Mr. Smith et al., EFFECT OF SURFACE SPECIES ON ACTIVITY AND SELECTIVITY OF MOO3 SIO2 CATALYSTS IN PARTIAL OXIDATION OF METHANE TO FORMALDEHYDE/, Catalysis letters, 19(1), 1993, pp. 1-15
The effect of the nature of surface species on the activity and select
ivity Of MoO3/SiO2 catalysts has been investigated for the partial oxi
dation of methane to formaldehyde. Characterization techniques includi
ng BET surface area, ambient and in situ Raman spectroscopy, X-ray pho
toelectron spectroscopy, and temperature-programmed reduction were use
d in conjunction with steady-state reaction studies to relate the pres
ence of different surface species to the activity and selectivity of t
he catalyst. Results of these experiments indicate the presence of a h
ighly dispersed silicomolybdic species with terminal Mo=O sites appear
ing at lower MoO3 loadings. As the weight loading increases, these sit
es are transformed into polymolybdate species, forming more Mo-O-Mo br
idging sites at the expense of Mo=O sites. At high weight loadings, cr
ystalline MoO3 begins to form. The abundance of the Mo=O sites is beli
eved to affect activity and selectivity in the partial oxidation of me
thane to formaldehyde.