Preparation Of Ni-Based Intermetallic Compounds And Their Catalytic Performance For Selective Hydrogenation Of Phenylacetylene

Selective hydrogenation of phenylacetylene to styrene is a very important catalytic process in the petrochemical industry, in which Ni-based intermetallic compound catalysts have attracted wide attention owing to their promising performance. However, Ni-based intermetallic compound catalysts prepared by conventional methods normally show uncontrollable size, shape, structure and poor stability. In this work, by virtue of the unique structural features of layered double hydroxides (LDHs), series of supported Ni-based intermetallic compound catalysts were designed and prepared via a topological transformation process of LDH precursor, which exhibit excellent catalytic performance toward selective hydrogenation of phenylacetylene to styrene. Based on a rational control over the type of M component (P, Se, Te, Bi) and their content, the geometric and electronic structure of the synthesized NixMy intermetallic compounds can be effectively tuned. In addition, the relationship between the NixMy active sites structure and catalytic properties, as well as the catalytic mechanism of NixMy intermetallic compound catalysts have been systematically investigated by using in-situ characterization techniques and DFT theoretical calculation. Our approach holds significant promise for nickel-based intermetallic compounds as efficient catalysts toward selective hydrogenation of phenylacetylene; and the deep understanding on structure-property correlation is helpful for new catalyst design and preparation.The main research contents and results are as follows:1. Structure control over Ni_xP_y intermetallic compounds and their catalyltic performance toward selective hydrogenation of phenylacetyleneHerein, we report a new synthetic strategy for the fabrication of supported nickel phosphides (Ni_xP_y) on Al2O3 matrix via a facile two-step procedure involving preparation of supported Ni particles from LDHs precursors, followed by a further reaction with a certain amount of red phosphorous. The resulting Al2O3-supported Ni12P5, Ni2P and NiP2 catalysts were evaluated by selective hydrogenation of phenylacetylene. Catalytic performance evaluation shows that with the increase of P/Ni ratio, the activity of as-prepared catalysts decreases gradually while the selectivity dramatically enhances, and the best catalytic behavior is eventually obtained over the Ni2P/Al2O3 catalyst with a selectivity of 88.2% at a conversion of 98.6%. EXAFS, XPS, in situ FTIR and DFT calculations reveal that the incorporation of P could endow both significant isolation effect and electron effect on Ni active sites. As a result, the increased Ni-Ni bond length and the reduced electron density of Ni sties effectively facilitate the production of alkene and its subsequent desorption, respectively, accounting for the largely enhanced selectivity to alkene.2、Preparation of NiM (M=Se, Te, Bi) intermetallic compounds and their catalyltic performance toward selective hydrogenation of phenylacetyleneThree Ni-based intermetallic compound catalysts (NiSe, NiTe and NiBi) were also prepared based on the similar synthetic strategy mentioned above, by incorporating M (M= Se, Te, Bi) component with the Ni catalyst precursor derived from LDHs. The resulting three intermetallic compounds possess a similar crystal structure and surface arrangement of Ni and M atom revealed by XRD and DFT calculations, but they exhibit distinct difference in catalytic behavior toward selective hydrogenation of phenylacetylene to styrene, and NiBi catalyst exhibits the best catalytic performance with a selectivity of 85% at a conversion of 95%. H2-TPR and DFT calculations demonstrate that the electron densities of Ni active sites in the three Ni-M intermetallic compounds are rather different, due to the different levels of electron modification of M on metallic Ni. This significantly influences the activation and dissociation of hydrogenation molecule, thereby accounting for tunable catalytic performance of the three Ni-M intermetallic compounds toward selective hydrogenation of phenylacetylene.