Initial Step of Flue Gas DesulfurizationAn IR Study of the Reaction of SO2 with NOx on CaO-

Flue gas desulfurization contributes much to the prevention of acid rain. In a dry-type flue gas desulfurization, promotive effect of NO on SO 2 absorption is observed. To elucidate the reaction mechanisms for absorption of SO 2 by a calcium compound in a dry-type flue gas desulfurization, the states of adsorbed SO 2, NO, and NO 2 on CaO and the reactivity of the adsorbed SO 2 with NO, NO 2, and O 2 were studied by IR and temperature-programmed desorption (TPD). Sulfur dioxide (SO 2 ) and NO 2 were adsorbed on CaO mainly in the form of sulfite ion (SO 3 2 - ) and nitrato (NO 3 ) complex, respectively. Nitrogen oxide (NO) is adsorbed in the forms of nitrito (NO 2 ) complexes, free nitro, and nitro or chelating nitro complexes. The sulfite ion reacts with the adsorbed species of NO to be oxidized to sulfate ion (SO 4 2 - ) but reacts neither with the nitrato complex nor with O 2 . The nitrito complexes, free nitro, and nitro or chelating nitro complexes act as an oxidizing agent toward sulfite ion on CaO to form sulfate ion. The transformation of SO 3 2 - ion into SO 4 2 - ion by NO is further accelerated in the presence of O 2 .