Synthesis Of Cordierite Supported Layered Double Hydroxides-derived CuCoFe Mixed Metal Oxide Catalysts And Their Performance For Simultaneous Removal Of VOCs And NO_x

VOCs and NO_x are the main air pollutants,which cause serious harm to the atmospheric environment and human health.With China’s increasingly strict emission standards for air pollutants,effective control of VOCs and NO_x is required.Especially in many industrial plants（such as chemical plants engaged in the production chemical materials,etc.）,VOCs and NO_x are exist at the same time,therefore,it is very important to simultaneously remove VOCs and NO_x.Catalytic combustion technology is one of the effective ways to remove VOCs.Selective catalytic reduction technology（SCR）can achieve the efficient removal of NO_x.According to the characteristics of chemical plant flue gas components,in this paper,a new type of transition metal oxide catalyst with highly dispersed active components and good thermal stability was obtained by optimizing the metal ion combination of layered double hydroxides（LDHs）for toluene and NO_x remove.Besides,a cordierite supported monolithic catalyst was prepared for practical engineering needs,the removal performance of toluene and NO_x was investigated as well.Firstly,a series of Co Fe-based LDHs with different Co/Fe ratios were synthesized by the co-precipitation method.Co Fe O_x-based LDHs-derived metal oxide powder catalysts were obtained after calcination at certain temperatures.The preferred Co₃Fe₁O_x catalysts calcined at 400℃ reaches 72% conversion of toluene and 30% conversion of nitrogen oxides at 250℃,its activity needs to be further improved.After introduced copper to Co₃Fe₁O_x catalysts,due to the synergistic effect between copper and cobalt,the Cu₁Co₂Fe₁O_x powder catalyst obtained by calcination at 400℃ has 100% toluene conversion and 42% nitrogen oxide conversion at 250℃,and the nitrogen selectivity can reach 95%,showing good catalytic activity.H₂-TPR results indicated the presence of synergetic interaction between cobalt and copper species due to the close contact and good dispersion of the oxide phases.NH₃-TPD analyses show that Cu₁Co₂Fe₁O_x has abundant acid sites.XPS,Raman and ESR analyses demonstrated that Cu₁Co₂Fe₁O_x has much more oxygen vacancies than all other control catalysts.Thus the Cu₁Co₂Fe₁O_x catalyst was found to have higher catalytic activity and excellent thermal stability for simultaneous removal of toluene and NO_x.In order to better meet the actual engineering needs,the optimized Cu₁Co₂Fe₁ LDH is supported on the cordierite honeycomb ceramic carrier by coating method to prepare monolithic catalyst,and the coating process and parameters are optimized.When the mass ratio of water,aluminum sol and LDH is 10/4/2.5 and the coating time is 2,the catalyst showed the best catalytic performance after calcination at400℃,which can achieve 100% conversion of toluene,58%conversion of nitrogen oxide and 94% selectivity to nitrogen at 250℃.When the calcination temperature increased to 600℃,the obtained monolithic catalyst still has 87% toluene conversion and 46% nitrogen oxide conversion at 250℃,indicating that the catalyst has good thermal stability.In addition,the monolithic catalyst prepared after calcination at 400℃ showed good water resistance and durability,the tolueneand NO_x conversion was still 89% and 43%NO_x,respectively,in the presence of 5% H₂O（250℃）.At the same time,there was almost no change in catalytic activity after continuous operation at 250℃ for 30 h.In summary,the monolithic catalyst prepared in this study has good performance and great practical application potential.