Promotion effect of residual K on the decomposition of N2O over cobalt–cerium mixed oxide catalyst (original) (raw)
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Environmental Science & Technology, 2009
A series of alkali metal-and alkaline earth metal-doped cobalt-cerium composite oxide catalysts were prepared by the citrate method and tested for the decomposition of N 2 O. Strong promotion effects of alkali and alkaline earth metals on the activity of the catalyst were obtained in the order Li < Na < K < Rb < Cs and Mg < Ca < Sr, Ba. The promotion effects of alkaline earth metals were much weaker than the effects of alkali metals. To investigate the origin of the promotion effect, X-ray diffraction, Brunauer-Emmett-Teller surface area measurement, X-ray photoelectron spectroscopy, temperature-programmed desorption, and hydrogen temperatureprogrammed reduction methods were used to characterize the alkali metal-doped catalyst. The analytical results indicated that alkali metals improved the redox ability of active site Co 2+ by acting as electronic promoters. Catalytic decomposition of N 2 O proceeds through an oxidation-reduction mechanism with participation of electrons from Co 2+ , thus the increase in the redox ability of Co 2+ should lead to an increase in the activity of the catalyst.
Catalytic decomposition of N2O over CeO2 promoted Co3O4 spinel catalyst
Applied Catalysis B: Environmental, 2007
A series of CeO 2 promoted cobalt spinel catalysts were prepared by the co-precipitation method and tested for the decomposition of nitrous oxide (N 2 O). Addition of CeO 2 to Co 3 O 4 led to an improvement in the catalytic activity for N 2 O decomposition. The catalyst was most active when the molar ratio of Ce/Co was around 0.05. Complete N 2 O conversion could be attained over the CoCe0.05 catalyst below 400 8C even in the presence of O 2 , H 2 O or NO. Methods of XRD, FE-SEM, BET, XPS, H 2 -TPR and O 2 -TPD were used to characterize these catalysts. The analytical results indicated that the addition of CeO 2 could increase the surface area of Co 3 O 4 , and then improve the reduction of Co 3+ to Co 2+ by facilitating the desorption of adsorbed oxygen species, which is the rate-determining step of the N 2 O decomposition over cobalt spinel catalyst. We conclude that these effects, caused by the addition of CeO 2 , are responsible for the enhancement of catalytic activity of Co 3 O 4 .
Nanostructured Co–Ce-O systems for catalytic decomposition of N2O
Catalysis Today, 2012
Two series of nanostructured materials were obtained by the reverse microemulsion method. It was confirmed obtaining of the nanometric crystallites of Co-substituted ceria solid solutions up to 15 mol% of Co, while the reverse oxide system was biphase, even at so low content of CeO 2 as 1 mol%. The differences in pores structure of the both series were observed as well as the size of crystallites, however limited within nanometric range. The biphase materials showed higher catalytic activity than the solid solutions of Co in ceria phase, though this activity increased with Co content in CeO 2 phase.
Catalysts, 2019
Ceria-based oxides have been widely explored recently in the direct decomposition of N2O (deN2O) due to their unique redox/surface properties and lower cost as compared to noble metal-based catalysts. Cobalt oxide dispersed on ceria is among the most active mixed oxides with its efficiency strongly affected by counterpart features, such as particle size and morphology. In this work, the morphological effect of ceria nanostructures (nanorods (ΝR), nanocubes (NC), nanopolyhedra (NP)) on the solid-state properties and the deN2O performance of the Co3O4/CeO2 binary system is investigated. Several characterization methods involving N2 adsorption at −196 °C, X-ray diffraction (XRD), temperature programmed reduction (TPR), X-ray photoelectron spectroscopy (XPS) and transmission electron microscopy (ΤΕΜ) were carried out to disclose structure–property relationships. The results revealed the importance of support morphology on the physicochemical properties and the N2O conversion performance...
Direct nitrous oxide decomposition with CoOx-CeO2 catalysts
Applied Catalysis B: Environmental, 2011
The focus of the performed studies were CoO x -CeO 2 oxide catalysts for nitrous oxide decomposition. All CoO x -CeO 2 systems exhibit similar or higher activity than the undoped cobalt catalyst. It has been found that in temperatures up to 800 • C in a N 2 O-Ar stream cobalt in these catalysts is in the form of Co 3 O 4 . At higher temperatures it is reduced to CoO. In a N 2 O-O 2 -Ar stream Co 3 O 4 is the main cobalt-containing phase in the entire studied temperature range. The obtained results revealed that the activity of CoO x -CeO 2 systems with a high cobalt loading increases with temperature only up to 800 • C in a N 2 O-Ar stream. Upon further temperature increase the activity of these catalysts decreases, as in the case of the undoped cobalt catalyst. This is due to the reduction of Co 3 O 4 to CoO. Hence, when oxygen is present in the feed and cobalt is in the form of Co 3 O 4 , the activity is higher. In contrast, the activity of catalysts with the cobalt molar ratio no greater than 0.64 is the same in both N 2 O-Ar and N 2 O-O 2 -Ar streams and increases with temperature in the entire studied range (700-850 • C). It has been demonstrated that at 850 • C in a N 2 O-Ar stream CoO x -CeO 2 systems contain two types of CoO, which require different conditions to be oxidized. This is a result of a different strength of interaction with CeO 2 . It can be concluded that the activity of CoO x -CeO 2 systems results from the activity of Co 3 O 4 and of the cobalt oxide-ceria interface. The share of each component is determined by the cobalt content.
Effect of preparation methods on the catalytic activity of Co3O4 for the decomposition of N2O
Research on Chemical Intermediates, 2017
La 0.9 Sr 0.1 CoO 3 perovskite oxides were prepared by a hard template and a sol-gel method, respectively. The catalytic activities for oxidation of CO and C 3 H 6 were examined. XRD, BET, TEM, TPR, and TGA techniques have been used to characterize structural properties, reducibility, mobility of lattice oxygen, and oxygen release rate. La 0.9 Sr 0.1 CoO 3 synthesized by the hard template (SBA-15) method had a higher surface area and smaller particle size, providing more surface adsorbed oxygen. TPR and TGA results showed that oxygen in La 0.9 Sr 0.1 CoO 3 prepared by the hard template method can be more easily extracted in H 2 atmosphere than oxygen in the sol-gel prepared sample. These improved properties of La 0.9 Sr 0.1 CoO 3 synthesized by the hard template (SBA-15) method facilitate catalytic oxidation reactions resulting in enhanced light-off performance for oxidation of CO or C 3 H 6 compared to the sample prepared by the sol-gel method. Furthermore, the La 0.9 Sr 0.1 CoO 3 catalyst prepared by the hard template method showed improved activity for the simultaneous oxidation of CO and C 3 H 6 under simulated diesel exhaust conditions. Both catalysts showed almost no deactivation after 48 h on stream.
Applied Sciences, 2014
The effect of the calcination conditions on the catalytic activity for N2O decomposition of 2.5% RhOx/CeO2 catalysts has been investigated. Ramp and flash calcinations have been studied (starting calcinations at 25 or 250/350 °C, respectively) both for cerium nitrate and ceria-impregnated rhodium nitrate decomposition. The cerium nitrate calcination ramp has neither an effect on the physico-chemical properties of ceria, observed by XRD, Raman spectroscopy and N2 adsorption, nor an effect on the catalysts performance for N2O decomposition. On the contrary, flash calcination of rhodium nitrate improved the catalytic activity for N2O decomposition. This is attributed to the smaller size of RhOx nanoparticles obtained (smaller than 1 nm) which allow a higher rhodium oxide-ceria interface, favoring the reducibility of the ceria surface and stabilizing the RhOx species under reaction conditions.
2014
The effect of the calcination conditions on the catalytic activity for N2O decomposition of 2.5% RhOx/CeO2 catalysts has been investigated. Ramp and flash calcinations have been studied (starting calcinations at 25 or 250/350 °C, respectively) both for cerium nitrate and ceria-impregnated rhodium nitrate decomposition. The cerium nitrate calcination ramp has neither an effect on the physico-chemical properties of ceria, observed by XRD, Raman spectroscopy and N2 adsorption, nor an effect on the catalysts performance for N2O decomposition. On the contrary, flash calcination of rhodium nitrate improved the catalytic activity for N2O decomposition. This is attributed to the smaller size of RhOx nanoparticles obtained (smaller than 1 nm) which allow a higher rhodium oxide-ceria interface, favoring the reducibility of the ceria surface and stabilizing the RhOx species under reaction conditions.
Applied Catalysis B: Environmental, 2010
Rh, Pd and Pt have been supported on ␥-Al 2 O 3 , pure CeO 2 and La-or Pr-doped CeO 2 , and these catalysts have been tested for N 2 O decomposition. The effect of CO and O 2 in the feed has been studied. The characterisation techniques used were Raman spectroscopy, XRD, N 2 adsorption at −196 • C, H 2-TPR and TEM. The catalytic activity for N 2 O decomposition of the noble metals follows the trend Rh > Pd > Pt, and the support affects significantly the activity. For CeO 2-containing catalyst, a relationship between N 2 O decomposition capacity and H 2 reduction of ceria has been found, the easier is the reduction the higher is the catalytic activity. The rate-limiting step of the N 2 O decomposition mechanism over noble metal/ceria catalysts seems to be the reduction of the catalytic active sites. For Rh catalysts, ceria supports are involved actively in the decomposition of N 2 O, and all the ceria-based supports improve the catalytic activity of Rh with regard to ␥-Al 2 O 3 due to the redox properties of ceria. The Pd catalysts with pure and doped ceria support showed similar activity, this being higher than that of Pd/␥-Al 2 O 3. Pt/CeO 2 is the most active catalyst among those of Pt, but ceria doping by La or Pr has a negative effect on the activity. The most active catalyst among those prepared in this study is Rh/CeO 2 (Pr).
Ordered mesoporous CuO-CeO2 mixed oxides as an effective catalyst for N2O decomposition
2014
Ordered mesoporous CuO-CeO 2 mixed oxides with different Cu loadings were synthesized by means of hard template replication approach using mesoporous silica KIT-6 as a template. Prepared materials were characterized by SEM-EDX, XRD, UV-Vis DR, N 2 adsorption/desorption, and H 2-TPR techniques. The catalytic decomposition of N 2 O was studied in a fixed-bed reactor in the temperature range from 300 to 600 °C and GHSV=45000 h-1. Solids prepared by replication approach showed superior catalytic activity in comparison to materials synthesized by conventional preparation methods. Among the solids tested, the highest conversion of N 2 O was observed in the presence of a catalyst containing 40 mol. % Cu. Reduction of prepared samples occurs at much lower temperatures in comparison to individual CuO and CeO 2 oxides due to synergetic effect present in mixed oxides. N 2 O decomposition tests revealed very good agreement between the catalytic activity and material reducibility, which increased with increasing Cu content from 25 to 40 mol. %. Formation of segregated CuO phase was observed for samples with Cu content above 40 mol. %. Accordingly to UV-Vis examination, all solids contain Cu +1 and Ce +3 , which play a crucial role in the N 2 O decomposition mechanism. In wet (1.5 vol. % H 2 O) or NO (1.5 vol. %)