A novel catalyst of copper hydroxyphosphate (Cu₂(OH)PO₄) with high activity in hydroxylation of phenol by hydrogen peroxide

A novel catalyst of copper hydroxyphosphate (Cu₂(OH)PO₄) that has not microporous and mesoporous pores (surface area <0.01 m²/g) has been successfully synthesized from hydrothermal method by using ethylenediamine, phosphoric acid, and copper acetate. Catalytic data in hydroxylation of phenol by hydrogen peroxide as a model reaction for oxidation catalysis showed that the copper hydroxyphosphate is very active catalyst, and its activity is even higher than that of microporous TS-1 catalyst that is known as one of the most effective catalysts. Furthermore, we observed that the Cu₂(OH)PO₄ catalyst is readily regenerable to its active state by recalcining the expired form in air. Comparison of various catalysts suggests that the unusual catalytic activity on the Cu₂(OH)PO₄ catalyst may be related to unique structure of as-synthesized Cu₂(OH)PO₄. Characterization of catalytic process by ESR method gives very strong signals assigned to radical ·OH species, showing their possible catalytic mechanism.