Structure and Vibrational Properties of Potassium-Promoted Tungsten Oxide Catalyst Monomeric Sites Supported on Alumina (K2O/WO3/Al2O3) Characterized Using Periodic Density Functional Theory

Al2O3-supported tungsten oxide catalysts have been instrumental in many industrially relevant reactions and their reactivity is controlled by their molecular structure. In turn, their molecular structure has primarily been derived via Raman measurements with assignments made using model compounds of known local (molecular) coordination. In this work, the structure and simulated Raman spectra of unpromoted and K+-promoted tungsten oxide catalyst monomeric sites supported on γ-Al2O3(110) (K2O/WOx/γ-Al2O3(110)) were studied using periodic DFT methods. Two different WOx-grafted monomers on the γ-Al2O3(110) surface were identified with a total energy difference of 0.17 eV between both structures. Importantly, both structures showed the presence of W═O and W–OH moieties, thus providing additional insights into experimental Raman data, which typically describe only W═O moieties. The grafted WO3 species were stabilized when the present W–OH groups were oriented toward the alumina surface leading to the formation ...