Porous Pseudoboehmite as an Active Matrix of Fluid Catalytic Cracking Catalysts: Effects on Pore Structure and Cracking Performance

Fluid catalytic cracking (FCC) catalysts rich in meso-macro pores are the main development trend to avoid serious diffusion limitation in the FCC process. This study investigated the pore structure characteristics of two kinds of FCC catalysts (FCC-1 and FCC-2) prepared with different porous pseudoboehmite (PB1 or PB2), especially the effects of size, morphology, and stacking mode of PB1 and PB2 matrix particles on the meso-macro pore structure of catalysts. PB1 in granular or spherical shape tends to stack closely and form smaller interparticle pores centered at 5.7 nm, while PB2 in rod or fibrous shape is more conducive to stack loosely and generate much more abundant larger interparticle pores centered at 12.6 nm. Compared to the PB1-based FCC-1 catalyst with mesopores centered at 4.2 nm, the PB2-based FCC-2 catalyst presents more pores in the 5-100 nm range and larger pore volume based on the N2 adsorption method, the frequency of count for pores at 10-100 nm increasing from 25.8% to 62.0% based on focused ion beam-scanning electron microscopy (FIB-SEM). The 3D pore network analysis of FIB-SEM further calculates the porosity (24.3%), interconnected pores (22.9%), and the ratio of interconnected pores to total pores (94.2%) of the FCC-2 catalyst. The FCC-2 catalyst shows superior heavy oil cracking ability and product selectivity than the FCC-1 catalyst, which could be ascribed to the better diffusion performance of larger meso-macro pores. It provides a new matrix-based approach for constructing FCC catalysts rich in meso-macro pore structures, in addition to in situ crystallization and hierarchical porous zeolites.