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

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

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Pd_(1)-Sn_(x)/Al_(2)O_(3)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/Al_(2)O_(3)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.

The selective hydrogenation of 1,3-butadiene over Pd-Sn/Al_(2)O_(3)bimetallic catalysts was investigated by heterogeneous parahydrogen-induced polarization(PHIP).A series of Pd_(1)-Sn_(x)/Al_(2)O_(3)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.