|Budget Amount *help
¥11,400,000 (Direct Cost : ¥11,400,000)
Fiscal Year 2000 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1999 : ¥1,600,000 (Direct Cost : ¥1,600,000)
Fiscal Year 1998 : ¥8,200,000 (Direct Cost : ¥8,200,000)
In order to develop a catalyst for low temperature selective reduction of NO with Ammonia, Al_2O_3, TiO_2, ZrO_2, and metal salts impregnated metal oxides as catalysts were studied in a continuous quartz fixed bed reactor system. It was observed that Al_2O_3, TiO_2 and ZrO_2 had an activity for selective catalytic reduction of NO at about 90℃. Their activity were influenced by reaction temperature, water vapor, sulfurous acid and ammonia gas. The selectivity of NO to N_2 over the metal oxides were in the order : ZrO_2>TiO_2>Al_2O_3. The activity of these three catalysts decayed with the elapsed reaction time since the accumulation of the ammonium salts plugged the pores of the catalysts. The activity decayed catalysts could be regenerated by water washing. Th mechanism of the selective catalytic reduction of NO with ammonia was also studied. The existence of SO_2 is indispensable to the selective catalytic reduction of NO at low temperature (90℃). SO_2 was supposed to contribute to the
production of the active surface oxigen, which was significant to the reduction of NO with NH_3. The mechanism of low temperature reduction of NO to N_2 was proposed through an intermediate NH_4NO_2, which can be decompose to N_2 and H_2O below 100℃.
From the study using metal salts supported Al_2O_3, TiO_2 or ZrO_2 catalyst, it was found that the activity of the metal chloride impregnated metal oxide catalyst was higher than that of the same sulfate if metal oxide was same. The activity of the catalyst depended on reaction temperature, ammonia concentration and the kind of support metal oxide. It was found that the SbCl_3, NiCl_2 and AlCl_3 supported Al_2O_3 were relatively high active among the catalysts. However the loading amount of SbCl_3 supported Al_2O_3 were negligible. From this result, it was supposed that the chloride ion remained over the Al_2O_3 contributed to its activity. For confirmation the hypothesis, the Al_2O_3 was treated with some HCl aqueous solution and concluded that the chloride ion accelerated the selective catalytic reduction of NO.The spent SbCl_3, NiCl_2 and AlCl_3 supported Al_2O_3 catalysts could not regenerated by water washing method because some amount of the salt was extracted by water. However, the spent HCl treated Al_2O_3 catalyst could be regenerated by water washing followed by retreatment with a HCl aqueous solution.
The activity of the HCl treated Al_2O_3 catalyst is not enough to practical application to the next generation selective catalytic reduction process for NO removal. However, this catalyst is a new type catalyst for NO removal. If we can modified this catalyst and increase its activity, this new type catalyst is hopeful for practical use in the next generation process. Less