On the optimal Cs/Co ratio responsible for the N2ON_2O decomposition activity of the foam supported cobalt oxide catalysts

Structured foam catalysts for N2O decomposition containing Co and Cs were prepared via conventional and organic-assisted impregnation method (acetic acid, citric acid, glycerol, glycine, urea). Organic-assisted impregnation caused higher abundance of smaller particles and different faceting. Glycerol usage leads to increase of specific rate constant for N2O decomposition, urea leads to its decrease. The optimal amount of Cs in Co3O4 deposited on the foam was 2–3 times higher than in the bulk Co3O4-Cs due to the dispersion of part of the Cs species over the bare support. The use of glycerol caused a better surface coverage by spinel phase, thus leaving less space for spreading the cesium on the support instead of on the spinel phase. The positive effect of glycerol on the performance of the catalysts with optimized cesium content was attributed to refaceting of the spinal nanocrystals, and greater resistance of the (1 0 0) planes to gaseous NO/H2O contaminates.Web of Science1612art. no. 10531

Co-Mn-Al mixed oxides promoted by K for direct NO decomposition: Effect of preparation parameters

Fundamental research on direct NO decomposition is still needed for the design of a sufficiently active, stable and selective catalyst. Co-based mixed oxides promoted by alkali metals are promising catalysts for direct NO decomposition, but which parameters play the key role in NO decomposition over mixed oxide catalysts? How do applied preparation conditions affect the obtained catalyst's properties? Co4MnAlOx mixed oxides promoted by potassium calcined at various conditions were tested for direct NO decomposition with the aim to determine their activity, stability and selectivity. The catalysts were prepared by co-precipitation of the corresponding nitrates and subsequently promoted by KNO3. The catalysts were characterized by atomic absorption spectrometry (AAS)/inductive coupled plasma (ICP), X-ray photoelectron spectrometry (XPS), XRD, N-2 physisorption, temperature programmed desorption of CO2 (TPD-CO2), temperature programmed reduction by hydrogen (TPR-H-2), species-resolved thermal alkali desorption (SR-TAD), work function measurement and STEM. The preparation procedure affects physico-chemical properties of the catalysts, especially those that are associated with the potassium promoter presence. The addition of K is essential for catalytic activity, as it substantially affects the catalyst reducibility and basicity-key properties of a deNO catalyst. However, SR-TAD revealed that potassium migration, redistribution and volatilization are strongly dependent on the catalyst calcination temperature-higher calcination temperature leads to potassium stabilization. It also caused the formation of new phases and thus affected the main properties-S-BET, crystallinity and residual potassium amount.Web of Science97art. no. 59

Cesiem promotovaný Co3O4 katalyzátor nanesený na keramické pěně pro snižování emisí oxidu dusného

Nitrous oxide is a significant pollutant. Large stationary sources of N2O emissions, such as nitric acid plants, are the most suitable for N2O emissions abatement. Direct N2O catalytic decomposition is a promising option for N2O abatement. Cs-doped Co3O4 is known to be active for N2O catalytic decomposition. Dispersion of the active components over a structured support surface may largely improve the applicability of the catalyst in industrial scale. Apart from the active components’ chemical composition, the resultant catalyst activity is influenced by the method of their deposition on the support as well. In this work, the preparation of Co3O4 De-N2O catalyst on ceramic foam structured support by organic-assisted impregnation is investigated. Acetic acid, citric acid, glycerol, glycine and urea are tested as organic impregnation agents. The catalysts are characterized by AAS, BET, SEM, TPR-H2 and XRD. Using glycerol as the organic impregnation agent leads to the highest improvement of the catalyst De-N2O activity. Preparation of the catalyst by glycerol-assisted impregnation is further optimized. The optimal glycerol-to-cobalt molar ratio of the impregnation solution is found to be 1:1. The optimized glycerol-assisted impregnation method is used for preparation of Cs-doped Co3O4 catalysts on ceramic foams. Based on De-N2O catalytic tests in simulated nitric acid plant tail-gas (N2O, O2, H2O, NO, N2), the optimal Cs loading is found to be between 1.5 and 1.9 wt. % of Co3O4.Oxid dusný je významným polutantem. Pro snižování emisí N2O je výhodné zaměřit se na velké stacionární zdroje emisí N2O, jako je výroba kyseliny dusičné. Jednou z možností snížení emisí N2O je jeho přímý katalytický rozklad. Je známo, že Co3O4 s Cs-promotorem je aktivní v katalytickém rozkladu N2O. Nanesení aktivních komponent na povrch strukturovaného nosiče může významně zvýšit uplatnitelnost katalyzátoru v průmyslovém měřítku. Kromě chemického složení aktivních komponent je aktivita výsledného katalyzátoru ovlivněna rovněž metodou jejich nanášení na nosič. V této práci je zkoumána příprava De-N2O katalyzátorů na bázi Co3O4 na keramické pěně jako strukturovaném nosiči pomocí impregnace z roztoku s organickým činidlem. Jako organická impregnační činidla jsou testovány kyselina octová, kyselina citronová, glycerol, glycin a močovina. Katalyzátory jsou charakterizovány pomocí AAS, BET, SEM, TPR-H2 a XRD. Použití glycerolu vede k největšímu zvýšení De-N2O aktivity katalyzátoru. Příprava katalyzátoru pomocí impregnace s glycerolem je dále optimalizována. Je zjištěn optimální molární poměr glycerol-kobalt v impregnačním roztoku 1:1. Optimalizovaná metoda impregnace s glycerolem je užita k přípravě Co3O4 s Cs-promotorem na keramické pěně. Na základě De-N2O katalytických testů v simulovaném koncovém plynu výroby kyseliny dusičné (N2O, O2, H2O, NO, N2) je nalezen optimální obsah Cs mezi 1,5 a 1,9 hm. % Co3O4.619 - Katedra fyzikální chemie a teorie technologických procesůvýborn

Optimization of the process of deposition of cobalt based catalysts for nitrous oxide decomposition on the structured support.

Bakalářská práce se zabývá nízkoteplotním katalytickým rozkladem oxidu dusného pomocí katalyzátorů na strukturovaných nosičích. Oxid dusný je významným polutantem podílejícím se na skleníkovém efektu a poškozování ozonové vrstvy. Rozklad oxidu dusného působením vhodného katalyzátoru je vhodnou metodou snížení jeho emisí ze stacionárních zdrojů. V rámci této bakalářské práce byly připraveny katalyzátory, jejichž aktivní složka Co3O4/Cs nebo Co4MnAlOx/K byla naneseny impregnací na keramické pěny, a katalyzátory, jejichž aktivní složka Co3O4/Cs byla impregnací nanesena na keramické pěny s mezivrstvou (MgO, MnO2, SiO2 nebo TiO2). Připravené katalyzátory byly charakterizovány pomocí XRD a byla testována jejich aktivita pro rozklad oxidu dusného v inertním prostředí. Na základě těchto měření byl studován vliv počtu nanesených vrstev aktivní fáze Co3O4/Cs nebo Co4MnAlOx/K a vliv použité mezivrstvy při jedné vrstvě aktivní fáze Co3O4/Cs. U obou použitých aktivních fází je optimálním počtem nanesených vrstev jedna vrstva. Žádná z použitých mezivrstev nezvyšuje aktivitu katalyzátoru oproti aktivitě katalyzátoru s jednou vrstvě Co3O4/Cs nanesenou na pěně bez mezivrstvy.This bachelor thesis deals with low-temperature catalytic decomposition of nitrous oxide using catalysts on structured supports. Nitrous oxide is a significant pollutant contribuing to the greenhouse effect and ozone depletion. Decomposition of nitrous oxide using a suitable catalyst is an appropriate way to abate nitrous oxide emissions from stationary sources. For this bachelor thesis, catalysts with the active components of Co3O4/Cs or Co4MnAlOx/K deposited by impregnation on ceramic foams, and catalysts with the active components of Co3O4/Cs deposited by impregnation on ceramic foams with an interlayer (MgO, MnO2, SiO2 or TiO2) were prepared. The catalysts prepared were characterised using XRD and their catalytic activity for the decomposition of nitrous oxide in an inert gas was measured. The effect of the number of active Co3O4/Cs or Co4MnAlOx/K layers deposited and the effect of the interlayer used for one active Co3O4/Cs layer were studied. For both active phases used, the optimal number of layers deposited is one layer. None of the interlayers used increases the activity of the catalyst compared to that of a catalyst with one layer of Co3O4/Cs deposited on a foam without an interlayer.617 - Katedra chemievýborn

How loading of Co3O4-Cs on an open-cell foam influences N2O decomposition

Co3O4 modified with Cs was deposited on an alpha- Al2O3 open-cell foam, characterized by X-ray diffraction (XRD), N2 physisorption, temperature-programmed reduction by hydrogen (TPR-H2), and scanning electron microscopy-energy-dispersive Xray analysis (SEM-EDAX) and tested for the low-temperature decomposition of N2O. The aim was to study the effect of the amount of active phase on N2O conversion. Three different approaches were used: (i) the application of foam supports with different cell sizes, (ii) influencing catalyst loading using impregnation solutions with different precursor concentrations, and (iii) deposition of the active phase precursor by repeated immersion-calcination cycles. Increasing the geometric surface area of the support, and thus catalyst loading, was successfully done using the support with higher pore densities. A higher loading was also achieved by increasing the nitrate precursor concentration in the impregnation solution. In both cases, the catalyst activity increased with an increase in the amount of the active phase. Compared to that, a repeated impregnation procedure can ensure the deposition of a higher amount of active phase in comparison to that obtained with one-step impregnation, but only the last layer is used in the reaction and the rest of the active phase remains unutilized, which makes this type of preparation unfavorable. The high catalytic activity was preserved at 450 degrees C even in the presence of O2, H2O, and NO.Web of Science6231309130

Washcoated open-cell foam cobalt spinel catalysts for N2O decomposition

The Co3O4 modified with 1 wt.% Cs was deposited on alpha-Al2O3 open-cell foam covered with different washcoats (MgO, MnO2, SiO2, TiO2), investigated by XRD, Raman microspectroscopy, nitrogen physisorption, XPS, SEM and TPR-H2 in order to elucidate interactions between Cs-Co3O4 and the washcoat and their effect on surface area, reducibility, dispersion, and low temperature decomposition of N2O. The samples with SiO2 and TiO2 washcoats had the largest surface areas. Only SiO2 did not interact with the active phase and did not change the reducibility of the catalyst. Although the same Cs concentration was adjusted during preparation of all catalysts, differences in the Cs/Co surface molar ratio were observed due to a different level of Co3O4 particles aggregation and cesium dispersion. Catalytic activity correlated with the surface Cs/Co molar ratio closely interconnected with the surface Co3+/Co2+ molar ratio while there were no direct relationships to the redox properties and surface area. The highest activity was achieved for the MgO washcoat prepared from carbonate with the highest Co3+/Co2+ molar ratio corresponding to the optimal Cs/Co surface molar ratio around 0.1.Web of Science533art. no. 11275

Washcoated open-cell foam cobalt spinel catalysts for N2ON_2O decomposition

The Co3O4 modified with 1 wt.% Cs was deposited on alpha-Al2O3 open-cell foam covered with different washcoats (MgO, MnO2, SiO2, TiO2), investigated by XRD, Raman microspectroscopy, nitrogen physisorption, XPS, SEM and TPR-H2 in order to elucidate interactions between Cs-Co3O4 and the washcoat and their effect on surface area, reducibility, dispersion, and low temperature decomposition of N2O. The samples with SiO2 and TiO2 washcoats had the largest surface areas. Only SiO2 did not interact with the active phase and did not change the reducibility of the catalyst. Although the same Cs concentration was adjusted during preparation of all catalysts, differences in the Cs/Co surface molar ratio were observed due to a different level of Co3O4 particles aggregation and cesium dispersion. Catalytic activity correlated with the surface Cs/Co molar ratio closely interconnected with the surface Co3+/Co2+ molar ratio while there were no direct relationships to the redox properties and surface area. The highest activity was achieved for the MgO washcoat prepared from carbonate with the highest Co3+/Co2+ molar ratio corresponding to the optimal Cs/Co surface molar ratio around 0.1.Web of Science533art. no. 11275

Effect of support on the catalytic activity of Co3O4−CsCo_3O_4-Cs deposited on open-cell ceramic foams for N2ON_2O decomposition

Cobalt mixed oxide with cesium promoter was deposited on different ceramic open-cell foams (Al2O3 + SiO2, ZrO2 and SiO2 + Al2O3 + C-graphite, Lanik Ltd., Czech Republic) by wet impregnation method. The catalysts were tested for N2O decomposition and characterized by AAS, XRD, TPR-H-2, FTIR, Raman, XPS, SEM and nitrogen adsorption. The same impregnation procedure resulted in different amounts of deposited Co3O4-Cs on each support and different dispersion of Co3O4 and Cs on the surface. The Al2O3 + SiO2 (Al-Si) based ceramic foam was recognized as the most suitable support. The difference in the catalytic activity of unsupported Co3O4 Cs and Co-Cs/Al-Si could be explained in terms of different dispersion levels of individual components on the support, leading to changes in the Cs/Co surface molar ratio of atoms in close contact and subsequent changes in reducibility. Direct correlation of specific rate constant for N2O decomposition and surface Cs/Co molar ratio was found.Web of Science129art. no. 11089