(560hl) Raman-Spectrokinetics to Gain Insights on Support Effects of Supported Vanadium Oxide Catalysts

Bridging the gap between observed structure and measured reactivity of supported metal oxide catalysts continues to be a challenging goal for the complex catalytic systems typically used in oxidative and non-oxidative dehydrogenation of hydrocarbons. Supported ternary metal oxides are no exception with reactivity being influenced by catalyst coverage, relative amounts of species on the support, and the kind of support used. In this study, by combining operando Raman spectroscopy with conventional time-resolved reaction kinetics, we measure the redox reaction rates of surface species directly from the Raman spectra. This approach, coined Raman-spectrokinetics, exceeds one major limitation of measuring kinetics by mass spectrometry (MS) and gas chromatography (GC). It allows us to observe reaction rates at a specific catalytic site while conventional MS and GC analysis only provide overall reaction rates (average rates from the entire samples’ sites). This study is a continuation of an earlier study which explored the oxidation of (VO_x)_m/(NbO_y)_n/SiO₂catalysts. Herein, we aim to determine support effects using our Raman-spectrokinetics approach to gain new insights on the oxidation kinetics of supported vanadium oxide catalysts by following the evolution/depletion of the vandyl (V=O) vibration as a function of O₂/H₂concentration. It is known that turnover frequency in catalysts remains constant as a function of coverage, and we are observing the same phenomena via Raman-spectrokinetics. It is our expectation that this study will launch our use of the Raman-spectrokinetics approach in studying the reactivity of metal oxides at different MO_xcoverage (2D and 3D species), on different supports (SiO₂, Al₂O₃, TiO₂, ZrO₂), with different promoters ((M₁O_x)_m-(M₂O_y)_n/support multi-component systems), and with different surface structures. These insights will further our goal of preparing catalysts with rational design choices in order to achieve unprecedented catalytic performances with supported metal oxide catalysts.