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Organisationseinheit der BAM
VMCM-41 catalysts from two different tetravalent Vanadium sources, hydrothermally synthesized after a mild gelation step at room temperature, were used as catalysts for the selective oxidation of methane to formaldehyde.
Vanadyl acetylacetonate as VMCM-41 precursor, facilitates highest VOx density with predominance of monomeric and a small portion of low-oligomeric VOx species. It produces CH2O in high yield and the highest space time yield (STYCH2O) reaches 5.3 kgCH2O·kgcat −1·h−1 at 600 °C (rate of formation, rCH2O of 363 h−1).
VMCM-41 synthesized from vanadyl sulfate hydrate precursor contains a more significant portion of low-oligomeric species. With a lower V loading, these VOx species are significantly less active resulting in a Maximum STYCH2O of 2.7 kgCH2O·kgcat −1·h−1 at 625 °C (rCH2O of 243 h−1).
Structural changes of highly active Pd/MeOx (Me = Fe, Co, Ni) during catalytic methane combustion
(2018)
Fe2O3, Co3O4 and NiO nanoparticles were prepared via a citrate method and further functionalized with Pd by impregnation. The pure oxides as well as Pd/Fe2O3, Pd/Co3O4, and Pd/NiO (1, 5 and 10 wt % Pd) were employed for catalytic methane combustion under methane lean (1 vol %)/oxygen rich (18 vol %, balanced with nitrogen) conditions. Already, the pure metal oxides showed a high catalytic activity leading to complete conversion temperature of T100 ≤ 500 °C. H2-TPR (Temperature-programmed reduction) experiments revealed that Pd-functionalized metal oxides exhibited enhanced redox activity compared to the pure oxides leading to improved catalytic combustion activity at lower temperatures. At a loading of 1 wt % Pd, 1Pd/Co3O4 (T100 = 360 °C) outperforms 1Pd/Fe2O3 (T100 = 410 °C) as well as 1Pd/NiO (T100 = 380 °C). At a loading of 10 wt % Pd, T100 could only be slightly reduced in all cases. 1Pd/Co3O4 and 1Pd/NiO show reasonable stability over 70 h on stream at T100. XPS (X-ray photoelectron spectroscopy) and STEM (Scanning transmission electron microscopy) investigations revealed strong interactions between Pd and NiO as well as Co3O4, respectively, leading to dynamic transformations and reoxidation of Pd due to solid state reactions, which leads to the high long-term stability.