Acid Strength of H3PW x Mo12−x O40 and H6P2W x Mo18−x O62 Heteropolyacid Catalysts as a Probe of Acid Catalysis for 2-Propanol Conversion Reaction

Abstract

Acid strength of H₃PW _x Mo_12−x O₄₀ (x = 0, 3, 6, 9, and 12) Keggin heteropolyacid (HPA) and H₆P₂W _x Mo_18−x O₆₂ (x = 0, 3, 9, 15, and 18) Wells-Dawson HPA catalysts was determined by NH₃-TPD measurements. Desorption peak temperature (acid strength) of H₃PW _x Mo_12−x O₄₀ and H₆P₂W _x Mo_18−x O₆₂ catalysts showed the same trend with respect to tungsten substitution, and increased with increasing tungsten substitution in both families of HPA catalysts. In order to correlate the acid strength with the acid catalysis of HPAs, vapor-phase 2-propanol conversion reaction was carried out as a model reaction. Yield for propylene (a product formed by acid catalysis of HPA) increased with increasing tungsten substitution and with increasing desorption peak temperature (acid strength) across both HPA families, regardless of the identity of HPA catalyst (without HPA structural sensitivity). The acid strength of H₃PW _x Mo_12−x O₄₀ and H₆P₂W _x Mo_18−x O₆₂ catalysts could be utilized as a probe of acid catalysis for 2-propanol conversion reaction.