PROPERTIES OF COPPER CHROMITE CATALYSTS IN HYDROGENATION REACTIONS

A pretreatment involving a 4-h reduction under H-2 at 573 K, compared to either 473 or 673 K, gave the highest specific activity for furfura l and crotonaldehyde hydrogenation over an unpromoted copper chromite catalyst. Both H-2 and CO chemisorption declined monotonically with in creasing reduction temperature, but turnover frequencies also showed a maximum after a pretreatment at 573 K. DRIFTS identified a band, asso ciated with CO adsorbed on Cu+1 sites, which reached a maximum intensi ty after a 573 K pretreatment, while XRD patterns also provided eviden ce for a CuCrO2 phase and showed a continuous increase in Cu-0 as temp erature increased, Selectivity to furfuryl alcohol ranged from 35-80% and reaction orders on furfural and H-2 were near unity. In contrast, crotonaldehyde hydrogenation gave primarily butyraldehyde with only ar ound 3% crotyl alcohol and a near zero-order dependence on crotonaldeh yde, although the H-2 dependence was still near first order. IR spectr a under reaction conditions revealed adsorbed crotonaldehyde, provided evidence for an unsaturated alkoxide intermediate and detected no but yraldehyde on the surface. A simple Langmuir-Hinshelwood sequence nice ly explained both reactions, it was consistent with the DRIFTS results obtained during crotonaldehyde hydrogenation, and the resultant rate expression gave meaningful entropies and enthalpies of adsorption for H-2 and crotonaldehyde. (C) 1997 Academic Press.