Preparation Of Bidk Ni₂p By Low-temperature Reduction And Its Selective Hydrogenation Performance

The large-scale aromatic production units require to remove small fraction of olefins from the aromatics. As the operation of such units result in the increase of olefins content in reformed gasoline, developing hydrogenation catalysts with good selectivity has been an industrial problem to be solved urgently. Therefore, the selective hydrogenation of Ni2P catalysts (a kind of non-noble metal catalyst) for olefins and alkynes is studied in this thesis.Temperature programmed reduction (TPR) is a general method to prepare transition metal phosphides. However, Ni2P prepared by traditional TPR has high reduction temperature with high energy consumption, which can cause a phosphorus loss and not suitable for the relatively mild selective hydrogenation reaction. Aiming at such problems, two approaches to decrease reduction temperature are proposed in this thesis in order to change catalyst precursors and to improve the reducing efficiency of hydrogen.First of all, Ni2P catalysts are prepared by solid-state synthesis method at room temperature. XRD and XRF characterization indicated that the catalysts precursors prepared by this method were Ni2P2S6, the final active phase of which is Ni2P after reduction at 300?. Also, TEM characterization showed that Ni2P-S catalysts had smaller particle size and better crystallinity. Moreover, the results of hydrogenation reaction confirmed that Ni2P-S showed significantly higher hydrogenation activities for alkenes and alkynes without loss of aromatics in comparison with Ni2P-TPR.In order to decrease the reduction temperature, Ni2P catalysts were also prepared with hydrogen plasma process method, in which nickel phosphate and nickel hypophosphite were used as precursors respectively. This method was proved to be feasible by the XRD characterization results. In addition, Ni2P catalysts had high hydrogenation activity without loss of aromatics with plasma method. The catalytic performance for styrene hydrogenation was in the order of Ni2P-(HY-PR)>Ni2P-PR>Ni2P-TPR. This thesis evaluated the effect on hydrogenation properties for alkenes of Ni2P-PR with passivation gas. The result showed that hydrogenation activity for alkenes passivated by O2 was higher than that passivated by H2S along with unchanged product distribution, which demonstrated passivation process did not change the active sites of catalysts but only altered its surface structure. Similarly, the effect of sodium salt and P/Ni ratios on hydrogenation activity was investigated during the Ni2P-(HY-PR) preparation process. The result showed that an excess of sodium salt and P had an adverse effect on the catalysts.