Abstract
The improvement of methane combustion activity was observed in cyclic temperature-programed and isothermal reactions over Pd/ZrO2 catalysts by simple reduction/reoxidation treatment. The catalytic activity increased during the initial stages of isothermal reaction, and the light-off temperature was lowered as the number of cycles increased in the cyclic temperature-programed reaction. To reveal the origin of activation, variations in the reduction properties after the activation period were carefully investigated through CH4 temperature-programed reduction (TPR) measurements. From the CH4-TPR results, it was confirmed that the reduction temperature decreased significantly after activation. The observation of the CH4-TPR peak at relatively low temperatures is directly proportional to the catalytic activity of CH4 combustion. It was therefore concluded that repeated reduction/reoxidation occurred in the reactant stream, and this phenomenon allowed the combustion reaction to proceed more easily at lower temperatures.
Highlights
Methane is the main constituent of natural gas and is commonly employed as an energy resource.methane is the second largest contributor to global warming after carbon dioxide, and it has a global warming potential 21 times higher than the same mass of carbon dioxide [1]
PdO to metallic Pd0 [8,22,23], and by the accumulation of hydroxyl groups originating from adsorbed water molecules [5,13,26,27] we previously found that catalytic deactivation was prevented on Pd/ZrO2 catalysts [35] with activation being observed only during combustion under identical reaction conditions compared to those employed
We report the catalytic activity of Pd/ZrO2 (x) catalysts treated at different calcination temperatures (i.e., 500–900 ◦ C), and subsequent phenomenon investigation of their catalytic performances in the methane combustion reaction
Summary
Methane is the main constituent of natural gas and is commonly employed as an energy resource. The use of a low temperature ignition catalyst in gas turbines can avoid the necessity to preheat the reactant stream [15] In this context, several studies have reported that the pre-reduction of a catalyst can improve its reactivity, in particular at low temperatures [6,12,17,18,19,20]. Demoulin et al [6] reported activation over Pd/γ-Al2 O3 , which resulted in an increased methane conversion from ~30%~80% over 30 h They proposed that this activation phenomenon was caused by the removal of contaminants from the catalyst surface, sintering of the palladium phase, and structural changes. We expect that the obtained results can be applied as the fundamental foundation for the catalytic methane combustion process, especially for the activity and reaction mechanism at low temperatures
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