Using PFG‐NMR and iGC to Study Diffusion and Adsorption in Heterogeneous Catalysts

Abstract

Mass transport in porous systems is inherently complex, but also of utmost importance for industrial processes such as heterogeneous catalysis. For each of the different length scales of diffusive motion involved, specific characterization techniques have been developed – including, but not limited to PFG‐NMR, ZLC measurements and iGC. While each method can deliver detailed information on certain types of diffusion, none of them delivers a full picture of mass transport across multiple length scales. The goal of the present work was to evaluate the technical feasibility and characterization potential of the hyphenated combination of PFG‐NMR and iGC in a coupled experimental setup. Challenges, advantages, and limitations of this approach are discussed. It is shown that the simultaneous detection of self‐diffusion on short length scales (as probed by PFG‐NMR) and transport diffusion covering longer distances (detectable by iGC) cannot be realized under the used conditions, essentially due to the lack of kinetic control at higher reactant loadings. The key advantage of the developed coupled setup is the ability of the iGC instrument to provide defined and readily variable levels of catalyst loading, which enables advanced pore connectivity studies by PFG‐NMR and yields thermodynamic data on reactant adsorption at the same time.