The structural stability of AlPO4-5 zeolite under pressure: Effect of the pressure transmission medium

Abstract

The structural stability of AlPO4-5 zeolite (AFI) has been studied as a function of pressure up to 34.4 GPa in a diamond anvil cell by using synchrotron x-ray diffraction. It is found that the AFI structural stability can be enhanced significantly when a mixture of silicone oil and liquid nitrogen is used as pressure transmission medium (PTM). In this case, the crystalline-to-amorphous transition pressure for AFI increased to be 15.9 GPa, much higher than that of 8.5 GPa observed in the experiment by using silicone oil as PTM. We found that the average distance of the interplanar crystal spacing along to most planes was expanded obviously when liquid nitrogen is used as one component in the PTM. The presence of liquid nitrogen in the PTM also affects the structural evolution of the AFI channel under pressure. The results demonstrated that nitrogen molecules can be inserted into the channels of porous zeolite AFI single crystals, exerting a supporting effect against the structure collapse of AFI and thus improving their structural stability.