Effect of sodium loading on Pt/ZrO₂ during ethanol steam reforming

Ethanol steam reforming (ESR) was investigated on unpromoted and several sodium promoted Pt/ZrO₂ catalysts. From DRIFTS experiments, the following steps during ESR were inferred: dissociation of ethanol to produce ethoxy species; oxidative dehydrogenation of ethoxy species to acetate; and acetate decomposition. Acetate decomposition depends on the catalyst formulation. Decarboxylation is the most favored route at high sodium loading (2.5 and 5 wt.%); acetate decomposes in the forward direction to CH₄ and a carbonate, which further decomposes to CO₂. In contrast, decarbonylation is prevalent for the unpromoted catalyst or catalysts having low sodium loading. Acetate likely decomposes to CH₃OH and CO. Adsorbed methanol may undergo further steam reforming by oxidative dehydrogenation to formate species, which decarbonylates via reverse decomposition to CO and H₂O. Temperature programmed desorption/reaction and activity data confirmed that alkali promotion, especially at 1.8 %Na and higher loading, facilitates the forward acetate decomposition step, favoring decarboxylation over decarbonylation.