Ammonia and water sorption properties of the mineral-layered nanomaterials used as the catalysts for NO x removal from exhaust gases

Abstract

The object of the study is the influence of acidity and hydrophilic properties of the surface of catalyst of the selective catalytic reduction (SCR) of nitrogen oxides by NH 3. A series of catalysts prepared with the ZrO 2-pillared montmorillonite from Jelsovy Potok have been promoted with manganese oxides. A part of the Na +-montmorillonite form has provisionally been treated with the 20% HCl. The acidity of materials was studied by the ammonia adsorption method at the temperature of 273 and 373 K. Acidic properties of catalysts depend on the step of the support preparation—the acidic activation. The activity of the SCR reaction of acid untreated support and the catalyst with MnO x which had few stronger acid centres was lower than the activity of the acid pre-treated catalyst. In this case the support had more strong acid centres. The active material of MnO x increased the NO conversion but not the influence on the amount of ammonia sorption. These centres are probably not acidic centers. The hydrophilic properties were studied by water vapour sorption at the temperature of 298 K. All the samples adsorbed the same amount of water, which suggests that the NO conversion does not influence hydrophilic properties. Water molecules were physically sorbed on the surface of materials and they were replaced with NH 3 in the presence of ammonia.