In situ electrochemical modification of catalytic activity for propane combustion of Pt/β′′-Al2O3 catalyst-electrodes

Abstract

The effect of electrochemical promotion (EP) of propane combustion was studied over a platinum film catalyst deposited on sodium b¢¢-Al 2 O 3 , a Na + conductor, in the temperature range 320-440°C. It was found that electrochemical pumping of sodium to the platinum surface markedly modifies its catalytic properties. For stoichiometric oxygen to propane ratio the system exhibited electrophobic behavior, i.e., addition of sodium resulted in decrease of the CO 2 production rate. Relative changes in the catalytic rate by up to 60 times larger than the corresponding change in sodium coverage were measured. The observed behavior is explained by taking into account the reaction mechanism and the effect of the electrochemically controlled sodium coverage on the bonding of coadsorbed reactant species.

Electrochemical characterization of the Pt/β′′–Al2O3 system under conditions of in situ electrochemical modification of catalytic activity for propane combustion

“…The deposition of the Pt catalyst-electrode (1.3 mg Pt) on the b 00 -Al 2 O 3 disk was performed by application of thin coatings of an Engelhard-CLAL M603B Pt paste followed by drying and calcination in air, first at 400°C (4°C min -1 ) for 2 h and then at 800°C (7°C min -1 ) for 20 min. Details concerning the morphology of the Pt electrode (scanning electron microscopy characterization) can be found elsewhere [18]. The surface mol (mol of active sites) N of the Pt catalyst-electrode, which had a geometric (superficial) area of 1.55 cm 2 , was equal to 2.5 9 10 -7 mol Pt, as measured [18] using the technique of isothermal titration [1,3] of adsorbed CO at 350°C assuming an 1:1 CO to Pt adsorption stoichiometry.…”

“…Details concerning the morphology of the Pt electrode (scanning electron microscopy characterization) can be found elsewhere [18]. The surface mol (mol of active sites) N of the Pt catalyst-electrode, which had a geometric (superficial) area of 1.55 cm 2 , was equal to 2.5 9 10 -7 mol Pt, as measured [18] using the technique of isothermal titration [1,3] of adsorbed CO at 350°C assuming an 1:1 CO to Pt adsorption stoichiometry. The Au counter electrode had the same geometric (superficial) area with the Pt working electrode and was deposited exactly opposite to it, on the other side of the b 00 -Al 2 O 3 disk.…”

“…Vernoux et al [8] observed cathodic and anodic cyclic voltammetric peaks in the reaction of propene combustion on Pt/NaSICon at 200°C which they attributed to the formation and decomposition of sodium carbonate and bicarbonate species. Kotsionopoulos and Bebelis [18] using linear sweep voltammetry under conditions of in situ electrochemical modification of catalytic activity for propane combustion of a Pt catalyst-electrode interfaced to b 00 -Al 2 O 3 , at temperatures between 320 and 480°C, concluded that more than one sodium phases, depending on temperature, are formed at the Pt/b 00 -Al 2 O 3 interface following electrochemical pumping of sodium ions to it. Dorado et al [13], studying the selective catalytic reduction (SCR) of NO by propene in presence of oxygen, performed cyclic voltammetry experiments to investigate the chemisorption of reactant species in the Pt/b 00 -Al 2 O 3 system at 240°C and under different gas atmospheres, namely He, C 3 H 6 /He, NO/He, C 3 H 6 /O 2 /He, C 3 H 6 /NO/He and C 3 H 6 /NO/O 2 /He mixtures with different concentrations of O 2 .…”

A Review of Surface Analysis Techniques for the Investigation of the Phenomenon of Electrochemical Promotion of Catalysis with Alkaline Ionic Conductors

“…Vayenas et al performed the first electrochemical promotion study with alkaline solid electrolyte (Na-βAl2O3) in 1991 [8]. From this pioneer work, Na + -conductors have been widely employed in many catalytic systems such as ethylene [9,10], CO [11], propane [12] and propylene oxidation [13], NO reduction [14][15][16], Fischer Tropsch synthesis [17], or hydrogenation of benzene [18] and CO2 [19]. On the other hand, the first EPOC study using a K + -conductor electrolyte (K2YZr(PO4)3) dates from 1997 and addressed the Fe-catalyzed ammonia decomposition [20].…”

Recent developments and trends in the electrochemical promotion of catalysis (EPOC)

“…Using various types of electrocatalysts (LSM/YSZ [46], Pt/YSZ [19,37,45,47], Rh/ YSZ [36,49], Pd/YSZ [65], Ag/YSZ [50], Pt/ b 00 -Al 2 O 3 (with Na ? conductivity) [48]) it has been found that the reaction exhibits purely electrophobic or in some cases (depending on the reaction conditions) inverted volcano behaviour.…”