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CO2photoreduction on mixed Ti/Zr-MOF-525: bicarbonate as the active intermediate and the role of Ti substitution
Author(s)
Puengpoka, Thanyaporn
Santatiwongchai, Jirapat
Bureekaew, Sareeya
Saleh, Muhammad
Junkaew, Anchalee
Impeng, Sarawoot
Date Issued
February 11, 2026
Type
Article
Abstract
The photocatalytic reduction of CO2 in metal–organic frameworks (MOFs) offers a sustainable route to C1 fuels and chemicals. Herein, density functional theory (DFT) calculations elucidate CO2 reduction on mixed Ti/Zr-MOF-525 clusters bearing missing linker defects, modeled by Zr6, Ti1Zr5, and Ti2Zr4 clusters. Two distinct mechanistic pathways are identified: the OH-passive and OH-assisted routes. In the passive case, CO2 binds weakly at a coordinatively unsaturated Ti/Zr site and undergoes direct hydrogenation to CO and HCOOH, with desorption being thermodynamically preferred over further hydrogenation. In contrast, the OH-assisted pathway proceeds via a bicarbonate-mediated mechanism, where surface –OH attacks adsorbed CO2 to form node-bound *HCO3. This step is both thermodynamically favorable and kinetically accessible (ΔG‡ < 0.5 eV). Subsequent proton-electron additions convert *HCO3 to *OCHO and H2O, favored by ∼1 eV over competing routes. These findings identify *HCO3 as the true reactive precursor and reveal that Ti substitution promotes deeper hydrogenation beyond two-electron products, enhancing CH4 formation on the Ti2Zr4 cluster. Overall, the results highlight the importance of node composition and surface hydroxyl groups in porphyrinic MOFs for optimizing multi-electron CO2 reduction and controlling product selectivity by tailoring the metal node environments.
Citation
Physical Chemistry Chemical Physics, 28(6), 3907-3914, 2026