Deep aromatics hydrogenation in the presence of DBT over Au–Pd/γ-alumina catalysts

Abstract

Alumina-supported Pd, Au and Au–Pd catalysts were investigated for the simultaneous hydrogenation (HYD) of naphthalene (NP) and toluene (T) in the presence of dibenzothiophene (DBT). The nature of supported Au, its resistance against S-poisoning when applied along with Pd in the hydrogenation of aromatics was studied. Additionally, the effect of two kinds of γ-alumina (A(N) and A(S)) with different textural properties on the structure and performance of the catalysts was evaluated. Irrespectively of the support used, all the catalysts showed resistance to S-poisoning and their activity followed an order of NP > T > DBT. For hydrogenation of naphthalene, the specific reaction rates normalized to Pd loading follows trend: Au–Pd/ A ( N ) ≫ Au – Pd /A(S) > Pd(A(N) > Pd/A(S). The higher activity in the hydrogenation of naphthalene of the separate Au 0 and Pd 0 phases on a type-N alumina support with respect to those supported on a type-S alumina was related to a more homogeneous dispersion of Pd 0 and Au 0 crystallites and a lower extent of coke formation. Under an excess of hydrogen, the monometallic gold catalysts did not show any activity in the HYD of toluene. However, the Au catalysts showed over-hydrogenation of NP to decalin, in contrast with the performance of the Pd and Au–Pd samples. This behaviour can be exploited to avoid the over-hydrogenation of naphthalene by using the bimetallic Au–Pd formulation.