载体孔结构对Pt/疏水陶瓷催化剂性能的影响

Influence of Pore Structure on the Performance of Pt/Ceramic Hydrophobic Catalyst

选用五种不同孔结构疏水陶瓷载体,采用浸渍-气相还原法制备用于水-氢交换的Pt/疏水陶瓷催化剂,经X射线衍射(XRD)、扫描电子显微镜(SEM)、H_2-程序升温还原法(H_2-TPR)及CO脉冲吸附等物性表征及催化剂催化活性(以催化交换活性kya表征)测试来考察载体孔结构对催化剂性能的影响。结果表明,随着平均孔径的降低,载体比表面积增加,催化剂铂粒子分散度提高,在30~70nm平均孔径范围内,催化剂活性随载体孔径的下降而得以提升;当平均孔径小于20nm时,反应气难以在较短时间内扩散至载体孔道内,相同时间内参与反应的活性位点总数较少,从而使得其催化活性有所下降。此外,载体孔隙率过高虽有助于提升比表面积,却使得载体结构较为疏松,在催化剂制备过程中载体孔结构易被破坏,对提升催化活性无利。平均孔径为37.5nm、载体比表面积为111.01m2/g、孔隙率为68.76%的载体可获得最优的催化效果,催化剂测试用量为4.5mL、氢气流速为4.23L/min时,其催化交换活性可达6.45s^(-1)。

Pt/hydrophobic ceramic catalysts used for H_2-H_2O liquid phase catalytic exchange were prepared with five different carriers by the impregnation method.The influences of the pore structure of carriers on the performance of catalysts were studied,and the characteristics of catalysts were tested by XRD,SEM,H_2-TPR and CO adsorption.With the decrease of average pore size,the specific surface area of carriers increases and then the Pt particle dispersion enhances.The catalytic activity increases with the decrease of average pore size in the range of 30-70 nm,while the reactant gas will have more difficulty to spread into the inner tunnel of carrier with the average pore size under 20 nm,resulting in the decreased catalytic activity.Although the enhanced porosity of carrier can create higher specific surface area,it will weaken the strength of pore structure,which will be destroyed during the preparation process and have no benefit to obtain favorable catalytic activity.The catalyst prepared by the carrier with average pore size of 37.5 nm,specific surface area of111.01m^2/g and the porosity of 68.76%can obtain the kyavalue of 6.45s^-1 with 4.5mL catalyst and 4.23L/min gas velocity.