Hydroisomerization of n-heptane on the Pt/H₃PW₁₂O₄₀/Zr-MCM-41 catalysts

Catalytic properties of the 1 wt.%Pt/25 wt.%H₃PW₁₂O₄₀/Zr-MCM-41-n (designated as Pt/HPW/WSZn, where n = Si/Zr = 25, 15, 8, 4, respectively) catalysts were evaluated in a microreactor system for the hydroisomerization of n-heptane at atmospheric condition. Catalytic results show that tungstophosphoric acid promoted mesoporous Pt/Zr-MCM-41 catalysts have potential important for the commercialization of n-heptane isomerization due to their high activity and unique selectivity to multibranched isoheptanes. It was found that 2-methylhexane was predominant in the monobranched isoheptanes and 2,3-dimethylpentane was the prevailing compound in the multibranched products. In the cracking products, only butane (isobutane and n-butane) and propane were formed. The formation of the multibranched isoheptanes had a close correlation with the mesopore diameters of the catalysts. The isomerization selectivity could be expressed by a parameter S_P, which is defined as a comprehensive function of Brönsted acid density, metal dispersion and geometry of the catalysts. The reaction mechanisms involving the formations of monobranched and multibranched isoheptanes as well as cracking products were discussed and postulated.