Effects of Deposited Contaminants on Amorphous Chromia SCR Catalysts for NO

The effects of the deposition of Na{+}, K{+} and SO{4}{2} on amorphous chromia SCR catalysts were investigated. It was found that deposition of Na{+} and K{+} brought about the changes not only in surface catalytic properties but also in the bulk structure of chromia. The deposition of Na{+} decreased the SCR activity at low temperatures but improved the activity and selectivity at higher temperatures. This could be due to the suppression of oxidation of NH{3}, which is the reductant in SCR process. In contrast, SO{4}{2} deposition reduced the SCR activity, probably due to enhanced adsorption of NH3. In terms of bulk properties, alkali metal ions accelerated the crystallisation of chromia and SO{4}{2} retarded it.