Optimizing Selectivity in VOx/TiO2 Catalysts for Ammoxidation: Insights from Structure–Performance Relationships
Multicomponent reactions such as ammoxidation are highly desirable for chemical synthesis. The complicated reaction network and catalytic active sites involved, however, make it rather challenging for extensive structure–performance relationship investigations and subsequent rational design of an efficient catalyst. In this work, efficient VOx/TiO2 catalysts with concise components and exquisite structure design demonstrated 95% selectivity at 98% conversion under 2070 h–1 for 3-picoline ammoxidation. After clarifying that the oxidative dehydrogenation process is rate-limiting, we assumed that the abundance of reactive surface lattice oxygen at the interface of vanadium–titanium is the key to high productivity and suppression of oxidation side reactions since low reaction temperature is beneficial for enlarging the difference in rates of different energy barriers. In addition, rather than applying the traditional neutralization method with alkaline components, in situ formed V2O5 crystallite was subtly to cover the strong acid sites on VOx/TiO2 catalysts in that the strong adsorption of pyridine nitrogen in 3-cyanopyridine on strong acid sites can lead to severe hydrolysis side reactions.
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