Lithium-Vanadium bronzes as model catalysts for the selective reduction of nitric oxide

The effect of alkali metals on the selective reduction of nitric oxide with ammonia has been studied on bulk iron oxide and bulk vanadium oxide. The influence of additions of LiOH, NaOH and KOH on the activity was screened by pulse experiments carried out in the absence of gaseous oxygen; FTIR reflectance spectra, NH3 adsorption data and some TPR data were also obtained. The results of these experiments gave rise to the idea that some kind of surface compound of the bronze type could be responsible for the increased activity which was measured with vanadia catalysts enriched with Li, Na or K. Vanadia bronzes were thus prepared as model compounds to study the interaction of vanadia with the alkali metals. The activities of these bronzes were measured in a continuous flow system in the presence of oxygen; FTIR transmission spectra, as well as ESR spectra, were obtained for some of the samples. The results show that the presence of lithium stabilizes the presence of V4+ ions. These V4+ ions probably weaken the V5+=O bond of adjacent species, thus increasing the reducibility of the catalyst and the activity for the reduction of NO.