<p>Metal oxide catalysts are widely employed in propane dehydrogenation (PDH) for propylene synthesis, requiring sequential reduction–reaction–regeneration cycles. However, the effect of water present in the inlet gas or reactor on the catalytic performance of various metal oxides remains insufficiently understood. This study examines the influence of water on supported metal oxide catalysts, specifically CoO_<i>x</i>/Al₂O₃, VO_<i>x</i>/Al₂O₃, and an industrial analog CrO_<i>x</i>/Al₂O₃ catalyst. By combining titration experiments, in situ Fourier transform infrared spectroscopy, kinetic analysis, and isotopic techniques, we demonstrate that even trace amounts of water can markedly suppress PDH performance via dissociative adsorption on the oxide surface. Methanol pretreatment effectively scavenges adsorbed water, recovering Lewis acid–base sites and consequently restoring PDH activity. This work underscores the profound inhibitory role of trace water in PDH over metal oxide catalysts and illustrates the potential of methanol pretreatment as an effective strategy to mitigate this limitation.</p>