Photocatalytic oxidation of low molecular weight alkanes: Observations with ZrO2–TiO2 supported thin films

Low molecular weight alkanes including, propane, isobutane and n-butane can be completely oxidized to carbon dioxide and water vapor using a tubular photoreactor containing supported ZrO2–TiO2 thin film photocatalyst. It is observed that efficient reactor design requires optimization of catalyst packing to minimize bypass of the contaminant gas and optimization of the reactor diameter to maximize catalyst illumination. Single gas streams of ∼1000 ppmv were fed into the optimized tubular reactor and evaluated for complete oxidation at relative humidity ranging from <2 to 60% and at reactor temperatures of 35, 70, and 100 °C. The magnitude of reaction rate constants for isobutane and n-butane are comparable while on average the reaction rates of propane were significantly smaller. Reaction rates of propane and n-butane respond similarly to humidity levels, but isobutane reactivity differs in response to humidity. Reaction rates increase significantly from 35 to 70 °C, but not from 70 to 100 °C. In a feed stream containing a tertiary mixture of these alkanes and passed through the reactor, n-butane had the highest photoconversion followed by isobutane and propane. Variations in the gases’ reactivity in single gas and tertiary experiments are attributed to differences in strength of adsorption to the catalyst and reaction pathways that led to different intermediate compounds.