Copper-based catalysts supported on novel Metal-Organic Framework MIL-125(Ti) for selective catalytic reduction of NO with CO

A type of novel copper-based catalysts supported on MIL-125(Ti), a kind of metal–organic frameworks (MOFs), noted as Cu-MIL-125(Ti), was synthesized for the selective catalytic reduction (SCR) of NO with CO. The reactivity of Cu-MIL-125 catalysts for selective catalytic reduction of NO by CO (SCR-CO) was evaluated in a fixed bed reactor. A number of characterization techniques were used to explore the basic physical–chemical properties and the reaction mechanism. The results showed that the large specific surface area and micro-mesopores of the MIL-125 carrier promoted the high dispersion of Cu species, leading to the outstanding SCR-CO performance. Among the results, 90 % NO conversion and 92 % N2 selectivity were proved for the 6.2Cu-MIL-125 catalyst at 325 °C in oxygen-rich environment. XRD results showed that the metal organic frame structure and TiO2 structure coexisted in the catalysts, which was the major factor to influence the NO reduction efficiency. XPS characterization and H2-TPR reduction results showed that the catalytic performance of the catalyst was mainly determined by the path of Cu2+ reduction to Cu+ and then Cu+ to Cu0. Lewis acid on the catalyst surface played an important role in the CO-SCR reaction. In situ DRIFTS study proved that NO was first adsorbed on the surface of the catalyst to form different nitrate, NCO and isocyanate species. Then the adsorbed NO and the intermediates reacted with gaseous CO, which is a typical interaction between adsorbed molecules and gas molecules. Oxygen vacancies on the catalyst surface was involved in the reaction of CO to CO2. The whole reaction follows the M–K mechanism and the E-R mechanism. A preliminary reaction pathway was proposed based on the in situ DRIFTS results.