Investigation of water assisted phase transformation process from AlPO4-5 to AlPO4-tridymite

Abstract

Water assisted phase transformation process from crystalized AlPO4-5 to AlPO4-tridymite was studied by the combination of X-ray diffraction (XRD), Scanning Electron Microscopy (SEM) and in situ multinuclear MAS NMR. It is found that water first activates the residue amorphous aluminophosphate in crystalized AlPO4-5 sample through hydrolysis and condensation reaction. Then the activated aluminophosphate species reassemble into AlPO4-tridymite crystalline. Meanwhile, AlPO4-5 transforms into orthorhombic phase during heating process. With further crystallization of AlPO4-tridymite, the amorphous phase is gradually consumed, and mass transportation between AlPO4-5 and AlPO4-tridymite is established through gradually amorphization of AlPO4-5. Finally, most of the AlPO4-5 transforms into the thermodynamically stable dense phase AlPO4-tridymite.

Variable Temperature and Pressure Operando MAS NMR for Catalysis Science and Related Materials

“…Such transformations have been reported for the crystallization of AlPO 4 -5 where operando 1 H, 13 C, 27 Al, and 31 P MAS NMR results were combined to reveal a semicrystalline phase that served as an intermediate during the hydrolysis and condensation reactions that constitute the crystallization mechanism. 16,25,26 In this example, NMR was able to clearly show the expulsion of excess water, phosphate, and aluminum to yield a crystalline catalytic solid. Similar principles can be applied to understand the formation of catalytic materials in zeolites.…”

Application of Multinuclear MAS NMR for the in situ Monitoring of Hydrothermal Synthesis of Zeolites

“…Among the materials studied up till now (Figure 10), aluminophosphates appear to be the most thoroughly investigated, since 27 Al and 31 P are the most convenient nuclei for NMR investigations. [24,28,30,31,40,62,[68][69][70] In the case of zeolite materials, the main efforts were directed at the investigation of zeolites A, X, MFI and BEA synthesis. [21,23,25,26,52,71,72] The selection of these materials was due to their wide industrial applications.…”

Three-dimensional crystal structure of novel aluminophosphate PST-5 solved using a powder charge flipping method

“…10 Aluminophosphates are usually unstable or are transformed into other topological structures under heat treatment in the presence of water; they are indeed prone to decompose or give way when irradiated by an electron beam. 11 Therefore, it is extremely difficult to readily determine the structures of aluminophosphates.…”