理论空燃比天然气汽车尾气中H_2O和O_2对CH_4与NO反应的影响

Effects of H_2O and O_2 on the Reaction of NO Reduction by CH_4 under Stoichiometric Natural Gas Vehicles

共沉淀法制备Ce Zr YLa+La Al复合氧化物载体,等体积浸渍法制备了Pt催化剂,用于研究理论空燃比天然气汽车(NGVs)尾气净化反应中CH4与NO的反应规律.并考察了10%(体积分数,φ)H2O和计量比O2对CO2存在时的CH4+NO反应的影响.结果表明:对于不同条件下的NO+CH4反应,主要生成N2和CO2,高温区有CO生成.低温区无O2时可以生成N2O,有O2时可以生成NO2;添加10%(φ)的H2O后,CH4转化活性降低,NO转化活性基本不变,这是由于H2O减弱了CH4与CO2的重整反应,但是对CH4与NO的反应基本没有影响;添加计量比的O2后,CH4转化活性提高,而NO转化活性降低,这是由于O2和NO之间存在竞争吸附,CH4被O2氧化为主要反应,从而减弱了NO的转化;同时添加计量比的O2和10%(φ)H2O,CH4与CO2的重整反应受到抑制,CH4与NO的反应、甲烷蒸汽重整反应和甲烷被O2氧化反应同时发生,CH4和NO的转化活性均提高.

Composite support CeZrYLa＋LaAI was prepared by co-precipitation, and platinum catalyst supported on the composite support was prepared by impregnation. The behavior of the Pt catalyst for the reaction of NO reduction by CH4 from the exhausts of natural gas vehicles （NGVs） was studied under stoichiometric conditions. Additionally, the effects of 10% （volume fraction,φ） H2O and stoichiometric O2 on the reaction in the presence of CO2 were also investigated. Results show that N2 and CO2 were the main products for the different reactions, CO was detected under high temperature, and NOx was detected under low temperature （in the presence of 02, the NOx was NO2, whereas the NOx was N2O when no 02 was present）. In the presence of 10% （φ） HO1 the conversion of CH4 noticeably decreased and NO conversion remained unchanged, possibly because the presence of H2O weakens the reforming reaction of CH4 with CO2, but does not affect the activity of NO reduction by CH,. In the presence of stoichiometric 02, there was an obvious increase of CH4 conversion and a decrease of NO conversion. These could be explained by the competition between NO and 02, where the oxidation of methane by 02 is the main reaction, limiting the reaction of NO reduction by CH,. Moreover, in the presence of 10% （φ） H2O and stoichiometric O2, CO2 reforming of CH4 was negligible. Numerous reactions were detected simultaneously, such as the oxidation of CH4 by NO, steam reforming of CH,, and the reduction of NO by CH4, thus improving the conversions of CH, and NO.