Formation, Spatial Distribution, and Dynamics of Lewis and Brønsted Acid Sites on α-MoO3(010): A Density Functional Theory Study

Abstract

The catalytic performance of α-MoO3 in lignin hydrodeoxygenation (HDO) depends on Lewis (oxygen vacancy) and Brønsted (hydroxyl) acid sites generated during H2 reduction. We present a density functional theory study of the α-MoO3(010) surface, addressing oxygen vacancy formation, hydrogen adsorption on all three surface oxygen types, coverage-dependent effects, hydrogen diffusion, and H2 dissociative adsorption. Hydrogen adsorption is thermodynamically preferred on the asymmetric bridging oxygen and kinetically reinforced by a low barrier to surface migration. Coverage-dependent calculations at HDO-relevant temperatures reveal that oxygen vacancies promote Brønsted site formation. H2 reduction proceeds with a substantial dissociation barrier to form an adsorbed water intermediate, branching into Lewis acid site formation via water desorption or Brønsted acid site formation via hydroxyl generation. Partial reduction of Mo6+ toward Mo5+ accompanies both vacancy creation and hydroxylation. These results provide a unified atomic-level framework connecting gas-phase reduction to a more realistic representation of the catalytically active surface.