Facile Synthesis of KFI-type Zeolite and Its Application to Selective Catalytic Reduction of NOx with NH3

The small-pore KFI-type zeolite was synthesized via the hydrothermal conversion of zeolite Y with Na+ and K+ ions without using an organic structure-directing agent (OSDA). The effects of alkali-metal ions and hydroxide ion on the crystallization of KFI were individually investigated by introducing both hydroxide and nitrate salts into synthesis media. The zeolite KFI synthesized under the optimized conditions was copper ion exchanged and then applied for selective catalytic reduction of NOx with an NH3 (NH3-SCR) reaction. Cu-KFI was found to exclusively contain isolated copper ions up to very high loading (Cu/Al2 = 75%) on the basis of the Cu K-edge extended X-ray absorption fine structure (EXAFS), X-ray absorption near-edge structure (XANES), ultraviolet visible near-infrared spectroscopy (UV–vis–NIR), and temperature-programmed reduction by H2 (H2-TPR) analyses. Interestingly, Cu-SSZ-13 and Cu-KFI have almost identical activation energies for the NH3-SCR reaction as well as the reduction temperature of “hydrated” copper ions by H2, indicating the presence of similar active sites on both catalysts. After severe hydrothermal aging at 800 °C for 16 h, Cu-KFI substantially maintained its structural integrity, which is remarkably stable in comparison with Cu-chabazite synthesized from organic-free media. The NH3-SCR activity test under realistic conditions showed that Cu-KFI with high Cu loading has activity comparable to that of Cu-SSZ-13 even after hydrothermal aging. All combined results evidently confirm that the zeolite-based catalyst prepared under organic-free conditions can also exhibit excellent hydrothermal stability, which is attributed to the high crystallinity of zeolite and the presence of only isolated copper ions.