Charge compensation dominates the distribution of silica in SAPO-34

Abstract

The distribution of Si atoms in the SAPO-34 framework determines its acidity and catalytic effects. This was investigated using the charge balance between the inorganic framework and trapped template ions. Three types of templates, which yielded R+, 2R+ and 2R2+ positive charges in the cages of SAPO-34, were obtained from single crystal data and they were used to direct the synthesis of SAPO-34 with different Si contents and formation of isolated Si atoms and Si islands in the lattice. The concentration limits of SiO2 in the gel for constituting isolated Si atoms were calculated and verified experimentally. Si islands, including 5-Si, 8-Si, 11-Si, 14-Si island were described on the basis of host-guest charge compensation. An overall view of the distribution of Si atoms in SAPO-34 was given and a criterion for the strength and density of acid sites in SAPO-34 for it to be an efficient catalyst for MTO was made available.