Hangchun Hu

Redox properties of niobium oxide catalysts

Niobia catalysts can contain niobium oxide as a two-dimensional niobium oxide overlayer (surface niobia species), an oxide support (niobia supported surface redox sites) or a mixed oxide (solid solution or compound of niobium oxide). The molecular structures and redox properties of these different niobia-containing catalysts are investigated for several different oxidation reactions. These studies reveal that niobia present as surface metal oxide species, an oxide support and mixed oxides can directly as well as indirectly influence the redox properties of oxide catalysts.

Development of active oxide catalysts for the direct oxidation of methane to formaldehyde

Formaldehyde is currently produced from methane by a three-step process involving H2/CO synthesis gas and methanol as intermediates, and development of a single-step process would have great economic incentive for producing this commodity chemical. A historical perspective is presented here in regard to the research carried out with heterogeneous metal oxide catalysts in attempts to achieve selective oxidative conversion of methane to formaldehyde. The concepts employed, both chemical and engineering, are described, and these include dual redox promoters and double-bed catalysts. More recent work in this laboratory has found V2O5/SiO2 catalysts to be very active partial oxidation catalysts. The space-time yield of and selectivity toward formaldehyde are improved by the presence of steam in the methane/air reactant mixture, and an attractive feature of the product mixture is the low quantity of carbon dioxide produced. Space-time yields of >1.2 kg CH2O/kg catalyst per h have been achieved.

Molecular design of supported metal oxide catalysts: An initial step to theoretical models

Abstract Molecular design of supported metal oxide catalysts is now possible from molecular level information obtained from Raman spectroscopy and the methanol oxidation reaction. The important factors that influence the molecular design of the supported metal oxide catalysts are the specific oxide support and the specific surface metal oxide. The structure or modification of the oxide support, however, has no effects on the surface metal oxide structure and reactivity. The surface coverage of the specific surface metal oxide, however, influences the reactivity during the methanol oxidation reaction. The synthesis method is not critical since it does not influence the surface metal oxide structure or reactivity. Calcination temperature is not important as long as moderate temperatures (350–500°C) are used. The current fundamental information available about the physical and chemical characteristics of the supported metal oxide catalysts provides a foundation for theoretical models to be developed with respect to their solid—solid and solid—gas interactions.

Molecular Design of Supported Metal Oxide Catalysts

Abstract This study demonstrates that molecular design of supported metal oxide catalysts is possible from molecular level information obtained from combined Raman spectroscopy and the methanol oxidation reaction. The important factors that influence the molecular design of the supported metal oxide catalysts are the specific oxide support (factor of ∼10 3 ) and the specific surface metal oxide (factor of ∼10 1 ). The synthesis method is not critical since it does not influence the surface metal oxide structure or reactivity. Calcination temperature is not important as long as moderate temperatures (350–500°C) are used.

Direct conversion of methane to methanol and formaldehyde over a double-layered catalyst bed in the presence of steam

Using a double-bed reactor configuration with an up-stream 1 mass% SO42–/1 mass% SrO/La2O3 catalyst to generate methyl radicals and a down-stream 1 mass% V2O5/SiO2 catalyst to stabilize the methyl radicals for reaction to form hydrolysable methoxide species, the methanol and formaldehyde space–time yields are increased up to five-fold for partial oxidation of methane in the presence of air and steam at moderate temperatures of 550–600 °C as compared with the single-bed 1 mass% V2O5/SiO2 catalyst, while little of these oxygenates are formed over a mechanically mixed catalyst bed.

Partial Oxidation of Methane by Molecular Oxygen Over Supported V2O5 Catalysts: A Catalytic and in situ Raman Spectroscopy Study

The direct conversion of methane to methanol and formaldehyde via partial oxidation is still a very challenging research area in fundamental heterogeneous catalysis. Many catalyst systems have been investigated for this process and review articles are available in the literature.1,2 Silica supported V2O5 and MoO3 have been studied extensively, 3–6 and V2O5/SiO2 was found to be one of the most active and selective catalysts for methane partial oxidation to formaldehyde either by using N2O3 or molecular oxygen4,5 as oxidants. Besides steady-state catalytic tests, there are very few studies that have focused on correlations between the structures of catalysts and their catalytic performances or establishing the nature of the active sites for methane partial oxidation.