Comparative study of Cu, Ag and Ag-Cu catalysts over graphite in the ethanol dehydrogenation reaction: Catalytic activity, deactivation and regeneration

摘要

The physicochemical and catalytic properties of bimetallic AgCu catalysts and their monometallic counterparts supported on a high surface area graphite have been comparatively evaluated in the ethanol dehydrogenation reaction, performed in a continuous-flow reactor. While Cu was incorporated by the incipient wetness impregnation technique, for Ag catalysts two synthesis procedures were explored: incipient wetness impregnation and adsorption of Tollens' reagent. The catalysts prepared by wetness impregnation exhibited higher metal dispersion, being improved for the bimetallic catalysts in comparison with the monometallic counterparts. The results obtained in the catalytic tests revealed that Cu catalysts is nearly two orders of magnitude more active than Ag catalyst in the dehydrogenation reaction of ethanol on either a turnover frequency or a weight basis, but at the same time both catalysts were 100% selective to acetaldehyde. Whereas selectivity was not affected by the bimetallic composition, there was a substantial decrease in the reaction rate among the bimetallic catalysts as the Cu/Ag ratio diminished, due to blockage of copper surface active sites by silver. Both silver and copper, and the bimetallic catalysts, suffered from deactivation at 523 K, caused by blocking of active sites by adsorbed hydrocarbons on the catalyst surface (fouling). Carbonaceous deposits were removed through a thermal treatment under H-2 flow, which allowed the total recovery of the initial catalytic activity.