Designing Cu0-Cu+ dual sites for improved C-H bond fracture towards methanol steam reforming

Abstract

Copper-based catalysts serve as the predominant methanol steam reforming material although several fundamental issues remain ambiguous such as the identity of active center and the aspects of reaction mechanism. Herein, we prepare Cu/Cu(Al)O_x catalysts with amorphous alumina-stabilized Cu₂O adjoining Cu nanoparticle to provide Cu⁰-Cu⁺ sites. The optimized catalyst exhibits 99.5% CH₃OH conversion with a corresponding H₂ production rate of 110.8 μmol s^-1 g_cat^-1 with stability over 300 h at 240 °C. A binary function correlation between the CH₃OH reaction rate and surface concentrations of Cu⁰ and Cu⁺ is established based on kinetic studies. Intrinsic active sites in the catalyst are investigated with in situ spectroscopy characterization and theoretical calculations. Namely, we find that important oxygen-containing intermediates (CH₃O* and HCOO*) adsorb at Cu⁰-Cu⁺ sites with a moderate adsorption strength, which promotes electron transfer from the catalyst to surface species and significantly reduces the reaction barrier of the C-H bond cleavage in CH₃O* and HCOO* intermediates.