Thermocatalytic oxidation of dimethyl methylphosphonate (DMMP) was carried
out on nickel, iron, copper, and vanadium oxides supported on gamma-Al2O3.
The vanadium catalyst was found to exhibit exceptional catalytic activity,
even better than platinum catalysts. Varying the vanadium loading from 1 to
15% by weight indicated that 10% vanadium on Al2O3 was an optimal content.
In conjunction with XRD patterns, monolayer dispersion of V2O5 on Al2O3 wa
s considered to be beneficial to the longevity of these catalysts. Differen
t supports, including Al2O3, SiO2, and TiO2, were examined and SiO2 was the
optimum support because of its large surface area and the ability to resis
t poisoning by P2O5. On 10% V/SiO2 catalysts, 100% (to our limit of detecti
on of 0.1%) conversion of DMMP was reached for more than 100 h at 723 K. IR
, X-ray powder diffraction, ion chromatography, and XPS results illustrated
that the used catalysts contained phosphorus species. The presence of meth
ylphosphonic acid on the catalyst surface and downstream of the packed bed
reactor demonstrated the difficulty of P-CH3 cleavage. The deposition of co
ke in the catalyst bed and along the reactor wall resulted from the dehydra
tion of methanol and DMMP on P2O5. Accumulation of phosphorus species and c
oke on catalysts gave rise to a tremendous loss of surface area. However, P
2O5 itself was observed to catalyze the decomposition of DMMP. A mechanism
for this reaction was proposed to explain these experimental observations.
C) 2000 Academic Press.