Structure sensitivity of ethanol steam reforming over the Rh catalyst: Reaction kinetics and deactivation mechanisms

Abstract

Rh catalyst exhibits high activity and selectivity of hydrogen production for ethanol steam reforming (ESR). In this work, we used density functional theory calculations and microkinetic modeling to study the structure sensitivity of ESR over the Rh catalyst, with stepped Rh(211) and terraced Rh(111) as models. The dominant reaction paths on the two surfaces were determined by pruning a complex network under different conditions. Further microkinetic analysis of the dominant reaction pathways suggested that Rh(211) shows higher activity and CO2 selectivity than Rh(111), but lower stability due to carbon deposition. High steam/ethanol ratio was found to be important to the reaction which can reduce carbon accumulation and improve CO2 selectivity. The transition state of CH3CH2OH dissociation is rate-controlling over both surfaces at high temperatures, while the removal processes of C* is rate controlling on Rh(211) at low temperatures, resulting in deactivation of the step edge sites. After screening several metal dopants over Rh(211), we found that the d-band center is well correlated with carbon adsorption energy, and stability trend is consistent with experiments. Our work could provide understanding of structure sensitivity and guidelines of rational Rh-based catalyst design for the ESR reaction.