Selective nox reduction over metal supported on alumina catalysts derived from sol-gel method

Abstract

The selective catalytic reduction of NOx by propene and urea were studied over gold and platinum on alumina supported catalysts. These catalysts were prepared from sol-gel technique together with other conventional methods. They were tested over the temperature range of 150-500 .c under various conditions. The presence of water and SO2 coupled with different oxygen concentrations in reactant gas streams were employed in order to investigate the catalytic activities. It was found that the preparation method had strong influence on the catalytic performance. Among different gold catalysts, the one that prepared from single step sol-gel exhibited the highest activity. However, the impregnated sol-gel alumina was the best catalyst in terms of overall performance that the formation of N2 was also concerned. In selective reduction of NOx by propene, almost 100% NOx conversion was found. In addition, its activity window was enlarged in higher oxygen concentrations. Water was considered to enhance NOx conversion. Conversely, it suppressed the selectivity towards N2. Furthermore, the catalysts exhibited good stability under prolonged time on stream in both dry and humid conditions. In contrast, both gold and platinum catalysts showed the average activity in selective NOx reduction with urea. Increasing in the activity with the temperature was observed on gold catalysts while platinum catalyst reached the maximum NOx conversion around 250-300 .c. The study of catalytic performance with urea was extended over platinum catalyst. It gave negative NOx conversion at high temperature region for urea delivery from aqueous solution system. This resulted from the oxidation of derivative nitrogen-containing compounds from urea