Preferential oxidation of carbon monoxide on supported gold catalystsстатья
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Дата последнего поиска статьи во внешних источниках: 7 декабря 2016 г.
Аннотация:Catalyst precursors containing 1% Au were synthesized by the impregnation of Al2O3 and CeO2-Al2O3 supports with an aqueous solution of HAuCl4 followed by drying, treatment with aqueous ammonia for the removal of chlorine residues, and final drying at 90°C. The oxidation of CO in gas containing ∼1 vol % O2, ∼1 vol % CO, 60 vol % H2, and the balance N2 on the activated catalysts was studied. In a number of experiments, to 18 vol % water was added to the gas mixture. The activation of precursors by the initial gas was studied. It was found that the prolonged storage of a precursor in air made its activation difficult to perform. The 1%Au/Al2O3 catalyst activated by the gas mixture stably operated in the preferential oxidation of CO at room temperature with the occurrence of the reaction in the mode of catalyst surface ignition (a hot spot at the bed inlet) under a change in the feed gas flow rate by a factor of 3. The effect of the presence of additional CO2 (to 39 vol %) on the oxidation of H2 was studied: the catalyst activity decreased. Because the reaction of CO2 reduction to CO did not occur, the effect can be due to the adsorption of CO2 on gold. The effect of the addition of water vapor to the feed gas was studied with the use of 1%Au/CeO2-Al2O3 as an example. The exo/endo effects related to the adsorption/desorption of water on the catalyst surface were detected upon steam supply and shutoff at a bed temperature of 100–150°C. It was noted that the addition of water vapor to a certain level favorably affected the selectivity (decreased the residual concentration of CO). The boundary water concentration, at which the effect became negative, depended on catalyst bed temperature. The higher was the bed temperature, the greater amount of water could be added until the manifestation of a negative effect.