Seemingly Anomalous Angular Distributions in H + D2 Reactive Scattering

J. Jankunas, R. N. Zare, F. Bouakline, S. C. Althorpe, D. Herraez-Aguilar, F. J. Aoiz
2012 Science  
MFI lamellae are unique among the available aluminosilicate zeolite lamellae because they have pores that run across the lamella thickness (3). The nanometer-scale diffusion lengths of pillared MFI and SPP allow for fast transport even for molecules with small micropore diffusivity. In this respect, pillared MFI and SPP are valuable model materials for the quantitative assessment of diffusion limitations and intrinsic kinetics. The self-etherification of benzyl alcohol in the presence of DTBP
more » ... sed in order to deactivate the external sites) was considered as an example. The plot of the effectiveness factor versus the Thiele modulus shows excellent agreement with the experimental data (23, 29), from which it can be concluded that Brønsted acid sites in the micropores of SPP and pillared MFI have reactivity similar to those in conventional and nanocrystalline MFI, and that the observed differences in apparent reaction rates can be fully accounted for by diffusion limitations. A comparison of effectiveness factors with that of a commercially available ZSM-5 catalyst (dashed line in Fig. 4B ) reveals that 3DOm-i, pillared MFI, and SPP catalysts exhibit higher apparent reaction rates. Improved behavior of pillared MFI and SPP was also established in other reactions. For example, etherification of 5-hydroxymethyl-2-furaldehyde (HMF) to 5,5′-oxy(bismethylene)-2-furaldehyde (OBMF) proceeds to completion, whereas commercial ZSM-5 suffers from deactivation (Fig. 4C) . Because OBMF is a desirable biobased intermediate (30), this finding underscores the potential of single-unit cell layers in applications beyond petrochemical processing. Branching of zeolite nanometer-sized lamellae, through repetitive twinning or other intergrowth processes, is a new low-cost approach toward hierarchical materials with interconnected micropores and mesopores. It is in principle ap-plicable to all zeolite structures that can (i) be grown anisotropically as thin layers and (ii) can support branching at certain acute angles (supplementary text and fig. S16 ).
doi:10.1126/science.1221329 pmid:22745425 fatcat:7xji24vigbfajhh2vfm76odzgm