Selectivity Anomaly in CO ₂ Hydrogenation over In–Pd Intermetallic Compounds

Understanding factors controlling product selectivity in CO2 hydrogenation remains a central research theme for catalytic CO2 utilization. Here, we report a composition-dependent selectivity anomaly in the In–Pd intermetallic series (viz., InPd2, InPd, In3Pd2), where In3Pd2 exhibits 100% CO selectivity via the reverse water–gas shift (RWGS) pathway, in sharp contrast to the high methanol selectivity achieved on other In-rich or Pd-rich metals or intermetallic compounds. Comprehensive characterization reveals that this anomaly arises from Pd enrichment on the surface of In3Pd2 IMC nanoparticles. The enriched Pd sites, modulated by In-to-Pd electron transfer, favor CO formation. In addition, the In-rich sites neighboring the Pd-rich islands facilitate rapid CO desorption. The resulting nanostructure on the surface of In3Pd2 IMCs renders an electronic interaction between In and Pd to promote CO formation and suppress C–H bond formation. This rationale is supported by both density functional theory (DFT) calculations and experimental evidence. These findings demonstrate that compositional control in intermetallic catalysts enables switchable CO2 hydrogenation selectivity and offers a rational approach to designing catalysts with tailored product distributions.