(322c) Support Effects in Butadiene Hydrogenation over Cu and PtCu Dilute-Limit Alloys

Selective hydrogenation is crucial for many industrial processes. One key example is the semi-hydrogenation of 1,3-butadiene into butenes (especially 1-butene) without over-hydrogenation into n-butane. Cu is selective for this reaction but not highly active. Alloying with highly active metals such as Pt at the extremely dilute limit (Cu:Pt≥100) can significantly improve catalytic activity while maintaining high selectivity. These can form single-atom alloys (SAAs) wherein dopant atoms are atomically isolated from one another amidst a sea of Cu atoms, which can offer unique catalytic behaviors and high dopant metal dispersions. Typically investigated on less-reactive supports such as γ-Al₂O₃, it is largely unknown how the support influences SAA promotion. In this work, we investigate the support effects on Cu and Pt-doped Cu (PtCu) synthesized via colloidal methods and dispersed on Al₂O₃, SiO₂, TiO₂, and CeO₂.

Colloidal methods ensure comparable metal loadings and particle morphologies across anchoring on different supports. Despite this, CeO₂- and SiO₂-supported Cu exhibited substantially higher butadiene conversions than Cu on Al₂O₃ and TiO₂. While all materials demonstrate high selectivities for butenes at lower temperatures (~90-100%), SiO₂ and CeO₂-supported catalysts showed higher 1-butene selectivities (up to ~80% near 393 K). The introduction of Pt enhanced butadiene conversion for all materials, though the magnitude of promotion varied strongly with support in the order Al₂O₃ (170x) >> TiO₂ (11x) ~ CeO₂ (9x) > SiO₂ (4x) at 393 K. The propensity to over-hydrogenate and consequently form butane was also strongly support dependent, with total butene selectivities noticeably dropping below 100% for SiO₂ and CeO₂ but not for Al₂O₃. Butene distributions additionally changed for all materials, with increases in 2-butenes vs 1-butenes due to shifts in primary kinetics rather than isomerizations. Overall, these findings highlight that support effects are non-trivial in SAAs, motivating the careful selection of supports when invoking this promotion strategy.