Unveiling mutual interference and hydrogen spillover mechanisms in the simultaneous hydrogenation of sulfamethoxazole and monoiodoacetic acid over Pd/CNT

The growing complexity of water contaminants necessitates a deeper understanding of the interplay between multiple pollutants and catalytic sites. Herein, we explore the simultaneous removal of sulfamethoxazole (SMX) and monoiodoacetic acid (MIAA) via liquid-phase catalytic hydrogenation over Pd nanoparticles supported on diverse carriers (CNT, C₃N₄, Al₂O₃, and SBA-15). Although all catalysts performed well in single-component tests, only Pd/CNT exhibited robust dual-removal capability in mixed systems, achieving complete deiodination of MIAA and 92.4% reduction of SMX within 60 min. Intriguingly, a mutual interference phenomenon was unveiled: MIAA suppressed SMX reduction, while SMX (and other aromatics) unexpectedly accelerated MIAA deiodination. Mechanistic studies identified the pivotal role of hydrogen spillover on Pd/CNT, which possessed a superior H₂ uptake capacity. This facilitated the generation of surface-mobile active H that migrate to the support, enabling a binary active site mechanism. We propose a sequential pathway comprising H₂ dissociative activation, spillover, direct Pd-catalyzed deiodination of MIAA, and CNT-mediated hydrogenation of SMX via spilled-over H species. These findings highlight the exceptional promise of Pd/CNT for the remediation of complex organic contaminants and provide fundamental guidance for designing bifunctional hydrogenation catalysts.