Small-pore aluminium phosphate molecular sieves with chabazite structure. Incorporation of magnesium in structures -34 and -44

Abstract

MgAPO and MgSAPO with -34 and -44 framework structures have been synthesized with various amounts of magnesium. Magic-angle spinning (MAS) NMR results showed the presence of three phosphorus environments: P(4Al, 0Mg), P(3Al, 1Mg) and P(2Al, 2Mg) in MgAPO-44 and MgSAPO-44. In MgAPO-34, some of the NMR peaks are split, possibly owing to the presence of non-equivalent T sites. It was indicated from ²⁹Si MAS NMR results that in MgSAPOs, the magnesium content of the samples affects the silicon environment: with increased magnesium content, more silica-rich regions were formed. Structural acidity, determined from temperature-programmed desorption of ammonia, supported the results on the formation of silica-rich regions in the structure.