Effect of metal/acid balance in Pt-loaded large pore zeolites on the hydroisomerization of n-hexane and n-heptane

Large-pore zeolites H-Beta, H-Mordenite and H-Omega were loaded with platinum and applied for the hydroisomerization of n-hexane and n-heptane. The catalytic activity of Pt-loaded zeolite showed good correlation with the effective acidity probed by pyridine rather than with the total acidity probed by ammonia when equal amounts of metal sites are present. The selectivity to multibranched isomers over three different catalysts was found dependent upon the conversion of n-paraffin. At low conversion, the selectivity to multibranched isomers was higher over Pt-loaded zeolites with high acid strength. At high conversion level, however, the selectivity was mainly governed by the metal/acid balance. On H-Mordenite and H-Omega, large amount of strong acid sites are located in the small pore or cage. In Pt/H-MOR, the metal/acid balance was poor because there was detrimental loss of metal sites caused by isolation of Pt in the side pockets of 8-MR and/or pore blockage of the linear 12-MR channel. Even though the acidity of H-Beta was very low compared to H-MOR and H-Omega, Pt/H-Beta yielded the best performance for the hydroisomerization of n-paraffin because of better metal/acid balance in Pt/H-Beta.