Hetero-bimetallic paddlewheel complexes for enhanced CO 2 reduction selectivity in MOFs: a first principles study.

The reduction of carbon dioxide (CO 2 ) into value-added feedstock materials, fine chemicals, and fuels represents a crucial approach for meeting contemporary chemical demands while reducing dependence on petrochemical sources. Optimizing catalysts for the CO 2 reduction reaction (CO 2 RR) can entail employing first principles methodology to identify catalysts possessing desirable attributes, including the ability to form diverse products or selectively produce a limited set of products, or exhibit favorable reaction kinetics. In this study, we investigate CO 2 RR on bimetallic Cu-based paddlewheel complexes, aiming to understand the impact metal substitution with Mn(II), Co(II), or Ni(II) has on bimetallic paddlewheel metal-organic frameworks. Substituting one of the Cu sites of the paddlewheel complex with Mn results in a more catalytically active Cu center, poised to produce substantial quantities of formic acid (HCOOH) and smaller quantities of methane (CH 4 ) with a suppressed production of C 2 products such as ethanol (CH 3 CH 2 OH) or ethylene (C 2 H 4 ). Moreover, the presence of Mn significantly reduces the limiting potential for CO 2 reduction from 2.22 eV on the homo-bimetallic Cu paddlewheel complex to 1.19 eV, thereby necessitating a smaller applied potential. Conversely, within the Co-substituted paddlewheel complex, the Co site emerges as the primary catalytic center, selectively yielding CH 4 as the sole reduced CO 2 product, with a limiting potential of 1.22 eV. Notably, the Co site faces significant competition from H 2 production due to a lower limiting potential of 0.81 eV for hydrogen reduction. Our examination of the Cu-Ni paddlewheel complex, featuring a Ni substituent site, reveals two catalytically active centers, each promoting distinct reductive processes. Both the Ni and Cu sites exhibit a propensity for HCOOH formation, with the Ni site favoring further reduction to CH 4 , whereas the Cu site directs the reaction towards methanol (CH 3 OH) production. This study holds significance in informing and streamlining future experimental efforts for synthesizing and evaluating novel catalysts with superior capabilities for CO 2 reduction.