Mechanisms and design of heterogenized molecular catalysts for CO₂-to-alcohols

Heterogenized molecular catalysts open electrochemical CO₂ reduction pathways that are not accessible with just homogeneous complexes or extended metal surfaces. This review examines how macrocyclic metal‑nitrogen (MN₄) active sites, when fixed onto conductive supports, can be tailored to support the multi-electron, multi-proton processes necessary for producing alcohols. Instead of categorizing catalyst types, we focus on the mechanistic limitations that influence the selectivity for methanol, ethanol, and propanol. We analyze how factors such as the CO binding energy, the duration that intermediates remain, the kinetics of proton-coupled electron transfer, the local availability of CO₂, and entropic influences all collectively shape the reaction results. Six interconnected catalyst design strategies, including support and axial coordination, macrocycle framework engineering, geometry modulation through strain, dual-site and tandem architectures, nanoconfinement, and microenvironment control, are critically evaluated for their effectiveness at stabilizing deep reduction intermediates while minimizing competing reaction pathways. Deactivation mechanisms, including structural degradation, active site poisoning, detachment, and metal contamination, are further examined alongside stabilization strategies to guide the development of durable heterogenized molecular systems. By integrating mechanistic insights with materials design principles, we establish structure-function relationships that define operational windows for alcohol selectivity and outline practical considerations for translating CO-selective molecular platforms toward efficient CO₂ to alcohol electrosynthesis.