Journal of Catalysis 190, 396–405 (2000) doi:10.1006/jcat.1999.2755, available online at http://www.idealibrary.com on Direct Conversion of n-Butane to Isobutene over Pt–MCM22 G. D. Pirngruber, K. Seshan, and J. A. Lercher 1 Faculty of Chemical Technology, University of Twente, P.O. Box 217, 7500 A E Enschede, The Netherlands Received August 4, 1999; revised November 2, 1999; accepted November 2, 1999 MCM22 is a very active and selective catalyst for the skeletal isomerization of butene. At temperatures up to 775 K, Pt–MCM22 gives good results in the dehydroisomerization of n-butane, achiev- ing higheryields of isobutene than does Pt–ZSM5. Most notably, the formation of cracking products is low. Alternatively, MCM22 can also be used as an isomerization catalyst in combination with Pt–ZSM5 in order to increase the yield of isobutene in dehydro- isomerization. A disadvantage of the MCM22 materials, however, is their moderate stability, especially at higher temperatures. Dur- ing calcination/reduction of Pt–MCM22 partial dealumination of the framework occurs, leading to enhanced deactivation by coking. c  2000 Academic Press Key Words: dehydroisomerization of n-butane; MCM22; skeletal isomerization of n-butene. INTRODUCTION The dehydroisomerization of n -butane to isobutene is a challengingreaction.Due to thermodynamicconstraintsof dehydrogenation it has to be carried out at high temper- atures (above 750 K). Bifunctional catalysts for dehydro- isomerization have to be optimized with respect to their dehydrogenation and isomerization activity, as well as their stability toward deactivation. It has been shown that Pt– ZSM5 is a good catalyst for the dehydroisomerization of n -butane (1). Its major shortcoming is the rather high se- lectivity to by-products at high conversions stemming from oligomerization/cracking of butenes on the acid sites. Bet- ter results should be achieved by using other Pt supports that have a higher selectivity to butene isomerization vs oligomerization/cracking than ZSM5. FER and TON are known as selective catalysts for butene isomerization (2–4). When Pt–FER and Pt–TON were tested for dehydroiso- merization of n -butane, however, it turned out that besides the high selectivity of the parent zeolite in butene isomer- ization also other factorsplaya role (5).The zeolite support must also have a low activity for protolytic cracking of n - butane, which is a potential side reaction. Moreover, the manner in which Pt is dispersed and stabilized on the sup- port is very important. High dispersion in the pores of the 1 Present address: Institute for Chemical Technology, Technische Uni- versit ¨ at M ¨ unchen, Lichtenbergstr. 4, D-85748 Garching, Germany. zeolite, such as found with Pt–FER, seemed to lead to a very low dehydrogenation activity (5). MCM22 is a microporous material with a layered struc- ture (6). Within the layers a two-dimensional sinusoidal channel system exists, which is accessible through 10- membered-ring apertures. Between the layers supercages are formed, defined by 12-membered rings. The cages are accessible through 10-membered-ring apertures. The two channel systems are not connected. The product pattern of MCM22 in the isomerization and hydrocracking of de- cane,a test reaction for the determination ofunknown pore structures (7, 8), was similar to the product patterns of 10- membered-ring zeolites (9). Such zeolites have the right shape-selective propertiesfor butene isomerzation (10,11). Indeed, the successful application of MCM22 for this re- action was reported by Asensi et al. (12). Being suited for butene isomerization, MCM22 was also an interest- ing material for application in the dehydroisomerization of n -butane. Since our earlier studies had shown that the SiO 2 /Al 2 O 3 ratio has a large influence on the catalytic performance (1, 5), we tested two MCM22 samples (with SiO 2 /Al 2 O 3 ratios of 25 and 35, respectively) for the dehydroisomerization of n -butane.Inprinciple,evenhigherSiO 2 /Al 2 O 3 ratiosshould bebeneficial(1,5).ThesynthesisofhighlysiliceousMCM22 is difficult, however, and often leads to the formation of other crystal phases (13). In order to achieve a rather high ratio ofmetalto acid sites,which wasidentified to be benefi- cialfor the catalyst performance (1,5),we chose rather high metal loadings of 0.5–1 wt% Pt. The objective of the study was to evaluate the catalytic performance of Pt–MCM22 and correlate it with the physico-chemical properties of the materials. EXPERIMENTAL Catalyst Preparation MCM22 with SiO 2 /Al 2 O 3 = 35 was received from Prof. J. Weitkamp, University of Stuttgart (ST). It had been pre- pared according to the procedure outlined in Ref. (14). In order to remove the template the sample was calcined in a flow of 70% N 2 and 30% air at 813 K for 15 h (ramp rate 2 K/min). 0021-9517/00 $35.00 Copyright c  2000 by Academic Press All rights of reproduction in any form reserved. 396