Impact of cationic surfactant chain length during SAPO-11 molecular sieve synthesis on structure, acidity, and n-octane isomerization to di-methyl hexanes

• Published in: Journal of catalysis Vol. 294; pp. 161 - 170
• Main Authors: Guo, Lin, Bao, Xiaojun, Fan, Yu, Shi, Gang, Liu, Haiyan, Bai, Danjiang
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-10-2012; Elsevier; Elsevier BV
• Subjects: Acidity; active sites; carbon; Catalysis; catalysts; Cationic surfactants; Chain length; Chemistry; cracking; crystallites; Di-branched isomerization; Exact sciences and technology; External surface area; General and physical chemistry; isomerization; isomers; octane; SAPO-11; surface area; Surfactants; Theory of reactions, general kinetics. Catalysis. Nomenclature, chemical documentation, computer chemistry; Di-branched isomerization; External surface area; SAPO-11; Chain length; Cationic surfactants; Water; Support; Acidic site; Active site; Cationic surfactant; Alcohol; Selectivity; Surfactant; Ionic surfactant; Mechanism; Molecular sieve; Isomer; Crystallites; Synthesis; Alkanol; Hexane; Diffusion; Structure; Octane; Intermediate product; Isomerization; Acidity; Propanol; Carbon; Heterogeneous catalysis; Surface area; Catalyst
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/j.jcat.2012.07.016

With the increasing chain length of surfactants, the crystallite size of SAPO-11 firstly deceases and then increases, while the external surface area shows a reverse variation. The small-sized SAPO-11-based catalyst has superior di-branched isomer selectivity due to more active sites at pore mouths produced from the higher external surface area. [Display omitted]
► DoTAB with 12 carbons produces SAPO-11 with smaller size and more external surface. ► The high external surface area with small crystallites creates more pore mouths. ► The small-sized SAPO-11-based catalyst has superior di-branched isomer selectivity.
The structure, acidity, and n-octane di-branched isomerization of SAPO-11 synthesized with surfactants of different chain lengths in water–propanol system were investigated. The results showed that with the increasing chain length of surfactants, the crystallite size of SAPO-11 firstly decreased and then increased, but the external surface area and the active B acid sites of SAPO-11 firstly increased and then decreased. The smallest crystallite, the highest external surface area, and the most B acid sites were obtained simultaneously with the surfactant of 12 carbon atoms. The isomerization results of n-octane indicated that among the series Pt/SAPO-11 catalysts, the catalyst with DoTAB-directed SAPO-11 as support had the highest selectivity to di-branched isomers and the lowest cracking selectivity due to the largest external surface area that created more active sites to promote the formation of di-branched isomers by the key-lock mechanism and improve the diffusion of intermediates and products for reducing cracking reactions.