Studies on synthesis of a new hexagonal copper aluminophosphate and its catalytic behavior for phenol hydroxylation

A new type of non-soluble copper aluminophosphate (denoted as CuAlPO) was synthesized by static hydrothermal crystallization and characterized by using several physicochemical techniques. XRD analysis reveals that CuAlPO can be obtained from a reactive gel of molar composition: iso-Pr₂NH:0.3CuO : 0.7Al₂O₃-P₂O₅ : 80H₂O in a Teflon-lined stainless steel autoclave at 180°C for 72 h and has the same crystal structure as that of hexagonal SiO₂ (JCPDS No. 83-2299). The sources of CuO, Al₂O₃ and P₂O₅ were copper sulfate pentahydrate, aluminum isopropoxide and o-phosphoric acid (mass fraction: 85%), respectively. SEM shows a characteristic hexagonal morphology and a crystallite size of about 2 μm for both the as-synthesized CuAlPO and the calcined CuAlPO (550°C, 6 h). Low specific surface area (2.0 m²/g) and pore volume (0.004 mL/g) of CuAlPO were observed by N₂-adsorption measurement. Catalytic evaluation tests demonstrate that an excellent transformation of phenol into catechol and hydroquinone over the material was achieved in water under the benign reaction conditions with a phenol conversion of 29.5% being observed at room temperature (30°C).