Effect of the metal loading in the hydroisomerization of n-octane over beta agglomerated zeolite based catalysts

The hydroisomerization of n-octane over catalysts containing palladium and/or platinum as the hydrogenating-dehydrogenating function and beta agglomerated zeolite as the acid function was studied. A slight decrease in the strong acid density of monometallic catalysts with increasing metal content, mainly on platinum samples, was observed due to the acid sites to be partially covered by metal particles. The diameter of the metal particles in bimetallic catalysts was higher than that corresponding to the monometallic ones with the same metal content. Catalytic results showed that the reaction scheme is influenced by the hydrogenating/acid balance. It was observed that the octane isomer yield increased with the hydrogenating/acid balance (defined as the ratio between the number of hydrogenating sites and the strong acid ones, nPd/nA and nPt/nA), then remaining constant at nPd/nA > 0.15 and nPt/nA > 0.20. In this last situation, the isomerization reaction over the acid sites was the limiting step of n-octane transformation, since the octane isomer yield does not depend on the metal content. n-Octane conversion was lower in the bimetallic catalysts than that observed in monometallic ones with the same metal content. The different conversion values would be attributed to the different interaction between the two metals in the bimetallic catalysts. A decrease of the multibranched isomers formation was observed when the palladium content increased in the bimetallic catalysts. Platinum present in these catalysts did not promote the methane and ethane formation, because its possible interaction with palladium in a bimetallic particle. (c) 2005 Elsevier B.V. All rights reserved.