Structural and catalytic activity studies of silver/chromia catalysts

This paper describes investigations of some chemical as well as catalytic properties of materials obtained by calcining a mixture of chromic oxide gel and silver nitrate (molar ratio Ag2O :CT2O3) Toe parent mixture was calcined for 5 h, in air, at the temperature range 300-700 degrees C. The characterization of the catalysts with chemical analyses, thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), X-ray diffraction (XRD), Fourier transform infrared (FTIR) and scanning electron microscope (SEM) has confirmed that samples calcined at the temperature range 300-500 degrees C were composed of silver chromate as a major phase together with a minor amount of chromic oxide. Silver chromite formation starts at about 600 degrees C and this phase becomes the major phase for the samples calcined at 700 degrees C. The conversion of ethanol was carried out over the 400-700 degrees C calcined samples. The reaction was performed in a fixed-bed reactor at atmospheric pressure at the temperature range 150-400 degrees C. On using nitrogen as a carrier gas, acetaldehyde, diethyl ether and ethylene were the major products with a little amount of ethyl acetate (less than 1%). Carrying out the catalytic experiments using air as a carrier gas showed that acetaldehyde and carbon dioxide were the reaction products. The complete oxidation of ethanol to carbon dioxide and water was observed at temperature higher than 250 degrees C for the catalysts calcined at the temperature range 400-600 degrees C. TPR and TPO investigations were carried out in order to relate the activity changes to some structural changes accompanying the catalytic process. Such structural changes were monitored using XRD, FTIR and SEM analyses of some tested catalysts. (C) 2000 Elsevier Science B.V. All rights reserved.