Effect of the preparation method on particle size and reaction selectivity on naphthalene hydrogenation over Ni/H-MOR catalysts

Abstract

Three Ni catalyst supported on mordenite zeolite with the same content of nickel, ∼2 wt.%, were prepared by incipient wetness impregnation (IWI), ionic exchange (IE), and deposition-precipitation (DP) methods. The catalysts were characterized by, X-ray diffraction (XRD), textural properties, temperature-programmed reduction (TPR), transmission electron microscopy (TEM) and scanning electron microscopy / energy-dispersive spectroscopy (SEM/EDS). For all the catalysts conversion and selectivity were studied in naphthalene hydrogenation without or with thiophene in the feedstock. Despite the low nickel content, the three preparations showed a high initial total naphthalene conversion up to 94%. The Ni-IWI catalyst exhibited high selectivity to tetralin and deactivated very fast. Ni-IE catalyst had good activity; however, it shows deactivation and the main products are related to acid reactions. The Ni-DP shows high hydrogenation activity and was the most active catalyst, it generated decalins, especially cis-decalin and at a long reaction time on stream, the catalyst remains active. TEM and TPR results suggest that this behavior is related to the crystal sizes which in turn is conected with the preparation method. In presence of thiophene, all the catalysts deactivate; but the Ni-DP deactivation was slower.