Computational Design of Single-atom Modified Ti-MOFs for Photocatalytic CO₂ Reduction to C₁ Chemicals

In this work, density functional theory (DFT) calculations were conducted to investigate a series of transition metals (Cr, Mn, Fe, Co, Ni, Cu, Zn, Zr, Nb, Ru, Rh, Pd, Ag, Hf, Ta, Os, Ir, and Pt) as single-atom components introduced into Ti-BPDC (BPDC=2,2'-bipyridine-5,5'-dicarboxylic acid) as catalysts (M/Ti-BPDC) for the photocatalytic reduction of CO₂. The results show that Fe/Ti-BPDC is the most active candidate for CO₂ reduction to HCOOH due to its small limiting potential (-0.40 V). Ag, Cr, Mn, Ru, Zr, Nb, Rh, and Cu modified Ti-BPDC are also active to HCOOH since their limiting potentials are moderate although the reaction mechanisms are different across these materials. Most of the studied catalysts show poor activity and selectivity to CO product because the stability of *COOH/*OCOH intermediates is significantly weaker than *OCHO/*HCOO species. The moderate binding strength of *CO on Pd/Ti-BPDC is responsible for its superior catalytic activity toward CH₃OH generation. Electronic structural analysis was performed to uncover the origin of the activity trend for CO₂ reduction to different products on M/Ti-BPDC. The calculation results indicate that the activity and selectivity of CO₂ photoreduction can be effectively tuned by designing single-atom metal-based MOF catalysts.