Interactions of ethanol and 2-propanol with oxidized and reduced WO3(001) thin film surfaces, grown epitaxially on a sapphire substrate, were studied with calibrated thermal desorption spectroscopy (CTDS). Coverage-dependent desorption spectra show that alcohol molecules diffuse rapidly on the WO3 thin film surfaces. Ethanol and 2-propanol desorb molecularly between 200 and 450 K with evolution of water. The remaining alkoxy intermediates decompose via beta-H elimination, followed by C-O bond scission, to produce ethylene and propylene, respectively. At low coverage, diffusion and competition between reaction rates of dehydroxylation vs associative molecular desorption of alcohol control the alkoxy coverage after the surface hydroxyls are depleted. The remaining alkoxy species undergo beta-H elimination and C-O bond scission to produce the alkene. The selectivity toward alkene is controlled by surface reaction kinetics, rather than by surface structure.