Tuning butene selectivities by Cu modification on Pd-based catalyst for the selective hydrogenation of 1,3-butadiene

Pd-based bimetallic catalysts have shown unique selectivity to alkenes in the selective hydrogenation reactions, but often at the expense of activity. Therefore, the modification by a non-precious metal with similar or increased activity is crucial in lowering the catalyst cost. In the current study, gamma-Al2O3 supported Pd-Cu catalysts with different metal ratios were investigated in the selective hydrogenation of 1,3-butadiene. The adsorption properties of hydrogen and C4 species over model surfaces Pd(1 1 1), Pd1Cu3(1 1 1) and Cu(1 1 1) were studied by DFT calculations, and it was predicted that the Pd-Cu bimetallic catalysts should be more selective to butenes than the Pd monometallic catalyst. Moreover, the gamma-Al2O3 supported Pd-Cu catalysts were prepared by incipient wetness co-impregnation, and were characterized by TEM, CO pulse titration, TPR, N2O chemisorption, FT-IR of adsorbed CO and XPS; the catalytic study was performed in a fixed-bed reactor as well as in a batch reactor equipped with FT-IR. By the addition of Cu, Pd active sites were diluted, and the particle sizes were reduced. The Pd-Cu bimetallic catalysts exhibited surprisingly higher activity than Pd at low temperatures. In consistent with the DFT results, Pd-Cu bimetallic catalysts showed higher selectivities to total butenes and 1-butene. By analyzing the characterization and the hydrogenation test results, the electronic effect and geometric effect should be responsible in enhancing activity and tuning selectivity. (C) 2019 Elsevier Inc. All rights reserved.