Synthesis, Characterization Of Transition Metal Phosphides And Their Applications In Hydrazine Decomposition

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.