低浓度甲烷燃烧用Pd/α-Al_2O_3蜂窝催化剂的制备

Preparation of Pd/α-Al_2O_3 Honeycombs for Catalytic Lean Burn of CH_4

针对甲烷催化燃烧反应,用浸渍法制备Pd/α-Al_2O_3催化剂粉体,并涂覆到氧化铝蜂窝陶瓷基体上制成蜂窝催化剂。考察了Pd浸渍液pH值、Pd的负载量、焙烧温度及活性粉体涂覆量对催化活性的影响。采用扫描电镜(SEM)、透射电镜(TEM)、X射线衍射(XRD)、电感耦合等离子体发射光谱(ICP)及CO化学吸附等方法对催化剂涂层的形貌,涂层中Pd含量及Pd颗粒大小进行了表征。结果表明,浸渍液pH值为5时获得了高分散的Pd品粒(粒径约2 nm);500～600℃焙烧可获得高活性,700℃焙烧则使晶粒烧结,导致活性下降。涂层中Pd质量分率0.33%、涂覆量厚度约为50 μm时可同时得到小的Pd晶粒及薄且均一的涂层,对Pd的利用率最高,获得了最优的催化剂活性。

For catalytic lean burn of methane, Pd/a-Al2O3 honeycomb catalysts were prepared by washcoating the a-Al2O3 ceramic honeycomb substrates with the powder catalystswhich were madein advance by impregnation method. The influences of preparation factors, such as the pH value of impregnation liquid, Pd loadings, calcination temperature and the amount of washcoat, on catalytic activity were investigated. Scanning electron microscope （SEM）, Transmission electron microscope （TEM）, X-ray diffraction （XRD）, Inductive Coupled Plasma （ICP） and CO chemisorption were adopted to characterize the morphology of washcoat, the loading of Pd, and the crystalline size of Pd particles. It was found through experiment that Pd particles attained the highest dispersion （2 nm） when pH value of the impregnation liquid was kept at 5. Catalysts calcined at 500--600 ℃ showed high catalytic activities, while calcination at 700 ℃ caused the sintering of Pd particles and reduction in catalyst activity. At last, a thin and even coating on the honeycomb catalyst washcoated with 50 micron catalyst powder which was loaded with 0.33% well-dispersed Pd particles could be obtained, which were the highest Pd utility and catalytic activity.