1, 3-Butadienen Hydrogenation on Supported Pd-Sn Bimetallic Catalysts Investigated by Parahydrogen-induced Polarization

Abstract

The selective hydrogenation of 1, 3-butadiene over Pd-Sn/Al2O3 bimetallic catalysts was investigated by heterogeneous parahydrogen-induced polarization (PHIP). A series of Pd1-Snx/Al2O3 bimetallic catalysts with different Pd/Sn ratios were synthesized by incipient wetness co-impregnation method. It was observed that the Pd/Sn ratios of the catalysts had a significant effect on the reaction activity of 1, 3-butadiene and the selectivity to butene. A monotonic decrease of reaction conversion was observed as the Pd/Sn ratio decreased, while the selectivity to butene showed an opposite trend. This can be attributed to the ensemble effect and the ligand effect caused by the increasing tin component content: as the Pd/Sn ratio decreases, less palladium component was exposed on the surface, leading to low activity. The electronic properties of the Pd atoms were altered, which led to a weaker adsorption strength of the semi-hydrogenation product butene and an increased selectivity. Smaller Pd ensembles were exposed on Sn-rich catalysts surface, which favored a higher ratio of pairwise addition process, leading to a stronger PHIP effect. The isomerization measurements by PASADENA (parahydrogen and synthesis allow for dramatically enhanced nuclear alignment) showed that the isomerization process between 1-butene and 2-butene decreased with the increase of Sn content. This can be accounted for by the easier desorption of 1-butene on Sn-rich catalysts.

Keywords

• 1
• 3-butadiene hydrogenation
• bimetallic catalyst
• nuclear magnetic resonance (nmr)
• isomerization process
• parahydrogen-induced polarization (phip)