Decomposition of dimethyl methylphosphonate on TiO 2(1 1 0): principal component analysis applied to X-ray photoelectron spectroscopy

Abstract

The surface chemistry of dimethyl methylphosphonate (DMMP) has been studied on a TiO 2(1 1 0) surface using X-ray photoelectron spectroscopy (XPS) and temperature programmed desorption (TPD). The application of principal component analysis (PCA) to the C(1s) and P(2p) XPS data showed that at least two linearly independent carbon-containing species and two linearly independent phosphorous-containing species are present on the surface between room temperature and 700 K. At room temperature, the main surface species contains intact P–OCH 3 bonds and is most likely molecularly adsorbed DMMP. Between room temperature and 700 K, the adsorbed DMMP decomposes to produce methane and H 2 as the primary gaseous products. Molecular DMMP also desorbs from the surface below 550 K. After heating to 800 K, all of the carbon is removed from the surface, whereas a single phosphorous-containing species is detected even after heating to 1000 K.