Comparative evaluation of synthesis routes of Cu/zeolite Y catalysts for catalytic wet peroxide oxidation of quinoline in fixed-bed reactor

Abstract

In order to find a better alternative of conventional aqueous ion-exchange method, several Cu/zeolite Y samples were synthesized by different routes and examined for the catalytic wet peroxide oxidation of quinoline aqueous solution in continuous fixed-bed reactor. The characterization of catalysts using ICPMS, XRD, N2 sorption, UV–vis DRS, FESEM and XPS techniques reveals the profound influence of preparation methods on synergy between copper-support interfaces. Aqueous ion-exchange (CuYAIE) and wet-impregnation (CuYIMP) methods promoted isolated Cu1+/2+ species; however, large crystallites of CuO were present on the external surface of precipitation-impregnation (CuYPI) catalyst. Interestingly, CuYPI showed hierarchical porosity and increase of surface area from 567 to 909 m2 g−1. The generation of mesoporosity in CuYPI was result of higher desilication from zeolite framework due to synergetic effect of copper and NaOH. Almost comparable mineralization (61–65%) and H2O2 stoichiometric efficiencies (44.2–45.7%) were observed for CuYAIE and CuYIMP samples. Higher catalytic activities of both catalysts in comparison to CuYPI suggest that isolated sites are the most redox-active sites for H2O2 activation and play more important role than high surface area, i.e., for CuYPI. Wet-impregnation was found better than aqueous ion-exchange method. CuYIMP exhibited high operation stability with >60% mineralization at LHSV = 4 h−1, particle size = 1.2–1.7 mm, H2O2/quinoline = 48 and T = 80 °C. Copper leaching was majorly influenced by LHSV and particle size. The system was following Eley-Rideal mechanism and kinetic parameters were calculated using model based on this mechanism.