A series of SAPO-11 molecular sieves were synthesized in the concentrated gel system by reducing the water content in the synthesis system. With SAPO-11 molecular sieves as supports, NiW-supported catalysts were prepared for the hydroisomerization of n-hexadecane. SAPO-11 molecular sieves and catalysts were characterized by XRD, SEM, N 2 adsorption–desorption, NH 3 -TPD, Py-IR, HRTEM and XPS. The results showed that reducing the water content in the synthesis system could increase the mesoporous volume of SAPO-11 molecular sieve and improve the acidity of SAPO-11. For the corresponding catalysts, using SAPO-11 synthesized in concentrated gel system as the support weakened the interaction between the active phase and the support, and increased the dispersion and stacking number of the active phase, which effectively improved the catalytic performance of the catalyst. The yield of i-hexadecane of the catalyst NiW/45W-SA corresponding to SAPO-11 synthesized in conventional water content system was 28.14%, while that of the catalyst NiW/5W-SA corresponding to SAPO-11 synthesized in concentrated gel system was 52.24%. According to the distribution of isomers, it is inferred that hydroisomerization of n-hexadecane over NiW/SAPO-11 follows the pore-mouth mechanism.
SAPO-11 molecular sieves with different crystal sizes and particle sizes, especially nanosized small-crystal SAPO-11 molecular sieves, were successfully synthesized, and the corresponding NiWS-supported catalysts were prepared for the hydroisomerization of n-hexadecane. XRD, SEM, N2 adsorption–desorption, Py-IR, and HRTEM were used to analyze the effects of crystal size and particle size of the supports on their physicochemical properties, active phase properties, and catalytic performance of the catalysts. Through reaction evaluation and analysis of isomeric products, the effects of the size change of the support on the hydroisomerization performance of the catalyst and the hydroisomerization depth of n-hexadecane were determined. Through comprehensive analysis of the cracking products, it was determined that secondary cracking occurred when the conversion of n-hexadecane on the NiW/SAPO-11-S catalyst reached about 42.7%, and the secondary isomerization occurred when the conversion of n-hexadecane reached about 80%. The hydroisomerization reaction network of n-hexadecane over the NiWS/SAPO-11 catalyst was studied emphatically, and it was found for the first time that the secondary cracking of n-hexadecane during hydroisomerization followed the C3-β-scission mechanism.
Synthesis of highly-crystallized ZSM-48 zeolite with low SiO 2 /Al 2 O 3 ratio was successfully performed via seed-assisted route. The influence of various factors on the seed-assisted synthesis was investigated systematically, including the seeds dosages, different seeds species, adding order of seeds, hydrothermal temperature and time, silica and aluminum sources, and gel compositions. The crystallinity, morphology, textural and acidic properties of ZSM-48 were characterized by various techniques, such as XRD , SEM, FTIR, Py-IR, N 2 physisorption , 29 Si and 27 Al MAS NMR. Aluminum sources posed a critical influence on the crystallinity with NaAlO 2 more beneficial to obtain well-crystallized ZSM-48, whereas the crystallinity seemed slightly susceptible to silica sources. SEM results revealed that the crystal size was significantly reduced from ca. 20 μm to around 2 μm after introduced the seeds. Kinetic analysis suggested that the added seeds can significantly reduce the apparent activation energy of nucleation and crystallization, encourage the formation of crystal nuclei and promote crystallization. The Pt-supported seed-assisted samples exhibited considerably higher density of acid sites than that loaded on seed-free sample. The hydroisomerization of n -hexadecane was investigated over various Pt-supported catalysts, and the Pt-supported seed-assisted samples exhibited the highest i-C 16 yield of ca. 75 wt% at conversion over 87 wt%.
危险品化学品经营许可证（带存储）