Effect of catalyst support on the photocatalytic destruction of VOCs in a packed-bed reactor

The removal of volatile organic compounds (VOCs) from the air aboard spacecrafts is necessary to maintain the health of crewmembers. The use of photocatalysis has proven effective for the removal of VOCs. A majority of studies have focused on thin films, which have a low adsorption capacity for contaminants and intermediate oxidation byproducts. Thus, this study investigates the use of adsorbent materials impregnated or coated with titania to: (1) provide a system that can remove VOCs for a period of time in the absence of UV irradiation to reduce power requirements and/or offer contaminant removal in the event of lamp failure and (2) improve the photocatalytic oxidation efficiency by concentrating VOCs and intermediate oxidation byproducts near the surface of the photocatalyst. Two adsorbent materials (porous silica gel and BioNuchar120 activated carbon) and glass beads were tested as catalyst supports for the destruction of a target VOC, in this case methanol (Co = 50 ppm_v). These materials were tested in annular reactors of two different sizes (8 mm and 25 mm) for methanol removal via adsorption (i.e., in the dark) and simultaneous adsorption and oxidation (i.e., in the presence of UV light). In addition, the effect of relative humidity (12% and 95%) was studied to evaluate the competitive effects of water vapor on each system. In the case of high (95%) relative humidity, the titania-coated carbon and silica-titania composite performed similarly in the small annulus reactor achieving about 95% methanol removal while the titania-coated glass beads performed slightly worse, achieving between 80 and 90% removal. The titania-doped adsorbent materials performed similarly in the large annulus reactor, achieving about 50% methanol removal. When the influent stream contained a low (12%) relative humidity, both the silica-titania composite and titania-coated carbon achieved a greater methanol adsorption capacity and higher methanol oxidation rate.