Nanoporous Hybrid Catalysts: Pd/Nanosized Al2O3/H-Beta Zeolite for Isomerization of Naphtha

摘要

Nanoporous hybrid catalyst is illustrated with the synthesis of isoparaffin from naphtha on Pd/nano-sized (defined as 5-50 nm, and here called as ns) Al2O3/H-beta zeolite catalyst. Applying and improving the isomerization catalyst which have been developed for n-hexane with the nanometer-scale design for combining three components was examined for n-heptane. In the combination, ns Al2O3 combined to H-beta zeolite could improve activity and suppress cracking selectivity into a lower level comparing with the non-combined zeolite, ns Al2O3 reduced the acidity of strong acid sites on the zeolite particle surface. The developed catalyst, Pd/ns Al2O3/H-beta zeolite, was effective for the isomerization of both n-hexane and n-heptane, but π-heptane was more easily decomposed in comparison with n-hexane. However, improved high activity and selectivity were also obtained in n-heptane case by removal of residual chlorine from the catalyst, which decreased the number of acid sites acting as cracking sites formed by residual chlorine on ns Al2O3. Reduced Pd/πs Al2O3H-beta zeolite catalyst with removed residual chlorines had the highest Pd dispersion because the chloride anions act effectively for cationic Pd dispersion on ns Al2O3 which can adsorb chloride anions. Since ns Al2O3 was also highly dispersed onto the zeolite particle surface, acid sites were formed at the boundary. The catalyst has highly dispersed Pd metal because of the stable Pd was highly dispersed on the acid sites by removing chlorine.