The Influence Of Mixing Process On The Structure And Its Evolution Process Of Cu-ZnO Catalyst Precursor

As the most widely used industrial catalyst in the synthesis of methanol with the syngas,the Cu-based catalyst is usually prepared by traditional co-precipitation method.For the stirred tank reactor used in the co-precipitation,there is a big difference in the spatial distribution of mixing strength and the back-mixing is always serious.The precipitation reaction of Cue+ and Zn2+ belong to a rapid reaction,which is seriously affected by the mixing of process of reagents.In this paper,we try to explore the the effect of the mixing process on the evolution and catalytic activity of the Cu-based catalyst and how the difference in this structure affects the heat decomposition process by changing the flow rate of the solution in the microchannel reactor and comparing with the traditional co-precipitation method.The iodine-iodate research system is used in the paper and we found that the mixing time of the microchannel reactor is mainly in the range of 0.11s-0.1s,which indicates that the mixing effect of the microchannel reactor is stronger than that of the traditional batch reactor.Then,it is pointed out that the mixing strength in the precipitation reaction process is critical to the formation of the catalyst structure of precursors according to the study on the structure and the subsequent evolution process of the precursors prepared from different preparation methods.The targeted experiments are designed in the stirred tank reactor and micro-channel reactor to verify the above view.The main conclusions are as follows:In the process of precipitation,the precursors with a homogeneous Cu-Zn distribution are easy to form after the mixing strength is improved(the mixing time decreases)whose main structure is zincian malachite with high zinc content and uniform Cu-Zn distribution.On the contrary,the zinc content of the zincian malachite is lower and the distribution is uneven when the mixing intensity is low which is easy to lead the formation of aurichalcite and the deviation of Cu/Zn ration with that of raw material.As a result,the uneven distribution in the precursor will aggravate the de-mixing of the CuO and ZnO which will leads to form evident CuO and ZnO particles showed in HRTEM photos of samples prepared by traditional co-precipitation.The de-mixing will not produce larger particles during the thermal decomposition process when the Cu-Zn distribution in the precursors is homogenous according to the analysis of the fact that there is no large particles found in the samples prepared by microchannel reactor.The result of the comparative experiment break through the opinion that the occurrence of large particles is due to the thermodynamic instability and indicate that the non-uniform of precursors is also one of the necessary conditions for the generation of large particles and reveals the mechanism of the precursor structure acting on the catalyst structure evolution process.Demonstrated by the XRD,DTG,XPS and H2-TPR characterization methods,the homogenous precursor possess good dispersion,more Cu-Zn interface and stronger Cu-Zn interaction during the thermal decomposition process,which is favorable for the improvement of catalytic activity.