Photocatalytic degradation of methanol using silica-titania composite pellets: Effect of pore size on mass transfer and reaction kinetics

Nanostructured silica-titania composites (STC) synthesized with varying pore sizes (45, 134, and 299 Å) were tested for the removal of methanol from a humid air stream. The STC pellets were characterized for surface area and pore size distribution and tested in a packed-bed photocatalytic reactor for methanol removal and oxidation. While the pore size distributions for all STC were unimodal, STC with larger average pore sizes exhibited a broader pore size distribution. The efficiency of methanol oxidation was dependent on the surface area of the STC and the space time of the gas in the reactor. For all STC tested, the rate of methanol oxidation was not limited by resistances to external or internal mass transfer. For 134 and 299 Å STC, a lag time of 1.0 and 1.2 s, respectively, was observed before mineralization began. After this lag time, which was zero for the 45 Å STC, the data followed pseudo first-order reaction kinetics and the rate constant, k, was 0.40 s^-1 for all pore sizes.