Inverting methanol dehydrogenation selectivity by crowding atomic Ni species over α-MoC catalysts

Abstract

Metal carbides with earth-abundant elements are widely regarded as promising alternatives of noble metal catalysts. Although comparable catalytic performances have been observed for metal carbides in several types of reactions, precise control of reaction pathways on them remains a formidable challenge, partially due to strong adsorption of reactants or intermediates. In this study, we show that bimolecular dehydrogenation of methanol to methyl formate and H2 is kinetically favored on bare α-MoC catalysts, while monomolecular dehydrogenation to CO and H2 becomes the dominant pathway when α-MoC is decorated with crowding atomic Ni species. Under optimal conditions, excellent selectivities of the target products (> 90%) were achieved in both cases, with unprecedented production rates of methyl formate and H2 for the former and latter mechanisms, respectively. Kinetic, spectroscopic, and computational assessments were integrated to clarify the mechanism driving this remarkable selectivity inversion. Isolated Ni sites bound to α-MoC exhibit superior dehydrogenation activity, which promotes complete cleavage of C-H bonds in methanol-derived intermediates rather than the C-O coupling between them. Our study offers an effective approach to modulating the selectivity of carbide-based catalysts in alcohol dehydrogenation towards different target products.