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Third Meeting of the |
Grazie! |
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Novel Nano-Dispersed Early
Transition Oxide Catalysts
Dr. Charles H. F. Peden ABSTRACT Supported transition metal oxides (TMOs) are among the most important family of catalysts used in the chemical and petroleum industries, with applications for that include polymerization, selective oxidation, oxidative dehydrogenation, isomerization, metathesis, and selective catalytic reduction. This wide range of useful chemistry is a reflection of the equally wide range of variability in the chemical and physical properties of this important class of catalytic materials. Especially interesting for the supported systems is that the oxide species can adopt a variety of surface structures that are strongly dependent on the sample preparation, such as the metal oxide precursor, the loading amount of the oxide, and the thermal history of these materials. In order to reduce the complexity of TMO catalysts to levels addressable and controllable at the atomic level, we are using newly developed methods for the preparation of tungsten, vanadium, titanium and molybdenum oxide catalyst supported on mesoporous silica, with emphasis on the importance of synthesis conditions on dispersion, structure and activity of the resulting materials. We use a suite of complementary techniques such as DRS UV/Vis, BET, 1H NMR, XRD, UV-Raman, and TEM to study the structural properties of the supported metal oxides, and probe reactions such as 2-butanol dehydration and ethanol partial oxidation to demonstrate the potential advantages of the newly synthesized catalysts. Specifically, highly dispersed oxides of titanium, molybdenum, and tungsten oxide on mesoporous silica were synthesized using a solution-based atomic-layer deposition (ALD) method. It is also demonstrated that attainment of high dispersions of vanadium oxide on mesoporous silica requires the presence of at least a single layer of titanium oxide due to the well-known poor interaction between vanadia and silica. The highly dispersed catalysts prepared here by ALD methods exhibited superior catalytic performance relative to those prepared using conventional incipient wetness impregnation. These studies are part of a large program involving experimental and computational studies of gas-phase transition metal oxide clusters and model, single crystal oxide catalyst materials. A few representative results from these complementary studies will also be presented. |
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