Selective catalytic reduction of NOx, by propene over copper-exchanged pillared clays

Copper-exchanged pillared clays were examined as an SCR catalyst for NO_x, removal by propene. Both micropores and mesopores were simultaneously developed by pillaring a bentonite with TiO₂. Therefore, TiO₂-pillared clay has about 8 to 9 times higher surface area and 3 times higher pore volume than the parent unpillared bentonite. The presence of water in the feed gas stream caused a small and reversible inhibition effect on NO removal activity of Cu/Ti-PILC. The water tolerance of Cu/Ti-PILC was higher than copper-exchanged zeolites such as CuHM and Cu/ZSM-5 due to its high hydrophobicity as confirmed by H₂O-TPD experiment. Copper-exchanged PILC was confirmed to be an active catalyst for NO_x, removal by propene. The addition of copper to TiO₂-pillared clay greatly enhanced the catalytic activity for NO removal. Cupric ions on Ti-PILC were active reaction sites for the present reaction system. The state of copper species on the surface of Ti-PILC varied with the content of copper and TiO₂. The catalyst having more easily reducible cupric ions showed maximum NO conversion at relatively lower reaction temperatures. It indicates that the redox behavior of cupric ions is directly related to NO removal mechanism. The redox property of cupric ions depended on the copper content and dehydration temperature of PILC.