Effect Of CeO₂ On The Selective Hydrogenation Activity And Resistance Of Poisonous Substance Over Bulk Transition Metal Phosphide Catalysts

Bulk phosphide catalysts were prepared by temperature programmed reduction method, and CeO2-promoted bulk phosphide catalysts (Cex-Ni2P, Cex-Ni2P(â… ), Cex-MoP, Cex-MoP(â… ), where x means the Ce/Ni, Ce/Mo molar ratio) were prepared by co-precipitation and impregnation methods. The hydrogenation activities of MoP and CeO2-promoted bulk MoP catalysts were evaluated using 1.0 wt% phenylacetylene in alcohol as reactants. Piperidine and CS2 was introduced into the same reactant to evaluate the hydrogenation activities of bulk phosphide and CeO2-promoted phosphide catalysts, in order to know the influence of nitride and sulfide on the hydrogenation activities of these catalysts.XRD characterization of CeO2-promoted bulk Ni2P catalysts indicated that with the introduction of CeO2, the formation of Ni5P4 was restrained and the particle size of CeO2-promoted catalysts was decreased. XRD characterization of CeO2-promoted bulk MoP catalysts indicated that with the introduction of CeO2, intensity of diagnostic diffraction peak was weaken and the particle size of CeO2-promoted MoP was decreased. XPS characterization of CeO2-promoted bulk Ni2P catalysts indicated that CeO2 specie was located on the catalysts surface, and had strong electronic interaction with surface species of the catalysts, leading the formation of an"electronic-rich" state on the surface of catalysts. With the introduction of CeO2, hydrogenation activity of MoP was significantly enhanced, and the hydrogenation activity of Cex-MoP increased with increasing CeO2 content. The real promoter in catalysts is Ce3+, which is formed in the process of high temperature H2 reduction. Ce3+ is a strong electron donor, and can transfer electrons to the surface of MoP. The electron transfer of Ce3+ to MoP increase the electron cloud density of surface, so the hydrogenation activities of MoP were enhanced.The hydrogenation activities of bulk Ni2P and MoP were restrained by the introduction of piperidine and CS2. Piperdine can competitive adsorption in the activity center of hydrogenation with phenylethylene, so the hydrogenation of phenylethylene to ethylbenzene was restained, but the hydrogenation of phenylacetylene was not changed during the addition of piperdine. The hydrogenation of phenylethylene to ethylbenzene and the hydrogenation of phenylacetylene were both strongly depressed by the introduction of CS2 into reactant. The result indicated the activity center of hydrogenation was poisoned by CS2. The influence of piperidine did not changed with marginala CeO2, and just disappeared when Ce/Ni and Ce/Mo molar ratio is 0.1. But the hydrogenation of catalysts was enhanced by the introduction of CeO2 when CS2 was introduced into the reactant. CS2 is firstly adsorbed in the Ce species, so the sulfur tolerant of CeO2-promoted Ni2P and CeO2-promoted MoP was enhanced.