Pd-Sn双金属催化剂催化1,3-丁二烯加氢反应的仲氢诱导极化研究

本文首先利用等体积共浸渍法合成了一系列Pd/Sn比(原子比)不同的Pd₁-Sn_x/Al₂O₃双金属催化剂，然后通过多相催化仲氢诱导极化(PHIP)技术研究了Pd-Sn/Al₂O₃双金属催化剂上1,3-丁二烯选择性加氢反应．结果发现催化剂的Pd/Sn比会影响1,3-丁二烯反应活性和丁烯选择性：随着Pd/Sn比的下降，反应中1,3-丁二烯转化率降低，丁烯选择性提高．利用PASADENA(parahydrogen and synthesis allow for dramatically enhanced nuclear alignment)技术，发现Pd/Sn比的变化影响了1-丁烯与2-丁烯之间的异构化过程：随着Pd/Sn比的下降，1-丁烯异构化率降低，这是由于Sn组分含量的提高减少了表面暴露的Pd组分，使得催化剂反应活性降低；Sn组分含量的提高同时导致了Pd电子密度的上升，使得选择性还原产物丁烯更易脱附，阻止其进一步加氢生成丁烷，并抑制了1-丁烯异构化反应过程...

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

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-Sn_x/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.