Enhanced H2 production at the atomic Ni–Ce interface following methanol steam reforming†

Abstract

Hydrogen production with high efficiency and low CO selectivity in methanol steam reforming (MSR) is of pivotal importance. However, there is limited understanding of the active sites and reaction mechanisms during catalysis. In this study, we maximized the interfacial site, known as the active component in MSR, of Ni–CeO_x by atomically dispersed Ni and Ce over the carbon–nitrogen support to generate the Ni and Ce dual-atomic catalyst (DAC), which achieved 6.5 μmol_H2 g_cat.⁻¹ s⁻¹ H₂ generation rate and 0.8% CO selectivity at 99.1% methanol conversion at 513 K. The finely dispersed Ni and Ce structure was confirmed by systematic characterization of AC HAADF-STEM and EXAFS. Electron transfer from Ce to Ni was confirmed simultaneously by quasi-in situ XPS analysis. Moreover, the reaction mechanism of methanol steam reforming was clarified by combining kinetic studies with isotope-tracing/exchange analysis (i.e., KIEs and steady-state isotopic transient kinetic analysis (SSITKA)), which suggests that the steam reforming consists of two tandem reaction processes: methanol decomposition (MD) and water–gas shift (WGS) reaction, with methanol and water activation at independent active sites (e.g., Ni and oxygen vacancy over CeO_x), and that hydrogen generation was primarily determined by both C–H bond rupture and O_L–H (O_L represents the lattice oxygen) cleavage within methoxy and hydroxyl groups, respectively, with the catalytic surface mainly covered by CO and methoxy groups. A shift of WGS involvement in hydrogen generation from negligibly influenced to significantly promoted was selectively observed once modifying the reaction from differential conditions to a high methanol conversion regime, and two quantification methods have been established by comparing the molecule ratio between CO and CO₂ or H₂.