(240b) Supported Gold Catalysts for CO Oxidation in Microchannel Reactors

The use of renewable sources to produce hydrogen that will feed fuel cells requires the oxidation of the produced CO during the reforming process in order to avoid catalyst poisoning. Water-gas-shift and CO oxidation reactions take care of reducing the CO concentration at the reformer-outlet to acceptable levels for the fuel cell (below 10 ppm). Besides this, miniaturization and the requirements for portable devices (cell phones, lap tops, ?) have pushed the research on microchannel catalytic reactors for these reactions. Gold catalysts are highly active and selective in low temperature CO oxidation and WGS reactions. Gold activity depends on the size and shape of gold particles , the gold oxidation state and nature of the support , , , , which have been classified as inert (Al2O3, SiO2, MgO) or active ones (Fe2O3, CeO2, MnO2) in function of their reducibility . When using a catalytic microreactor both the activity and selectivity of the catalyst as well as the reactivity of the metallic alloy in the reaction atmosphere may determine the life cycle of the catalytic device. In this work we study the oxidation of CO over CeO2 and MnO2 (cryptomelane) supported gold deposited on microchannels built on austenitic (AISI 304) and aluminium-alloyed ferritic (FeCrAlloy) stainless steels. In this way we test the chemical compatibility between the oxides forming the steel scale and the catalytic deposits as well as the possible modifications induced in the catalytic performances due to the steel nature. The catalytic results obtained in the microchannel device are compared with the ones obtained for the un-deposited powders. Two catalysts have been prepared (1%Au/CeO2 and 1% Au/cryptomelane) and microchannel reactors built from AISI 304 and FeCrAlloy sheets coated and tested in CO oxidation and WGS reactions. The powders catalysts, and the fresh and reacted monoliths devices have been characterised. The coated microchannel reactors were characterised by BET, XRD, TEM and adherence tests. The 1%Au/CeO2 catalyst results in total CO oxidation conversion at lower temperatures than 1%Au/cryptomelane. However, at room temperature, the Au/cryptomelane catalyst shows higher conversion than the Au/CeO2 solid. Moreover, differences of behaviour were detected for the 1%Au/cryptomelane in successive cycles of reaction, which has been attributed to structural effects.

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