| Selective Catalytic Reduction (SCR) method with NH3as reductant is promoted and applied quickly recently as a mature technology in the field of NOx removal to meet the increasingly strict exhaust emission regulations. Quite a lot of studies have been performed on the research of catalysts, which act as the key factor in the NH3-SCR method, from screening of active elements to preparation methods. Titania-silica composite recently has attracted the attention of many application fields such as photocatalysis, benzene hydrogenation and novel materials for its superior chemico-physical/reactivity properties. Titania-silica composite has been introduced into NH3-SCR field by some researchers to investigate the DeNOx performance of TiO2-SiO2based vanadia catalysts, but few literatures concern the application of it with other SCR-active elements. Considering the excellent properties possessed by titania-silica composite, here we have taken the Ce-V and Mn-Ce SCR catalysts as research objects to study the effects of silica addition on their DeNOx performances.(1)The effect of silica addition on the DeNOx performance of TiO2based Ceria-Vanadia oxide catalyst has been conducted, results show that the active temperature range of the catalyst has a tendancy to move rightward where the low-temperature catalytic efficiency of CeVOx/Ti02-SiO2catalyst is declining as the percent of SiO2increases in the carrier, while its DeNOx activity is promoted in high-temperature field above350℃. The N2selectivity of Ceria-Vanadia catalysts is similar to that of their activities. The characterization results of the catalysts by BET, NH3-TPD, XRD and SEM reveal that the addition of silicon has quite a positive effect on their specific surface area and their pore features, as well it can increase the number of weak acid sites on the catalyst surfaces. Besides, the crystalline process of TiO2base could be inhibited by SiO2, thus helping the active elements to be better dispersed on the bases.(2) The influence of silica addition into another SCR active catalyst-Manganese-Ceria composite-has also been studied. The experiment results indicate that20%addition of SiO2into the TiO2base can achieve the best effect which could extend the100%NOX conversion efficiency to300℃with its N2selectivity improved.(3) The effect of calcination temperature during the preparation process of MnCeOx/Ti02—SiO220%SiO2catalyst has been carried out. It is found that the catalyst being calcinated under300℃possesses a quite well developed specific area and pore features, and its NOX conversion efficiency can reach90%above at100℃. As the calcination temperature increases, the low-temperature DeNOx performance of MnCeOx/Ti02-SiO220%SiO2catalyst is deteriorated while an opposite positive effect is found when the reaction temperature rises above300℃. This phenomenon may be associated with the appropriate developed specific surface area, pore features and a suitable number of acid sites on the catalyst’s surface under a preferential given calcination temperature.(4) The reaction process and mechanism of the MnCeOx/Ti02SiO220%SiO2(300) catalyst has been investigated by in situ DRIFTS. The analysis result concludes that quite abundant acid sites reside on the surface of the MnCeOx/Ti02SiO220%SiO2(300) catalyst and NH3and NO can strongly adsorb on the surface of the catalyst as coordinated NH3species and bridged and bidentate nitrates respectively. The NH3-SCR process occurring on the surface of the MnCe0x/Ti02SiO220%SiO2(300) catalyst mainly follows the Eley-Rideal mechanism with the coordinately adsorbed NH3species and bridged nitrates as primary active components. |
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