Enhanced methylcyclohexane dehydrogenation to toluene over Ir/USY catalyst

Abstract

Selective dehydrogenation of methylcyclohexane (MCH) to toluene over Ir, Pt, Pd and Ni supported on ultrastable USY zeolite was studied in the context of the hydrogen storage using MCH-toluene-hydrogen cycle. The MCH dehydrogenation was carried out in a fixed-bed flow reactor at 250 °C, total hydrogen pressure of 30 bar and WHSV of 92.4 h−1. The fresh and spent catalysts were characterized by variety of techniques such as X-ray fluorescence spectrometry, N2 physisorption, TPD-NH3, TPR, TEM, X-ray photoelectron and Raman spectroscopic techniques. Under steady-state conditions, the initial activity of the catalysts followed the order: Ir/USY >> Pt/USY > Pd/USY > Ni/USY. The reduced Ir/USY catalyst exhibited higher activity and selectivity toward toluene (≈90%) than its Pt, Pd and Ni-based counterparts. From the combined TPR and TEM analysis, the enhancement of activity and selectivity of the Ir/USY sample with respect to the Pt/USY catalyst was ascribed to moderate metal-support interaction leading to formation of larger Ir particles having lower amount of hydrogenolysis sites (kink sites). MCH hydroconversion over the Ir/USY catalyst decayed strongly during the time course of the reaction whereas simultaneously an increase in the toluene selectivity occurred. The catalyst activation by sulfidation was found to be less effective than the catalyst activation by reduction.