【作者】 程瑞华；

【导师】 张涛；

【作者基本信息】 中国科学院研究生院（大连化学物理研究所） ， 工业催化， 2006， 博士

【摘要】 过渡金属磷化物是一种新型的催化材料,在加氢脱硫、加氢脱氮反应中表现出良好的特性,但是现有研究中没有对高比表面磷化钼的制备方法展开考察,也很少对磷化钼在其他反应中的应用进行报道。本论文采用柠檬酸-程序升温还原法制备了高比表面的磷化物,同时以微量吸附量热为手段,用CO作为探针分子考察了MoP的表面活性位。进而考察了磷化物的肼分解性能,并利用原位红外光谱对肼分解的吸附和反应过程进行了研究。利用柠檬酸和Mo的螯合作用可以降低MoP的团聚程度并使产物形成中孔/微孔孔道,明显地增加了MoP的比表面积。该方法对增加其他磷化物表面积及提高MoP在氧化铝表面的分散度都有一定的作用。微量吸附量热实验证实非担载MoP表面只存在一种活性位。新方法增加了活性位的数目,并保持了担载或非担载MoP活性物质的分布。过渡金属磷化物的肼分解活性依次为:MoP~WP>CoP>Ni2P。肼在MoP催化剂上吸附和反应的红外结果表明肼主要在MoP/Al2O3催化剂的Mo位上吸附和反应的。肼在MoP上的分解活性比较稳定,而在Mo2N上失活明显。NH3的微量吸附量热实验表明NH3在Mo2N上的吸附强于MoP上。在N2H4和CO的共吸附原位红外实验中,可以观察到在MoP/Al2O3上CO的吸附峰红移现象,但在Mo2N/Al2O3上不存在CO的吸附峰。这说明肼分解产物在Mo2N上的吸附很强,不容易脱附,从而导致Mo2N催化剂逐渐失活。更多还原

【Abstract】 As a novel class of catalyst, transition metal phosphide has been explored and showed highly active for hydrodesulfurization (HDS) and hydrode- nitrogenation (HDN), but few studies were reported in other catalytic reactions. This thesis focused on the synthesis of MoP with high surface area and highly dispersed MoP/Al2O3, as well as the characterization of active sites by microcalorimetry with CO as probe molecular. Decomposition of hydrazine was also explored with these phosphides, and the decomposition mechanism was studied with in-situ FTIR.The high surface area of MoP was prepared by the citric acid-temperature programmed reduction method. The decrease in agglomeration and the formation of pores were responsible for the increase in the surface area of MoP. This method appeared to be a versatile method for producing high surface area transition metal phosphides and supported MoP/Al2O3 catalysts.Studies on the chemisorption of CO by microcalorimetry gave some insights into the nature of active sites on MoP. CO was primarily adsorbed at one MoP surface site, which had high differential energy, for both MoP prepared by the two methods. The high surface area MoP had an increase in the number of active sites but there was no change in the chemical nature of MoP.The decomposition activity of hydrazine over a series of unsupported phosphides decreased as follow: MoP~WP>CoP>Ni2P. From the IR spectra, when N2H4 was adsorbed on MoP/Al2O3, there appeared a band at 1484 cm-1 which wasassigned to NH4+. Hydrazine was found to adsorb mainly on Mo site as revealed by co-adsorption with CO and N2H4.Phosphide catalysts were found to be active and stable at room temperature. Microcalorimetric adsorption of NH3 revealed that NH3 molecules were adsorbed more strongly on Mo2N than on MoP. The in-situ FTIR results of co-adsorption of CO and N2H4 over MoP/Al2O3 and Mo2N/Al2O3 exhibited two distinct features, i.e. the absence of CO adsorption band on Mo2N/Al2O3 and the lowering of frequency of CO adsorption band on the MoP/Al2O3, suggesting the relatively weaker adsorption of the intermediates or products of the decomposition of N2H4 on MoP/Al2O3 than those on Mo2N/Al2O3. The moderately adsorbed species on MoP favored to desorb from the active sites, thus a better stability of MoP was achieved.更多还原