Exploring milling atmosphere effects in mechanochemical synthesis of Pd–Cu supported catalysts for the semihydrogenation of acetylene in equimolar ethylene mixtures
Abstract
Supported bimetallic nanoparticles (NPs) have evolved as promising candidates for heterogeneous catalysis. Among various synthesis methods, ball milling has recently emerged as an effective approach for the preparation of high performing catalysts in diverse applications. Recognizing that solid–gas interactions in such a solvent-free environment might be crucial, we investigated the influence of the gas atmosphere (oxidative, inert, and reductive) during ball milling on the structural and electronic properties of Pd–Cu alloy NPs supported on high surface area α-Al2O3. Milling under an oxidative atmosphere leads to Cu-segregation to the surface, forming CuO, PdO, and a small fraction of metallic Pd alongside the Pd–Cu alloy phase. In contrast, in the case of an inert atmosphere, the major phase is the Pd–Cu alloy with a very minimal fraction of unalloyed metallic components. Milling under a reductive atmosphere reveals reverse segregation with metallic Pd segregating to the surface. Additional thermal treatment further promotes the alloy formation in all cases, but oxide species from synthesis under oxidative atmosphere are retained. Unveiling structure–property correlations, the materials were tested in the catalytic selective hydrogenation of acetylene to ethylene in equimolar acetylene/ethylene mixtures under industrially relevant pressure. Results demonstrate that the ball-milling atmosphere significantly influences catalytic performance, driven by the structural and electronic variations induced during synthesis. This study underscores the critical role gas environments may have in mechanochemical processes and highlights their potential to fine-tune catalyst properties for improved performance.