TPD/AES (Temperature Programmed Desorption/Auger Electron Spectroscopy) Study of the Interaction of Dimethyl Methylphosphonate with Alpha-Fe(2)O(3) and SiO(2)

摘要

The interaction of dimethyl methylphosphonate (DMMP) dosed at 170 K onto SiO2 and alpha-Fe2O3 was studied by temperature programmed desorption (TPD) and Auger electron spectroscopy (AES). On dehydrated SiO2 there was no DMMP decomposition and there were two DMMP TPD peaks, a multilayer state at 200-210 K and a monolayer state at 275 K. On hydrated SiO2 no more 10% of a monolayer of DMMP decomposed and the only detectable TPD products were methylphosphonate (MP) and methanol. On clean alpha-Fe2O3 multilayer DMMP was observed but no molecular peak corresponding to the monolayer. Decomposition led to Co2, CO, CH3OH, HCOOH, H2, H2O, and an adsorbed phosphate species. The presence of the phosphate species did not completely inhibit the decomposition of subsequent doses of DMMP even after saturation of the AES P(114)/Fe(703) signal ratio ar 0.45 to 0.55. The AES P(114)/Fe(703) signal ration decreased at temperatures above 600 K. Migration of the phosphorus to an iron oxide-phosphate phase below the surface is proposed to explain the continued DMMP decomposition.