负载氧化镧的活性炭还原NO的研究

Reduction of NO by La_2O_3-loaded activated carbon

稀土金属具有一些特殊的性能,这使得其对碳质材料还原NO的反应可能表现出特殊的催化效果,而此方面的研究没有报道。为了研究稀土金属对活性炭还原NO反应的催化效果,采用浸渍法制备了负载氧化镧的活性炭颗粒(La/C),并在无氧的固定床反应器中进行了程序升温反应和等温反应,考察了气体流量、NO的入口浓度、反应温度和氧化镧负载量对反应活性的影响,同时对反应机理和动力学进行了初步探讨。研究结果表明负载氧化镧的活性炭还原NO的反应是一级反应。由于炭表面3%(质量分数)的氧化镧的存在,C-NO反应的起始反应温度从500℃降低到300℃,反应活性大大提高,反应活化能从88.95kJ/mol降低到51.05kJ/mol。氧化镧的负载量对反应活性有重要影响,但负载量的大量增加对反应活性的提高效果甚微,最佳负载量为1.5%。La/C体系在反应中较稳定,而反应温度的升高对其稳定性不利。

The La2O3-loaded activated carbon granules （La/C） were prepared by impregnation. Temperature programmed reaction and isothermal reaction in fixed bed reactor in the absence of oxygen were employed to explore the mechanism and kinetics of NO reduction in La/C. Comparative runs were performed to determine the effects of gas flow rate, concentration of NO, reaction temperature and loading of La2O3. The experimental data was well represented by the first order kinetics model. With 3 % （w/w） loading of La on the activated carbon, NO reduction began at a lower temperature of 300℃ （from 500℃ with no metal）, the calculated activation energy was lowered to 51.1 kJ/mol （from 88.9 kJ/mol）, and the reactivity increased substantially. Data also demonstrated that La/C was a better catalyst than the Ca/C prepared in a similar manner. The NO removal increased with increasing reaction temperature and/or % of La2O3 loading; the reduction at 400-500 C with 1.5% loading was most cost effective. The La/C treatment was stable; however, the stability decreased quickly as the reaction temperature went above 500℃.