V2O5-Al2O3 and Fe2O3-Al2O3, catalysts were effective for the reduction of NOx in a waste gas from a sintering furnace. In this paper, the techniques of regeneration are discussed on the basis of the results oftained by ion microanalyzer, X-ray fluorescence diffractometer, and X-ray diffraction spectrometer. In general a heat treatment was effective to regenerate the catalysts, deactivated merely by SOx in a dust free flue gas. However, the catalysts used in a waste gas from a sintering furnace could not be recovered by a heat treatment (Figs. 4, 9). This is due to the adhesion of the dust components such as K, Ca, Na, Fe, and Si to the catalysts (Figs. 5, 10). Among the dust components, K mostly lowered the catalytic activity for NOx reduction. Therefore, the studies were made on the behavior of accumulated K on the catalysts surfaces and to establish the effective techniques to remove K from the catalysts. In the case of V2O5-Al2O3, catalyst, K was concentrated on the outer surface of the catalyst particle (Fig. 2); it could be removed by washing with hot water (Fig. 7). An effective recovery of,the catalytic activity was attained by washing (Fig. 6). On the contrary, in the case of Fe2O3-Al2O3, catalyst, K permeated in an inner part of the catalyst particle (Fig. 3) and the removal of K from the catalyst by washing was difficult. Potassium, permeated in the catalyst, migrated and concentrated on the outer surface of the catalyst particle by heating in air at 550°C (Fig. 10). Therefore, K could be removed from the catalyst, by washing with hot water (Figs. 13, 14) after heating in air at 550°C. The catalytic activity was well recovered by this method. © 1979, The Chemical Society of Japan. All rights reserved.
