Methylcyclohexane Ring Contraction

Zeolite crystal size can be a critical performance parameter in case of reactions with intracrystalline diffusion limitations. Minimizing diffusion limitations is possible through use of nano-zeolites. However, it should be noted that, due to the high ratio of external to internal surface area nano-zeolites may enhance reactions that are catalyzed in the pore mouths relative to reactions for which the transition states are within the zeolite channels. A 1.0 (xm spherical zeolite crystal has an external surface area of approximately 3 m /g, no more than about 1% of the BET surface area typically measured for zeolites. However, if the crystal diameter were to be reduced to 0.1 (xm, then the external surface area becomes closer to about 10% of the BET surface area [41]. For example, the increased 1,2-DMCP 1,3-DMCP ratio observed with decreased crystallite size over bifunctional SAPO-11 catalyst during methylcyclohexane ring contraction was attributed to the increased role of the external surface in promoting non-shape selective reactions [65]. 

Vaughan, D.E.W., Strohmaier, K.C., Kliewer, W.R., and Leta, D.P. (2005) Methylcyclohexane ring-contraction a sensitive solid acidity and shape selectivity probe reaction. J. Phys. Chem. B, 109 (6), 2222-2226. 

Fig. 18 Schematic diagram of ring contraction intermediates from methylcyclohexane. Adapted from ref. 95.

Scheme 8.10 Acid catalysed ring contraction of methylcyclohexane.

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