γ-Al₂O₃-Supported XMo₆ Anderson Heteropolyoxomolybdates: Adsorption Studies for X = Te^VI, Al^III, Co^III, Cr^III and Ni^II by DR Spectroscopy and TPR Analysis

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.