To obtain a purification material for efficient removal of NOx and hydrocarbons from waste combustion gas by combining an Ag catalyst in a 1st stage with a porous inorg. oxide catalyst in a 2nd stage and a Pt catalyst in a 3rd stage.
Catalyst beds are arranged in 1st, 2nd and 3rd stages from the waste gas inflow side. A catalyst obtd. by carrying Ag and/or Ag oxide on a carrier such as T-alumina is used in the 1st stage. A porous inorg. oxide having a large surface area and satisfactory heat resistance, e.g., γ-alumina or silica or a catalyst obtd. by carrying the oxide on an inert porous substrate is used in the 2nd stage. A ternary catalyst for removal of hydrocarbons obtd. by carrying Pt, Rh, etc., on a carrier is used in the 3rd stage. By this combination, NOx and hydrocarbons are efficiently removed from waste combustion gas contg. a larger amt. of oxygen than the amt. of oxygen reacting theoretically with unburnt components.
OSHIMA TAKEYUKI
SHIMIZU HIROMASU
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