COPRECIPITATED NI-AL AND NI-CU-AL CATALYSTS FOR METHANE DECOMPOSITION AND CARBON DEPOSITION .1. GENESIS OF CALCINED AND REDUCED CATALYSTS

The structure of coprecipitated Ni-Al and Ni-Cu-Al catalysts with high nickel content (60-90 wt.-% Ni-alumina) has been investigated by X-ray powder diffraction, extended X-ray absorption fine structure (EXAFS) spectroscopy and Auger electron spectroscopy of calcined and reduced samples. The alumina was shown to behave as a textural promoter. The model of the reduced Ni-Al catalyst consisted of highly dispersed nickel and alumina particles with a Ni-Al spinel phase at their interface. The Ni-Al spinel phase had mainly an inverse structure. In the reduced sample the para-crystallinity of nickel was evidenced by precise diffraction measurements using synchrotron radiation. The spinel structure was not observed when copper was introduced. As a result, the alumina particles were more dispersed and covered the surface of the Ni-Cu particles enriched with copper.