Synthesis of SAPO-31 Nanorod in Ethylene Glycol–Water Medium and Its Catalytic Performance in the n-Hexadecane Hydroisomerization

Abstract— Silicoaluminophosphates (SAPOs) molecular sieves with one-dimensional channels as acid component of bifunctional catalysts loading metal have been attracted attention in the field of clean fuel production due to their mild acidity and shape-selectivity. Herein, a series of novel SAPO-31 molecular sieve nanorod aggregations (S31-xEG) were synthesized in an ethylene glycol–water (EG–H₂O) crystallization medium, and the morphology and acidity, as well as the location of Si atoms on the framework were adjusted by changing the EG/H₂O ratio. The S31–xEG samples exhibit morphology of aggregation composed of nanorods with mean diameter of ~30 nm and length of 3~4 μm, as well as reduced total Brønsted acid density, which is in good linear correlation with the amount of the framework Si atom with Si(1~4Al) chemical environment. The catalytic performances of 0.5Pd/S31 and 0.5Pd/S31-20EG bifunctional catalysts prepared by loading 0.5 wt % Pd on the SAPO-31 (S31) synthesized in the water as crystallization medium and S31–20EG (EG/H₂O = 2 : 3) were tested in the n-hexadecane hydroisomerization, respectively, and both catalysts showed high iso-hexadecane yield (~85.0%), while 0.5Pd/S31–20EG demonstrated larger turnover frequency (TOF) value and proportion of mono-branched iso-hexadecane in the thermodynamic control region (at n-hexadecane conversion of ~90%) due to a synergistic catalysis between metal and Brønsted acid sites.