Structure-directing role of molecules containing benzyl rings in the synthesis of a large-pore aluminophosphate molecular sieve: an experimental and computational study.
We describe the synthesis of AlPO-5 and SAPO-5 materials (AFI topology) using five different tertiary amines or quaternary ammonium ions containing one or two benzyl rings as structure-directing agents (SDAs). All of the molecules successfully direct the crystallization of AlPO-5; however, only the most efficient templates are able to crystallize SAPO-5. The observed differences in template efficiency can be rationalized in terms of the interaction energy between these molecules and the AFI framework. In ranking the template molecules, we notice that a well-defined molecular shape enhances the templating ability, but molecules that are too rigid are not able to adapt to the AlPO framework, yielding an inferior templating ability. Results of atomic-level modeling show that templates with one benzyl ring self-assemble in the main AFI channel by forming dimers with the benzyl rings parallel to each other; templates with two benzyl rings assemble instead into longer chains in which the benzyl ring of one molecule faces the ring of the subsequent one. Both mono- and dibenzyl templates show a high space-filling ability in AFI. Kinetic and thermodynamic factors that might affect the structure-directing activity of the molecules are examined.
Gómez-Hortigüela
Luis
L
Instituto de Catalisis y Petroleoquímica, C/Marie Curie 2, 28049 Cantoblanco, Madrid, Spain. lhortiguela@icp.csic.es
Pérez-Pariente
Joaquín
J
Corà
Furio
F
Catlow
C Richard A
CR
Blasco
Teresa
T
D017607:Aluminum Compounds / Q000138:chemical synthesis* / Q000737:chemistry; D001555:Benzene Derivatives / Q000737:chemistry*; D003198:Computer Simulation; D018360:Crystallography, X-Ray; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D008956:Models, Chemical; D008958:Models, Molecular; D010316:Particle Size; D010710:Phosphates / Q000138:chemical synthesis* / Q000737:chemistry; D016062:Porosity; D012015:Reference Standards; D012680:Sensitivity and Specificity
D017607:Aluminum Compounds; D001555:Benzene Derivatives; D010710:Phosphates; C012714:aluminum phosphate