Abstract
A catalyst preparation method, consisting of slurry washcoating with γ-Al2O3 followed by impregnating platinum on the microreactor walls, has been investigated. The effect of various factors in the preparation procedures on the adhesion of the washcoated γ-Al2O3 was studied, including the slurry property (i.e., the binder type, concentration and molecular weight, γ-Al2O3 concentration and particle size, pH), and the (micro)reactor substrate and channel shape. The results show that the adhesion of γ-Al2O3 washcoat strongly depended on the slurry rheological characteristics. A good adhesion on FeCrAlloy substrates was obtained using the slurry with polyvinyl alcohol as the binder (typical concentration at 3–5 wt% and molecular weight of 57,000–186,000), 20 wt% γ-Al2O3 (particle size being around 3 µm) and pH = 3.5. FeCrAlloy as the substrate exhibited an excellent coating adhesion in rectangular or round channels, primarily due to the formation of alumina film over the surface during thermal pretreatment. The aluminum-free stainless steel as the substrate only showed a good adhesion in a round channel. Well-adhered Pt/γ-Al2O3 catalysts were then applied in a microreactor comprising parallelized microchannels made of FeCrAlloy under the optimized coating procedures, and investigated in terms of its performance in the catalytic methane combustion. It is shown that the reaction temperature has a greater influence on the methane conversion than the flow rate, and a favorable coverage of methane and oxygen on the catalyst surface is essential to obtain a good catalytic performance. These reaction results are in line with the temperature behavior measured along the microreactor.
Highlights
Microreactors, with characteristic channel dimensions on the order of ca. 1 mm or below, have shown great potentials in intensifying reaction processes in comparison to conventional reactors [1,2,3]
A good adhesion on FeCrAlloy substrates was obtained using the slurry with polyvinyl alcohol as the binder, 20 wt% γ-Al2O3 and pH = 3.5
Well-adhered and stable washcoated layers were obtained on the parallel microchannels of the platelets by employing polyvinyl alcohol (PVA) or Tylose as the binder
Summary
Microreactors, with characteristic channel dimensions on the order of ca. 1 mm or below, have shown great potentials in intensifying reaction processes in comparison to conventional reactors (e.g. fixed-bed reactors for solid-catalyzed gas phase and multiphase reactions) [1,2,3]. The specific surface area of microreactors could reach 10,000 to 50,000 m2 m−3 [4,5], compared to around 100 m2 m−3 for traditional reactors, thereby leading to substantially enhanced mass and heat transfer rates [6,7]. The improved mass transfer can lead to enhanced reaction rates (e.g., in the presence of multiphase fluids or solid catalysts). The heat transfer enhancement avoids the presence of temperature hot spots due to the local accumulation of reaction heat in the microreactor, a feature especially favorable for handling strongly exothermic reactions or coupled exothermic and endothermic catalytic reactions [8]. The modular, flexible and compact microreactor design allows an easy upscaling from the laboratory to the industrial scale aiming at mass production [4]. One challenge is how to Nomenclature dC FCH4,i FCH4,o FCOx,o
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