活性炭低温催化还原NOx影响因素及反应机理分析

以活性炭为催化剂,NH3为还原剂考察了温度,氧含量,SO2和H2O等因素对NOx去除率的影响;同时采用暂态响应技术研究了活性炭低温氨选择性催化还原(SCR)NOx的反应机理.结果表明:在实验条件下,NOx去除率随温度的增加逐渐降低,随氧含量的升高逐渐升高,但当φ(O2)大于2.5%时去除率增加缓慢,说明活性炭具有良好的低温SCR活性,氧的加入促进了NOx的催化还原,在活性炭低温氨选择性催化还原NOx的反应中,将NO预氧化为NO2可提高NOx的还原率;在短时间内SO2的通入对其SCR反应影响较小;H2O的加入大大降低了活性炭的SCR活性,使活性炭催化剂毒化.该SCR反应按Eley-Rideal机理进行,NH3的吸附过程为该催化过程的控制性步骤.

Analysis of Affecting Factors and Reaction Mechanism of Low-Temperature Selective Catalytic Reduction of NOx over Activated Carbon

The activated carbon was used as catalyzer and the ammonia as reducer to study the factors affecting NO_x conversion efficiency,such as temperature, oxygen content,SO_2 and H_2O,etc.The mechanism of the low-temperature selective catalytic reduction(SCR) of NO_x over activated carbon was studied with transient response technique.The results show that at the experimental condition,NO_x conversion efficiency gradually decreases with the increase of the temperature,and gradually increases with the increase of oxygen content.But the conversion efficiency increases slowly when oxygen content is more than 2.5%.This shows that the activated carbon has favorable low-temperature SCR activity.The adding of oxygen could promote catalytic reduction of NO_x.The reduction rate could be enhanced by pre-oxidizing NO to NO_2.The effect of the SO_2 was less in a short time,but the SCR activity decreased when the H_2O was added and the activated carbon was poisoned.The experiment indicated that the SCR was in the mechanism of Eley-Rideal,and the NH_3 adsorption is the controlling step of the whole process.