Porous systems based on layered materials with different structures: a comparative study

The main goal of this work was the preparation, characterisation and comparison (in respect to textural and catalytic properties) of porous systems based on three different types of layered materials: Na-ilerite (Al-free layered sodium silicate), bentonite (clay mineral) and MWW-precursor (layered zeolite). For the preparation of the porous systems two combinations of post-synthetic modifications were used: swelling/pillaring and swelling/delamination. The aim was to investigate the influence of these post-synthetic modifications on the textural properties of the selected Na-ilerite, bentonite and MWW-precursor as well as the influence of these changes on the catalytic activity in NH3-SCR. The swelling/pillaring modification produced porous structures with higher surface area and higher pore volume compared to swelling/delamination modification. The microporous surface area (Smicro) of the SiO2-pillared ilerite increased from 0.16 m2g-1 in the parent Na-ilerite to 898 m2g-1 in the SiO2 pillared one. In the case of MWW swelling/delamination produced a porous system with huge mesoporous volume Vmeso = 1.26 cm3g-1 compared to the parent MWW-precursor, which is purely microporous.
In NH3-SCR Fe-containing SiO2-pillared MWW and delaminated MWW catalysts showed the highest catalytic activity with 57 and 48 % NOx reduction at 500 °C, respectively, although the BET surface area of both catalysts is much lower compared to that of SiO2-pillared ilerite. The explanation is that the SiO2-pillared ilerite is an Al- free material, since Na-ilerite is an Al-free layered silicate. When Al was added to the system the catalytic activity of ilerite increased up to 56 % in the ilerite pillared with Al2O3.