Synthesis, characterization, thermal stability, acidity and catalytic properties of large-pore MAPO-46

Abstract

Large-pore MAPO-46 with three-dimensional pore structure and hexagonal symmetry has been synthesized. MAPO-46 has AFS topology. The effect of the organic template (di-n-propylamine) concentration in the gel on the crystallinity and phase purity of MAPO-46 was studied. The N2, H2O and n-hexane sorption capacity of MAPO-46 is higher than MAPO-36 and AIPO4-5, which is consistent with the presence of 12- and 8-ring pore openings and a large structural void volume in the crystal structure. Morphological investigations, surface and thermal analysis of the material have been carried out. Effects of thermal treatment on the structural stability and N2 sorption capacity at 78 K of MAPO-46 have also been investigated. MAPO-46 exhibits a lower thermal stability than MAPO-36 and AIPO4-5. In situ IR spectroscopic investigations of chemisorbed pyridine on MAPO-46 revealed the presence of Bronsted and Lewis acid sites. The site-energy distribution on MAPO-46 was investigated by the temperature-programmed desorption (TPD) of pyridine and the stepwise-programmed desorption (SPD) of the base from 323 to 673 K. MAPO-46 possesses a stronger acidity than MAPO-5, SAPO-5 and AIPO4-5. MAPO-46 possesses a significant catalytic activity in the cracking of aliphatic hydrocarbons, conversion of o-xylene, disproportionation of toluene and also conversion of ethanol to aromatics at 673 K. In ethanol, o-xylene, toluene and cumene conversion reactions, MAPO-46 exhibited higher catalytic activity than MAPO-5. The acidity and catalytic activity results both indicated that MAPO-46 has a lower acidity and catalytic activity than MAPO-36. The deactivation of MAPO-46 in the cumene cracking reaction was found to be slower than that of MAPO-36 and MAPO-5 in the same reaction.