Pd/MWCNTs贫燃甲烷催化燃烧性能研究

以MWCNTs为载体,用HNO_3做氧化剂对MWCNTs进行处理,通过XPS研究了处理前后MWCNTs表面官能团的变化,并采用超声浸渍法制得Pd/MWCNTs催化剂,借助TEM,揭示了Pd粒子在催化剂表面分散度和粒径与MWCNTs表面含氧量、羟基和羰基间的关系。并考察了Pd/MWCNTs催化剂预处理方法对低浓甲烷催化燃烧活性和稳定性的影响,研究表明,Pd的价态以及Pd粒子的粒径,都与催化剂的甲烷燃烧活性直接关联。单质Pd的氧化和Pd粒径的长大是导致催化剂性能衰减的原因。通过原位FT-IR技术对反应气氛下中间物种的监测,提出了Pd/MWCNTs催化剂上的低浓度甲烷催化氧化反应机理。

Catalytic combustion of methane over Pd/MWCNTs under lean fuel conditions

The raw multi-walled carbon nanotubes (MWCNTs) were treated with nitric acid. The shift of the surface functional groups on the MWCNTs was observed with XPS. The Pd/MWCNTs catalysts were synthesized by the ultrasonic impregnation method. The total contents of oxygen, hydroxyl and carbonyl groups were measured. The dispersion and size distribution of Pd particles were characterized with TEM. The dependence of Pd dispersion on the oxygen-containing functional groups was validated. The effect of pretreatment on the catalytic activity and stability for methane combustion was investigated under lean fuel conditions. It is shown that the catalytic activity depends on the valence state and particle size of palladium. The transformation from Pd to PdO possibly caused the decrease in the catalytic activity. Another factor inducing deactivation is Pd particle aggregation. The reaction mechanism for methane combustion over the Pd/MWCNTs catalyst is postulated on the basis of the intermediate species detected by in-situ FT-IR spectroscopy.