Electrochemical Promotion of Nanostructured Palladium Catalyst for Complete Methane Oxidation

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.

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“…Electrochemical promotion of catalysis (EPOC), also named NEMCA (non-Faradaic electrochemical modification of catalytic activity) effect, is a very promising concept for boosting catalytic processes [200]. This general, well-established phenomenon in catalysis aims at controlling in-situ both the activity and the selectivity of a catalyst through application of electric stimuli [201]. EPOC is observed in presence of solid electrolyte materials and porous catalysts.…”

Theoretical insight into the origin of the electrochemical promotion of ethylene oxidation on ruthenium oxide

“…The rates increase due to EPOC and supporting the catalysts on active metal oxides were similar in the case of platinum and ruthenium catalysts 11 . Furthermore, many highly dispersed electrochemically promoted systems have been established, rendering the practical application of EPOC more attractive 11,12,[21][22][23][24][13][14][15][16][17][18][19][20] . Experimentally, the origin of EPOC is mostly explained by the electrochemically induced promoters (see Figure 1), which have been substantiated by many in-situ and ex-situ techniques: x-ray photoelectron spectroscopy (XPS) 25,26 , in-situ XPS 27 , temperatureprogrammed desorption (TPD) 28,29 , scanning tunneling microscopy (STM), photoemission spectroscopy (PES) 30 , in-situ AC impedance spectroscopy 31,32 , and isotopic exchange 33 .…”

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“…On the other hand, a major part of contributions (9/21) concerns original research on nitrogen oxides reduction processes [20][21][22][23][24][25][26][27][28], reflecting the fact that this topic still remains hot among the targets of environmental catalysis. Five out of 21 studies concern CO and hydrocarbons oxidation processes [29][30][31][32][33] while the remained 4/21 concern CO 2 capture/recycling processes under the view of cyclic economy [34][35][36][37].…”

“…Based on the fact that Pd is one of the most active catalysts for complete methane oxidation Baranova and coworkers [32] used the concept of electrochemical promotion of catalysis (EPOC) to further promote the reaction over palladium nano-structured catalysts deposited on yttria-stabilized zirconia (YSZ) solid electrolyte. Anodic polarization (O 2− supply to the catalyst) resulted to a rate enhancement up to~3 at 450 • C with an apparent Faradaic efficiency as high as 3000 (for a current application as low as 1 µA).…”