The influence of holmium on catalytic properties of Fe or Cu-modified vermiculites

Natural layered clay, vermiculite, was modified and tested as catalyst for the selective catalytic reduction of NOx with ammonia (NH3-SCR). Its modification included the application of the blowing agent (azodicarbonamide), acid treatment and pillaring with Al2O3. Active phase (transition metals: Cu or Fe) was introduced via impregnation. The obtained materials were characterized by N-2 sorption (texture), XRD (structure), DR-UV-Vis (oxidation state and aggregation of the active phase), H-2-TPR (reducibility of the active phase), in situ DRIFTS (types of adsorbed species due to contact of the sample NH3) and NH3-TPD (type/strength of the acidic sites). The initial modification procedures (treatment with azodicarboamide) resulted in the increase of specific surface area of vermiculite. The introduction of transition metal ions provided a significant amount of acidic sites. The promoting impact of holmium was confirmed by the increased strength of the sites. The highest catalytic activity was exhibited by the sample Fe-containing vermiculite and doped with Ho.