Comparative acidity of BEA and Y zeolite composites with 12-tungstophosphoric and 12-tungstosilicic acids

Catalytic materials supported on solid matrices have driven progress in classical processes in the search for high catalytic activity. This report provides a comprehensive comparison of twelve composites prepared by impregnation of two heteropolyacids (H3PW12O40 and H4SiW12O40) on zeolites BEA and Y (X%HPA/Zeolite). The materials were characterized by XRD, FT-IR, multinuclear MAS NMR, N-2 and pyridine adsorption and calorimetry. The Keggin structure of the HPA and zeolite were confirmed by P-31/Si-29/Al-27 MAS NMR, FT-IR and XRD. Generally, for X%HPA/zeolite, dealumination occurred after impregnation. Secondary intrareticular mesopores were more evident on zeolite BEA than on zeolite Y and the decreased specific surface area and pore volume with increased HPA loading was indicative of HPA deposition on their outer surface. There was a relatively strong interaction between the HPA and the zeolite surface, which involved extraframework aluminum (EFAL) sites hydrogen bonded to protons of HPA. 39%HPW/BEA and 40%HPW/Y showed Bronsted sites with high strength (average -145 kJ mol(-1)), which were strong enough to catalyze the esterification of n-butanol with acetic acid, yielding 83 and 78% conversion, respectively. The catalysts could be reutilized three times without any appreciable loss in the conversion.