Small Pore Aluminum Phosphate Molecular Sieves with Chabazite Structure: Incorporation of Manganese in the Structures -34 and -44

Abstract

MnAPO and MnSAPO (APO = aluminum phosphate; SAPO = silicoaluminophosphate) with −34 and −44 framework structures have been synthesized. Rapid synthesis of MnAPO-34 could be achieved using morpholine as the template that subsequently changes to MnAPO-20 during synthesis. The presence of manganese in the framework has been established by a number of experimental techniques. ESR spectra of the low manganese-containing samples were better resolved, and by comparison of these with the ESR of Mn2+-exchanged samples, it was possible to conclude that Mn2+ was present in the framework of the MnSAPOs. The nature of the silicon site depended on the manganese content of the sample as seen from 29Si MASNMR. With higher manganese content, more silica-rich regions next to SAPO domains in the framework were formed. In MnAPO-44, a complete ordering of the T atoms appeared to have been achieved with every P atom being surrounded by three Al and one Mn. DTA-TG, infrared, and UV−visible spectra of the samples will be discussed.