MORE ACTIVE AND SULFUR RESISTANT BIMETALLIC Pd-Ni CATALYSTS

The influence of the kind of metal precursor and the sequence of impregnation on the properties of Pd-Ni catalysts was evaluated during the test reaction of selective hydrogenation of styrene to ethylbenzene by means of physicochemical characterization. The focus was put on the final hydrogenating activity and the resistance to deactivation by sulfided compounds (thiophene). The used techniques of characterization were ICP, XPS, XDR, TPR, CO chemisorption and TEM. XPS results indicated the presence of different Pd species: Pdδ-, Pdº and Pdδ+. In the case of the Ni containing catalysts, Niº and NiO species were also detected. These palladium and nickel species would be responsables of the variation of activity and sulfurresistance of the catalysts. NiClPd catalysts had a higher resistance to deactivation by sulfur poisoning. This was associated to a higher concentration of Pdη+ClxOy species that would prevent the adsorption of thiophene by both steric and electronic effects. It could also be due to the lower concentration of Pdº and Niº on these catalysts, as compared to those shown by the PdNiCl catalysts. Both the Pdº and Niº species are more prone to poisoning because of their higher electronic availability.

本研究通过物理化学表征手段，在苯乙烯选择性加氢制备乙苯的模型反应中，评估了金属前驱体种类与浸渍顺序对钯-镍（Pd-Ni）催化剂性能的影响。研究重点关注催化剂的最终加氢活性以及抗噻吩（thiophene）等硫化物中毒失活的性能。所采用的表征技术包括电感耦合等离子体发射光谱（ICP）、X射线光电子能谱（XPS）、X射线衍射（XDR）、程序升温还原（TPR）、CO化学吸附以及透射电子显微镜（TEM）。XPS分析结果显示，催化剂表面存在多种钯物种：Pdδ-、Pd⁰与Pdδ+。对于含镍的催化剂，体系中还同时检测到了Ni⁰与NiO物种。上述钯与镍物种被认为是导致催化剂加氢活性与抗硫性能出现差异的核心因素。NiClPd型催化剂展现出更优异的抗硫中毒失活能力，这与其表面更高浓度的Pdη+ClxOy物种密切相关——该物种可通过空间位阻与电子效应双重机制抑制噻吩的吸附。该现象也可能与这类催化剂表面Pd⁰与Ni⁰的浓度更低有关，相较于PdNiCl型催化剂，其Pd⁰与Ni⁰的占比更高。Pd⁰与Ni⁰物种因具有更高的电子可及性，更易发生硫中毒失活。