Iterative Organic Modification of Pt Catalysts for Dual Electronic and Site-Selective Control in Heterogeneous Enantioselective Hydrogenation

The performance of heterogeneous catalysts in structure-sensitive reactions is governed by the interplay between the electronic states of active metals and the distribution of surface sites, particularly under-coordinated (UC) and well-coordinated (WC) sites. Conventional surface modifications with organic molecules can tune electronic properties but often result in indiscriminate surface coverage, collapsing site preference and limiting their utility in catalyst design. In this study, we introduce an iterative modification strategy using ethylenediamine (EDA) as a representative organic modifier to decouple electronic tuning from undesired site blocking. Successive cycles of EDA treatment and mild thermal processing progressively introduced N-containing species that strongly interacted with Pt nanoparticles, increasing the fraction of electron-deficient Pt sites. Concurrently, EDA residues preferentially occupied UC sites, leading to selective exposure of WC sites and a systematic increase in the WC/UC ratio. This dual regulation was enabled by the iterative modification strategy, whereas single-step treatment with excessive EDA caused nonselective coverage and loss of site selectivity. The combined electronic and structural control achieved by iterative EDA modification enhanced both catalytic activity and enantioselectivity in the hydrogenation of α-keto esters, yielding enantiomeric excess values of up to 96.5% while maintaining stability over repeated cycles. These findings establish iterative organic modification as a broadly applicable approach for catalyst surface engineering in structure-sensitive heterogeneous reactions.