The pore network architecture of porous heterogeneous
catalyst
supports has a significant effect on the kinetics of mass transfer
occurring within them. Therefore, characterizing and understanding
structure–transport relationships is essential to guide new
designs of heterogeneous catalysts with higher activity and selectivity
and superior resistance to deactivation. This study combines classical
characterization via N2 adsorption and desorption and mercury
porosimetry with advanced scanning electron microscopy (SEM) imaging
and processing approaches to quantify the spatial heterogeneity of
γ-alumina (γ-Al2O3), a catalyst
support of great industrial relevance. Based on this, a model is proposed
for the spatial organization of γ-Al2O3, containing alumina inclusions of different porosities with respect
to the alumina matrix. Using original, advanced SEM image analysis
techniques, including deep learning semantic segmentation and porosity
measurement under gray-level calibration, the inclusion volume fraction
and interphase porosity difference were identified and quantified
as the key parameters that served as input for effective tortuosity
factor predictions using effective medium theory (EMT)-based models.
For the studied aluminas, spatial porosity heterogeneity impact on
the effective tortuosity factor was found to be negligible, yet it
was proven to become significant for an inclusion content of at least
30% and an interphase porosity difference of over 20%. The proposed
methodology based on machine-learning-supported image analysis, in
conjunction with other analytical techniques, is a general platform
that should have a broader impact on porous materials characterization.