多孔莫来石陶瓷球催化剂载体孔结构设计及调控研究

Due to the active site for the catalytic reaction is distributed over the surface of the catalytic support, the specific surface area of catalyst is lowered, which restricts the adsorption /catalytic efficiency of the fluidized-bed reactor. To increase the specific surface area of catalyst, the present study focuses on the fabrication of highly porous ceramic microspheres with interconnected fiber-based network structure via oil-drop molding method accompanied by freeze casting process. And the pore structure is designed through the ice-templated pore in freeze casting process and the in-situ mullite whisker in sintering process. By analyzing the pore structure of green body and the topography of in-situ mullite grains, the effect of the curvature radius on the pore structure of green body, and the effect of pore structure of green body on the morphology and particle size of mullite grains is to be revealed so that a porous mullite microspheres with interconnected pore structure and high specific surface area can be designed and controlled. And furthermore, the effect of the characteristic parameters of pore structure and morphology of mullite grains on the catalytic activity and mechanical strength is to be investigated. This can be help to obtain the ideal porous mullite microspheres should have both high mechanical strength and high catalytic activity by tailoring the pore structure of porous mullite microspheres. This project will have important theoretical value on the application of the obtained microspheres in fluidized-bed reactor by additional functionalization step.

目前流化床用球形催化剂的活性组分易被限制在球形载体表面，有效比表面积较小，严重制约其吸附/催化效率。本项目以提高载体有效比表面积为目标，将油中滴液法与冷冻成型工艺相结合，利用冰晶模板造孔和原位生成的莫来石晶须共同设计孔结构，制备一种具有纤维网络状结构的多孔陶瓷球载体。分析成型后的坯体孔结构及烧结后的晶粒形貌，重点揭示液滴曲率半径对坯体孔结构的影响，阐明烧结过程中孔结构对莫来石晶粒形貌的影响机制，构建一种具有连通孔结构、高比表面积的多孔莫来石陶瓷球；在研究孔结构特征参数和莫来石晶粒形貌对催化效率和机械强度的影响规律的基础上，揭示孔结构对性能的调控机制，进而实现催化效率和力学性能的匹配。为多孔莫来石陶瓷球的进一步功能化，实现其在流化床中的应用提供理论支持。

目前，球形陶瓷催化剂载体低比表面积、活性组分低负载率严重制约其吸附/催化效率。本项目提出采用滴液法和冷冻成型相结合的工艺制备高比表面积的类纤维网络状多孔莫来石陶瓷球载体，为活性组分提供充足的附着位点来提高负载率。从冷冻成型中冰晶形成和烧结过程莫来石晶须生长角度出发，探明多孔莫来石陶瓷球孔结构的构建机制；建立孔结构特征与机械性能之间的内在联系；并分析其负载活性组分后的催化/吸附性能，为多孔莫来石陶瓷球载体的开发和利用提供理论和技术支持。.通过本项目的实施，在多孔莫来石陶瓷球的可控制备及其功能化应用取得一系列进展，包括：（1）利用滴液法和冷冻成型相结合工艺制备出球形度好且粒度均匀的多孔莫来石陶瓷珠；（2）揭示了陶瓷球坯体在冷冻过程孔结构的形成机理：液滴被低温介质浸没和包围后，水结晶潜热由内向外释放，从而形成从液滴中心到表面径向方向的温度梯度，冰晶从球体表面向中心生长，从而呈现放射状孔结构；（3）研究了固相含量及烧结工艺对莫来石晶粒形貌影响，结果表明：高孔隙率及较大孔结构有利于高长径比莫来石生成，一方面，大孔及高气孔率有利于气体的扩散促进气固反应；另一方面，可削弱晶粒生长过程中的空间位阻效应；（4）通过磨损率测试分析发现：除固相含量外，长棒状晶粒形成的互锁结构也利于提高其磨损性能，然而，随着晶粒生长孔壁结构的消失会减低其磨损性能；（5）以多孔莫来石陶瓷球为载体负载ZIF-8，发现ZIF-8晶粒可均匀负载于莫来石晶粒表面，比表面积达到272 m2/g，对有机染料CR吸附性良好，验证了其作为催化剂载体的可行性。本项目执行期间，发表论文2篇（部分成果在整理投稿阶段），申请专利2项（授权1项），获省部级二等奖一项。