Effect of water layer on Cu-Zn co-precipitation in microreactor
(2.State Key Laboratory of Industrial Control Technology, Department of Control Science and Engineering, Zhejiang University, Hangzhou, Zhejiang, China 310027)
【Abstract】A method aiming to prepare more uniform Cu-Zn co-precipitate by coupling of diffusion and reaction process was probed in this article and Cu/ZnO co-precipitated catalysts with high catalytic activity were prepared by introducing water layer into the microreactor and adjusting the ratio of water layer to the total flow. The microstructures and evolution process of the catalysts were analyzed by HRTEM/EDS, X-ray diffraction (XRD), thermogravimetric analysis (TG), hydrogen temperature-programmed reduction (H2-TPR), and N2O chemical reaction methods. The results show that as the proportion of water layer increases, the Cu-Zn distribution of the initial precipitate is more uniform; zinc content in the precursor obtained by the aging is increased; the contact area of the oxides CuO and ZnO is increased; and the interaction force is continuously enhanced. Therefore, larger contact area between calcined oxides CuO and ZnO was achieved, leading to better dispersibility and stronger interaction, with the final catalytic activity of the catalyst significantly enhanced. Numerical analysis based on the model established by MATLAB revealed that the uniformity caused by slower reaction rate of Zn2+ can be neutralized by faster diffusion rate of its own. The diffusion–reaction equilibrium region, defined as capable to obtain uniform precipitate, was enlarged with the increasing ratio of water layer and larger proportion of uniform precipitate was achieved simultaneously.
【Keywords】 microreactor; co-precipitation; microstructure; model; numerical simulation; Cu-Zn distribution; diffusion–reaction equilibrium;
(Translated by WANG YX)
 REICHENBACH T, MONDAL K, JAGER M, et al. Ab initio study of CO2 hydrogenation mechanisms on inverse ZnO/Cu catalysts [J]. Journal of Catalysis, 2018, 360: 168–174.
 WENZE L, PENG L, DING X, et al. CO2 hydrogenation to methanol over Cu/ZnO catalysts synthesized via a facile solid-phase grinding process using oxalic acid [J]. Korean J. Chem. Eng., 2018, 35(1): 110–117.
 SALEHIRAD A, LATIFI S M. Effect of synthesis method on physicochemical and catalytic properties of Cu-Zn-based mesoporous nanocatalysts for water-gas shift reaction [J]. Research on Chemical Intermediates, 2017, 43(7): 3633–3649.
 JEONG Y, KANG J Y, KIM I, et al. Preparation of Cu/ZnO catalyst using a polyol method for alcohol-assisted low temperature methanol synthesis from syngas [J]. Korean J. Chem. Eng., 2016, 33(1): 114–119.
 CHEN Y P, JIANG X, LU J G. Effects of reaction progress in microchannel on microstructure of Cu-Zn catalyst [J]. CIESC Journal, 2015, 66(10): 3895–3902 (in Chinese).
 SHYAM K, PEDRO J R, JINGGUANG G C, et al. Active sites for CO2 hydrogenation to methanol on Cu/ZnO catalysts [J]. Science, 2017, 355: 1296–1299.
 ZHANG B, CHEN Y, LI J, et al. High efficiency Cu-ZnO hydrogenation catalyst:the tailoring of Cu-ZnO interface sites by molecular layer deposition [J]. ACS Catalysis, 2015, 5(9): 5567–5573.
 KULD S, THORHAUGE M, FALSIG H, et al. Quantifying the promotion of Cu catalysts by ZnO for methanol synthesis [J]. Science, 2016, 352(6288): 969–974.
 ÁLVAREZ G C, SCHUMANN J, BEHRENS M, et al. Reverse watergas shift reaction at the Cu/ZnO interface: influence of the Cu/Zn ratio on structure-activity correlations [J]. Applied Catalysis B: Environmental, 2016, 195: 104–111.
 BEHRENS M, SCHLÖGL R. How to prepare a good Cu/ZnO catalyst or the role of solid state chemistry for the synthesis of nanostructured catalysts [J]. Z. Anorg. Allg. Chem., 2013, 639(15): 2683–2695.
 BEMS B, SCHUR M, DASSENOY A, et al. Relations between synthesis and microstructural properties of copper/zinc hydroxycarbonates [J]. Chemistry-A European Journal, 2003, 9(9): 2039–2052.
 BEHRENS M, BRENNECKE D, GIRGSDIES F, et al. Understanding the complexity of a catalyst synthesis: co-precipitation of mixed Cu, Zn, Al hydroxycarbonate precursors for Cu/ZnO/Al2O3 catalysts investigated by titration experiments [J]. Applied Catalysis A: General, 2011, 392(1/2): 93–102.
 JIANG X, ZHENG L, LU J G, et al. Microstructure characters of Cu/ZnO catalyst precipitated inside microchannel reactor [J]. Journal of Molecular Catalysis A: Chemical, 2016, 423: 457–462.
 ANGELO L, GIRLEANU M, ERSEN O, et al. Catalyst synthesis by continuous coprecipitation under micro-fluidic conditions: application to the preparation of catalysts for methanol synthesis from CO2/H2 [J]. Catalysis Today, 2016, 270: 59–67.
 MICHAEL S, BETTINA B, ALINA D, et al. Continuous coprecipitation of catalysts in a micromixer:nanostructured Cu/ZnO composite for the synthesis of methanol [J]. Angew. Chem. Int. Ed., 2013, 42: 3815–3817.
 SIMSON G, PRASETYO E, REINER S, et al. Continuous precipitation of Cu/ZnO/Al2O3 catalysts for methanol synthesis in microstructured reactors with alternative precipitating agents [J]. Applied Catalysis A: General, 2013, 450: 1–12.
 JIANG X, QIN X F, LING C, et al. The effect of mixing on coprecipitation and evolution of microstructure of Cu-ZnO catalyst [J]. AIChE Journal, 2018, 64(7): 2647–2654.
 LING C, JIANG X, LU J G, et al. Influence of mixing inside microreactor on microstructural evolution of Cu-ZnO catalyst [J]. CIESC Journal, 2018, 69(2): 718–724 (in Chinese).
 PAWEŁK, KATARZYNA A-J, WIESŁAW P, et al. The evaluation of synthesis route impact on structure, morphology and LT-WGS activity of Cu/ZnO/Al2O3 catalysts [J]. Catal. Lett., 2017, 147: 1422–1433.
 ZANDER S, SEIDLHOFER B, BEHRENS M. In situ EDXRD study of the chemistry of aging of co-precipitated mixed Cu, Zn hydroxycarbonates-consequences for the preparation of Cu/ZnO catalysts [J]. Dalton Transactions, 2012, 41(43): 13413–13422.
 DAVID M W, ALI A M, JUSTIN S J H. Co-precipitated copper zinc oxide catalysts for ambient temperature carbon monoxide oxidation: effect of precipitate ageing on catalyst activity [J]. Phys. Chem. Chem. Phys., 2002, 4: 5915–5920.
 BALTES C, VUKOJEVI´C S, SCHÜTH F. Correlations between synthesis, precursor, and catalyst structure and activity of a large set of CuO/ZnO/Al2O3 catalysts for methanol synthesis[J]. Journal of Catalysis, 2008, 258: 334–344.
 LI J L, INUI T. Characterization of precursors of methanol synthesis catalysts, copper/zinc/aluminum oxides, precipitated at different pHs and temperatures [J]. Applied Catalysis A: General, 1996, 137(1): 105–117.
 WANG D J, TAO F R, ZHAO H H, et al. Preparation of Cu/ZnO/Al2O3 catalyst for CO2 hydrogenation to methanol by CO2 assisted aging [J]. Chinese Journal of Catalysis, 2011, 32(9/10): 1452–1456.
 JAMES G S. Lange’s Handbook of Chemistry [M]. 6th ed. America: Mc Graw-Hill Companies, Inc., 334–352.
 BEHRENS M, GIRGSDIES F. Structural effects of Cu/Zn substitution in the Malachite-Rosasite system [J]. Zeitschrift für anorganische und allgemeine Chemie, 2010, 636(6): 919–927.
 KÜHL S, FRIEDRICH M, ARMBRÜSTER M, et al. Cu, Zn, Al layered double hydroxides as precursors for copper catalysts in methanol steam reforming-pH-controlled synthesis by microemulsion technique [J]. Journal of Materials Chemistry, 2012, 22(19): 9632.
 MIAO S, D'ALNONCOURT R N, REINECKE T, et al. A study of the influence of composition on the microstructural properties of ZnO/Al2O3 mixed oxides [J]. European Journal of Inorganic Chemistry, 2009, 2009(7): 910–921.
 ROBINSON W, MOL J. Support effects in methanol synthesis over copper-containing catalysts [J]. Applied Catalysis, 1991, 76: 117–129.
 FIERRO G, LO J M, INVERSI M, et al. Study of the reducibility of copper in CuO-ZnO catalysts by temperature-programmed reduction [J]. Applied Catalysis A: General, 1996, 137(2): 327–348.
 LUO G S, WANG K, LÜY C, et al. Research and development of micro-scale multiphase reaction processes [J]. CIESC Journal, 2013, 64(1): 165–172 (in Chinese).
 CHEN G W, ZHAO Y C, LE J, et al. Transport phenomena in microchemical engineering [J]. CIESC Journal, 2013, 64(1): 63–75 (in Chinese).