Influence of Preparation Methods on the Catalytic Activity of Pd–Cu/Mn₂O₃ Catalyst in the Hydrogenation of 1,3-Butadiene

Mn₂O₃-supported Pd–Cu catalysts synthesized by two biogenic methods, sol-immobilization (SI) and adsorption–reduction, are compared to catalysts prepared via three conventional methods, impregnation (IP), deposition–precipitation with urea (DPU), and deposition of colloids stabilized with poly­(vinylpyrrolidone) (DCPVP). The as-synthesized supported alloy catalysts of sizes between 2 and 8 nm were employed in the gas-phase selective hydrogenation of 1,3-butadiene. Their alloy nature was proved from characterizations including diffuse reflectance infrared Fourier transform spectroscopy and CO adsorption tests, temperature-programmed reduction, X-ray photoelectron spectroscopy, and X-ray diffraction. It was observed that the synthesis method greatly affects the final surface constituent of catalyst Pd/Cu ratio and partial particle reconstruction occurs under CO exposure. The optimum catalyst constituent of Pd–Cu_0.06–Mn₂O₃ was selected since it provided excellent conversion with poor selectivity to unwanted butane. Selectivity of all of the catalysts directly correlated with increasing Cu content and Pd-to-butadiene conversion. The bioreduction-supported catalysts using SI with a Pd/Cu atomic ratio of 0.9:1.4 showed excellent balances between butadiene conversion of 99.1% and selectivity to total butene above 92%, which we attribute to repulsion to H and its neighboring adsorbed inherent C and N atoms with adjacent Pd atoms and alloy synergy. The IPC catalyst showed the worst performance but was highly selective to butenes. And the DCPVP and DPU catalysts with 100% conversion produced worse 1-butene selectivity.