Catalytic selectivity for producing an ideal product is a key topic for chemical transformation through heterogeneous catalysis. Tuning catalytic selectivity by integrating the second metal to form alloy has well demonstrated in literature. Here we reported a method to tune catalytic selectivity on another category of heterogeneous catalyst, transition metal oxide. By choosing oxidative dehydrogenation of ethane to ethylene as a probe reaction, we demonstrates here that doping nonmetallic atoms to surface lattice of catalyst can enhance catalytic selectivity to the ethylene through suppression of complete oxidation of ethane. Catalysts of Co3O4 with doped silicon atoms (Si-Co3O4) remain the spinel structure of pure Co3O4. They exhibit much higher selectivity for the production of ethylene through oxidative dehydrogenation of ethane compared to pure Co3O4 at 600oC by 41%. The suppression of activity of surface lattice oxygen atoms was evidenced by the observation that the surface lattice oxygen atoms (O16) of Si/Co3O4 cannot exchange oxygen atoms with gas phase O218 at temperature below 425oC while pure Co3O4 does. The same effect of promoting catalytic selectivity was found in Ge0.2-Co3O4 with high catalytic selectivity than pure Co3O4. The difference in releasing surface lattice oxygen atoms and dissociating molecular oxygen between pure Co3O4 and Si/Co3O4 was supported by DFT calculations. The activation barriers for dissociation of molecular O2 to atoms oxygen and hopping barrier of surface oxygen vacancies of Si/Co3O4 are obviously higher than pure Co3O4. These experimental and computational studies established a correlation between increase of catalytic selectivity and suppression of the activity of surface lattice oxygen atoms. This insight suggests an approach for increasing catalytic selectivity of ODH through suppressing activity of surface lattice oxygen through doping non-metallic elements. This approach was confirmed by the higher selectivity of ODH on Co3O4 doped with Ge than pure Co3O4.

Tuning catalytic selectivity on metal oxide through doping nonmetallic atoms

251st National Meeting (2016)

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