Theoretical exploration of the origin of selectivity for the oxidative carbonylation reaction catalyzed by a single Pd atom embedded on graphene

Abstract

The vapor-phase carbonylation of methyl nitrite (MN) can selectively give dimethyl carbonate (DMC) or dimethyl oxalate (DMO) when using Pd-based catalysts. Density functional theory calculations were performed to explore the origin of this selectivity and its relationship with the electronic structures of the Pd centers by employing a catalytic model of a single Pd atom embedded on graphene. Through a systematic study, Pd–COOCH₃ is identified as a key intermediate which plays two roles in the reaction. The nucleophilicity of the Pd–C bond of Pd–COOCH₃ enables carbonylation with CO to give DMO, while the electrophilicity of the π* orbital of the carbonyl species, *COOCH₃, allows coupling with MN to afford DMC. This two-fold reactivity could be regulated by the local coordination environments of the Pd centers. Pd centers each embedded on either a graphene defect, N-doped graphene, or oxidized graphene, Pd₁@C₃, Pd₁@N₃, and Pd₁@O₃, respectively, were investigated to understand the effect of the local coordination environment on the reaction. The calculation results show that the electron-donating nature of Pd₁@N₃ enhances the nucleophilicity of the Pd–C bond and promotes the activity and selectivity toward DMO production, while the electron-withdrawing nature of Pd₁@O₃ has an inhibitory effect. The current study will find applications as a theoretical guide for the rational design of related catalysts.