Kinetics of selective catalytic reduction of NO by NH_3 on Fe-Mo/ZSM-5 catalyst

The catalyst of Fe-Mo/ZSM-5 has been found to be more active than Fe-ZSM-5 and Mo/ZSM-5 separately for selective catalytic reduction (SCR) of nitric oxide (NO) with NH_3.The kinetics of the SCR reaction in the presence of O_2 was studied in this work.The results showed that the observed reaction orders were 0.74-0.99,0.01-0.13,and 0 for NO,O_2 and NH_3 at 350-450℃,respectively. And the apparent activation energy of the SCR was 65 kJ/mol on the Fe-Mo/ZSM-5 catalyst.The SCR mechanism was also deduced. Adsorbed NO species can react directly with adsorbed ammonia species on the active sites to form N_2 and H_2O.Gaseous O_2 might serve as a reoxidizing agent for the active sites that have undergone reduction in the SCR process.It is also important to note that a certain amount of NO was decomposed directly over the Fe-Mo/ZSM-5 catalyst in the absence of NH_3.     

Effects of support acidity on the reaction mechanisms of selective catalytic reduction of NO by CH4 in excess oxygen

The reaction mechanisms of selective catalytic reduction (SCR) of nitric oxide (NO) by methane (CH₄) over solid superacid-based catalysts were proposed and testified by DRIFTS studies on transient reaction as well as by kinetic models. Catalysts derived from different supports would lead to different reaction pathways, and the acidity of solid superacid played an important role in determining the reaction mechanisms and the catalytic activities. Higher ratios of Br?nsted acid sites to Lewis acid sites would lead to stronger oxidation of methane and then could facilitate the step of methane activation. Strong Br?nsted acid sites would not necessarily lead to better catalytic performance, however, since the active surface NO_y species and the corresponding reaction routes were determined by the overall acidity strength of the support. The reaction routes where NO₂ moiety was engaged as an important intermediate involved moderate oxidation of methane, the rate of which could determine the overall activity. The reaction involving NO moiety was likely to be determined by the step of reduction of NO. Therefore, to enhance the SCR activity of solid superacid catalysts, reactions between appropriate couples of active NO_y species and activated hydrocarbon intermediates should be realized by modification of the support acidity.     

Effect of Mo contents on properties of Mo/ZSM-5 zeolite catalyst for NOx reduction

Mo/ZSM-5 catalysts with different Mo content were prepared by impregnation method. The effect of Mo content on the property of Mo/ZSM-5 catalysts and their performance for selective catalytic reduction(SCR) of NO with ammonia was investigated by XRD, ICP,XPS and NO-TPD respectively. The results showed that the catalytic activity of Mo/ZSM-5 for SCR of NO is strongly influenced by the Mo loading in HZSM-5 zeolites. The NOx conversion reached the highest value of 64.2% at 375℃ when Mo content is about 10.9%, and the temperatures at which the maximum of NOx conversion obtained were declined with the increase of Mo content. From XRD results, it can be seen that it exhibits the distinct interaction between Mo and HZSM-5 when Mo content is about 10.9%. This may result in a suitable phase structure in Mo/ZSM-5 catalyst, which is advantageous for NO reduction. XPS and NO-TPD results also showed that the catalytic activity of Mo/ZSM-5 may be related to the Mo percent on the surface.     

低温SCR脱硝催化剂过渡金属氧化物改性及硫中毒失活机制研究

以浸渍法制备MnOx-CeOx/ACF催化剂.在110~230℃温度范围内,MnOx-CeOx/ACF催化剂具有较好地低温选择性催化还原脱除NOx的活性.结果表明,该催化剂在150℃和230℃的脱硝效率分别达到80%和90%.加入Fe、Cu和V等过渡金属氧化物对MnOx-CeOx/ACF催化剂进行改性.该类过渡金属氧化物的加入对MnOx-CeOx/ACF的活性具有抑制作用.相比于MnOx-CeOx/ACF以及Cu和V改性的催化剂,Fe改性催化剂在一定时期内具有良好的抗SO2性能.在SO2存在下,Fe改性催化剂在初始6h内其脱硝效率保持在75%以上.X射线光电子能谱(XPS)和傅立叶转换红外光谱(FTIR)分析结果表明,催化剂失活包括两部分机制,一是形成硫酸铵盐,可粘附在催化剂表面使催化剂失活;另外一个机制是作为活性成分的锰铈等金属氧化物被SO2硫化形成金属硫酸盐.     

V2O5/ACF低温选择性催化还原烟气中NO的研究

文章对V2O5/ACF(活性炭纤维)进行低温选择性催化还原(SCR)NO的影响研究。实验表明:ACF用硝酸处理形成ACFN,然后采用等体积浸渍法制备V2O5/ACFN催化剂,NO脱除率明显增加。同时研究了V2O5负载量、反应温度、NH3初始浓度、NO初始浓度、O2含量等因素对NO脱除效率的影响,发现V2O5/ACFN在180℃低温时,在NH3/NO为1.1、NO初始体积分数1000×10-6和O2体积分数5%时NO脱除效率较高。     

SO2对CoH-ZSM-5催化CH4还原NO催化性能的影响

研究了富氧条件下SO₂对CoH-ZSM-5上CH₄选择还原NO(CH₄-SCR)的影响,应用SO₂-TPSR,NO+(O₂)-TPD等方法研究了产生中毒的原因并定量研究了被毒化的活性位.反应在773 K进行时,加入体积分数78×10^-6SO₂,NO的转化率由72%逐渐降低并稳定在58%,提高反应温度至823 K,NO稳定转化率上升至62%.同时加入2.5