The selective oxidation of methane, the primary component of natural gas, remains an important challenge in catalysis. We used colloidal gold-palladium nanoparticles, rather than the same nanoparticles supported on titanium oxide, to oxidize methane to methanol with high selectivity (92%) in aqueous solution at mild temperatures. Then, using isotopically labeled oxygen (O) as an oxidant in the presence of hydrogen peroxide (HO) we demonstrated that the resulting methanol incorporated a substantial fraction (70%) of gas-phase O More oxygenated products were formed than the amount of HO consumed, suggesting that the controlled breakdown of HO activates methane, which subsequently incorporates molecular oxygen through a radical process. If a source of methyl radicals can be established, then the selective oxidation of methane to methanol using molecular oxygen is possible.
Heat treating Fe/ZSM-5 under hydrogen leads to high dispersion of Fe species and higher alcohol selectivity in the oxidation of alkanes, as compared to oxygen treated catalysts.
Methane upgrading into energy-dense liquid derivatives (such as methanol or mid-range hydrocarbons) is a highly desirable process to increase its utilisation. The selective oxidation of methane using hydrogen peroxide has been investigated using unsupported gold-palladium nanoparticles prepared using colloidal methods. The effect of the reaction conditions and the catalyst parameters have been systematically investigated. Poly(vinyl)pyrrolidone (PVP) stabilised Au-Pd colloids produce methyl hydroperoxide as the primary reaction product, which is subsequently converted to methanol with high oxygenate selectivity. The stability and re-use characteristics of the colloidal catalyst have also been assessed for methane oxidation with hydrogen peroxide.
We used rheology and confocal microscopy techniques to characterise the flow of emulsions as the droplets were confined by increasing the drop volume fraction and reducing the distance between the shearing surfaces. Slip was minimised by matching the density of the oil and water phases. Attractive interactions between the drops caused them to flocculate. The contribution of the emulsion microstructure to its shear response becomes significant when the oil drop flocs almost span the distance between the surfaces. We found that confining the flow of droplet flocs causes a transition from a fluid phase with shear thinning flow behaviour into a jammed, solid-like material. The large deformations caused by flow at the maximum drop packing fraction induce droplet coalescence within highly localised regions of the emulsion.
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