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负载型Au催化剂在乙炔选择加氢反应中表现出很高的乙烯选择性,但其转化率相对较低.通过添加第二种金属如Pd,Fe,Ag和Cu等,制备双金属催化剂是提高其在加氢反应中催化活性的一种非常有效的手段.其中Au-Pd双金属催化剂是最受关注的体系之一,Pd的加入可以非常显著地提高其催化乙炔选择加氢反应的活性.据文献报道,与Pd同一主族的Ni也具有较好的加氢活性.尽管与Pd相比,Ni很难与Au形成合金,但目前已有Au-Ni双金属催化剂在多种反应中表现出协同效应的报道,如水气变换、CO氧化以及芳香硝基化合物选择加氢等.因此,向Au催化剂中添加Ni也可能提高催化剂在乙炔选择加氢反应中的催化活性.因此,我们采用两步法制备了一系列Si O2负载的具有不同Ni:Au原子比的Au-Ni双金属催化剂,并将其用于乙炔选择加氢反应,发现Au-Ni双金属催化剂在该反应中表现出了显著的协同效应,其活性明显优于相应单金属催化剂的活性.尽管其乙烯选择性略低于单金属Au催化剂,但明显高于单金属Ni催化剂.通过调节还原温度和/或Ni:Au的比例,对催化剂的性能进行了优化.结果显示,当Ni:Au=0.5时,催化剂表现出最优的综合性能,即兼具较高的乙炔转化率和乙烯选择性.为了研究Au-Ni双金属催化剂中金属纳米粒子的结构、组成以及Au-Ni之间的相互作用,我们对催化剂进行了X射线衍射(XRD)、高分辨透射电镜(HRTEM)、能量散射谱(EDS)以及原位红外光谱(DRIFTS)表征.XRD和TEM结果显示,催化剂中的Au-Ni双金属纳米粒子都具有高分散和粒径均匀的特点.通过EDS分析,发现在Au-Ni双金属催化剂中的单个金属纳米粒子同时含有Au和Ni两种元素,尽管每个纳米粒子中Ni:Au的比例有差异.HRTEM结果发现,Au-Ni双金属纳米粒子的晶格间距介于Au(111)和Ni(111)的晶面间距之间,说明在Au-Ni双金属催化剂中有Au-Ni合金形成.原位DRIFTS结果显示,在Au-Ni双金属催化剂中,Au的存在促进了Ni的还原,说明Au与Ni之间存在紧密的相互作用.综上可见,Au和Ni在乙炔选择加氢反应中所表现出的协同效应主要归功于Au-Ni合金的形成,其中金属态Ni起主要的活性作用,而Au的存在则提高了催化剂的乙烯选择性.
Supported Au catalysts exhibit high ethylene selectivity in acetylene selective hydrogenation but relatively low conversion.The preparation of bimetallic catalysts is enhanced by the addition of a second metal such as Pd, Fe, Ag, Cu, etc. Its catalytic activity in the hydrogenation reaction is a very effective means.Among them, Au-Pd bimetallic catalyst is one of the most concerned system, the addition of Pd can significantly improve the catalytic activity of acetylene selective hydrogenation reaction. It has been reported in the literature that Ni, which is the same main group as Pd, has good hydrogenation activity. Although it is difficult for Ni to form an alloy with Au compared to Pd, Au-Ni bimetallic catalysts have been used in many reactions Such as water-gas shift, CO oxidation, selective hydrogenation of aromatic nitro compounds, etc. Therefore, the addition of Ni to the Au catalyst may also increase the catalytic activity of the catalyst in the acetylene selective hydrogenation reaction.Therefore, we use two A series of Si O2-supported Au-Ni bimetallic catalysts with different Ni: Au atomic ratios were prepared by the step method and used for the selective hydrogenation of acetylene. It was found that the Au-Ni bimetallic catalyst exhibited a Significant synergies, Its activity is obviously better than that of the corresponding monometallic catalyst.Although its ethylene selectivity is slightly lower than that of the single metal Au catalyst, it is obviously higher than that of the single metal Ni catalyst. By adjusting the reduction temperature and / or the ratio of Ni: Au, the catalyst performance The results showed that the catalyst exhibited the best overall performance when the Ni: Au = 0.5, ie, high conversion of acetylene and ethylene selectivity.In order to study the catalytic performance of Au-Ni bimetallic catalyst, XRD, HRTEM, EDS and DRIFTS were used to characterize the structure, composition and interaction of Au-Ni. XRD and TEM results show that the Au-Ni bimetallic nanoparticles in the catalyst are both highly dispersed and uniform in size.By EDS analysis, it is found that the single metal nanoparticles in the Au-Ni bimetallic catalyst contain both Au and Ni Two kinds of elements, though the ratio of Ni: Au in each nanoparticle is different.HRTEM results show that the lattice spacing of Au-Ni bimetallic nanoparticles is between the interplanar distance of Au (111) and Ni (111) , Described in Au-Ni bimetallic catalysts Au-Ni alloy.The in-situ DRIFTS results show that the presence of Au promotes the reduction of Ni in the Au-Ni bimetallic catalyst, indicating the close interaction between Au and Ni. The synergistic effect in acetylene selective hydrogenation reaction is mainly attributed to the formation of Au-Ni alloy, in which metallic Ni plays a major role in the activity, while the presence of Au increases the ethylene selectivity of the catalyst.