Abstract
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.
Highlights
Nowadays, methane is being considered as a renewable energy carrier [1]
Pd and NiO as well as Pd and Co3 O4 were recorded over time, leading to a change of the nature of the active sites, which is discussed according to X-ray Photoelectron Spectroscopy (XPS) (X-ray photoelectron spectroscopy) and Transmission Electron Microscopy (TEM)
The combustion temperature decreases of about 100–150 ◦ C by functionalization of the metal oxides with 1 wt % Pd and full conversion over
Summary
Methane is being considered as a renewable energy carrier [1] It is a questionable development since methane possesses a 25 times higher greenhouse gas potential [2], and low temperature exhaust gas streams from combustion engines contain up to 5000 ppm of unburned methane [3]. The reduction of methane emissions is addressed to novel catalysts, which are highly active at low temperature over time on stream. Such catalysts are still not yet available. Pd and NiO as well as Pd and Co3 O4 were recorded over time, leading to a change of the nature of the active sites, which is discussed according to XPS (X-ray photoelectron spectroscopy) and TEM (Transmission electron microscopy) data
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