Abstract
Electrochemical promotion of catalysis (EPOC) was investigated for methane complete oxidation over palladium nano-structured catalysts deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. The catalytic rate was evaluated at different temperatures (400, 425 and 450 °C), reactant ratios and polarization values. The electrophobic behavior of the catalyst, i.e., reaction rate increase upon anodic polarization was observed for all temperatures and gas compositions with an apparent Faradaic efficiency as high as 3000 (a current application as low as 1 μA) and maximum rate enhancement ratio up to 2.7. Temperature increase resulted in higher enhancement ratios under closed-circuit conditions. Electrochemical promotion experiments showed persistent behavior, where the catalyst remained in the promoted state upon current or potential interruption for a long period of time. An increase in the polarization time resulted in a longer-lasting persistent promotion (p-EPOC) and required more time for the reaction rate to reach its initial open-circuit value. This was attributed to continuous promotion by the stored oxygen in palladium oxide, which was formed during the anodic polarization in agreement with p-EPOC mechanism reported earlier.
Highlights
Natural Gas Vehicles (NGVs) have gained considerable attention in the last decade due to much lower greenhouse gas emissions and lower price of methane compared to diesel or gasoline. CH4 is abundant in natural gas form, but methane can be produced using anaerobic digestion technologies of bio-derived sources [1,2,3,4]
From the practical point of view it is essential to work with low loadings of noble-metal catalysts that exhibit high dispersion and large active surface area In the present work, we report electrochemical promotion of nano-structured, highly dispersed Pd catalyst prepared by polyol reduction method for CH4 complete oxidation in the temperature range of 400 and 450 ◦ C and various gas compositions
Electrochemical promotion of Pd nanostructured catalyst was investigated for the methane oxidation reaction in the 400–450 ◦ C temperature range
Summary
Natural Gas Vehicles (NGVs) have gained considerable attention in the last decade due to much lower greenhouse gas emissions and lower price of methane compared to diesel or gasoline. The addition of CeO2 layer between the YSZ solid-electrolyte and Pd film catalyst increased the open-circuit catalytic rate but decreased the apparent Faradaic efficiency due to the higher electric resistance [18]. From previous EPOC studies on Pd for complete CH4 oxidation, it is clear that the catalyst preparation method has a strong influence on Pd morphology, structure, oxidation state and as a result, on its catalytic activity, degree of promotion and stability under open and closed circuit conditions. From the practical point of view it is essential to work with low loadings of noble-metal catalysts that exhibit high dispersion and large active surface area In the present work, we report electrochemical promotion of nano-structured, highly dispersed Pd catalyst prepared by polyol reduction method for CH4 complete oxidation in the temperature range of 400 and 450 ◦ C and various gas compositions.
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