CuO/ZrO_2催化水煤气变换反应制氢:ZrO_2载体焙烧温度的影响

CuO/ZrO_2 catalysts for the production of H_2 through the water-gas shift reaction:Effect of calcination temperature of ZrO_2

以经不同温度(120、250、350、450℃)焙烧处理的ZrO_2为载体,采用沉积-沉淀法制备了系列CuO/ZrO_2催化剂;考察了富氢气氛下催化剂的水煤气变换反应(WGS)催化性能。结果表明,CuO/ZrO_2催化剂的催化活性随ZrO_2载体焙烧温度的升高呈现先升高后降低的"火山型"变化趋势,在焙烧温度为250℃时取得最高值。采用X射线粉末衍射、N_2物理吸附-脱附、N_2O滴定、H_2程序升温还原和CO程序升温还原及质谱跟踪等技术研究了系列ZrO_2载体及CuO/ZrO_2催化剂的结构和还原性能。结果表明,随着ZrO_2焙烧温度的升高,一方面,CuO/ZrO_2催化剂的Cu分散度逐渐降低,与ZrO_2具有强相互作用的高分散活性Cu-[O]-Zr物种("[]"表示ZrO_2表面氧空位)逐渐减少;另一方面,Cu-[O]-Zr物种的还原能力逐渐增强,并诱导催化剂活性表面羟基的还原能力也相应增强(CO为还原剂),即降低了催化剂对WGS反应的起活温度。两方面的综合作用使得ZrO_2载体焙烧温度为250℃(中等温度)时,CuO/ZrO_2催化剂的WGS催化活性最高。

A series of CuO/ZrO2 catalysts were prepared by a deposition-precipitation method using ZrO2 calcined at various temperatures(120,250,350 and 450℃)as supports.The water-gas shift(WGS)reaction was carried out on these catalysts using H2 rich reactant gas(15%CO,55%H2,23%N2,7%CO2).It was shown that the catalytic activity of the catalysts increased at first and then decreased with increasing calcination temperature of ZrO2.The catalyst supported on ZrO2 calcined at 250℃showed the highest catalytic activity.The structure and reducibility of CuO/ZrO2 catalysts were studied by various techniques,such as XRD,N2-physisorption,N2 O titration,H2-TPR and CO-TPR-MS.The results showthat the Cu dispersion and the proportion of catalytically active Cu-[O]-Zr species('[]'represents an oxygen vacancy on ZrO2 support)decrease with the increase of ZrO2 calcination temperature.The calcination of ZrO2 at higher temperature leads to an improvement of the reducibility of Cu-[O]-Zr species and hydroxyl groups on the CuO/ZrO2 catalysts,resulting in an easier onset of the surface WGS reaction between surface hydroxyl groups and CO reductant.The two factors reach a balance for the catalyst supported on ZrO2 calcined at 250℃(moderate temperature),as is thought to be responsible for the highest WGS activity of this catalyst.