Evaluation of hydrogen transfer in FCC catalysts. A new approach for cyclohexene as a test reactant

The conversion of cyclohexene over different commercial FCC catalysts in a batch fluidized-bed reactor under very short contact times at 300 degrees C, was described by means of a simple lumped kinetic model that accounted for the observed yield patterns. The main branch of reaction starting from the adsorption of cyclohexene was used to assess an index based on kinetic parameters that defines the relative significance of hydrogen transfer reactions in a set that also includes proton transfer and cracking reactions. Complementary experiments with pulses of reactant on a fixed-bed reactor allowed to establish the best temperature to obtain maximum sensitivity to hydrogen transfer. The same evolutions were observed for the relationships between the index of hydrogen transfer and the paired acid site density with the Y zeolite unit cell size, confirming that two regions can be defined separated by unit cell sizes of about 24.28-24.30 Angstrom, the correlations being stronger at low values of this parameter. (C) 1999 Elsevier Science Ltd. All rights reserved.