Hetero-Bimetallic Paddlewheel Complexes for Enhanced CO2 Reduction Selectivity: A First Principles Study

Abstract

The reduction of carbon dioxide (CO2) 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 CO2 reduction reaction can entail employing first principles methods to identify catalysts possessing desirable attributes, including the ability to form diverse products, selectively form few products, or exhibit favorable reaction kinetics. In this study, we investigate the CO2 reduction reaction on bimetallic Cu paddlewheel complexes, aiming to understand the impact metal substitution with Mn, Co, or Ni has on bimetallic paddlewheel metal-organic frameworks (MOFs). 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 minor quantities of methane (CH4) with a suppressed production of C2 products such as ethanol (CH3CH2OH) or ethylene (C2H4). Moreover, the presence of Mn significantly reduces the limiting potential for CO2 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 CH4 as the sole reduced CO2 product, with a limiting potential of 1.22 eV. Notably, the Co site faces substantial competition from H2 production, attributed 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 CH4, while the Cu site directs the reaction towards methanol (CH3OH) production. The significance of this study lies in its potential to inform and streamline future experimental efforts, facilitating the synthesis and evaluation of novel catalysts with superior capabilities for CO2 reduction.