Catalyst of Palladium Supported on H-Beta Zeolite with Nanosized Al₂O₃ for Isomerization of n-Heptane

Abstract

To investigate the synthesis of isoparaffin from heavy naphtha, n-heptane conversion was studied. Applying and improving the isomerization catalyst developed for n-hexane was examined for n-heptane. The developed catalyst, Pd/nano-sized (defined as 5-50 nm, and here called as ns) Al₂O₃/H-BEA zeolite, was effective for the isomerization of both n-hexane and n-heptane, but n-heptane was more easily decomposed in comparison with n-hexane. In the case of n-heptane, cracking product selectivity was extremely high at about 85 % at 300 °C. However, improved high activity and selectivity were obtained 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. If the content of ns Al₂O₃ combined to H-BEA zeolite changed in the catalyst, cracking selectivity remained constant at a lower level comparing with the non-combined zeolite. ns Al₂O₃ also reduced the acidity of strong acid sites on the zeolite particle surface. X-ray photoelectron spectroscopy showed that reduced Pd/ns Al₂O₃/H-BEA 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.