Modification of acid supports by solid-state redox reaction Part I. Preparation and characterization

The solid-state redox reaction of a number of metals in contact with ZSM-5 and Y zeolites, gamma-alumina, and silica was investigated by temperature-programmed hydrogen evolution (TPHE), diffuse reflectance Fourier transform IR spectroscopy (DRIFT), X-ray absorption near-edge structure spectroscopy (XANES), and X-ray powder diffraction (XRD). Among all studied metals, gallium, zinc, manganese, and iron were found to undergo a solid-state redox reaction. On zeolites, Bronsted acid sites and extraframework species and on gamma-alumina all kinds of hydroxyl species are involved, whereas on silica silanol groups undergo reaction. Magnesium, on the other hand, reacted with the water adsorbed on the supports to magnesium oxide evolving hydrogen. No reaction was observed for the systems with nickel, aluminum, and tin. The solid-state redox reaction was found to be a function of the melting point provided that the metal is base enough. (C) 2003 Elsevier Inc. All rights reserved.