Hydroisomerization of n -Heptane Over Cr Promoted Pt-bearing H 3 PW 12 O 40 Catalysts Supported on Dealuminated USY Zeol
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Hydroisomerization of n-Heptane Over Cr Promoted Pt-bearing H3PW12O40 Catalysts Supported on Dealuminated USY Zeolite Ruiping Wei Æ Jun Wang Æ Guomin Xiao
Received: 29 August 2008 / Accepted: 19 September 2008 / Published online: 11 October 2008 Ó Springer Science+Business Media, LLC 2008
Abstract The Pt-bearing H3PW12O40 (PW) catalysts, promoted by Cr or La, supported on dealuminated USY zeolite were prepared and their catalytic activities were evaluated in the hydroisomerization of n-heptane with an atmospheric fixed-bed reactor. The catalysts were characterized by XRD, BET, IR and H2-chemisorption. The results showed that the dealuminated USY support retained the Y zeolite structure and the PW well kept its Keggin structure in the supported PW catalysts and the doping of Cr or La into the catalysts enhanced the dispersion of Pt on the catalyst surface. The Pt-bearing PW catalysts doped with Cr or La, especially Cr, exhibited much higher catalytic activity and selectivity than the catalysts without dopants. Both the conversion and selectivity were discussed in relation with physicochemical properties of catalysts. Keywords 12-Tungstophoric acid Bimetal catalyst USY Hydroisomerization of n-heptane
1 Introduction Compared to other technologies such as blending with oxygenates and aromatics, light isoparaffins are increasingly
R. Wei (&) G. Xiao School of Chemistry and Chemical Engineering, Southeast University, Nanjing 211198, People’s Republic of China e-mail: [email protected] J. Wang State Key Laboratory of Materials-Oriented Chemical Engineering, College of Chemistry and Chemical Engineering, Nanjing University of Technology, Nanjing 210009, People’s Republic of China
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important octane number enhancers in gasoline pool due to the more and more environmental legislations have been enacted regarding the quality of the advanced liquid fuel quality [1]. Hydroisomerization of C5/C6 is a commercial approach to achieve light isoparaffins, where chlorinated Pt/Al2O3 or Pt/mordenite has been traditionally used as catalyst [2]. Nowadays, hydroisomerization of paraffins with the chain-length longer than C6 is highly desirable because the new standard of gasline demands to reduce the content of aromatics and olefins [1–4]. So it is of great importance to use catalytic isomerization of n-heptane, with a very low research octane number (RON = 0), for the production of more valuable products such as monobranched isomers (RON = 40–65) or multi-branched isomers (RON = 80–112) [5]. However, the well-known Pt/ mordenite catalyst would crack the n-heptane and the catalysts are easy to deactivate [3]. Therefore, many efforts have been devoted to seeking effective catalysts which can promote the selectivity of the branched paraffins in the hydroisomerization of paraffins with the chain-length longer than C6 [2, 4]. A number of reports has described the skeletal isomerization of n-heptane in the presence of hydrogen over bifunctional catalysts, such as Pt–Hb zeolite [6], Pt–Y zeolite [7], Pt or Pd promoted heteropolya
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