de Winter D A Matthijs, Meirer Florian, Weckhuysen Bert M
Inorganic Chemistry and Catalysis Group, Debye Institute for Nanomaterials Science, Utrecht University , Universiteitsweg 99, 3584 CG Utrecht, The Netherlands.
ACS Catal. 2016 May 6;6(5):3158-3167. doi: 10.1021/acscatal.6b00302. Epub 2016 Apr 18.
The overall performance of a catalyst particle strongly depends on the ability of mass transport through its pore space. Characterizing the three-dimensional structure of the macro- and mesopore space of a catalyst particle and establishing a correlation with transport efficiency is an essential step toward designing highly effective catalyst particles. In this work, a generally applicable workflow is presented to characterize the transport efficiency of individual catalyst particles. The developed workflow involves a multiscale characterization approach making use of a focused ion beam-scanning electron microscope (FIB-SEM). SEM imaging is performed on cross sections of 10.000 μm, visualizing a set of catalyst particles, while FIB-SEM tomography visualized the pore space of a large number of 8 μm cubes (subvolumes) of individual catalyst particles. Geometrical parameters (porosity, pore connectivity, and heterogeneity) of the material were used to generate large numbers of virtual 3D volumes resembling the sample's pore space characteristics, while being suitable for computationally demanding transport simulations. The transport ability, defined as the ratio of unhindered flow over hindered flow, is then determined via transport simulations through the virtual volumes. The simulation results are used as input for an upscaling routine based on an analogy with electrical networks, taking into account the spatial heterogeneity of the pore space over greater length scales. This novel approach is demonstrated for two distinct types of industrially manufactured fluid catalytic cracking (FCC) particles with zeolite Y as the active cracking component. Differences in physicochemical and catalytic properties were found to relate to differences in heterogeneities in the spatial porosity distribution. In addition to the characterization of existing FCC particles, our method of correlating pore space with transport efficiency does also allow for an up-front evaluation of the transport efficiency of new designs of FCC catalyst particles.
催化剂颗粒的整体性能在很大程度上取决于物质通过其孔隙空间的传输能力。表征催化剂颗粒大孔和中孔空间的三维结构，并建立与传输效率的相关性，是设计高效催化剂颗粒的关键一步。在这项工作中，我们提出了一种普遍适用的工作流程来表征单个催化剂颗粒的传输效率。所开发的工作流程涉及一种利用聚焦离子束扫描电子显微镜（FIB-SEM）的多尺度表征方法。在10.000μm的横截面上进行扫描电子显微镜成像，以可视化一组催化剂颗粒，而FIB-SEM断层扫描则可视化单个催化剂颗粒的大量8μm立方体（子体积）的孔隙空间。利用材料的几何参数（孔隙率、孔隙连通性和非均质性）生成大量类似于样品孔隙空间特征的虚拟三维体积，同时适用于计算要求较高的传输模拟。然后通过对虚拟体积的传输模拟来确定传输能力，传输能力定义为无阻流量与受阻流量之比。模拟结果被用作基于与电网类比的放大程序的输入，同时考虑到更大长度尺度上孔隙空间的空间非均质性。针对两种以Y型沸石为活性裂化组分的工业制造的流化催化裂化（FCC）颗粒，展示了这种新方法。发现物理化学和催化性能的差异与空间孔隙率分布的非均质性差异有关。除了对现有FCC颗粒进行表征外，我们将孔隙空间与传输效率相关联的方法还允许对FCC催化剂颗粒新设计的传输效率进行前期评估。
