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Abstract: We studied unsupported V x O y nanoparticles prepared by a novel nonaqueous route in the selective oxidation of n-butane to maleic anhydride. The evolution of the electronic and geometric structure of the material was characterized by X-ray photoemission spectroscopy, electron energy-loss spectroscopy, transmission electron microscopy, and electron diffraction before and after the reaction at different temperatures. A change from a water-mediated Cacking functionality of the catalyst forming acetic acid to an oxidizing functionality resulting in maleic anhydride was observed. It was found that the particles underwent a radical modification of the geometric and electronic structure that finally resulted in V2O5 crystals. Experimentally derived conclusions are related to some conceptual claims from the literature. [Copyright &y& Elsevier]

Abstract: Structure–activity relationships of a nanostructured Cu/ZrO2 catalyst for the steam reforming of methanol (MSR) were investigated under reaction conditions by in situ X-ray absorption spectroscopy (XAS) and X-ray diffraction (XRD) combined with on-line mass spectrometry (MS). Temperature-programmed activation by reduction in hydrogen or by reduction in a mixture of methanol and water (feed) was studied by time-resolved Cu K edge XANES and TG/DSC/MS measurements. Small and disordered CuO particles were identified as the main copper phase present in the precursors. After extended time on stream and treatment at 673 K in hydrogen, no significant sintering of the copper particles or deactivation of the reduced Cu/ZrO2 catalysts was detected, indicating a superior stability of the material. The initially low steam-reforming activity of the Cu/ZrO2 catalyst after reduction in hydrogen could be significantly increased by a temporary addition of oxygen to the feed. This increased activity after oxidative treatment is correlated with an increasing amount of oxygen in the copper particles. 63Cu NMR studies detected only a minor degree of microstrain in the active copper phase of the Cu/ZrO2 catalyst. The decreased reducibility of CuO/ZrO2, the low degree of microstrain, and the correlation between the amount of oxygen remaining in the copper particles and the catalytic activity indicate a different metal support interaction compared with Cu/ZnO catalysts. [Copyright &y& Elsevier]

Abstract: Steam reforming of methanol (SRM) was investigated over Cu/ZrO2/CeO2 (CZC) catalysts prepared via a novel synthetic method based on coprecipitation and polymer templating. Structural characterization of the samples was performed by N2 adsorption–desorption, N2O decomposition, and X-ray diffraction. The variation of the Cu loading resulted in an increased Cu crystallite size and a decreased specific surface area of the active particles. Catalytic investigations were carried out in a fixed-bed reactor at 105 Pa, with a CH3OH:H2O ratio of 1:1. The samples with Cu contents higher than 5% exhibited good long-term stabilities and low CO levels during continuous operation. The kinetic model suggested for the transformation involved the reverse water–gas shift (RWGS) and methanol decomposition (MD), in addition to the SRM reaction. Kinetic measurements were made in the temperature range of 503–573 K, and the experimental results could be well simulated. The highest methanol conversions and the lowest CO levels were observed in the temperature range of 523–543 K. The apparent activation energies for the individual reactions were found to depend on the Cu content of the catalyst. Since the influence of mass transport limitations on the kinetic data could be excluded, it was established that the variation of the Cu concentration in the precursor material altered the microstructure of the Cu particles and, accordingly, the active Cu surface, which resulted in the formation of significantly different catalysts. [Copyright &y& Elsevier]