La／Mn改性Pd／γ-Al2O3催化剂对甲烷催化燃烧的影响

Influence of Pd/γ-Al_2O_3 Catalyst Modified by La/Mn on Methane Catalytic Combustion

采用浸渍法制备了La、Mn助剂改性γ-Al2O3的4种负载钯型催化剂，运用BET、X射线衍射（x-ray diffractomter，XRD等方法对催化剂的结构进行表征，对催化甲烷燃烧活性进行评价。结果表明，过渡金属Mn的掺入提高了对甲烷的活性，但也加快了γ-Al2O3向α-Al2O3的相变。稀土金属La的掺入并末提高其对甲烷的活性。但高温焙烧下La的存在抑制了γ-Al2O3向α-Al2O3的相变，提高了催化剂的高温热稳定性。在低温阶段，0．5Pd／Mn／Al2O3表现出较好的催化活性，而在高温阶段，0．5Pd／LaMnAl11O19的活性优于其他催化剂。作为CH4中间产物，在700-820℃时，由于PdO-Pd的分解，CO的产量逐渐增加。之后，在催化氧化和均相燃烧的共同作用下，CO的产量急剧减少，接近830℃时几乎完全消失。

Four kinds of palladium catalysts, supported on γ-Al2O3 and promoted by La and/or Mn, were prepared by impregnation method. The physico-chemical properties of these catalysts were characterized by BET and XRD techniques. The effect of methane combustion activity of the catalyst samples were investigated. The results indicat that the catalyst mixed with the transition metal Mn leads to an enhancement in methane combustion, whereas accelerates transition of 7-Al2O3 to α-Al2O3. The catalyst mixed with the earth metal La does not improve methane combustion activity obviously, but restrains transition 7-Al2O3 to α-Al2O3 as well as enhances thermal stability of catalysts under high-temperature calcination. 0.5Pd/Mn/Al2O3 performs reasonably better catalytic activity during low temperature stage, however 0.5Pd/LaMnAl11O19 shows the best catalytic active among the all catalysts under high temperature stage. As a interim product of CH4, CO yield increases gradually between 700 ℃ and 800℃, which is caused by decomposition of PdO to Pd with less activity. After that, CO yield derceases quickly and nearly disappears when the temperature rises to 830 ℃caused by cooperate effect of catalytic activity and homogeneous combustion.