Novel construction and synthesis mechanism of b-axis oriented flower-like SAPO-11 molecular sieve in OSC-containing system for efficient hydroisomerization of long-chain n-alkanes

Changing Template/Al2O3 Ratio in Reaction Gel—An Effective Way to Regulate Nature of Intermediate Phases and Properties of SAPO-11 Molecular Sieves during Crystallization

“…The highest activity and selectivity are shown by the sample Pt/SAPO-11-1.0, which is characterized by nanosized crystals with a low aspect ratio and a higher concentration of available acid sites ( Figure 12 ). Due to this porous structure, diffusion limitations for reacting molecules are reduced, leading to a decrease in their residence time inside the channels and the contribution of the secondary cracking reaction on the acid sites [ 46 , 47 , 48 ]. For the Pt/SAPO-11-1.8 sample, the lowest selectivity for the C 16 isomers is observed due to the presence of primary crystals with higher aspect ratios, in which the residence time of molecules in the channels is significantly increased, and the contribution of cracking reactions is increased.…”

Synthesis, Modification, and Performance Regulation of SAPO-11 Molecular Sieve and Development of n-Alkane Hydroisomerization Catalyst: A Mini-Review

“…The 29 Si MAS NMR spectra analysis of the samples with the same silicon content showed that SAPO-11 prepared with surfactant contained a relatively high concentration of Si(nAl, 4 − nSi), 0 < n < 4, while SAPO-11 prepared without surfactant mainly contained large area of Si(4Si) islands. These results supported the viewpoint that the introduction of surfactant in the synthesis process was helpful to better Si dispersion, reduced the size of Si(4Si) islands, and increased the number and strength of acid sites.…”

“…48 If the reactants are long-chain n-alkanes and the carbon chain is long enough, the reaction molecules will not completely enter the pores but partially enter the pores to complete the reaction, and the other end will stay near the orifice or on the surface of the molecular sieve. 29 2.4. Lock−Key Mechanism.…”

“…The mechanism holds that in the process of hydroisomerization of n -alkanes, if the reactants are short-chain n -alkanes, all reactant molecules will enter the pores of the molecular sieve to complete the reaction process and generate branched alkanes . If the reactants are long-chain n -alkanes and the carbon chain is long enough, the reaction molecules will not completely enter the pores but partially enter the pores to complete the reaction, and the other end will stay near the orifice or on the surface of the molecular sieve …”

“…At the same time, various factors in the synthesis process will also bring about differences in physicochemical properties of the SAPO-11 molecular sieve. In addition, when the traditional SAPO-11 molecular sieve is used as the support to prepare hydroisomerization catalyst, there are still some problems, such as difficult control of acidity, small pore size, too strong interaction between metal components and support of the catalyst, and poor dispersion of active metals on the catalyst. − These problems can be properly solved by modifying the SAPO-11 molecular sieve. Pore structure, acidity, and crystal size of SAPO-11 molecular sieve are three important properties that affect the activity and the selectivity of target products of hydroisomerization catalyst.…”