CH<sub>4</sub> Carbonylation to Acetic Acid Using\nH<sub>2</sub>O as an Oxidant on a Rh-Functionalized UiO-67 Combined\nwith Oriented External Electric Fields: Selectivity and Mechanistic\nInsights from DFT Calculations

Acetic acid (CH<sub>3</sub>COOH), as an industrially\nimportant\npetrochemical product, is predominantly produced via multistep energy-intensive\nprocesses. The development of a rhodium single-site heterogeneous\ncatalyst has received considerable attention due to its potential\nto transform CH<sub>4</sub> into CH<sub>3</sub>COOH in a single step.\nHerein, the reaction mechanism for the generation of CH<sub>3</sub>COOH from CH<sub>4</sub>, CO, and H<sub>2</sub>O catalyzed by Rh-functionalized\nmetal–organic framework (MOF) UiO-67 and the selectivity of\nproducts CH<sub>3</sub>COOH, formic acid (HCOOH), methanol (CH<sub>3</sub>OH), and acetaldehyde (CH<sub>3</sub>CHO) under the oriented\nexternal electric fields (OEEFs) were systematically explored by density\nfunctional theory (DFT) calculations. The results reveal that the\ninsertion of CO into Rh–CH<sub>3</sub> is the rate-determining\nstep with a free energy barrier of 21.0 kcal/mol in CH<sub>4</sub> carbonylation to CH<sub>3</sub>COOH. Upon applying an OEEF of <i>F</i><sub><i>x</i></sub> = +0.0050 au along the C–C\nbond, the rate-determining step shifts toward H<sub>2</sub>O decomposition\nwith the barrier of 19.6 kcal/mol, significantly improving the selectivity\nfor CH<sub>3</sub>COOH production, compared to the major competitive\nHCOOH route. The Brønsted–Evans–Polanyi (BEP) relationships\nbetween key transition states, field strength, and NPA charge transfer\nwere established. This study may guide the rational design of atomically\ndispersed MOF catalysts for the selective coconversion of CH<sub>4</sub> and CO to CH<sub>3</sub>COOH using H<sub>2</sub>O as the oxidant\nunder the OEEF.