LEAN NOX REDUCTION WITH HYDROCARBONS OVER GA/S-ZROX AND S-GAZR/ZEOLITE CATALYSTS

Ga/S-ZrOx and sulfated GaZr/Zeolite catalysts were found to be very effective for the reduction of NOx in a lean environment with hydrocarbons. Ga/S-ZrOx was much more active than S-ZrOx or Ga/ZrOx as well as a wide variety of Ga supported amorphous super acids. Incorporating ZSM-5 into the catalyst formulation, i.e. S-GaZr/ZSM-5, increased NOx reduction activity particularly at low temperatures. The effects of zeolite support, sulfation, and mono vs. bimetallic supported samples were investigated. For ZSM-5, sulfation and the combination of Ga with Zr proved to be most active. Ga/S-ZrOx and S-GaZr/ZSM-5 were investigated with C3H8, C3H6, CH4, and CO as reductants and compared to Cu/ZSM-5. Unlike Cu/ZSM-5 which was most active with C3H6, Ga/S-ZrOx and S-GaZr/ZSM-5 were more active with C3H8, than with C3H6. S-GaZr/ZSM-5 was also active with CH4. All three catalysts were inactive with CO and did not catalyze the NOx decomposition reaction. Both Ga/S-ZrOx and S-GaZr/ZSM-5 were more hydrothermally stable than Cu/ZSM-5. However, their activities decreased significantly with increasing space velocity or in the presence of water in the feed making them impractical catalysts for mobile or stationary sources.