Effect of calcination temperature on the structure and catalytic performance of copper–ceria mixed oxide catalysts in phenol hydroxylation

Abstract

We report on highly active CuO@CeO₂ catalysts prepared by the surfactant-template method and calcined at different temperatures. Then the obtained catalysts were characterized by means of various analytical techniques. Our findings show that the BET surface area and pore volume of the CuO@CeO₂ catalyst measured by N₂ adsorption–desorption are decreasing with the elevation of calcination temperature. From the results of XRD and XPS, we determined the oxidation state of copper in the copper–ceria mixed oxide catalysts. The CuO@CeO₂ catalysts displayed good catalytic activity for the phenol hydroxylation using H₂O₂ as an oxidant. Moreover, we found that the catalytic activity is improved for high calcining temperature and the optimum conditions were obtained when the catalyst CuO@CeO₂ is calcined at 800 °C, which lead to higher phenol conversion of 54.62% with 92.87% of selectivity for catechol and hydroquinone. More importantly, the catalyst seems to be easily recovered by simple centrifugation. The results of catalyst recycling illustrated that the catalytic activity remained high even after five cycles with slight Cu leaching and slight loss of activity. Finally, a possible mechanism in phenol hydroxylation by H₂O₂ over CuO@CeO₂ catalyst was also proposed.