Etching behavior of TEAOH in the post-synthesis of hierarchical SAPO-34

Etching behavior of TEAOH in the post-synthesis of hierarchical SAPO-34 was investigated in 25-200 C range for 0.125-128 h. Mechanism was discussed based on the compositions and properties characterized by ICP-AES, XRD, SEM, N-2-adsoption/desorption and NH3-TPD. It is found that the solubility of SAPO-34 in TEAOH decreases while the dissolution rate of SAPO-34 increases with the raise of temperature. The etching is supposed to begin with the break of Al-O(H)-Si bond, and then the Al-OH-related Al-O-P bonds and the new exposed inner Al-O(H)-Si bonds. The low-temperature etching favors the dissolution of Al-OH-related Al-O-P bonds and behaves as a layer-to-layer peel-off process from the outer surface to the inner of crystal. This peel-off process has hardly any selectivity to atoms and leads only a small amount of mesopores. The moderate- and high-temperature etching favors the breaking of the new exposed inner Al-O(H)-Si bonds, acts as a drilling and fragmentizing process, leads the formation of abundant mesopores in short time, and then the mesopores merge and the crystals are fragmentized. The dissolution of Al-O(H)-Si and then Al-O-P bonds at moderate and high temperature leads P/Al increase a little and Si/Al increase remarkable. The dissolution of Al-O(H)-Si also damages the framework and reduces the acidity of sample. In addition to the dissolution effect, high temperature (200 C) also leads the re-deposition of Al-rich amorphous or low crystallinity product.

Automated summary

The etching behavior of TEAOH in the post-synthesis of hierarchical SAPO-34 was investigated, and the results showed that the solubility of SAPO-34 decreases while the dissolution rate increases with the raise of temperature. The etching is believed to start with the break of Al-O(H)-Si bond and then break the Al-OH-related Al-O-P bonds and the new exposed inner Al-O(H)-Si bonds. Low-temperature etching favors the dissolution of Al-OH-related Al-O-P bonds and behaves as a layer-to-layer peel-off process, while moderate- and high-temperature etching leads to the formation of abundant mesopores and fragmentation of crystals.