Optimization of the Metal Phase Composition of Ir–Pd/SiO2–Al2O3 Catalysts to Increase Thiotolerance in Selective Ring Opening of Decalin

The activity and S-tolerance of monometallic and bimetallic Ir–Pd catalysts with different atomic ratio (Ir/Pd = 0.5, 1 and 2) and the same total metal content (1 wt%) supported on SiO2–Al2O3 were studied in the hydroconversion of decalin. In the absence of sulfur, bimetallic catalysts showed less activity and selectivity to decalin ring opening products compared to the iridium monometallic catalyst. However they exhibited a greater tolerance to thiophene poisoning (S = 10 ppm). The catalysts with Ir/Pd = 1 and 2 (atomic ratio), with similar metal dispersion, had better resistance to sulfur. The optimal ratio found, Ir/Pd = 1, could be related to the formation of bimetallic particles and an adequate acidity. The total acidity of the catalysts decreased with an increasing Ir/Pd atomic ratio. The addition of sulfur did not significantly modify the selectivity to ring opening products but reduced the formation of dehydrogenated (undesirable) and cracking products. The distribution of the cracking products confirmed that in the absence of S the metallic function controls the decalin ring opening mechanism, except with the monometallic Pd catalyst. With the addition of S the acid function predominates because the activity results correlate with the acidity of the catalysts.