Performance of Co-Fe@Alumina catalysts in comparison to monometallic Co@Alumina and Fe@Alumina catalysts for microwave assisted COx-free hydrogen production

Abstract

Alumina supported mono and bimetallic Co and Fe catalysts, with different metal loading and different Co/Fe ratio, were used for decomposition reaction of ammonia to produce COx-free hydrogen in the microwave reactor system by mixing with mesoporous carbon. The structural and surface properties of the catalysts before and after being exposed to microwave radiation at the catalytic bed were examined by different techniques. Catalysts exhibited high catalytic performance in the microwave system, such that total conversion was achieved at 400 °C under the flow of ammonia (GHSV of 36,000 ml/gcat.h), while they showed negligible activity in the conventionally heated reactor system. Microwave exposure causes the formation of cobalt carbide and iron carbide in the structure of monometallic cobalt and monometallic iron catalysts, respectively. Moreover a phase transition from γ-alumina toα -alumina was recognized for both of them. Long term exposure to microwave further enhance the carbide formation that could be effective getting stable conversion values in time on stream experiments. While, alumina supported monometallic cobalt catalysts gave better yield than alumina supported monometallic iron catalysts in both of the systems, bimetallic catalysts showed better activity than monometallic catalysts, especially at temperatures lower than 400 °C.