Tuning Catalytic Selectivity of Oxidative Catalysis through Deposition of Nonmetallic Atoms in Surface Lattice of Metal Oxide

Catalytic selectivity for producing an ideal product is a key topic for chemical transformations through heterogeneous catalysis. Tuning catalytic selectivity by integrating the second metal to form an alloy has been well demonstrated in the literature. Here we report a method to tune catalytic selectivity in oxidative catalysis on another category of heterogeneous catalysts, transition-metal oxides. By choosing the oxidative dehydrogenation (ODH) of ethane to ethylene as a probe reaction, we demonstrated that doping nonmetallic atoms to the surface lattice of catalyst of a transition-metal oxide can enhance catalytic selectivity through suppression of complete oxidation of the reactant molecules. Catalysts of Co3O4 with doped silicon atoms (Si-x-Co3O4) maintaining the spinel structure of pure Co3O4 exhibit much higher selectivity for the production of ethylene through ODH of ethane in comparison to pure Co3O4 at 600 degrees C by 40%. The suppression of activity of surface lattice oxygen atoms was evidenced by the observation that the surface lattice oxygen atoms of Si-x-Co3O4 cannot exchange oxygen atoms with gas-phase oxygen at low temperatures while pure Co3O4 can. The difference in releasing surface lattice oxygen atoms and dissociating molecular oxygen between pure Co3O4 and Si-x-Co3O4, was supported by DFT calculations. The calculated activation barriers for dissociation of molecular O-2 and energy barriers for hopping surface oxygen vacancies of Si-x-Co3O4, are obviously higher than those of pure Co3O4, respectively. These experimental exploration and computational studies established a correlation between increase of catalytic selectivity and suppression of the activity of surface lattice oxygen atoms/oxygen vacancies. This correlation suggests an approach for increasing the catalytic selectivity of oxidative catalysis through suppressing activity of surface lattice oxygen atoms/vacancies via doping atoms of a nonmetallic element. This new approach was further confirmed by the observed higher catalytic selectivity for production of ethylene on Geol-Co3O4 in comparison to pure Co3O4.