Oxidative decomposition of dimethyl methylphosphonate on rutile TiO₂(110): the role of oxygen vacancies

Abstract

The decomposition of dimethyl methylphosphonate (DMMP, (CH3O)2P(O)(CH3)), a simulant to the toxic nerve agent Sarin, on the rutile TiO2(110) surface has been studied with temperature programmed desorption (TPD) and density...

Decomposition of the Toxic Nerve Agent Sarin on Oxygen Vacancy Sites of Rutile TiO2(110)

“…On the pristine surface, the cleavage of the P–OC 3 H 7 or P–F bond of sarin was found to have high barriers (2.27 eV and 1.77 eV, respectively). This behavior has been observed as well on DMMP, where the cleavage of a P–OCH 3 bond requires overcoming a barrier higher than 2 eV . On the pristine surface, the P–F bond of sarin is less difficult to cleave compared to the P–OC 3 H 7 bond, but still, the barrier is large.…”

“…55−57 All surface calculations use the k-point mesh of 1 × 1 × 1. The literature and our test calculations 11 showed that using a k-points mesh of 3 × 3 × 1, larger surface or thicker surface models show no significant difference compared to our selected 2 × 4 surface calculated at the γ point. 11 ■…”

“…To model the defective surface, one oxygen atom in the bridging site (O 2c ) was removed (Figure S2) as it was found to be the most stable vacancy site. − The removal of 1 O 2c represents a vacancy site coverage of 0.125 ML, which agrees well with the experimentally observed vacancy coverage of r-TiO 2 (110) crystals (between 0.08 and 0.15 ML). − All surface calculations use the k -point mesh of 1 × 1 × 1. The literature and our test calculations showed that using a k -points mesh of 3 × 3 × 1, larger surface or thicker surface models show no significant difference compared to our selected 2 × 4 surface calculated at the γ point …”

“…FTIR studies on powder titania showed that the P–OCH 3 bond cleavage is facilitated by the presence of surface hydroxyls at temperatures starting from 214 K . This is denoted by the shift of the P–CH 3 signal and a decrease of the surface O–H signal, and leads to the formation of adsorbed methyl phosphonic acid and possibly to the release of methanol. − This is similar to the behavior of DMMP observed on ZnO, zirconium hydroxide, and Zr-based metal–organic frameworks (MOFs) where DMMP is transformed into penta-coordinated phosphor-center intermediate by surface hydroxyl groups prior to the release of methanol at room temperature. − Our previous work on rutile TiO 2 (110) also showed the effect of oxygen vacancies in facilitating the P–OCH 3 bond cleavage, reducing its barrier from >2 to 1.4 eV and rendering the process possible at 600 K. It was also found that the product formation (methanol and formaldehyde) could only result from a methoxy disproportionation reaction resulting from decomposed DMMP on defect sites . The influence of defects and different surface morphology on the decomposition of DIMP has been observed as well.…”

“…19−23 Our previous work on rutile TiO 2 (110) also showed the effect of oxygen vacancies in facilitating the P−OCH 3 bond cleavage, reducing its barrier from >2 to 1.4 eV and rendering the process possible at 600 K. It was also found that the product formation (methanol and formaldehyde) could only result from a methoxy disproportionation reaction resulting from decomposed DMMP on defect sites. 11 The influence of defects and different surface morphology on the decomposition of DIMP has been observed as well. On alumina, the release of 2propanol is observed; however, on silica, the release of propene was observed instead.…”