摘要
考察了富氧条件下Mn/ZSM-5催化剂上CH4选择催化还原NO反应,并采用H2程序升温还原、SO2程序升温表面反应和NO程序升温脱附等手段对催化剂进行了表征.结果表明,催化剂活性与制备方法和Mn负载量密切相关.离子交换法制备的Mn/ZSM-5催化剂活性明显优于浸渍法制备的催化剂;NO转化率随着Mn负载量的增加而增加,至2.06%时达到最大值(57.3%),然后随着Mn负载量的增加而降低.采用离子交换法或较低Mn负载量(≤2.06%)抑制了催化剂中非化学计量的MnOx(1.5<x<2)物种的形成,减缓了CH4的氧化燃烧反应,因而CH4还原NO的选择性提高.在含SO2体系中,Mn/ZSM-5活性在550oC以下时明显下降,但在600oC以上基本不受影响.这是由于在550oC以下时SO2在Mn/ZSM-5表面形成了稳定的吸附硫物种,覆盖了部分活性位,导致催化剂活性降低;而在600oC以上时含硫物种基本脱附完全,因而对催化剂活性影响不大.
The selective catalytic reduction of NO in excess O2 by CH4 was investigated over a series of ZSM-5-supported manganese catalysts（Mn/ZSM-5）.The catalytic activity depended on preparation method and Mn loading.An ion exchange method resulted in a higher activity than an impregnation method.Catalytic activity increased with increasing Mn loading until a Mn loading of 2.06% that gave a maximum NO conversion of 57.3%.H2 temperature-programmed reduction results showed that the ion exchange method and low Mn loadings（≤ 2.06%） restricted the formation of non-stoichiometric MnOx（1.5 〈x〈 2） species that have higher oxidative activity,and thus suppressed the combustion of CH4 by O2,which increased the selectivity for NO reduction.In a SO2 containing stream,a substantial decrease in NO conversion was seen at ≤ 550 ℃ but not at ≥ 600 ℃.SO2 temperature-programmed surface reaction and NO temperature-programmed desorption demonstrated that sulfur species were formed at temperature ≤ 550 ℃,and these covered active sites and decreased the catalytic activity.The sulfur species desorbed at ≥ 600 ℃,thus the addition of SO2 did not have a significant impact on the catalytic activity.
出处
《催化学报》
SCIE
EI
CAS
CSCD
北大核心
2010年第9期1107-1114,共8页
基金
国家自然科学基金(20876102)
高等学校博士学科点专项科研基金(200801120006)
山西省自然科学基金(2008011022)
关键词
一氧化氮
甲烷
选择催化还原
锰
ZSM-5
二氧化硫
nitrogen oxide
methane
selective catalytic reduction
manganese
ZSM-5
sulfuric dioxide
