Theoretical Study on the Catalytic CO<sub>2</sub> Hydrogenation over the MOF-808-Encapsulated Single-Atom Metal Catalysts
Jinlu Liu, Wenjuan Xue, Weiwei Zhang, Donghai Mei
Abstract
The search for new catalytic agents for reducing excess CO 2 in the atmosphere is a challenging but essential task. Due to the well-defined porous structures and unique physicochemical properties, metal–organic frameworks (MOFs) have been regarded as one of the promising materials in the catalytic conversion of CO 2 into valuable platform chemicals. In particular, introducing the second metal (M) atom to form the M II –O–Zr 4+ single-atom metal sites on the Zr nodes of MOF-808 would further greatly improve the catalytic performance. Herein, CO 2 hydrogenation reaction mechanisms and kinetics over a series of MOF-808-encapsulated single-atom metal catalysts, i.e., M II –MOF-808 (M II = Cu II, Fe II, Pt II, Ni II, and Pd II ), were systematically studied using density functional theory calculations. First, it has been found that the stability for the encapsulation of a divalent metal ion follows the trend of Pt II > Ni II > Pd II > Cu II > Fe II, while they all possess moderate anchoring stability on the MOF-808 with the Gibbs replacement energies ranging from −233.7 to −310.3 kcal/mol. Two plausible CO 2 hydrogenation pathways on Cu II –MOF-808 catalysts, i.e., formate and carboxyl routes, were studied. The formate route is more favorable, in which the H 2 COOH*-to-H 2 CO* step is kinetically the most relevant step over Cu II –MOF-808. Using the energetic span model, the relative turnover frequencies of CO 2 hydrogenation to various C1 products over M II –MOF-808 were calculated. The Cu II –MOF-808 catalyst is found to be the most active catalyst among five M II –MOF-808 catalysts.