本文選題：銅 + 鈀�。� 參考：《催化學報》2017年09期

【摘要】：大量乙烯中少量乙炔的去除是化工生產(chǎn)中的重要過程之一,理想途徑是將其選擇加氫生成乙烯.負載型Pd催化劑因具有很高的乙炔轉(zhuǎn)化率而被廣泛用于該過程,但乙烯選擇性很低,同時會使原料氣中的乙烯被加氫,造成原料氣的浪費.采用其它元素對Pd納米粒子表面修飾,覆蓋部分活性位,可以在一定程度上提高乙烯選擇性,但是會大大降低Pd的利用率.因此,制備兼具高活性和高選擇性且經(jīng)濟實用的催化劑,仍是這一過程亟待解決的主要問題之一.我們的前期工作中,將Pd與IB族金屬(Au,Ag,Cu)分別結(jié)合制備得到了一系列含Pd的合金單原子催化劑(SAC),發(fā)現(xiàn)它們在大量乙烯存在條件下的乙炔選擇加氫反應中表現(xiàn)出優(yōu)異的催化性能.其中,Pd的用量僅為ppm級別,大大提高了Pd的利用率.作為IB族最為廉價的金屬,Pd與Cu形成的合金SAC在提高Pd原子利用率的同時,能夠進一步降低催化劑的經(jīng)濟成本.然而,當形成合金SAC時,Cu/Pd原子比例的極限值仍然不確定.本文通過固定Pd的擔載量,采用簡單的等體積共浸漬的方法,制備了一系列不同Cu/Pd原子比例的氧化硅負載的雙金屬催化劑.首先,我們采用程序升溫還原(TPR)和X射線衍射(XRD)對催化劑的還原能力和雙金屬納米粒子的尺寸進行了考察.進一步,采用X射線吸收光譜(XAS,包括EXAFS和XANES)對雙金屬催化劑中Pd的配位環(huán)境進行了分析.最后,結(jié)合它們在大量乙烯存在條件下的乙炔選擇加氫反應中的催化性能,對形成合金SAC時Cu/Pd原子比例進行了討論.TPR結(jié)果顯示,Cu與Pd結(jié)合時會促進雙金屬納米粒子的還原.XRD結(jié)果表明,隨著Cu含量的降低,雙金屬納米粒子的尺寸明顯減小.XANES結(jié)果證實,當Pd與Cu結(jié)合時,Pd會帶有部分負電荷,這也與Pd的電負性大于Cu相一致.通過對EXAFS擬合結(jié)果進行分析,我們發(fā)現(xiàn)當Cu/Pd的原子比例≥40/1時,Pd原子可以被Cu原子完全分隔開,形成含Pd的合金SAC,使其在大量乙烯存在條件下的乙炔選擇加氫反應中表現(xiàn)出優(yōu)異的催化性能.通過對還原溫度的考察,我們發(fā)現(xiàn)還原溫度由250 oC升高到400 oC時,對同一催化劑的催化性能影響不大;EXAFS擬合結(jié)果顯示,對比分別經(jīng)過250和400 oC還原后的催化劑,Pd的配位環(huán)境變化不明顯,這可能是導致催化性能相似的主要原因.
[Abstract]:The removal of a small amount of acetylene from a large amount of ethylene is one of the important processes in chemical production. The ideal way is to produce ethylene by selective hydrogenation. The supported PD catalyst is widely used in this process because of its high conversion of acetylene, but the selectivity of ethylene is very low, and the ethylene in feedstock gas will be hydrogenated, resulting in waste of feedstock gas. Surface modification of PD nanoparticles with other elements covering some active sites can improve ethylene selectivity to a certain extent but greatly reduce PD utilization. Therefore, the preparation of high activity, high selectivity and economical and practical catalysts is still one of the main problems to be solved in this process. In our previous work, a series of alloy monoatomic catalysts (SAC) containing PD were prepared by combining PD with IB group metals (Au-Ag Cu). It was found that SAC exhibited excellent catalytic performance in the selective hydrogenation of acetylene in the presence of a large amount of ethylene. The dosage of Pd was only ppm level, which greatly improved the utilization rate of PD. The alloy SAC, which is the cheapest metal of IB group, formed by Cu and Pd, can further reduce the economic cost of catalyst while increasing the utilization ratio of PD atoms. However, the limit value of Cu / PD atomic ratio is still uncertain when SAC is formed. In this paper, a series of silicon oxide supported bimetallic catalysts with different Cu / PD atomic ratios were prepared by a simple equal volume co-impregnation method with fixed PD loading. Firstly, temperature programmed reduction (TPR) and X-ray diffraction (XRD) were used to investigate the reduction ability of the catalyst and the size of bimetallic nanoparticles. Furthermore, the coordination environment of PD in bimetallic catalysts was analyzed by X-ray absorption spectroscopy (XAS), including EXAFS and XANES. Finally, combined with their catalytic performance in the selective hydrogenation of acetylene in the presence of a large amount of ethylene, The ratio of Cu / PD atoms in the formation of alloy SAC was discussed. TPR results showed that Cu / PD could promote the reduction of bimetallic nanoparticles. XRD results showed that the size of bimetallic nanoparticles decreased obviously with the decrease of Cu content. When PD binds with Cu, Pd has partial negative charge, which is consistent with the fact that PD is more electronegativity than Cu. By analyzing the EXAFS fitting results, we find that when the atomic ratio of Cu / PD is 鈮，

本文編號：2088714