NOx conversion on LSM15-CGO10 cell stacks with BaO impregnation

Abstract

The electrochemical conversion of NO x on non-impregnated and BaO-impregnated LSM15-CGO10 (La 0.85 Sr 0.15 MnO 3 -Ce 0.9 Gd 0.1 O 1.95 ) 5 porous cell stacks has been investigated, and extensive impedance analysis have been performed to identify the effect of the BaO on the electrode processes. The investigation was conducted in the temperature range 300-500 °C, a polarisation range from 3 V to 9 V and in atmospheres containing 1000 ppm NO, 1000 ppm NO + 10% O 2 and 10% O 2 . On the non-impregnated cell stacks no NO x conversion was observed at any of the investigated conditions. However, BaO impregnation greatly enhanced the NO x conversion and at 400 °C and 9 V polarisation a BaO-impregnated cell stack showed 60% NO x conversion into N 2 with 8% current efficiency in 1000 ppm NO + 10% 10 O 2 . This demonstrates high NO x conversion can be achieved on an entirely ceramic cell without expensive noble metals. Furthermore the NO x conversion and current efficiency was shown to be strongly dependent on temperature and polarisation. The impedance analysis revealed that the BaO-impregnation increased the overall activity of the cell stacks, but also changed the adsorption state of NO x on the electrodes; whether the increased activity or the changed adsorption state is mainly responsible for the improved NO x conversion remains unknown. IntroductionIn Europe the NO x -emission from the road transport has been significantly reduced during the last 10 years, mainly due to the introduction of the three-way-catalyst on gasoline vehicles 1 . Due to the negative impact of NO x -emissions on both human health and the environment 2 , a further reduction in the NO x emissions from the car fleet is desirable. However a major challenge in that connection is the increased number of diesel vehicles, as the conventional three-way-catalyst is incapable of removing NO x from diesel exhaust. For this reason much research is currently focused on NO x -removal technologies for diesel exhaust, the most heavily investigated technologies being selective catalytic reduction with ammonia (NH 3 -SCR), selective catalytic reduction with hydrocarbons (HC-SCR) and the NO x -storage and reduction (NSR) catalyst 3 . In all these three technologies there is the need for a reducing agent, either coming from operating the engine occasionally in an excess fuel to air-ratio (HC-SCR and NSR) or supplied by a separate system (NH 3 -SCR). A NO x removal technology without the need for the addition of a reducing agent would be simpler and therefore advantageous compared to the aforementioned technologies.A suggestion for such a technology is electrochemical NO x removal, where the NO x is reduced to N 2 and O 2 by electrons supplied to a polarised electrode 4 . The technology is inspired by the finding in 1975 by Pancharatnam et al. 5 that NO can be reduced to N 2 during polarisation of a zirconia based cell in the absence of oxygen, and later it was shown by Cicero et al. 6 and Hibino et al. 7 that NO x also could be electrochemically reduced in the...

NOx and propene conversion on La0.85Sr0.15MnO3+d/Ce0.9Gd0.1O1.95 symmetrical cells

“…In the cells with noninfiltrated electrodes, propene could interact with adsorbed oxygen, thereby forming more active oxygen species for dissociation on the electrode surface. The near-equivalent capacitance correlated well with the capacitance values related to oxygen adsorption and dissociation on the electrode surface reported in earlier findings from our group [22,33].…”

“…The capacitance value of the Arc II was close to capacitance values associated with oxygen adsorption and dissociation on the composite electrode [22]. The higher capacitance of the cells with BaO-infiltrated electrodes could be related to the production of active oxygen species by reduction of nitrates.…”

“…Adsorption on BaO is believed to proceed through NO2 [22], whereas the chemisorption of NO is expected on Pt [29,36]. This means that when both, Pt and BaO nanoparticles are present, the adsorption and reduction of NO can proceed via different pathways.…”

“…Traulsen et al [22] investigated the use of BaO as a storage compound in an all-ceramic electrochemical cell with La0.85Sr0.15MnO3/Ce0.9Gd0.1O1.95 electrodes (LSM15/CGO10) and found that NO could be reduced to N2 with a conversion of 60 % at 400 °C in the presence of 10 % oxygen. Additionally, perovskites have been suggested as substitutes for Pt in NSR technology [23].…”

Electrochemical Removal of NOx on Ceria-Based Catalyst-Electrodes

“…The former deals with multilayers configurations with a NO x adsorption layer deposited at the top of a catalyst-electrode layer [9,11]. The latter seems to be more promising and refers to the infiltration of a NO x sorbent, such as BaO, into the porosity of the catalyst-electrode [12][13][14]. For instance, remarkable results have been obtained with the infiltration of both BaO particles and a Pt/Al 2 O 3 catalyst into the porosity of symmetrical electrodes of (La 0.85 Sr 0.15 ) 0.99 MnO 3 (LSM) interfaced on a dense GDC membrane [12].…”