Abstract: Nitrogen oxides are effectively removed from a gaseous mixture comprising the same and oxygen by adding ammonia thereto and contacting with a suitable catalyst for the nitrogen oxide-ammonia reaction. While the presence of sulfur dioxide is not essential to such removal, best results are achieved when sulfur dioxide is also present in the gaseous mixture. When sulfur dioxide is present, and particularly when the same is present in a concentration in excess of that required for most effective nitrogen oxide conversion, the excess sulfur dioxide may be separated prior to the nitrogen oxide conversion, simultaneously therewith or subsequent thereto.

Abstract: Sulfur oxides and nitrogen oxides are removed from flue gas by scrubbing the flue gas with an aqueous ammoniacal solution containing ammonium thiosulfate and either ammonium sulfite or ammonium hydroxide. The presence of ammonium thiosulfate in the absorbent solution also inhibits the oxidation of sulfur dioxide to hexavalent sulfur. The scrubber effluent solution or a portion thereof is acidified in order to liberate sulfur dioxide in a concentrated stream.

Abstract: Flue gas is desulfurized by absorbing it onto a selective absorbent-catalytic material. The absorbed SO.sub.2 is recovered by contacting it in a desorption cycle with a reducing desorption gas. In one embodiment, multiple absorbent beds are employed and alternate absorption-desorption cycles are used in each of the multiple beds with the flue gas and the desorption gas used alternately. The sulfur oxide is recovered in concentrated form in the desorption gas stream and is then utilized as feed in a conventional sulfuric acid plant yielding concentrated sulfuric acid.