Synergetic Cu0 and Cu+ on the surface of Al2O3 support enhancing methanol steam reforming reaction

Abstract

The methanol steam reforming (MSR) reaction was a crucial pathway for hydrogen production, with Cu-based catalysts widely applied. It was established that the isolated Cu0-site path and Cu+-site path were responsible for methanol conversion. However, a “Seesaw Effect” existed between the activation of *CH3O and the formation of CO2. Specifically, Cu0 site favored *CH3O activation but facilitated the reverse water gas shift (RWGS) process. Conversely, Cu+ site suppressed CO and promoted CO2 formation but had a reduced ability for *CH3O dehydrogenation. In this work, a Cu0-Cu+ synergy path was proposed, Cu0 sites activate CH3OH into *CH2O, and the subsequent conversion of *CH2O is catalyzed over the Cu+ site. Characterization and calculation results demonstrated that this synergy path subtly avoids two rate-determining steps (*CH3O → *CH2O on Cu+ sites and bi-*CHOO → *CO2 on Cu0 site). The migration of *CH2O from the Cu0 site to Cu+ sites was a critical step in constructing a synergy path. Moreover, MSR performance was governed by the quantity of synergy sites (Cu0/Cu+) and the amount of matched Cu0-Cu+ sites, both of which could be adjusted by varying the Cu loading (1–20%). An optimal 9% Cu enhanced the synergy interaction, with a Cu0/Cu+ ratio of 1.2 and the highest amount of Cu0-Cu+ sites (609.4 μmol/g), giving rise to high methanol conversion and low CO concentration. The discovery in this work provided theoretical guidance for constructing high-performance Cu-based catalysts.