Experiment Study On CeO₂/TiO₂ Catalysts Doped With Transitional Metals For Selective Catalytic Reduction Of NO_x With Ammonia

Selective catalytic reduction（SCR） of NO_x has been widely-used for the removal of NO_x from Coal-fired power plant. V-based catalysts for above reaction are still problems, such as narrow reaction temperature range, oxidizing SO₂ to SO3 easily, generating N₂ O at a high temperature, toxicity of vanadia to the environment, etc. As a nontoxic and inexpensive material, ceria has excellent ability of oxygen storage and redox properties. However, regarding the effect of transitional metals on metal oxide catalysts, the SCR reaction was systematically investigated by using transitional metal oxides-CeO₂/TiO₂ catalysts in this dissertation.Firstly, several transitional metals were doped into CeO₂/TiO₂ catalysts. It was found that W doping could greatly improve the activity of the catalyst（ NO conversion reached more than 90% at the temperature range of 275-500℃）.Preparation parameters and operating parameters were studied based on the CeO₂-WO3/TiO₂ catalyst. When the calcinations temperature is 500℃, the activity of catalyst was highest. The appropriate mass ratio of CeO₂, WO3 and TiO₂ was 20, 10 and 100. High activity of catalyst was obtained within a wide range of gas hourly space velocity from 50,000 h-1 to 120,000 h-1. The presence of NH₃ played an important role in SCR reaction. The optimal molar ratio of [NH₃] and [NO] was 1. The activity of Ce O₂-WO3/TiO₂ catalyst was not affected when the volume fraction of oxygen was higher than 3%. Catalysts have good adaptability on NO concentration. It was also found that the resistance to SO₂ and H2 O of catalysts was enhanced with the introduction of W.The excellent catalytic performance is associated with the highly dispersed Ce and Ti as well as the smaller particle diameter by the introduction of W. Meanwhile, the interaction between ceria and tungsten oxide could increase the amount of surface adsorbed oxygen and Ce3+, and promote oxygen storage capacity and redox ability.The reaction kinetics were studied on the selective catalytic reduction of NO with NH₃ over the CeO₂-WO3/TiO₂ catalyst. The result showed that the reaction was a first-order reaction with NO, a zero-order reaction with NH₃ and nearly quarter-order with O₂. The reaction followed the Eley-Rideal mechanism model. The activation energy of CeO₂-WO3/TiO₂ catalysts was 32.1 kJ/mol. It was much lower than the values obtained on CeO₂/TiO₂ catalysts.