On the performance of porous silica supported VOx catalysts in the partial oxidation of methane

In the present study, various VOx containing catalysts were prepared using nanoporous glass and mesoporous silicas (e.g. MCM-41 and SBA-15) as supports. The solids were characterised and tested towards partial oxidation of methane to oxygenates at 923 K. The catalysts were synthesised using two different methods such as (i) wet impregnation (WI) and (ii) incipient wetness impregnation (IWI). BET-surface areas depend on the nature of the support and the type of method of preparation. UV–vis spectra clearly disclose the formation of mainly monomeric VOx species in the samples prepared through IWI. Pyr-FTIR reveals that all the catalysts irrespective of the method of preparation contain both Brønsted and Lewis sites. However, the distribution of these sites again depends on the method of preparation. TEM analysis indicates that the catalysts prepared through IWI provide high dispersion of molecular VOx species on the surface of the support compared to WI. Thus, the catalytic activity and selectivity were also found to depend strongly on the method of preparation. Among the two preparation methods, the catalysts synthesised through IWI revealed higher selectivity and higher space-time-yields to formaldehyde. VOx supported on SBA-15 exhibits superior performance compared to MCM-41. Nanoporous glass supported VOx only show poor performance.