Kinetics of the partial oxidation of methane to formaldehyde on silica catalyst

The kinetics of the partial oxidation of methane to formaldehyde (MPO) on a "precipitated" silica catalyst in the 500-800 degreesC range was investiga ted. The influence of temperature and reaction mixture composition on the d ensity of reduced sites of the catalyst under steady state was evaluated by in situ reaction temperature oxygen chemisorption measurements. The kineti cs of the MPO on silica is pseudo first and zero-order on P-CH4 and P-o2, r espectively, while the density of reduced sites depends upon the square roo t of the P-CH4/P-O2 ratio. The rate-determining step is the activation of C -H bond of CH4 molecules (E-red = 142 kJ.mol(-1)), while oxygen replenishme nt is a nonactivated reaction step (E-ox approximate to 20kJ.mol(-1)), A La ngmuir-Hinshelwood kinetic model accounting for a two-site dissociative act ivation mechanism of both CH4 and O-2, thoroughly describes the steady stat e of the silica surface and the reaction kinetics of the MPO in the 500-800 degreesC range.