The synergism of cadmium on the catalytic activity of Cd-Cr-O system II. Ethanol decomposition, catalysts reducibility, and in situ electrical conductivity measurements

In this paper, the conversion (dehydration/dehydrogenation) of ethanol over a series of chromia as well as cadmium/chromia catalysts calcined in the 400-1000 degreesC temperature range has been studied. The reaction was performed in a fixed-bed reactor at atmospheric pressure and in the 150-400 degreesC temperature range using nitrogen as a carrier gas. The reaction products were ethane, ethylene, and acetaldehyde together with trace amounts of ethyl acetate. The cadmium-containing catalysts, especially those calcined at 400 and 500 degreesC, showed higher dehydrogenation activity. This trend was attributed to the catalyst reducibility, which was correlated with the presence of chromate ions. Such ions enhance the reduction of cadmium ions to zerovalent cadmium. Catalysts reducibility was checked by means of EtOH-temperature-programmed reduction (TPR), XRD, and FT-IR analyses. Moreover, in situ electrical conductivity measurements during alcohol admission were carried out. A good parallelism was found between the catalyst activity and its reducibility, In this way, the presence of Cd-0-Cr2O3 mixture, as a result of cadmium chromate reduction, showed a synergistic effect towards ethanol conversion as well as acetaldehyde selectivity. This effect was ascribed to the formation of donor-acceptor pairs as a consequence of Cd-0-Cr2O3 mixture formation. (C) 2001 Elsevier Science B.V. All rights reserved.