Abstract
N2O remains a major greenhouse gas and contributor to global warming, therefore developing a catalyst that can decompose N2O at low temperatures is of global importance. We have investigated the use of LaSrCoFeOx perovskites for N2O decomposition and the effect of surface area, A and B site elements, Co–O bond strength, redox capabilities and oxygen mobility have been studied. It was found that by using a citric acid preparation method, perovskites with strong redox capabilities and weak Co–O bonds can be formed at relatively low calcination temperatures (550 °C) resulting in highly active catalysts. The enhanced activity is related to the presence of highly mobile oxygen species. Oxygen recombination on the catalyst surface is understood to be a prominent rate limiting step for N2O decomposition. Here the reduced strength of Co–O bonds and mobile lattice oxygen species suggest that the surface oxygen species have enhanced mobility, aiding recombination, and subsequent regeneration of the active sites. La0.75Sr0.25Co0.81Fe0.19Ox prepared by citric acid method converted 50% of the N2O in the feed (T50) at 448 °C.Graphic
Highlights
Nitrous oxide (N2O) has long been considered a potent greenhouse gas and, only accounting for 332 ppb of the atmosphere, the consequences of uncontrolled emission could be significant with respect to climate change [1].1 3 Vol.:(0123456789)N2O has a global warming potential of ca. 300 times that of CO2, [2, 3] a half-life of double that of CO2 (114 years compared to an average of 31 years), [4] and an ozone depletion potential comparable to many hydrochlorofluorocarbons (HCFCs)
When performing in situ X-ray diffraction (XRD), the sample must be packed into a sample holder; it is crucial that when the sample is heated, the sample remains flat and the holder fully packed to ensure that the incidence angle of the X-rays remain consistent
We have shown that by altering the ratios of the A and B site cations it is possible to produce a pure phase perovskite at low temperatures, and by varying the preparation method it is possible to produce perovskites with different ratios of oxygen species
Summary
Nitrous oxide (N2O) has long been considered a potent greenhouse gas and, only accounting for 332 ppb of the atmosphere, the consequences of uncontrolled emission could be significant with respect to climate change [1].1 3 Vol.:(0123456789)N2O has a global warming potential of ca. 300 times that of CO2, [2, 3] a half-life of double that of CO2 (114 years compared to an average of 31 years), [4] and an ozone depletion potential comparable to many hydrochlorofluorocarbons (HCFCs). Perovskites are represented by the general formula ABO3, where the A site is generally a large rare earth element such as La and the B site typically a smaller transition metal such as Co or Fe. The A site cation is generally catalytically inactive but alters the oxidation state of the B site creating oxygen vacancies [15]. The high temperatures required for the preparation of perovskites typically produce materials with low specific surface areas, usually less than 10 m2 g−1 [16, 18]. The oxidation state of the B site cation and the resulting oxygen vacancy can be controlled by substitution of an external cation into the matrix. Oxygen vacancies can provide adsorption sites for reactants and subsequent activation can take place, their presence in the perovskite structure can be directly linked to their catalytic activity [26]
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