| The project concerns with design, synthesis and characterization of molecular and extended structure materials composed of vanadium oxides and evaluation of their catalytic oxidative dehydrogenation (ODH) properties. A long-term objective is to develop an understanding of the structure-property relationships in ODH catalysts.;Chapter 1 provides an overview of the field of metal oxides, polyoxometalates, and catalytic oxidative dehydrogenation of propane. This chapter also defines the research problem concerning this thesis and its fundamental and practical significance.;Chapters 2-4 describe the synthesis, characterization and ODH of propane catalytic properties of a select number of structurally correlated vanadium oxide based materials. The ODH catalysts studied in this work include molecular compounds - (NH4)8[VIV12V V6O42(SO4)0.85(VO 4)0.15]•10H2O (NH4-POV) and NH4V 10O28, layered structure materials - MgVV 2VIV2O10•10H2O (MV4) and V2O5, a chain structure - NHu4VO3, and a nanostructured three-dimensional framework material - [CoV 18O42(H2O)12 (XO4)]•24H 2O (X = V, S) (Co-POV), composed of {V18O42(XO 4)} (X = S, V) building units, which is the molecular cluster present in NH4-POV, interconnected by {-O-Co-O-} bridging groups. Alternatively, since the building unit clusters {V18O42XO4} can be viewed as derived from sheets of V2O5, the 3-D structure of Co-POV can be viewed as made of V2O5 and CoO units. Therefore the ODH property of Co-POV was compared with the ODH property of the molecular cluster NH4-POV on one hand and with the V2O 5 and CoO on the other hand. Co-POV was shown to have superior catalytic performance for ODH of propane as compared with its constituent metal oxides, V2O5, CoO and their mixture. ODH of propane reaction over NH4-POV catalyst has higher propylene selectivity of above 60% at moderate temperatures as compared to 37% selectivity of Co-POV catalyst. On the other hand, MV4 showed catalytic activity at marginally low temperature 200 °C due to propane activation energy (Ea) of 27 kJ/mol, the lowest Ea found in this study. Co-POV was also utilized as a model compound to describe the effect of varying doses of gamma-ray irradiation on the catalytic ODH properties of polyoxometalates for the first time. gamma-ray irradiation enhanced catalysts' selectivity to propylene during the oxidative dehydrogenation of propane. |
