Applied Catalysis A: General 218 (2001) 161–170 Thiophene decomposition on Pt-supported zeolites: a TPD study L.J. Simon a,b , M. Rep a , J.G. van Ommen a , J.A. Lercher b,∗ a Catalytic Processes and Materials, Faculty of Chemical Technology, University of Twente, PO Box 217, 7500 AE Enschede, The Netherlands b Lehrstuhl für Technische Chemie II, Technische Universität München, Lichtenbergstr. 4, D-85748 Garching, Germany Received 28 August 2000; received in revised form 20 April 2001; accepted 24 April 2001 Abstract The decomposition of thiophene on a series of partially exchanged MOR and LTL zeolites in the presence and absence of Pt was studied by temperature-programmed desorption (TPD). The increase of the alkali cation concentration increased the fraction of thiophene that desorbed from the samples without reacting. Increasing the concentration of acid sites increased coke and hydrogen sulfide formation. Hydrogen desorption increased with increasing acid site concentration and available Pt surface area. Hydrogen is formed presumably via a bimolecular decomposition of thiophene at Brønsted acid sites and is spilt over to Pt, where it recombines and desorbs. In contrast to Pt/H-MOR, physical mixtures of Pt/SiO 2 and H-MOR were unable to produce significant amounts of hydrogen. This suggests that the thiophene decomposition occurs at metal–support interface sites or at sites with close distances to the Pt particle. Subtle differences between samples can be related to such minor variations in the distribution of acid sites and metal particles. © 2001 Elsevier Science B.V. All rights reserved. Keywords: MOR; LTL; TPD; Thiophene 1. Introduction Hydrodesulfurization (HDS) is one of the major processes in petroleum industries to produce clean fuels and was generally done using sulfided Co/Mo or Ni/Mo on Al 2 O 3 [1,2]. However, zeolite-based catalysts have been reported as new HDS catalysts [3]. Sugioka et al. [4,5] reported high thiophene HDS activity and stability for noble metal on H-ZSM5 and Y zeolites. The high activity of these catalysts compared to conventionally used Co/Mo/Al 2 O 3 was explained by a possible spillover of atomic hydrogen, which after decomposition of molecular hydrogen on the metal, hydrogenate the zeolite surface species formed by thiophene decomposition. However, no di- ∗ Corresponding author. Tel.: +49-8928913540; fax: +49-8928913544. E-mail address: johannes.lercher@ch.tum.de (J.A. Lercher). rect evidence of the spillover of the hydrogen has been described. Iglesia et al. [6] described a high activ- ity for thiophene HDS on cation-modified H-ZSM5. Coupling hydrogenation/dehydrogenation reactions by using propane as hydrogen source, the authors in- creased the thiophene HDS activity, showing that the thiophene HDS activity is related to the potential of the catalyst to form H atoms. Thiophene adsorption on various oxides and zeolite surfaces has been previously described [7–11]. Atten- tion has been paid to the formation and characteriza- tion of conducting thiophene-based polymers on solid acids [12,13]. Thiophene decomposition on surfaces has been shown to depend strongly on the acid site distribution. For H-ZSM5, the strength of interaction between thiophene and the support decreases in the order Na-ZSM5 > K-ZSM5 > H-ZSM5 [14]. The strength of the interaction between adsorbed thiophene and alkali cations (i.e. Na + and K + ) was higher than 0926-860X/01/$ – see front matter © 2001 Elsevier Science B.V. All rights reserved. PII:S0926-860X(01)00637-8