In-situ Synthesis of Gallium-Containing SAPO-11 Molecular Sieves and Superior Catalytic Performance of Their NiWS Supported Catalysts for Hydroisomerization of n-Hexadecane

In order to prepare a high-performance SAPO-11 (silicoaluminophosphate-11) based non-noble metal supported catalyst for the hydroisomerization of long-chain n-alkanes, gallium-modified SAPO-11 molecular sieve was successfully synthesized by the in-situ synthesis method, and the NiWS supported catalyst was prepared for the hydroisomerization of n-hexadecane. The effects of Ga-modification on the physicochemical properties of SAPO-11 molecular sieve, the active phase properties, and the catalytic performance of the catalyst were studied. Through a series of physicochemical characterizations, it was found that the introduction of Ga increased the mesoporous volume of SAPO-11 molecular sieve, reduced their acid density and strength, but improved the amount of medium-strong Brønsted acid. The Ga-modification weakened the interaction between the active metals and the support, increased the sulfidation degree of active metals, and increased the stacking number and dispersion of active phase. The results of catalytic performance evaluation showed that the catalytic activity and isomerization selectivity of the Ga-modified SAPO-11 molecular sieve based catalysts were improved, and the yield of i-hexadecane of NiW/2Ga-SAPO-11 was the highest, which was 40.30 % higher than that of NiW/SAPO-11. By analyzing the distribution of isomeric products, it was found that the Ga-modified SAPO-11 molecular sieve was helpful in improving the hydroisomerization depth of n-hexadecane over the catalyst.