Diffusion limitations and the negative impact of deactivation on product yields and distributions in zeolites and other microporous catalysts can be considerably reduced by hierarchical architectures with a distribution of pore and grain sizes, facilitating controlled molecular access to and away from active sites (see [1,2] and many references therein).To be effective, however, the intrinsic reaction kinetics and transport mechanisms in these hierarchical designs should be accounted for at multiple scales: inside zeolite nanocrystals, at or across crystal boundaries, and in the meso/macroporous matrix [1-4].Theoretical optimization studies help to indicate which mechanisms predominate, which pore and grain size distributions are favorable, and how sensitive the designs are to various parameters [4-9]. This may guide synthetic efforts that can rely on increasingly nano-resolved approaches, with input from spectroscopy and other characterization tools [2,3,10-15].Industrial process and reactor engineering requirements, including safety and cost, are challenging constraints when implementing novel catalyst designs, however the projected improvements offer excellent opportunities for rational innovation if sensitivity to the various parameters is better understood [14,15].
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