Thermolytic molecular precursor route to site-isolated vanadia–silica materials and their catalytic performance in methane selective oxidation

Abstract

The thermolytic molecular precursor (TMP) method was used to prepare site-isolated, high-surface area vanadia–silica (V/SBA15) materials of various V loadings via the grafting of two precursors, OV[OSi(O t Bu) 3] 3 ( 1) and OV(O t Bu) 3 ( 2). Spectroscopic analysis indicates that excellent synthetic control was established for the exclusive formation of a pseudotetrahedral monovanadate (VO 4) structure on all catalyst surfaces. Another V/SBA15 catalyst was prepared via conventional incipient wetness impregnation (WI) with aqueous NH 4VO 3. A spectroscopic investigation of this catalyst revealed the presence of monovanadate and polyvanadate species along with small domains of V 2O 5. The TMP materials behave as single-site catalysts in the selective oxidation of methane to formaldehyde up to a V coverage of 0.47 V nm −2 and demonstrate superior activity compared with the WI catalyst. A space–time yield of 5.84 kg CH 2O kg −1 cat h −1 was observed, more than twice the highest value previously reported.