Supercritical antisolvent precipitation of amorphous copper–zinc georgeite and acetate precursors for the preparation of ambient-pressure water-gas-shift copper/zinc oxide catalysts

© 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim A series of copper–zinc acetate and zincian georgeite precursors have been produced by supercritical CO 2 antisolvent (SAS) precipitation as precursors to Cu/ZnO catalysts for the water gas shift (WGS) reaction. The amorphous materials were prepared by varying the water/ethanol volumetric ratio in the initial metal acetate solutions. Water addition promoted georgeite formation at the expense of mixed metal acetates, which are formed in the absence of the water co-solvent. Optimum SAS precipitation occurs without water to give high surface areas, whereas high water content gives inferior surface areas and copper–zinc segregation. Calcination of the acetates is exothermic, producing a mixture of metal oxides with high crystallinity. However, thermal decomposition of zincian georgeite resulted in highly dispersed CuO and ZnO crystallites with poor structural order. The georgeite-derived catalysts give superior WGS performance to the acetate-derived catalysts, which is attributed to enhanced copper–zinc interactions that originate from the precursor

Preparation of a highly active ternary Cu-Zn-Al oxide methanol synthesis catalyst by supercritical CO2 anti-solvent precipitation

Methanol synthesis using Cu/ZnO/Al2O3 catalysts is a well-established industrial process. Catalyst development is always an important factor and this has resulted in the current fully optimised commercial catalyst that is prepared by co-precipitation via hydroxycarbonate precursors. Recently, the synthesis of a CuZn hydroxycarbonate precursor, analogous to the rare mineral georgeite, was reported to produce a high activity methanol synthesis catalyst. Here we report the addition of Al 3+ , the third component found in industrial catalysts, to the zincian georgeite-derived catalyst prepared using a supercritical CO 2 anti-solvent precipitation methodology. The co-addition of an AlO(OH) sol to the Cu/Zn precursor solution was found to not disrupt the formation of the CuZn georgeite phase, while providing efficient mixing of the Al 3+ within the material. The catalyst derived from the CuZn georgeite precursor phase doped with Al 3+ showed a high level of methanol synthesis productivity, which was comparable to that of the binary CuZn georgeite derived catalyst. This material also exhibited enhanced stability during an accelerated ageing test compared to the non-Al doped zincian georgeite material. Performance was benchmarked against an industrially relevant Cu/ZnO/Al2O3 standard catalyst

DataSheet1_Relationship between hydrothermal temperatures and structural properties of CeO2 and enhanced catalytic activity of propene/toluene/CO oxidation by Au/CeO2 catalysts.docx

A simple hydrothermal synthesis of CeO2 was implemented to obtain a series of CeO2-supported gold (Au) catalysts, used for the total oxidation of propene/toluene/CO gas mixtures and the oxidation of CO. CeO2 preparation started from a cerium hydrogen carbonate precursor using a range of different hydrothermal temperatures (HT) from 120 to 180°C. High-resolution transmission electron microscopy, X-ray diffraction, and H2-temperature-programmed reduction data indicated that CeO2 morphology varied with the HT, and was composed of the more active (200) surface. Following Au deposition onto the CeO2 support, this active crystal plane resulted in the most widely dispersed Au nanoparticles on the CeO2 support. The catalytic performance of the CeO2-supported Au catalysts for both oxidation reactions improved as the reducibility increased to generate lattice oxygen vacancies and the number of adsorbed peroxide species on the CeO2 support increased due to addition of Au. The Au catalyst on the CeO2 support prepared at 120°C was the most active in both propene/toluene/CO oxidation and independent CO oxidation.</p

Dominant Effect of Support Wettability on the Reaction Pathway for Catalytic Wet Air Oxidation over Pt and Ru Nanoparticle Catalysts

Support wettability can play a key role in directing the activation of oxygen during catalytic wet air oxidation over nanoparticle catalysts. When the nanoparticles are composed of metallic Pt, the optimum support is hydrophobic, but when they are ionic Ru, a hydrophilic support is more effective. This reversal in support effect is consistent with two distinct surface pathways: one in which gas-phase O₂ is directly adsorbed on the Pt⁰ surface and the other in which dissolved O₂ is activated on RuO₂ immersed in the contaminated aqueous phase. The known effects of ceria on these precious metal catalysts are of secondary importance to support wettability

Etherification Reactions of Furfuryl Alcohol in the Presence of Orthoesters and Ketals: Application to the Synthesis of Furfuryl Ether Biofuels

Strategies for the efficient transformation of abundant and sustainable bioderived molecules, such as furfuryl alcohol (FAlc), into higher value products are currently a vibrant research area. Herein, we demonstrate that furfuryl ethers, which are of significant interest as biorenewable fuel additives, are efficiently produced employing an etherification reaction of furfuryl alcohol and short chain alkyl alcohols in the presence of a recyclable ZSM-5 catalyst and an orthoester, such as trimethyl orthoformate (TMOF) or triethyl orthoformate (TEOF), used as a sacrificial reagent. These etherification reactions proceed at temperatures significantly lower than those of the previous etherification procedures, and they provide the furfuryl ether products in high yield. Importantly, the low temperature employed improves the selectivity by minimizing the formation of hydrolysis products and the competing polymerization reactions leading to humin byproducts. By carrying out the reaction in higher alcohol solvents, such as ethanol, 1-propanol, and 1-butanol, we are able to capitalize on the ability of ZSM-5 to catalyze the orthoester exchange reaction of TMOF or TEOF to produce the corresponding furfuyl ethers in a novel, telescoped orthoester exchange–etherification reaction sequence. Finally, we also demonstrate that the etherification reaction proceeds efficiently in the presence of acetals and ketals, such as dimethoxypropane and diethoxypropane. This latter development is highly significant given the greater scope for the regeneration of acetal and ketal reagents

Preparation of Biomass-Derived Furfuryl Acetals by Transacetalization Reactions Catalyzed by Nanoporous Aluminosilicates

Nanoporous aluminosilicate materials efficiently catalyze the formation of furaldehyde dimethyl acetal directly from methanol in high yields and in short reaction times. The facile nature of this reaction has led to the development of a telescoped protocol in which the acyclic acetal is produced in situ and subsequently functions as a substrate for a transacetalization reaction with glycerol to produce the corresponding dioxane and dioxolane products, which are potentially useful biofuel additives. These products are generated in high yield without the requirement for high reaction temperatures of prolonged reaction times, and the aluminosilicate catalysts are operationally simple to produce, are effective with either purified furaldehyde or crude furaldehyde, and are fully recyclable

Nanoporous Aluminosilicate-Mediated Synthesis of Ethers by a Dehydrative Etherification Approach

High aluminum containing nanoporous aluminosilicate materials, produced by an evaporation-induced self-assembly process, efficiently catalyze the formation of unsymmetrical ethers by a dehydrative etherification reaction in high isolated yields. By carrying out the reaction under dilute conditions, the quantities of reagents can be reduced to near stoichiometric quantities

Investigating Catalytic Properties Which Influence Dehydration and Oxidative Dehydrogenation in Aerobic Glycerol Oxidation over Pt/TiO₂

The use of heterogeneous catalysts to convert glycerol into lactic acid has been extensively investigated in recent years. Several different strategies have been employed, but importantly, the highest production rates of lactic acid are achieved through aerobic oxidation under alkaline conditions. Despite the progress made in this area, insight into how the catalytic properties influence the selectivity of the competing pathways, oxidative dehydrogenation and dehydration, remains limited. Developing a deeper understanding is therefore critical, if process commercialization is to be realized. Using a model Pt/TiO2 catalyst, we set out to investigate how the supported metal particle size and support phase influenced the selectivity of these two pathways. Both these parameters have a profound effect on the reaction selectivity. Using a range of characterization techniques and through adopting a systematic approach to experimental design, important observations were made. Both pathways are first instigated through the oxidative dehydrogenation of glycerol, leading to the formation of glyceraldehyde or dihydroxyacetone. If these intermediates desorb, they rapidly undergo dehydration through a reaction with the homogeneous base in solution. Based on the experimental evidence we therefore propose that selectivity to lactic acid is influenced by surface residence time

High-Temperature Stable Gold Nanoparticle Catalysts for Application under Severe Conditions: The Role of TiO₂ Nanodomains in Structure and Activity

Metal nanoparticles with precisely controlled size are highly attractive for heterogeneous catalysis. However, their poor thermal stability remains a major concern in their application at realistic operating conditions. This paper demonstrates the possibility of synthesizing gold nanoparticles with exceptional thermal stability. This has been achieved by using a simple conventional deposition–precipitation technique. The material employed as catalyst consists of gold supported on a TiO₂-impregnated SiO₂ bimodal mesoporous support. The resulting material shows gold nanoparticles with a narrow size distribution around 3.0 nm, homogeneously dispersed over the TiO₂/SiO₂ material. Most interestingly, the gold nanoparticles show exceptional thermal stability; calcination temperatures as high as 800 °C have been employed, and negligible changes in the gold particle size distribution are apparent. Additionally, the presence of an amorphous titanium silicate phase is partially preserved, and these factors lead to remarkable activity to catalyze a range of oxidation reactions

Selective Oxidation of Methane to Methanol Using Supported AuPd Catalysts Prepared by Stabilizer-Free Sol-Immobilization

The selective oxidation of methane to methanol, using H₂O₂, under mild reaction conditions was studied using bimetallic 1 wt % AuPd/TiO₂ prepared by stabilizer-free sol-immobilization. The as-prepared catalysts exhibited low, unselective oxidation activity and deleterious H₂O₂ decomposition, which was ascribed to the small mean particle size of the supported AuPd nanoparticles. Heat treatments were employed to facilitate particle size growth, yielding an improvement in the catalyst turnover frequency and decreasing the H₂O₂ decomposition rate. The effect of support phase was studied by preparing a range of AuPd catalysts supported on rutile TiO₂. The low surface area rutile TiO₂ yielded catalysts with effective oxygenate production but poor H₂O₂ utilization. The influence of the rutile-TiO₂ support was investigated further by producing catalysts with a lower metal loading to maintain a consistent metal loading per square meter compared to the 1 wt % AuPd/P25 TiO₂ catalyst. When calcined at 800 °C, the 0.13 wt % AuPd catalyst demonstrated significantly improved turnover frequency of 103 h^–1. In contrast, the turnover frequency was found to be ca. 2 h^–1 for the rutile-supported 1 wt % AuPd catalyst calcined at 800 °C. The catalysts were probed by electron microscopy and X-ray photoelectron spectroscopy to understand the influence of particle size and oxidation state on the utilization of H₂O₂ and oxygenate productivity. This work shows that the key to highly active catalysts involves the prevention of deleterious H₂O₂ decomposition, and this can be achieved through carefully controlling the nanoparticle size, metal loading, and metal oxidation state