n-Heptane Hydroisomerization over a SO42–/ZrO2@SAPO-11 Composite-Based Catalyst Derived from the Growth of UiO-66 on SAPO-11
A novel SO42–/ZrO2@SAPO-11 (SZ@SA-11) composite was synthesized via a two-step method, and the corresponding SZ@SA-11 supported Pt catalyst was applied to catalyze n-heptane hydroisomerization. First, UiO-66@SAPO-11 is produced by the growth of UiO-66 on SAPO-11 due to the covalent bonds between Zr and the oxygen in the hydroxyl groups of SAPO-11. Then, UiO-66@SAPO-11 is decomposed to form ZrO2@SAPO-11 via calcination in air, and the SZ@SA-11 composite is obtained by the impregnation of ZrO2@SAPO-11 with (NH4)2SO4 and subsequent calcination. Compared with the physical mixture of SO42–/ZrO2 and conventional SAPO-11 (SZ+SA-11), SZ@SA-11 possesses smaller ZrO2 particles and more tetragonal ZrO2. Moderate and strong Brønsted acid sites (MSBAS) are produced only via interactions between tetragonal ZrO2 and sulfate, so SZ@SA-11 with more tetragonal ZrO2 has a greater amount of MSBAS than SZ+SA-11. These advantages of SZ@SA-11 endow the corresponding Pt/SZ@SA-11 catalyst with a better performance for n-heptane hydroisomerization compared to Pt/(SZ+SA-11). In addition, compared with the other counterparts such as Pt/SZ and Pt/SA-11, Pt/SZ@SA-11 presents higher selectivity for total isomers (91.5%), higher selectivity for multibranched isomers (22.6%), and a lower cracking selectivity (8.1%) in n-heptane hydroisomerization. The strategy proposed herein provides a new insight into the acidity adjustment of the molecular-sieve-based catalysts for hydrocarbon hydroisomerization.
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