Preparation of Pt/γ-Al2O3 catalyst coating in microreactors for catalytic methane combustion

A catalyst preparation method, consisting of slurry washcoating with gamma-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 gamma-Al2O3 was studied, including the slurry property (i.e., the binder type, concentration and molecular weight, gamma-Al2O3 concentration and particle size, pH), and the (micro)reactor substrate and channel shape. The results show that the adhesion of gamma-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% gamma-Al2O3 (particle size being around 3 mu m) 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/gamma-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.