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Abstract: Modification by using mechanochemical treatment of vanadium phosphate catalysts on the microstructure, morphology, oxygen nature and catalytic performance for n-butane oxidation is described and discussed. In this work, the precursor, VOHPO4·0.5H2O prepared by reduction of VOPO4·2H2O by isobutyl alcohol was subjected to a high energy planetary ball mill for 30, 60 and 120min in ethanol. The ball milling process reduced the crystallite size of the catalysts and consequently increased their surface area. The morphologies of the milled catalysts are dependent on milling time. The highest reactivity and mobility of the lattice oxygen species has been achieved by the catalyst milled for 60min with lower reduction peak temperature and higher amount of oxygen atoms removed. The oxygen species removed from the active V4+ phase was shown to be correlated with the rate of reaction. A good relationship was also found between the oxygen species associated with V5+ and maleic anhydride selectivity. However, a larger amount of this oxygen species will give a deleterious effect on the conversion rate. The present study demonstrate that the mechanochemical method (with an appropriate duration) effectively enhanced the catalytic activity by increasing the surface area and controlling the reactivity, and that the amount of oxygen species contributed to the partial oxidation of n-butane to maleic anhydride. [Copyright &y& Elsevier]

Abstract: The crystal structure of ε-VOPO4 was determined in the space group Cc from X-ray powder diffraction data using a rigid body approach. The resulting structure is compared to a recently published, slightly different structure model (space group ) using Rietveld refinement. It was found that the new Cc model consistently yields a better fit to the observed data and exhibits a less distorted, more stable geometry. The crystal structure of ε-VOPO4 is discussed in comparison to β-VOPO4, monoclinic VPO4⋅H2O, and other related structures. [Copyright &y& Elsevier]

A series of gold/iron-oxide catalysts has been prepared by an inverse co-precipitation method from a mixture of HAuCl4·3H2O and Fe(NO3)3·9H2O. Samples calcined at 400 °C for 3 h exhibited poor activity towards CO oxidation, whereas uncalcined materials that had only been dried at 120 °C for 16 h exhibited a far superior catalytic activity. The most active material of this latter type is shown to have 100% CO conversion at 20 °C for at least 10 h. Detailed characterisation of the dried and the calcined materials using ICP and BET analysis, XRD, HREM, STEM-EDX and Mo¨ssbauer spectroscopy has shown significant differences in their microstructure. The dried materials consist of micron scale agglomerates of 4–8 nm disordered Fe5HO8·4H2O particles on which the Au is uniformly dispersed in the form of a mixture AuOOH·xH2O and Au0. By comparison, the calcined materials are comprised solely of 3–5 nm cuboctahedral metallic Au particles supported on 20 nm diameter well-crystalline α-Fe2O3 particles. Our microstructural observations and catalytic measurements are discussed in the context of the Bond–Thompson mixed Aux+/Au0 model for the low-temperature CO oxidation catalyst. [Copyright &y& Elsevier]