Diffusion‐driven design of Pd‐ C6 / BN : Effect of [Cnmim][Cl] alkyl chain length on acetylene semi‐hydrogenation mechanism

Selective hydrogenation of trace acetylene in ethylene‐rich streams is essential for polymer‐grade ethylene. We prepared Pd‐C n /BN catalysts ( n = 2, 4, 6, 8, 10) via a simple impregnation‐reduction method using imidazolium chlorides with varied alkyl chains as modifiers. Molecular dynamics simulations reveal that H₂ diffuses about three orders of magnitude faster than C 2 H 2 and C 2 H 4 in [C n mim][Cl], allowing preferential access of H 2 to palladium (Pd) sites. Longer alkyl chains reduce overall gas diffusion but enlarge the C 2 H 4 ‐C 2 H 2 diffusion difference, helping suppress over‐hydrogenation. Catalytic tests identify Pd‐C 6 /BN as the most active and selective catalyst; optimized 0.1Pd‐30C 6 /BN delivers 99% C 2 H 2 conversion and 90% C 2 H 4 selectivity at 170°C with stable performance over 120 h. Characterization and density functional theory show that [C 6 mim]Cl remains structurally intact, preferentially interacts with Pd, suppresses β‐PdH X formation, tunes Pd electronic structure and adsorption, and facilitates Pd reduction, underpinning the excellent catalytic performance.