Replacement of noble metal catalysts by CuMnO/CeO/CH catalyst in catalytic combustion of toluene.

To verify the feasibility of replacing noble metal catalysts by transition metals-based catalysts, monolithic CuMnO/CeO/cordierite honeycomb (CH) catalysts were prepared by conventional impregnation method and applied in microwave catalytic combustion of toluene. The research suggested that CuMnO/CeO/CH catalysts, demonstrated strong microwave-absorbing ability due to first dielectric loss and secondary magnetic loss, exhibited higher catalytic activities under microwave heating than electric heating. This is probably attributed to high temperature "hot spots" of microwave, the abundant pore structure of active particles of CuMnO/CeO/CH catalyst, and oxygen vacancies and O on the catalysts' surface. The research also suggested that under the conditions of an initial toluene concentration of 1500 mg m, airflow of 0.18 m³ h and gas hourly space velocity of 7000 h, toluene could be completely removed at a relatively low temperature of 276 °C and mineralized at 304 °C by microwave catalytic combustion. Compared with noble metal catalysts, CuMnO/0.03CeO/CH catalyst had a lower light-off temperature and nearly complete combustion temperature for toluene removal and mineralization under microwave heating, which confirms the possibility of replacing noble metal catalysts. Moreover, CuMnO/0.03CeO/CH catalyst exhibited excellent stability at a bed temperature of 300 ℃ after six cycles of a total of 960 min and achieved a 100 % removal and 94 % mineralization of toluene. This study also identified the key mechanism behind which is the electron transfers among Cu/Cu, Mn/Mn/Mn, and Ce/Ce that promoted the adsorption, activation, and transformation of gaseous oxygen. Hence, toluene is firstly adsorbed by active particles and then oxidized onto the hot spots by both O and O which follows the L-H mechanism and the MvK mechanism, respectively. Therefore, this research work provides further technological support for the development of transition metals-based catalysts and the application of microwave catalytic combustion in treating industrial VOCs waste gas.