Electrochemical Promotion of Oxidative Coupling of Methane on Platinum/Polybenzimidazole Catalyst

Abstract

The electrochemical promotion of catalytic methane oxidation was studied using a false(CH4,O2,normalArfalse),normalPt| polybenzimidazole false(PBIfalse)­H3PO4|normalPt,false(H2,normalArfalse) fuel cell at 135°C. It has been found that C2H2, CO2, and water are the main oxidation products. Without polarization the yield of C2H2 was 0.9% and the yield of CO2 was 7.3%. This means that C2 open-circuit selectivity was approximately 11%. Open-circuit voltage was around 0.6 V. It has been shown that the CH4→C2H2 catalytic reaction can be electrochemically promoted at negative polarization and exhibits a clear “volcano-type” promotion behavior, meaning that there was a maximum promotion effect at a polarization of −0.15 V, or 0.45 V catalyst potential vs. a hydrogen electrode (3.8% C2H2 yield). The catalytic rate enhancement ratio, rfalse(C2false)/rnormalofalse(C2false), at this maximum was 4.2. There was no C2H2 production at polarization ⩾0.1 and ⩽−0.3 V. The yield of C2H2 decreased with decreasing temperature. Dependence of CO2 yield on polarization also showed a “volcano-type” behavior with maximum yield of 8.3% at −0.15 V polarization. The catalytic rate enhancement ratio for CO2 production, rfalse(CO2false)/rnormalofalse(CO2false), at this maximum was 1.1, which means that this catalytic reaction is only slightly affected by the electrochemical polarization. This indicates that polarization especially affects the C2 selectivity of the catalyst. The obtained data was explained by the electrochemical production of Pt-H active centers at the electrolyte-catalyst-gaseous reactant interface false(λ≫1false). © 2002 The Electrochemical Society. All rights reserved.

Catalytic Reduction of NO by Methane Using a Pt∕C∕polybenzimidazole∕Pt∕C Fuel Cell

“…Particular methane would be convenient because the development of natural gas-powered vehicles will require the development of more active catalysts to remove N x O y from the exhaust. [1][2][3] The present work is a continuation of our research in the fields of electrochemical promotion [4][5][6] and fuel cells, first the phosphoric acid fuel cells 7 and in the last ten years the polybenzimidazole ͑PBI͒-phosphoric acid fuel cells. 8 The latter have a combination of advantages obtained from polymeric electrolyte fuel cells and phosphoric acid fuel cells, especially the ability to work at temperatures up to 200°C, i.e., elimination of the problem of CO poisoning of the Pt catalyst.…”

“…The classic example of this EPP case is an electrochemical production of sodium from the Na + ions in ␤Љ-Al 2 O 3 catalyst support. [19][20][21] Electrochemically produced oxygen 12 and hydrogen 5,6 can also be considered as promoters. In the studies of an electrochemical promotion of the catalytic NO reduction by propene at 375°C, Na was pumped to the surface of the catalyst using electrochemical reduction of Na + ions from Na ␤Љ-alumina support.…”

Electrochemical Promotion of NO Reduction by Hydrogen on a Platinum/Polybenzimidazole Catalyst

“…At high NO ϩ H 2 ϩ Ar flow rate ͑17 mL/ min; 17 and 354 mL/min, respectively, at atmospheric pressure͒, it has been found that NO reduction can be electrochemically promoted at negative polarization with maximum at approximately Ϫ0.15 V, i.e., close to the potential found for the maximum promotion of CH 4 oxidation at the same catalyst. 2 The maximum rate enhancement ratio was 4.65. The value of ⌳ calculated for maximum promotion effect conditions was 1.26 ϫ 10 3 , i.e., ⌳ ӷ 1.…”

“…This means that this effect has an EPP nature. 2 The closest published example of an electrochemically promoted catalytic reaction is the catalytic oxidation of CO by O 2 at the Pt catalyst on YSZ support. 19 According to Belyaev et al, this catalytic reaction is promoted by ZO 2 Ϫ oxygen species which are the products of the interaction between electrochemically produced ZO Ϫ species and chemically adsorbed oxygen species Z o O ͑where Z are the catalyst active sites at the catalyst-support-gas interface and Z o are the catalyst active sites at the catalyst-gas interface͒.…”

“…The value of is defined by the value of the polarization resistance of the electrochemical reaction at the catalyst support interface: if this resistance is low, Ϸ 1; if this resistance is high, Ϸ 0 and by polarization we mainly charge the catalyst-support electric double layer. 20 In our previous paper 2 we have defined three types of electrochemical promotion depending on values of the faradaic current ͑I͒ and ⌳, however it is more precise to separate electrochemical promotion and electrocatalysis.…”