Hydrogenation and ring opening of tetralin on noble metal supported on zirconium doped mesoporous silica catalysts

Zirconium-doped mesoporous silica with a Si/Zr ratio of 5 and moderate surface acidity has been used as a support for (co)-impregnated platinum, palladium, rhodium and palladium-platinum (Pd-Pt) (2 wt.%). The catalysts resulting after reduction have been extensively characterised and examined for their activity in the hydrogenation and hydrogenolysis/ring-opening of tetralin at 6 MPa of hydrogen pressure. BET surface areas are in the range 620-840 m(2) g(-1) and the average pore diameter is 3.4-3.8 nm. Smallest metal particle sizes (estimated from hydrogen chemisorption and transmission electron microscopy (TEM)) are observed for Rh (<2 nm for 2 wt.%). Thermoprogrammed reduction shows two distinct hydrogen consumption events attributed to the reduction of Rh(111) either in particles of two different sizes or in two different environments. Significant differences between the TPR of supported unreduced bimetallic Pd-Pt and those of the corresponding Pt and Pd oxides suggest formation of intermetallic aggregates in the former. Conversion of tetralin by all catalysts exceeds 85% in the temperature range 523-623 K, with trans-decalin being the principal product in the lower part of this range. Above 575 K, the selectivity pattern changes, with an increase in hydrogenolysis and/or ring-opening (cracking compounds, CC) products up to 20-40% of the yield, particularly for the Rh containing catalyst. The influence of H-2/tetralin molar ratio and of contact time were also investigated. Addition of dibenzothiophene (DBT) to the feed leads to some loss of conversion and change in product selectivity with bimetallic Pd-Pt catalysts, but reversion to a sulfur-free feed allows partial recovery 85% of its initial activity. (C) 2003 Elsevier B.V. All rights reserved.