Transition state shape-selective catalysis over AlPO-11 based molecular sieves

Abstract

MnAPO-11 molecular sieves with medium size elliptical pore were successfully synthesized by using diethylatnine and di-n-propylamine in highly pure crystalline state. The shape of crystalline MnAPO-11 obtained from diethylamine is thin plate form in which the plane is perpendicular to channel direction and the thickness of the plate is the length of the channel formed. The reactivity difference for the methylation of toluene over MnAPO-11 catalysts is related with the size of crystallite. Methylation of alkyl aromatic compounds was efficiently catalyzed by MnAPO-11 catalysts but aromatic ethylation was almost negligible. The difference of the reactivity is attributed to the dimension of the transition state for alkylations and the size of alcohol molecules is the key factor for the transition state dimension. The mole fraction of o-isomer for methylation of alkylaromatic compounds was depent on the size of the alkyl groups. The high selectivity of isobutene over MnAPO-11 and SAM-11 is also attributed to the elliptical pore structure. The short axis(O.39 nm) of pore is not enough for the transition state of formation of dimers which are precursor of propylene and pentenes.