Abstract
A microfluidic reactor enabled continuous co-precipitation synthesis of CuO/ZnO/Al2O3 catalysts for methanol production.
Highlights
Temperature programmed reduction in H2 (H2-temperature programmed reduction (TPR)) and Chemisorption For chemisorption analysis, a Micromeritics AutoChem 2950 HP equipped with a thermal conductivity detector (TCD) and an MKS Cirrus 2 mass spectrometer (MS) was used. 160 mg of a sample were placed in a U-shaped quartz glass reactor between two quartz wool plugs
Comparison of Cu/ZnO/(Al2O3) produced in the microfluidic and batch reactor The ternary Cu,Zn,(Al) hydroxycarbonate precursor materials were co-precipitated at constant pH in the magnetically stirred-batch reactor and the microfluidic reactor and after ageing, washing and drying, analyzed by Xray diffraction (XRD)
The results show that Cu/ZnO/Al2O3-microfluidically synthesized sample (MF) in pure CO synthesis gas feed yields dimethyl ether (DME) with selectivity of 14.1 % at 230 °C and 16.9 % at 250 °C
Summary
Methanol (MeOH) is an essential industrial bulk chemical but can be used as fuel additive or precursor for clean fuels.[1,2,3,4] Due to its high energy density methanol plays an important role in chemical energy and hydrogen storage including fuel-cell applications.[5,6,7,8] The most prominent catalytic system for industrial methanol synthesis since decades is based on Cu/ZnO/(Al2O3) and enormous efforts have been dedicated to the enhancement of its catalytic activity based on rational design via different preparation methods.[3, 5, 9,10,11,12,13,14,15,16,17,18,19] One widely applied method for the synthesis of Cu/ZnO/(Al2O3) is co-precipitation of soluble copper, zinc and aluminum precursors using e.g. sodium carbonate.[9, 20,21,22] Specific synthesis parameters such as pH, temperature, ageing time and mixing conditions play key roles in the resulting catalytic performance.[5, 9, 21, 23] Fundamental studies in this field e.g. by Behrens et al.[20] show that co-precipitation temperature between 60 °C and 70 °C and pH values between 6-7 as well as the ageing time and temperature are crucial to achieve optimum material properties. In the last decade, micromixing techniques have been increasingly applied for precipitation reactions.[26, 27, 29, 32] Advanced micromixing devices such as microfluidic reactors, T-mixers and confined impinging jet reactors are designed for fast and homogeneous mixing based on high mass transfer and short residence time.[27,28,29] In earlier studies, we used a novel microfluidic reactor especially designed for X-ray spectroscopic in situ studies to investigate colloidal noble metal NP formation during fast reduction reactions, focusing on the critical early stages of the process.[33,34,35,36] The experiments described here aimed at extending the application range of this type of microfluidic device towards coprecipitation reactions, focusing on Cu/ZnO/Al2O3 catalysts for methanol synthesis as a case study For this purpose, two streams of the reactants were injected separately into the micromixers integrated in the microfluidic chip. Cu/ZnO and Cu/ZnO/Al2O3 catalysts from conventional batch synthesis under conditions adopted from the literature were characterized and tested in order to illustrate potential advantages of microfluidic mixing during co-precipitation
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