Study On Preparation Of Cu-Mn Catalyst In Microreactor

Cu-Mn catalysts have high activity in the treatment of volatile organic compounds（VOCs）,and coprecipitation is one of the common methods for preparing Cu-Mn catalysts.The microreactor has the characteristics of rapid mixing and homogeneous reaction process,and can regulate the structure of coprecipitate well,which has unique advantages in studying the structure-activity relationship of Cu-Mn catalyst.In this paper,the microreactor preparation process was used to study the changes in the structure of Cu-Mn precipitates and Cu-Mn catalysts during mixing and aging processes,and to investigate the effect of Cu-Mn catalysts on the oxidative degradation of toluene.By reducing the aging temperature and slowing down the aging rate,the structural changes of Cu-Mn precipitates during the aging process were investigated.TG and XRD analysis show that the homogeneous initial precipitate composed of basic copper carbonate and manganese carbonate separates Cu and Mn at the early aging stage due to the rapid crystallization of MnCO₃.With the aging process,Cu²⁺gradually enters the MnCO₃ lattice to form Cu-Mn composite carbonate,and the distribution of Cu-Mn gradually becomes uniform.The Pearson correlation coefficient obtained by EDS line scanning verifies the uniformity of Cu-Mn.Raman spectrometric analysis showed that the uniform distribution of Cu and Mn in the precursor was conducive to enhancing the interaction between the two elements in the catalyst after calcination,thus improving the catalytic activity.Therefore,the high activity catalyst can be obtained by direct calcination of the unaged precipitates.The effect of mixing on the preparation of Cu-Mn catalyst was studied by changing the microreactor configuration and volume flow rate in the reactor.In the three microreactor experiments,with the increase of volume flow rate and mixing strength,the Cu-Mn interaction was enhanced,and the Cu-Mn catalyst activity was increased.XPS analysis showed that Mn³⁺/Mn⁴⁺ and O_latt/O_ads increased with the increase of volume flow rate,which was consistent with the change of catalytic activity,indicating that Mn³⁺and O_latt were important factors affecting catalytic activity.Cu and Mn feeding methods were used to offset the difference in precipitation rate between Mn²⁺ and Cu²⁺,and to explore the preparation of more uniform coprecipitates.The toluene catalytic activity of Cu-Mn catalyst increases first and then decreases with the increase of the length between the two feed ports under the condition of advanced Mn feed.The activity of catalyst S-7.0 was the best,and T₉₀=188.1℃,which was better than that of other catalysts prepared by microreactors.The decomposition temperature,Mn³⁺/Mn⁴⁺and O_latt/O_ads obtained by XPS analysis,and the offset of scattering peak at about 642 cm^-1 in Raman spectra all increased first and then decreased with the increase of the distance between the two feed ports,indicating that the dispersion of Cu-Mn in S-7.0 sample is the best.Cu-Mn interaction is the strongest.These results show that the coprecipitates can be prepared by successive feeding,and the catalysts with high activity can be obtained.