Microwave-assisted synthesis of [Cr]APO-5

The synthesis of the chromium-substituted aluminophosphate [Cr]APO-5 (AFI) using microwave irradiation was investigated systematically. The prepared materials were characterized by chemical analysis (ICP-AES), XRD, SEM, DR–UV–Vis spectroscopy, and sorption of different probe molecules, i.e., water, benzene, and nitrogen. Stable chromium incorporation into the AFI-framework can be achieved up to a chromium content of at least 3.2 mol% (5.6 wt.%). Besides the content of chromium and water, the nature and content of co-templates such as acetic acid or ethylene glycol in the gel for the microwave-assisted synthesis were varied. The concentration of the co-template is a key factor for successful [Cr]APO-5 synthesis. The microwave-assisted crystallization of [Cr]APO-5 was completed within 30 min whereas the conventional hydrothermal crystallization took at least 6 h for completion. Nevertheless, the yields and quality of [Cr]APO-5 obtained from hydrothermal and microwave-assisted synthesis are comparable.