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The electrochemical promotion of catalytic methane oxidation was studied using a (CH4,O-2,Ar), Pt\polybenzimidazole (PBI)-H3PO4\Pt,(H-2,Ar) fuel cell at 135degreesC. 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 C-2 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, r(C-2)/r(o)(C-2), at this maximum was 4.2. There was no C2H2 production at polarization greater than or equal to0.1 and less than or equal to-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, r(CO2)/r(o)(CO2), 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 C-2 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 (lambda much greater than 1).

The present work is a continuation of our investigation of the electrochemistry of the molten V 2 O 5 -M 2 S 2 O 7 system (M is an alka- li metal). 1-3 This melt has been found to be a realistic model of the V 2 O 5 -M 2 S 2 O 7 catalyst for sulfur dioxide oxidation with air which is used in sulfuric acid production and SO 2 removal from flue gases. It has been shown 1-3 that electrochemical measurements can provide important information about the vanadium complexes formed in the K 2 S 2 O 7 -V 2 O 5 and K 2 S 2 O 7 -KHSO 4 -V 2 O 5 molten systems and thus provide some insight concerning the reaction mechanism during catalysis. It has also been concluded that the voltammetric technique can be used to examine the alkali ion promotion effect on the V(V) } The effect of electrochemical polarization on the catalytic SO 2 oxidation in the molten V2O5-K2S2O7 system has been studied using a gold working electrode in the temperature range 400-460 8C. A similar experiment has been performed with the industrial cata- lyst VK-58. The aim of the present investigation was to study a possible non-Faradaic electrochemical promotion of the liquid- phase catalytic reaction. It has been shown that there are two negative potential promotion areas with maximum effects at appro x- imately 20.1 and 20.2 V, and one positive potential promotion area with the maximum effect between 0.1 and 0.3 V. There were no Faradaic reactions in the negative polarization region, and there was an anodic current which was less than 16% of the theore t- ical value for an exclusively Faradaic SO 2 oxidation. Therefore the promotion effects at negative polarization are completely non- Faradaic. All the promotion effects have been explained as mainly due to charging of the electric double layer at the gold elec trode. The effect at 20.2 V also depends on the V2O5 concentration and is more pronounced at higher V 2O5 concentrations. This has been ascribed to a destruction of the vanadium polymeric chains caused by the negative charge on the electrode. The Faradaic part of the promoting effect under positive polarization has been explained as the electrochemical pushing of the V(V) } V(IV) equilibri- um in the direction of V(V) formation. It has also been shown that when using the industrial VK-58 catalyst the activity can b e increased up to four times by using the negative polarization effect with maximum at 20.2 V.

The catalytic NO reduction by methane was studied using a (NO,CH4,Ar),Pt|polybenzimidazole(PBI)–H3PO4|Pt,(H2,Ar) fuel cell at 135 and 165°C. It has been found that, without any reducing agent (like CH4), NO can be electrochemically reduced in the (NO, Ar), Pt/C|PBI–H3PO4|Pt/C, (H2,Ar) fuel cell with participation of H+ or electrochemically produced hydrogen. When added, methane partially suppresses the electrochemical reduction of NO. Methane outlet concentration monitoring has shown the CH4 participation in the chemical catalytic reduction, i.e., methane co-adsorption with NO inhibited the electrochemical NO reduction and introduced a dominant chemical path of the NO reduction. The products of the NO reduction with methane were N2, C2H4, and water. The catalytic NO reduction by methane was promoted when the catalyst was negatively polarized (−0.2 V). Repeated negative polarization of the catalyst increased the NO conversion. Maximum NO conversion was 48%. This effect was explained as a result of the reaction of the electrochemically produced hydrogen.

The electrochemical promotion of catalytic NO reduction by hydrogen was studied using a (NO, H 2 , Ar), Pt polybenzimidazole (PBI)-H 3 PO 4 |Pt, (H 2 , Ar) fuel cell at 135°C. A mixture of NO/H 2 /Ar was used as the working mixture at one electrode and a mixture of H 2 /Ar was used as reference and counter gas at the other electrode. Products of NO reduction (N 2 and H 2 O) were analyzed by an on-line mass spectrometer. At high NO + H 2 + Ar flow rate (17 mL/min; 17 and 354 mL/min, respectively, at atmospheric pressure) the maximum rate enhancement ratio was 4.65. At low NO + H 2 + Ar flow rate (17 mL/min; 17 and 140 mL/min, respectively), NO reduction increased 20 times even without polarization compared to the high gas flow rate. The electrochemical promotion effect occurs at positive polarization with a maximum increase at approximately 0.08 V and with 1.5 times the zero polarization value. The promotion at the negative polarization can be attributed to the electrochemical production of the promoters. At low gas flow rates, a charge-induced change of the strength of chemisorptive bonds can take place.