Abstract
Studies of the selective catalytic reduction (SCR) of nitrogen oxide with methane over H-mordenites were made to develop a basic understanding of the role of acid sites in this reaction and the mechanism of deactivation of these solids. A series of H-mordenites with varying Si/AI ratios (5.9-16.9) were prepared by acid leaching. They were thoroughly characterized before and after reaction by 27 AlMAS NMR, XRD, FTIR spectroscopy, N 2 adsorption and ammonia TPD. A linear correlation was found between the conversion of NO to N 2 , the lattice aluminum content and the concentration of strong acid sites measured by ammonia chem isorption. The catalysts were partially deactivated after being on stream at 650°C, subsequently reaching a stable behavior. The origin of this phenomenon could be traced back to the additional dealwnination occurring at high temperatures in the reacting stream. This additional expulsion of aluminum from the lattice caused a proportional decrease in the concentration of strong acid sites.
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