, give an overview of its members and their expertise and review recent scientific achievements in materials science as well as chemical and physical analysis and techniques. Due to the extreme conditions a catalyst has to endure in the OER, a central requirement for a good oxygen evolution catalyst is not only its activity, but even more so its high stability. Hence, besides detailed degradation studies, a central feature of MAXNET Energy is a standardized test setup/protocol for catalyst stability, which we propose in this contribution.
[Show abstract][Hide abstract] ABSTRACT: One of the most significant investigations on heterogeneous photocatalytic process can be dated back to the 1970s, when Fujishima and Honda showed that the TiO2 electrode is capable of water splitting under suitable electromagnetic irradiation. Since then TiO2 based materials have become the dominant photocatalyst and have been investigated for decades due to their abundance, non-toxicity, and relatively high reactivity. However, the bandgap of pristine TiO2 is larger than 3 eV, which can only absorb light that has a wavelength of less than 400 nm. Unfortunately, this portion of photons only corresponds to 4-5% of the solar spectrum, which has limited the application of photocatalysis at an industrial scale. Moreover, the conduction band position of TiO2 is only slightly negative relative to that of the proton reduction potential, resulting in a relatively poor reduction power for solar-to-fuel conversion. Therefore, the development of alternative photocatalysts with visible light absorption and unable properties is essential in the application of photocatalysis techniques.
In this chapter, we will consider the most popular photocatalyst systems other than TiO2. Their synthesis methods, characteristics, optimisations and design will be presented. Last but not least, the design and synthesis of promoters, which play a very essential role in photocatalyst systems, will also be demonstrated at the end
of this chapter.
[Show abstract][Hide abstract] ABSTRACT: Vinyl chloride monomer (VCM) is a major chemical intermediate for the manufacture of polyvinyl chloride (PVC) which is the third most important polymer in use today. Hydrochlorination of acetylene is a major route for the production of vinyl chloride since production of the monomer is based in regions of the world where coal is abundant. Until now mercuric chloride supported on carbon is used as the catalyst in the commercial process and this exhibits severe problems associated with catalyst lifetime and mercury loss. It has been known for over thirty years that gold is a superior catalyst but it is only now that it is being commercialised. In this perspective we discuss the use and disadvantages of the mercury catalyst and the advent of the gold catalysts for this important reaction. The nature of the active site and the possible reaction mechanism is discussed. Recent advances in the design and preparation of active gold catalysts containing ultra-low levels of gold are described. In the final part a view to the future of this chemistry will be discussed as well as the possible avenues for the commercial potential of gold catalysis.
Preview · Article · Nov 2015 · Journal of the American Chemical Society
[Show abstract][Hide abstract] ABSTRACT: The oxidation of methanol to formaldehyde is a major chemical process carried out catalytically and iron molybdate is one of the major catalysts for this process. In this paper we explore the nature of the active and selective surfaces of iron molybdate catalysts and show that the effective catalysts comprise molybdenum rich surfaces. We conclude that it is therefore important to maximise the surface area of these active catalysts and to this end we have studied catalysts made using a new physical grinding method with oxalic acid. For super-stoichiometric materials (Fe:Mo = 1:2.2) the reaction data show that physical mixing produces effective catalysts, possibly offering an improvement over the conventional co-precipitation method.
[Show abstract][Hide abstract] ABSTRACT: Metal co-catalysts are essential for enhancing photocatalytic performance, especially in reduction reactions using semiconductor photocatalyst materials as a consequence of the reduced recombination kinetics of charge carriers by spatial charge separation. Generally Au, Pd, Pt, and their alloys are more promising candidates than Ag for photocatalytic H2 evolution experiments, although Ag can trap more electrons having more negative reduction potential than that of Au, Pd, and Pt. Here we have synthesized and examined well-defined Au, Ag, and core-shell structured Au–Ag nanoparticles as co-catalysts for TiO2 in photocatalytic H2 evolution. By varying the dissolved oxygen in the reaction suspension, we found that selective photocatalytic reduction can be achieved by fine tuning the co-catalyst materials. Whilst Au NPs are superior for proton reduction, Ag NPs exhibits excellent performance for oxygen reduction. All core-shell structured Au–Ag NPs show non-selectivity in photocatalytic reduction of proton and oxygen.
No preview · Article · Oct 2015 · Applied Catalysis A: General
[Show abstract][Hide abstract] ABSTRACT: The catalytic activity of a series of carbon-supported cobalt manganese oxide (CoMnOx) catalysts was investigated for the Fischer Tropsch synthesis reaction. The catalysts were compared with an unsupported CoMnOx catalyst under the same reaction conditions, and it was shown that the use of an activated carbon support increased both the catalyst activity and the selectivity to C2+ hydrocarbons, whilst lowering the selectivity to CH4 and CO2. Additionally, the effects of varying heat treatment temperatures and increasing the precursor ageing times were also investigated. Increasing the heat treatment temperature of the catalyst precursor between 300 and 500 °C led to an increase in activity, as well as an increase in selectivity to C2+ hydrocarbons, but it also increased the selectivity to CO2. At 600 °C there was a marked decrease in activity, and the main product was C5+ hydrocarbons. Ageing the initial precipitate led to a decrease in activity and also decreased the selectivity towards hydrocarbons.
[Show abstract][Hide abstract] ABSTRACT: The production of biodiesel from the transesterification of plant-derived triglycerides with methanol has been commercialized extensively. Impure glycerol is obtained as a by-product at roughly one-tenth the mass of the biodiesel. Utilization of this crude glycerol is important in improving the viability of the overall process. Here we show that crude glycerol can be reacted with water over very simple basic or redox oxide catalysts to produce methanol in high yields, together with other useful chemicals, in a one-step low-pressure process. Our discovery opens up the possibility of recycling the crude glycerol produced during biodiesel manufacture. Furthermore, we show that molecules containing at least two hydroxyl groups can be converted into methanol, which demonstrates some aspects of the generality of this new chemistry.
No preview · Article · Sep 2015 · Nature Chemistry
[Show abstract][Hide abstract] ABSTRACT: Vanadium phosphate catalysts have been widely studied for the selective oxidation of alkanes to a variety of products, including maleic and phthalic anhydride. More recently they are starting to find use as low temperature liquid phase oxidation catalysts. For all these applications the synthesis of the precursor is key to the performance of the final catalyst. Changes in the preparation procedure can alter the morphology, surface area, crystallinity, oxidation state and the phases present in the final catalyst which can all affect the selectivity and/or activity of the catalyst. Adding a diblock copolymer, poly(acrylic acid-co-maleic acid) (PAAMA), during the synthesis was found to influence the crystallinity and morphology of the VOHPO4·0.5H2O precursors obtained. An optimal level of copolymer was found to form precursors that showed a faster, more efficient, activation to the active catalyst, whereas high amounts of copolymer formed thin platelets, which were prone to oxidise to undesirable V5+ phases under reaction conditions, reducing the selectivity to maleic anhydride.
[Show abstract][Hide abstract] ABSTRACT: 1% Au/TiO2 catalysts prepared by a range of preparation methods were studied for the base-free oxidation of glucose. The highest catalytic activity was observed with the catalyst prepared by the sol-immobilization method. Furthermore we have studied the effect of the post-synthesis treatments of treatment with water, or heating in air on the activity. The catalyst calcined at 250 °C showed optimal activity and selectivity. Additionally, we studied the effect of the amount of stabilising ligand in the sol-immobilisation method and observed that this is a key parameter with respect to determining the catalyst's activity.
[Show abstract][Hide abstract] ABSTRACT: The hydrogenation of lactic acid to form 1,2-propanediol has been investigated using Ru nanoparticles supported on carbon as a catalyst. Two series of catalysts which were prepared by wet impregnation and sol-immobilization were investigated. Their activity was contrasted with that of a standard commercial Ru/C catalyst (all catalysts comprise 5 wt % Ru). The catalyst prepared using sol-immobilization was found to be more active than the wet impregnation materials. In addition, the catalyst made by sol-immobilization was initially more active than the standard commercial catalyst. However, when reacted for an extended time or with successive reuse cycles, the sol-immobilized catalyst became less active, whereas the standard commercial catalyst became steadily more active. Furthermore, both catalysts exhibited an induction period during the first 1000 s of reaction. Detailed scanning transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray absorption fine structure analysis data, when correlated with the catalytic performance results, showed that the high activity can be ascribed to highly dispersed Ru nanoparticles. Although the sol-immobilization method achieved these optimal discrete Ru nanoparticles immediately, as can be expected from this preparation methodology, the materials were unstable upon reuse. In addition, surface lactide species were detected on these particles using X-ray photoelectron spectroscopy, which could contribute to their deactivation. The commercial Ru/C catalysts, on the other hand, required treatment under reaction conditions to change from raft-like morphologies to the desired small nanoparticle morphology, during which time the catalytic performance progressively improved.
[Show abstract][Hide abstract] ABSTRACT: The selective oxidation of methane to methanol is a key challenge in catalysis. Iron and copper modified ZSM-5 catalysts are shown to be effective for this reaction using H2O2 as the oxidant under continuous flow operation. Co-impregnation of ZSM-5 with Fe and Cu by chemical vapour impregnation yielded catalysts that showed high selectivity to methanol (>92% selectivity, 0.5% conversion), as the only product in the liquid phase. The catalysts investigated did not deactivate during continuous reaction, and methanol selectivity remained high. The effect of reaction pressure, temperature, hydrogen peroxide concentration and catalyst mass were investigated. An increase in any of these led to increased methane conversion, with high methanol selectivity (≥73%) maintained throughout. Catalysts were characterised using DR-FTIR, DR-UV-Vis and 27Al MAS-NMR spectroscopy.