Unraveling the promoter role of Ba in Co–Ce catalysts for ammonia decomposition using microkinetic modeling

Abstract

Ammonia decomposition is an attractive process for decarbonized hydrogen production. Alkalis are known to promote the reaction, which is especially important to enable non-noble metal catalysts to achieve similar performances to the benchmark Ru catalyst. Herein, we evaluate the kinetic contribution of Ba as a promoter in Co–Ce catalysts, using a microkinetic approach to investigate the influence of the promoter on the elementary steps of ammonia decomposition. For this purpose, we performed experiments over a wide range of conditions with two Co–Ce catalysts, with and without Ba. The results were used to fit microkinetic models with enthalpy–entropy constraints for parameters such as prefactors, activation energies, and sticking coefficients. Based on the differences in these parameters, we compared surface coverages and partial equilibrium indices to show how Ba enhances the rate of N2 desorption, one of the two kinetically relevant steps, along with the NH2 dehydrogenation.