Enhancing hydrodeoxygenation-isomerization of FAME over M-SAPO-11 in one-step process: Effect of in-situ isomorphic substitution of transition metals and synergy of PtxSny alloy

Green biodiesel, a clean and renewable fuel, is often encouraged to use as the substitute for fossil fuel. Herein, a new strategy of in-situ isomorphic substitution of Al from SAPO-11 was reported to synthesize a series of M−SAPO−11 molecular sieves by the way of well controlling the substitution amount of transition metals, e.g., Fe, Co, Ni, Cu, and Zn. Owing to the unique morphology of spherical particles stacked layer by layer as well as the suitable pore structure properties, Pt/Fe3SAPO-11 showed a remarkable catalytic performance containing efficiency of deoxygenation with 100 %, selectivity of C15-C18 alkanes with 99.6 %, and selectivity of iso-C15-C18 alkanes with 34.8 % in one-step hydrotreatment process of fatty acid methyl ester. Through adding Sn and optimizing the atomic ratio of Sn/Pt alloy, the selectivity of iso-C15-C18 alkanes over Pt1Sn1/Fe3SAPO-11 catalyst increased from 34.8 % to 62.7 %. Pt1Sn1 and Pt2Sn3 alloy catalysts prepared by hydrothermal method using polyvinylpyrrolidone displayed a small particle size of 2 nm, and more contents of low chemical states on Pt and Sn species. Pt1Sn1 alloy exhibited a stronger adsorption energy of H and carbonyl oxygen (propionic acid) than Pt2Sn3 alloy by DFT calculation. Besides, Pt1Sn1/Fe3SAPO-11 with a stable catalytic ability can run as long as 1300 h in a mild reaction condition.