Au/MgO catalysts modified with ascorbic acid for low temperature CO oxidation

Abstract

Au/Mg(OH) 2 catalyst was modified with different amounts of ascorbic acid. After dehydration at 350 °C, in various atmospheres, the modified Au/MgO catalysts were characterized and tested in the oxidation of CO. It has been shown for the first time that at high CO pressure supported gold chemisorbs CO and the apparent gold dispersion can be determined. The oxidation of CO was investigated in the temperature range between −30 and 250 °C using both temperature-programmed oxidation technique and time on stream experiments. A characteristic feature of Au/MgO catalysts is the decrease of the activity upon increasing the reaction temperature from −30 to 110–120 °C. The results showed that the introduction of ascorbic acid had a definite positive effect on the activity of Au/MgO catalyst in low temperature CO oxidation. This effect strongly depended on the amount of ascorbic acid introduced and had a distinct optimum. Based on diffuse reflection UV–VIS and in situ FTIR spectroscopic data it is suggested that the addition of ascorbic acid (i) slightly alters the (ionic gold)/(metallic gold) ratio in both the parent (Au/Mg(OH) 2) and the working catalysts (Au/MgO) and (ii) suppresses the carbonate formation responsible for the deactivation. It is proposed that the activation of CO requires the formation of “(Au δ+ ) m –Au n ” ensemble sites, in which the ionic gold is involved in the activation of CO molecule via Au δ+ –carbonyl oxygen interaction.