| abstract |
A catalyst which is for use in the reductional removal of NOx contained in a waste gas with ammonia as a reducing agent and which, through long-term use at high temperatures, has undergone agglomeration of a vanadium oxide as an active ingredient and a decrease in activity is washed with an aqueous acid solution having a pH of 6 or lower, preferably 4 or lower. This washing mainly dissolves away the vanadium oxide agglomerated, which is an active ingredient. This vanadium oxide as an active ingredient is then deposited again. This method enables a thermally deteriorated catalyst to be regenerated, although this regeneration has been impossible. The washing with the aqueous acid solution or with an aqueous alkali solution exerts no influence on the mechanical strength of the catalyst. |