The catalytic properties of the γ-Al2O3 membranes could be improved by modification with silver. The selectivity to formaldehyde of a silver-modified alumina membrane (67 wt.-% Ag) was 36% at 300°C, which was higher than that of bulk silver. The values depended on the silver loading of the membrane layer and also decreased with increasing temperature. Deactivation of the membrane catalysts occurred after some time, apparently due to the consumption of the strongly adsorbed oxygen species on the silver surface. The activity of the samples could be recovered by treatment with oxygen at 400°C. It was found that regeneration could not be earned out with bulk silver in powder form, when it was placed on top of the membrane; in this case, a temperature of 800°C was needed to reactivate the catalyst, which can be considered as an indication of the higher activity of the finely dispersed silver particles in the membrane compared to that of the bulk material. Because the re-activation of the silver-modified membranes with oxygen proceeded slowly at 300°C, the simultaneous reaction and catalyst reactivation (by supplying oxygen to the membrane from the side of the support) could not be carried out efficiently at 300°C and higher temperatures were required. The activity of the γ-Al2O3 in those cases caused a problem with respect to the selectivity of the reaction.
|Number of pages||14|
|Publication status||Published - 1991|