The Study On The Influences Of Continuous Flow Co-precipitation Co-precipitation Process On TheCu-ZnO Microstructure Evolution Process

Methanol is important foundational chemical material and the catalytic technology of industrial methanol production commonly adapts syngas as the raw material. At present stage, Cu-ZnO based catalysts prepared by co-precipitation method are widely used in gas-solid system and gas-liquid-solid system. The co-precipitation process of Cu²⁺, Zn²⁺ is very fast which is seriously affected by the mixing process of reagents. For the classic co-precipitation process occurred in traditional stirred tank reactor, the complex flow pattern and severe back-mixing phenomenon inside the reactor make the microstructure of precipitates very difficult to depict. In this paper, we adapt microchannel reactor to prepare Cu-ZnO catalyst and utilize its simple flow pattern to obtain precipitates with relatively pure microstructure.Firstly we adapted several characterization methods such as XRD, DTG, HRTEM, XPS and N₂O-chemisorption to study the evolution process and microstructure characters of inititial precipitates prepared by microchannel reactor. The results indicated that to some extent the excellent mixing performance of microchannel reactor can allivate and eliminate the inconsistency of precipitation process in time and space, as a result, the distribution of Cu, Zn elements in the obtaind initial precipitates is more homogenous. As can be seen from the XRD pattern, in the ageing process the more homogenous distribution of Cu, Zn elments can lead more Zn²⁺ incorporated into malachite structure and the average content of Zn²⁺ in zinc malachite is higher. Desmonstrated by the DTG and XPS characterization methods, higher decomposion temperature of carbonate species and higher binding energy of Cu2p3/2 indicate that the samples prepared by microchannel reactor possed a stronger interface interaction and more intimate contact between Cu, Zn components. This supposition was directly confirmed by the HRTEM images. After the reduction step, due to the stronger interaction between components, the activity of per unit active copper was substantially enhanced. As a result, the catalysts prepared by microchannel reactor exhibited higher catalytic performance though the copper surface area is lower.In the following sections, we carried out an in-depth reaserch on the influences of the operation factors including the ratio of Cu/Zn, ageing time, ageing temperature, precipitation pH on the microstructure and catalytic performance of catalysts prepared by microchannel reactor. The results demonstrated that the Cu/Zn ratios had a direct impact on the category and structure of precursors. The catalysts derived from zincian malachite precursor improved the catalytic performance by enlarge the Cu surface area. With respect to the catalysts derived from aurichalcite, the intrinsic activity and methanol yield were improved due to the stronger interaction between components; Choosing the suitable ageing time and temperture, precipitation pH is favorable for the incorporation process of Zn²⁺, and then enhanced the interaction between copper and zinc components and improved the methanol activity. Besides, in our paper we found that the addition of Al components is helpful for enhancing the activity and thermostabilty of Cu-ZnO catalysts.