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Abstract: The oxygen evolution reaction (OER) is crucial to future energy systems based on water electrolysis. Iridium oxides are promising catalysts due to their resistance to corrosion under acidic and oxidizing conditions. Highly active iridium (oxy)hydroxides prepared using alkali metal bases transform into low activity rutile IrO2 at elevated temperatures (>350 °C) during catalyst/electrode preparation. Depending on the residual amount of alkali metals, we now show that this transformation can result in either rutile IrO2 or nano-crystalline Li-intercalated IrOx. While the transition to rutile results in poor activity, the Li-intercalated IrOx has comparative activity and improved stability when compared to the highly active amorphous material despite being treated at 500 °C. This highly active nanocrystalline form of lithium iridate could be more resistant to industrial procedures to produce PEM membranes and provide a route to stabilize the high populations of redox active sites of amorphous iridium (oxy)hydroxides.

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Abstract: The perovskite CaCu3Ti4O12 is known for its ability to photocatalytically degrade model dye molecules using visible light. Here in we show the influence of ball milling on the catalysts structure and performance in the degradation of Rhodamine B. The surface area of CaCu3Ti4O12 increased from 1 m2g-1 to >80 m2g-1 on milling with a retention of 96% CaCu3Ti4O12 phase purity, as determined by X-ray diffraction and extended X-ray absorption fine structure analysis. Multiple characterisation techniques showed an increase in structural defects on milling. Specifically, X-ray absorption near edge spectroscopy, supported by simulation, showed changes in the local electronic structure from the perspective of Cu and Ti. Photocatalytic degradation was notably higher with the milled sample than that observed for the as-synthesized sample, even after normalisation for surface area, with a doubling of surface normalised rate constant from 4.91x10-4 to 9.11x10-4 L min-1m2. The improvement in catalytic performance can be correlated to the structural changes observed.

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Abstract: Sn-Beta has emerged as a state-of-the-art catalyst for a range of sustainable chemical transformations. Conventionally prepared by bottom-up hydrothermal synthesis methods, recent research has demonstrated the efficiency of several top-down methods of preparation. One attractive top-down approach is Solid-State Incorporation, where a dealuminated Beta zeolite is physically mixed with a solid Sn precursor, in particular Sn (II) acetate, prior to heat treatment at 550 °C. This procedure is fast and benign, and metal incorporation requires no solvents and hence produces no aqueous Sn-containing waste streams. Although the performances of these catalysts have been well explored in recent years, the mechanism of heteroatom incorporation remains unknown, and hence, opportunities to improve the synthetic procedure via a molecular approach remain. Herein, we utilise a range of in situ spectroscopic techniques, alongside kinetic and computational methods, to elucidate the mechanisms that occur during preparation of the catalyst, and then improve the efficacy of the synthetic protocol. Specifically, we find that successful incorporation of Sn into the lattice occurs in several distinct steps, including i) preliminary coordination of the metal ion to the vacant lattice sites of the zeolite during physical grinding; ii) partial incorporation of the metal ion into the zeolite framework upon selective decomposition of the acetate ligands, which occurs upon heating the physical mixture in an inert gas flow from room temperature to 550 °C; and iii) full isomorphous substitution of Sn into the lattice alongside its simultaneous oxidation to Lewis acidic Sn(IV), when the physically mixed material is exposed to air during a short (<1 h) isotherm period. Long isotherm steps are shown to be unnecessary, and fully oxidised Sn(IV) precursors are shown to be unsuitable for successful incorporation into the lattice. We also find that the formation of extra-framework Sn oxides is primarily dependent on the quantity of Sn present in the initial physical mixture. Based on these findings, we demonstrate a faster synthetic protocol for the preparation of Sn-Beta materials via Solid-State Incorporation, and benchmark their performance of the catalyst for the Meerwein-Ponndorf-Verley transfer hydrogenation reaction and for the isomerisation of glucose to fructose.

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Abstract: The formation of highly active and stable acetylene hydrochlorination catalysts is of great industrial importance. The successful replacement of the highly toxic mercuric chloride catalyst with gold has led to a flurry of research in this area. One key aspect, which led to the commercialization of the gold catalyst is the use of thiosulphate as a stabilizing ligand. This study investigates the use of a range of sulfur containing compounds as promoters for production of highly active Au/C catalysts. Promotion is observed across a range of metal sulfates, non‐metal sulfates, and sulfuric acid treatments. This observed enhancement can be optimized by careful consideration of either pre‐ or post‐treatments, concentration of dopants used, and modification of washing steps. Pre‐treatment of the carbon support with sulfuric acid (0.76 m) resulted in the most active Au/C in this series with an acetylene conversion of ≈70% at 200 °C.

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Abstract: The replacement of HgCl2/C with Au/C as a catalyst for acetylene hydrochlorination represents a significant reduction in the environmental impact of this industrial process. Under reaction conditions atomically dispersed cationic Au species are the catalytic active site, representing a large-scale application of heterogeneous single-site catalysts. While the metal nuclearity and oxidation state under operating conditions has been investigated in catalysts prepared from aqua regia and thiosulphate, limited studies have focused on the ligand environment surrounding the metal centre. We now report K-edge soft X-ray absorption spectroscopy of the Cl and S ligand species used to stabilise these isolated cationic Au centres in the harsh reaction conditions. We demonstrate the presence of three distinct Cl species in the materials; inorganic Cl−, Au–Cl, and C–Cl and how these species evolve during reaction. Direct evidence of Au–S interactions is confirmed in catalysts prepared using thiosulfate precursors which show high stability towards reduction to inactive metal nanoparticles. This stability was clear during gas switching experiments, where exposure to C2H2 alone did not dramatically alter the Au electronic structure and consequently did not deactivate the thiosulfate catalyst.