Insights over titanium modified FeMgOx catalysts for selective catalytic reduction of NOx with NH3: Influence of precursors and crystalline structures

Abstract

Titanium modified FeMgOx catalysts with different precursors were prepared by coprecipitation method with microwave thermal treatment. The iron precursor is a key factor affecting the surface active component. The catalyst using FeSO4 and Mg(NO3 )2 as precursors exhibited enhanced catalytic activity from 225 to 400◦ C, with a maximum NOx conversion of 100%. Iron oxides existed as γ-Fe2 O3 in this catalyst. They exhibited highly enriched surface active oxygen and surface acidity, which were favorable for low-temperature selective catalytic reduction (SCR) reaction. Besides, it showed advantage in surface area, spherical particle distribution and pores connectivity. Amorphous iron-magnesium-titanium mixed oxides were the main phase of the catalysts using Fe(NO3 )3 as a precursor. This catalyst exhibited a narrow T90 of 200/250–350◦ C. Side reactions occurred after 300◦ C producing NOx, which reduced the NOx conversion. The strong acid sites inhibited the side reactions, and thus improved the catalytic performance above 300◦ C. The weak acid sites appeared below 200◦ C, and had a great impact on the low-temperature catalytic performance. Nevertheless, amorphous iron-magnesium-titanium mixed oxides blocked the absorption and activation between NH3 and the surface strong acid sites, which was strengthened on the γ-Fe2 O3 surface.