Abstract
The support-overlayer adsorptive interactions, generated when solutions of Anderson heteropolyoxomolybdates were supported as a monolayer on γ-Al2O3 by means of the equilibrium adsorption method, were studied by XRD analysis, DR spectroscopy, electron microscopy (SEM-EDAX) and TPR methods. The adsorption isotherms and corresponding adsorption parameters (number of active sites and adsorption constants) of the γ-Al2O3-supported ammonium heptamolybdate were obtained and discussed. The following sequence of adsorption strength was suggested: CoMo6 > CrMo6 > TeMo6 ~ AlMo6 > NiMo6. The effectiveness of the TPR technique as a tool for elucidating interaction effects was clearly demonstrated. The formation of a γ-Al2O3-supported Te-Mo mixed valence oxide appears to provide new and interesting catalytic possibilities.
Highlights
Various different types of heteropolyoxomolybdates have been studied over the past few years in an attempt to analyse their applicability in a range of fields of chemistry, catalysis (Mizuno and Misono 1994, 1998; Pope 1983, 1991).The replacement of traditional Mo–metal/support catalysts (prepared by the equilibrium impregnation of a support with an aqueous solution containing ammonium heptamolybdate and a metallic salt) by ones involving supported heteropolyoxomolybdatesoffers a new approach and interesting possibilities (Mizuno and Misono 1994, 1998; Cabello et al 2000)
The values of Kad obtained from the corresponding isotherms were several orders of magnitude greater than those observed for the AHM/g-Al2O3 system and even greater than that for the traditional Co–Mo/g-Al2O3 catalyst
Differences in the CrMo6/g-Al2O3 catalytic system result in the generation of a series of homogeneous and heterogeneous equilibrium processes during the initial impregnation steps
Summary
Various different types of heteropolyoxomolybdates have been studied over the past few years in an attempt to analyse their applicability in a range of fields of chemistry, catalysis (Mizuno and Misono 1994, 1998; Pope 1983, 1991).The replacement of traditional Mo–metal/support catalysts (prepared by the equilibrium impregnation of a support with an aqueous solution containing ammonium heptamolybdate and a metallic salt) by ones involving supported heteropolyoxomolybdatesoffers a new approach and interesting possibilities (Mizuno and Misono 1994, 1998; Cabello et al 2000). The present work involved an analysis of the support–overlayer adsorptive interactions occurring when g-Al2O3 was impregnated with aqueous solutions of XMo6 to form a monolayer on the support surface.
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