Synthesis and Characterization of Chromium-Added Pt/Beta Zeolite and its Catalytic Performance for n -Heptane Isomerizat
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Synthesis and Characterization of Chromium-Added Pt/Beta Zeolite and its Catalytic Performance for n-Heptane Isomerization Yoshiyuki Izutsu • Yuki Oku • Yusuke Hidaka • Kaname Yoshida • Yukichi Sasaki • Yasushi Sekine • Eiichi Kikuchi • Masahiko Matsukata
Received: 15 January 2013 / Accepted: 30 January 2013 / Published online: 15 February 2013 Ó Springer Science+Business Media New York 2013
Abstract Catalysis of Pt/beta zeolite catalyst modified via the addition of various elements (Ca, Cr, Mn, Fe, Co, Ni or Cu) for n-heptane skeletal isomerization was investigated at 513 K in a conventional flow reactor with a fixed catalyst bed. It was found that, among the catalysts tested, PtCr/beta was the most promising, since its use resulted in relatively high yields of multi-branched alkanes in conjunction with a very low selectivity for cracking products. Ion exchange was found to be an effective method for the addition of chromium to zeolite, compared to the evaporation to dryness process. Platinum particle sizes were observed using STEM. While particles *10–30 nm in size were evident on the surface of Pt/beta, they were rarely observed on the PtCr/beta catalyst. It was concluded that platinum homogeneously dispersed within beta zeolite micropores resulted in the observed decreased cracking activity during n-heptane isomerization and that the addition of chromium had been effective in increasing degree of platinum dispersion. Keywords Isomerization n-heptane *BEA zeolite Platinum Chromium
Y. Izutsu (&) Y. Oku Y. Hidaka Y. Sekine E. Kikuchi M. Matsukata Waseda University, 3-4-1 Okubo, Shinjuku, Tokyo 169-8555, Japan e-mail: [email protected] K. Yoshida Y. Sasaki Japan Fince Ceramics Center, 2-4-1 Mutsuno, Atsuta, Nagoya, Aichi 456-8587, Japan
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1 Introduction The skeletal isomerization of alkanes is a reaction process by which branched alkanes are produced from normal (straight chain) starting compounds. The multi-branched alkanes produced by this process can be used as components of gasoline blends so as to produce substrates with high octane numbers. Solid acid catalysts modified with precious metals are known to be active for the skeletal isomerization of alkanes. Pt/SO42-/ZrO2 and Pt/H-mordenite (MOR) have both been commercialized for the isomerization of alkanes with 4, 5 and 6 carbons. The isomerization of alkanes which have seven or more carbons is, however, more difficult, since carbocation intermediates of these larger compounds readily undergo cracking due to beta scission [1, 2]. For this reason, much research has focused on catalysts and reaction conditions which will suppress cracking during catalytic reaction process [2–13]. There have to date been a number of publications concerning the factors which can affect the relative ratio of isomerization to cracking in the catalytic processing of n-heptane. In the case of zeolite catalysts, the diffusion of alkane into the zeolite micropores has been proposed as a significant factor. Chica and Corma [14] have reported the results of n
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