In Situ Diffuse Reflectance IR Spectroscopic Investigation of n-Butane Isomerization on Promoted Sulfated Zirconia Catalysts

Introduction Sulfated zirconia (SZ) is an attractive catalyst for low temperature butane isomerization [1]. Its activity can be improved by 1–2 orders of magnitude through addition of promoters such as iron or manganese in cationic form [2,3]. The state of these promoters has been characterized, and depending on the method of preparation, a major fraction is found to form a solid solution with zirconia [4]. It has been proposed that promoters facilitate reaction initiation via oxidative dehydrogenation to butenes, which may be converted into the reaction carriers, viz. carbenium ions. Only indirect evidence such as better activity after activation in oxidizing than in inert atmosphere has been presented [5]. Reaction profiles recorded under moderate reaction conditions (e.g. 323 K, 1 kPa n-butane) show an induction period and zero conversion in the extrapolation to zero time on stream. Either the catalyst becomes active only in the feed, or intermediates accumulate on the surface. We have focused on manganese as a promoter and have used in situ diffuse reflectance IR spectroscopy (DRIFTS) to reveal the effects of activation or regeneration in inert gas or O2, and to monitor the events during the induction period. References 1. Hino, M., Arata, K., J. Am. Chem. Soc. 101, 6439 (1979). 2. Hsu, C.-Y., Heimbuch, C.R., Armes, C.T., Gates, B.C., Chem. Commun. 1645 (1992). 3. Lange, F.C., Cheung, T.-K., Gates, B.C., Catal. Lett. 41, 95 (1996). 4. Jentoft, F.C., Hahn, A., Kröhnert, J., Lorenz, G., Jentoft, R.E., Ressler, T., Wild, U., Schlögl, R., J. Catal. 224, 124 (2004). 5. Wan, K.T., Khouw, C.B., Davis, M.E., J. Catal. 158, 311 (1996)