The preparation of a catalyst doped with Cu and Al on MCM-41 and its catalytic reduction removal of dissolved oxygen in reclaimed water at low temperatures

Abstract

Dissolved oxygen (DO) is a primary corrosive substance in the transportation process of urban reclaimed water by pipelines. MCM-41 is widely used as a catalyst carrier because of its high specific surface area and low mass transfer resistance. The catalyst, namely Cu/Al-MCM-41 was prepared by doping Cu and Al in MCM-41 using one-step hydrothermal method and was used to catalyze reducing DO in reclaimed water by carbohydrazide. The effects of reaction temperature, the mass concentration of carbohydrazide, the initial pH value of water, and the mass concentration of catalyst on the removal rate of DO from reclaimed water were investigated in this paper. The reusability and catalytic mechanism of Cu/Al-MCM-41, the fresh catalyst, were determined and the used catalyst was characterized by XRD, FTIR, SEM, NH₃-TPD, and BET methods. It was concluded that Cu and Al were successfully doped into MCM-41, and the synthesized molecular sieves had a highly ordered hexagonal mesoporous structure. Moreover, the doping of Al metal into MCM-41 improved the acid strength and acid centers significantly. The DO removal rate could reach 98.54% under the temperature of 45 °C, which is 3 times the theoretical feed amount of carbohydrazide, at the initial pH value of 8.5 and the mass concentration of 0.7 g L⁻¹ of the catalyst after 60 min. The Cu/Al-MCM-41 catalyst still showed high catalytic activity after three tests. The active metal Cu could catalyze the decomposition of carbohydrazide into carbon dioxide, nitrogen, and hydrogen atoms The increase of hydrogen atom concentration adsorbed on the catalyst surface led to the rapid reduction of DO.