Changing the Si distribution in SAPO-11 by synthesis with surfactants improves the hydroisomerization/dewaxing properties

The silicoaluminophosphates SAPO-11 isodewaxing catalysts were synthesized with varying Si content following conventional methods and using a route involving the presence of surfactant. Smaller crystal size (similar to 80 nm) and higher external surface areas were found for the samples prepared with surfactant. This synthesis route using surfactant gives SAPO-I I samples with greater numbers of stronger acid sites than those prepared by conventional synthesis. The Si-29 MAS-NMR spectra obtained for samples containing the same amount of silicon showed that SAPO-11 prepared with surfactant contains a higher relative concentration of Si (nAl, 4-nSi), 0 < n < 4, border environments, whereas large patches of Si(4Si) are predominant in the samples prepared without surfactant. These results support the idea that introducing surfactant during synthesis contributes to better Si dispersion, decreasing the size of Si(4Si) patches and increasing the number and strength of acid sites. The hydroconversion of n-hexadecane on Pt/SAPO-11 samples indicates that the samples synthesized with surfactant with similar Si content and very close crystallite size to those synthesized by conventional methods are much more active and selective for the hydroisomerization of long-chain n-paraffins. (c) 2006 Elsevier Inc. All rights reserved.