Influence of Tight Confinement on Selective Oxidative Dehydrogenation of Ethane on MoVTeNb Mixed Oxides

M1 phase MoVTeNb mixed oxides exhibit unique catalytic properties that lead to high C 2 H 4 yields in oxidative conversion of C 2 H 6 at moderate temperatures. The role of the heptagonal channel micropores of the M1 phase in regulating reactivity and selectivity is assessed here using reactant size-dependent kinetic probes and density functional theory (DFT) treatments for C 2 H 6 and cyclohexane (C 6 H 12 ) activations inside and outside the micropores. The sizes of C 2 H 6 and the micropores suggest a tight guest–host fit, but C 6 H 12 cannot access intrapore sites. Measured C 2 H 6 to C 6 H 12 activation rate ratios on MoVTeNbO are much higher than those measured on nonmicroporous vanadium oxides (VO x /SiO 2 ) and estimated by DFT on external surfaces, suggesting that most C 2 H 6 activations on MoVTeNbO occur inside the micropores under typical conditions. C 2 H 6 exhibits higher activation energy than C 6 H 12 on VO x /SiO 2, consistent with the corresponding C–H bond strengths; the activation energy difference between C 2 H 6 and C 6 H 12 is lower on MoVTeNbO because micropores stabilize C–H activation transition states through van der Waals interactions. Product selectivities for C 2 H 6 and C 6 H 12 suggest that the ability of VO x /SiO 2 to activate C–H bonds and resist O-insertion in products is similar to the external surfaces of MoVTeNbO, but the micropores in the latter oxides are more selective for C–H activation. DFT calculations show that the tight confinement in micropores hinders the C–O contact necessary for O-insertion. These insights provide guidance for utilizing shapes and sizes of confining voids to mitigate selectivity limitations dictated by thermodynamics of sequential oxidation reactions and electronic properties of redox catalysts.