Highly active and stable Ni-Cu supported catalysts prepared by combustion synthesis for hydrogen production from ethanol

Abstract

We report on the high activity and stability towards deactivation during ethanol decomposition of mono (Ni, Cu) and bimetallic Ni-Cu catalysts supported on ceria and silica that were prepared by impregnated support solution combustion synthesis (ISCS). Ni supported on ceria, behaves much like bulk Ni, as it deactivates within a few hours of time on stream (TOS). Addition of Cu improves the stability of ceria supported Ni-Cu bimetallic catalysts but it still deactivates during 10 h of TOS. Ni prepared by dry impregnation on silica deactivates completely during a few h of TOS. Ni supported on silica prepared by ISCS, show a remarkable high stability for over 30 h TOS and Ni-Cu is stable over 100 h of TOS operating at 100% conversion.XRD, XPS, HRTEM, in-situ XAS and textural characterization of these catalysts show that the surface Ni concentration is small on silica-supported catalysts due to partial encapsulation of Ni by the silica support, which protects the metal particles from carbon formation, thus hindering deactivation. Addition of Cu to silica increases the number of active sites, but also decreases CO chemisorption on Ni indicating the formation of a Cu-Ni alloy, which had been reported to inhibit carbon formation on Ni. The combined effect of encapsulation and formation of Ni-Cu surface alloys result in the remarkable stability of the Cu-Ni silica supported catalyst.