Zn-Cr整体催化剂中Ce-Zr溶胶涂层的制备、表征及对甲醇自热重整反应的影响

Preparation,Characterization and Effect of Ce-Zr Washcoat on Zn-Cr Monolithic Catalysts for Methanol Autothermal Reforming

以溶胶-凝胶法制备出粒子尺度均一的Ce-Zr溶胶. TEM和XRD结果表明, 1073 K焙烧后, Ce-Zr复合氧化物的粒径仍保持在20～50 nm. 将Ce-Zr溶胶作为甲醇自热重整制氢Zn-Cr整体催化剂的涂层,考察了溶胶在涂层多次重复过程中的稳定性和干燥方式对Ce-Zr涂层龟裂程度的影响. 结果表明,对多次使用后的溶胶进行胶溶处理可以有效控制涂层制备过程中胶体粒子的大小; 微波干燥更加有利于蜂窝陶瓷载体各通道中Ce-Zr涂层的均匀干燥; Ce-Zr涂层的引入显著提高了甲醇自热重整Zn-Cr整体催化剂的稳定性,这归因于Ce-Zr涂层提高了催化剂的氧化还原活性,使其能量匹配更好,避免了热点的产生,从而抑制了催化剂的烧结与失活.

The Ce-Zr colloid with a narrow particle size distribution was prepared by the sol-gel method and used as a washcoat of the Zn-Cr monolithic catalyst for methanol autothermal reforming to hydrogen. The particle size of the Ce-Zr colloid can be effectively adjusted by peptization treatment in order to obtain highly adhesive and uniform washcoat. TEM and XRD results confirmed that Ce-Zr solid solution was formed and the particle size of Ce-Zr composite oxide powder calcined at 1 073 K was still maintained within 20～ 50 nm. To avoid coating flaking, different drying methods during coating process were investigated in details. The results indicated that the microwave method was more favorable for the drying of moisture in honeycomb channels, while the oven drying method caused washcoat severely cracking. The Zn-Cr/Ce-Zr monolithic catalyst was more stable than that of no Ce-Zr washcoat because of the unique redox property of Ce-Zr mixed oxide. The temperature of the catalyst bed indicated that Ce-Zr washcoat exhibited better energy match of exothermic reaction and endothermic reaction, avoiding the hot-spot and prohibiting active species sintering.