Unraveling the Role of Alkali on Cobalt Catalyst Performance in Ethanol Steam Reforming by Operando DRIFT Studies and DFT Modeling

Abstract

Hydrogen, a sustainable and environmentally friendly fuel, can be obtained through the ethanol steam reforming (ESR) process. The most promising catalysts for this process are those based on non-noble metals such as cobalt. The activity, selectivity, and stability of these catalysts strongly depend on the presence of alkali dopants. In this work, we have taken on the challenge of understanding the role of alkali. We synthesized a series of cobalt-containing catalysts supported on α-alumina and doped with Na, K, Rb, and Cs, which were thoroughly characterized using spectroscopic and microscopic techniques. We elucidated the significant difference in the efficiency of undoped and alkali-doped catalysts, based on diffuse reflectance infrared Fourier transform (DRIFT) operando spectroscopy studies under ESR conditions. The catalytic test results indicated a strong effect of alkali promoters on the interaction between the acetaldehyde byproduct and the Co/α-Al₂O₃ catalyst surface. Experimental data were confronted with the results of periodic DFT-GGA+U molecular modeling. It has been shown that electron transfer from alkali atoms to the cobalt active phase strongly influences the ethanol reforming pathway by increasing the adsorption energy of the aldehyde intermediate and facilitating the key C–C bond-breaking step.