First Demonstration of in Situ Electrochemical Control of a Base Metal Catalyst:  Spectroscopic and Kinetic Study of the CO + NO Reaction over Na-Promoted Cu

Abstract

Controlled, reversible electrochemical promotion (EP) of a base metal catalyst has been demonstrated for the first time. Electropumping of Na from a ′′ alumina solid electrolyte to a Cu film catalyst results in large improvements in both activity and selectivity of the latter. In the catalytic reduction of NO by CO, the reactive behavior, surface composition, and response to EP are a strong function of the composition of the reactant gas. Electron spectroscopic data show that these effects are due to pumping of Na to the catalyst where, under reaction conditions, it is present as NaNO 3 on an oxidized Cu surface. Taken together, the spectroscopic and reactor results show that Cu 0 sites are not of significance and that the catalytically active surface is dominated by Cu + and Cu 2+ sites. They also suggest that Cu + is of principal importance for the dissociative adsorption of NO and that EP is due to Na-induced enhancement of the adsorption and dissociation of NO at these sites.

Strong promotional effects of Li, K, Rb and Cs on the Pt-catalysed reduction of NO by propene

“…Previous XPS studies involving in situ transfer of promoted and poisoned ex-reactor electrochemically promoted catalysts to the spectrometer analysis chamber showed [23] that in the case of NO+C 3 H 6 the Na-containing promoting (or poisoning) phase consists principally of a mixture of NaNO 2 , NaNO 3 and NaCO 3 . Most recently, Lambert and co-workers [28,40] attributed the rate inhibition primarily to the formation of thick (three-dimensional) films of alkali carbonate that cover the surface and are stable at elevated reaction temperatures. They shown that such alkali carbonates are easily formed in the present of carbon-rich molecules, e.g.…”

“…propene [40]. On the other hand they showed [28] that when the promoter phase consists exclusively of alkali nitrates, submonolayer films of this component would be expected to be stable [41] at used reaction temperatures. In contrary, thick films of alkali nitrates cannot be built up at the used reaction temperatures because of their volatility.…”

“…In contrary, thick films of alkali nitrates cannot be built up at the used reaction temperatures because of their volatility. As a result the authors concluded that strong poisoning of alkali nitrates does not occur and that submonolayer quantities of such components survive at reaction temperature promoting the catalyst [28].…”

“…Most recently EP was also demonstrated on a base metal catalyst (Na-promoted Cu) for the NO+CO reaction [28]. It was shown in all these studies that Na supplied electrochemically from a ␤ -Al 2 O 3 solid electrolyte, a Na + ion conductor, strongly affects both catalytic activity and selectivity of all the above reactions [21][22][23]28]. In addition to this practical importance we gain further basic knowledge regarding the understanding of the role and the way of action of alkalis on Pt-group metal surfaces.…”

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

“…Indeed, the progress made in the development and understanding of the phenomenon of electrochemical promotion over the years could not be conceived without the in situ spectroscopy studies performed by the group of professor Lambert and co-workers [34][35][36][37][38][39][40][41][42][43][44][45]. In all cases, the spectra were obtained immediately after exposing the appropriately polarized catalyst film (either unpromoted or electrochemically promoted) to conditions of temperature and reactant partial pressures similar to those encountered in the electrochemical promotion reactor, in order to simulate the different surface conditions of interest.…”