Exploring the conversion mechanism of formaldehyde to CO2 and H2 catalyzed by bifunctional ruthenium catalysts: A DFT study

• The mechanistic preference of bifunctional catalysts in multi-step catalytic reactions was elucidated. • The origin of the divergent activities of the different functional ligands was revealed. • New strategies for regulating and evaluating the catalytic driving force were proposed. Bifunctional catalysts have a wide range of applications in chemical hydrogen storage. However, the versatile structure and complex influencing factors of catalysts still limit the current mechanistic understanding. Herein, a theoretical study based on density functional theory calculation is performed to illuminate the mechanistic preference of the conversion from formaldehyde to CO 2 and H 2 catalyzed by bifunctional ruthenium catalysts. The computational results indicate: (1) In contrast to the previously proposed mechanism, the catalyst is involved in the formaldehyde hydrolysis reaction and effectively reduces the activation free energy barrier. (2) Metal ligand cooperation mechanism is preferred instead of the metal-centred mechanism due to the stronger interaction between substrate and dual active sites on the bifunctional catalyst. (3) The catalyst with the O H group exhibits better catalytic activity compared with the N H group due to appropriate catalytic driving force, which is governed by the intrinsic electronic effects of the Lewis basic functional ligand. The p K a value can be used as a reliable descriptor to evaluate the catalytic activity of the functional ligand. Our study highlights the advantages of bifunctional catalysts in dehydrogenation-related reactions and proposes feasible strategies for the regulation of bifunctional catalyst activity, which is expected to provide new inspiration for future bifunctional catalyst design.