N2O catalytic decomposition — effect of pelleting pressure on activity of Co-Mn-Al mixed oxide catalysts (original) (raw)
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Catalysis Today, 2011
A series of Co-Mn-Al mixed oxides modified with alkali metals (Li, Na, and K) were prepared from Co-Mn-Al layered double hydroxide and tested for N 2 O catalytic decomposition in inert gas and in the presence of oxygen. Chemical analysis, XRD, N 2 sorption, TPD-O 2 and TPD-N 2 O were used to characterize the catalysts. During TPD-O 2 , higher amount of O 2 was desorbed from more active catalysts. The extent of O 2 inhibition related to the degree of surface coverage by oxygen.
Chinese Journal of Catalysis, 2011
Intrinsic data of N 2 O catalytic decomposition over a K-promoted Co-Mn-Al mixed oxide prepared by the thermal treatment of a layered double hydroxide was used for the design of a pilot reactor for the abatement of N 2 O emissions from the off-gases in HNO 3 production. A pseudo-homogeneous one-dimensional model of an ideal plug flow reactor under an isothermal regime (450 °C) was used for reactor design. A catalyst particle diameter of 3 mm is a compromise size because increasing the size of the catalyst particle leads to a decrease in the reaction rate because of an internal diffusion limitation, and particles with a smaller diameter cause a large pressure drop. A catalyst bed of 11.5 m 3 was estimated for the target N 2 O conversion of 90% upon the treatment of 30000 m 3 /h of exhaust gas (0.1 mol% N 2 O, 0.005 mol% NO, 0.9 mol% H 2 O, 5 mol% O 2) at 450 °C and 130 kPa.
Effect of promoters in Co–Mn–Al mixed oxide catalyst on N2O decomposition
Chemical Engineering Journal, 2010
Catalytic decomposition of N 2 O over calcined Co-Mn-Al layered double hydroxide (LDH) modified with slight amount of alkali (Li, Na, K), rare earth (La, Ce), or noble metals (Pd, Pt) was studied. Two methods of promoter addition were applied: impregnation of LDH-related Co-Mn-Al mixed oxide by a promotercontaining solution and incorporation of the promoter during coprecipitation of the LDH precursor. The method of preparation affected the reducibility of the obtained mixed oxide catalysts but its effect on the surface area (with the exception of a cerium-contained sample) and N 2 O conversion was less evident. The modification of the Co-Mn-Al mixed oxide with K or Na increased N 2 O conversion, while no effect or a decrease in the N 2 O conversion was observed over the other examined catalysts. Alkali metals act as electron promoters; therefore, the differences in catalytic activity may be related to changes of oxygentransition metal bond strength. The Co-Mn-Al mixed oxides with 1.8 wt% K exhibited a high catalytic activity even under the simultaneous presence of O 2 , H 2 O and NO x. The laboratory stability test revealed maintenance of the beneficial effect for 360 h.
Porosity and Structure of Hierarchically Porous Ni/Al2O3 Catalysts for CO2 Methanation
Catalysts, 2020
CO2 methanation is often performed on Ni/Al2O3 catalysts, which can suffer from mass transport limitations and, therefore, decreased efficiency. Here we show the application of a hierarchically porous Ni/Al2O3 catalyst for methanation of CO2. The material has a well-defined and connected meso- and macropore structure with a total porosity of 78%. The pore structure was thoroughly studied with conventional methods, i.e., N2 sorption, Hg porosimetry, and He pycnometry, and advanced imaging techniques, i.e., electron tomography and ptychographic X-ray computed tomography. Tomography can quantify the pore system in a manner that is not possible using conventional porosimetry. Macrokinetic simulations were performed based on the measures obtained by porosity analysis. These show the potential benefit of enhanced mass-transfer properties of the hierarchical pore system compared to a pure mesoporous catalyst at industrially relevant conditions. Besides the investigation of the pore system,...
Catalysts
Nitrous oxide (N2O), produced from several human activities, is considered a greenhouse gas with significant environmental impacts. The most promising abatement technology consists of the catalytic decomposition of N2O into nitrogen and oxygen. Many recently published papers dealing with N2O catalytic decomposition over Ni-substituted Co3O4 are related to the treatment of N2O concentrations less than 2 vol% in the feed stream. The present work is focused on developing catalysts active in the presence of a gaseous stream richer in N2O, up to 20 vol%, both as powder and in structured configurations suitable for industrial application. With this aim, different nickel-cobalt mixed oxides (NixCo1−xCo2O4) were prepared, characterized, and tested. Subsequently, since alumina-based slurries assure successful deposition of the catalytic species on the structured carrier, a screening was performed on three nickel-cobalt-alumina mixed oxides. As the latter samples turned out to be excellent ca...
A study on N2O catalytic decomposition over Co/MgO catalysts
Journal of Hazardous Materials, 2009
a b s t r a c t Different oxide supported cobalt catalysts were prepared by co-precipitation method and tested for the decomposition of nitrous oxide. Co/MgO with cobalt loading of 15% showed the best activity and a 100% N 2 O conversion was obtained at temperatures higher than 700 K. The active phase of cobalt species in Co/MgO catalysts was Co 3 O 4 highly dispersed in the matrices of MgO, based on XRD and XPS results as well as the kinetic analysis. The existence of NO, O 2 and H 2 O in reaction system showed different negative effects on N 2 O decomposition. Nevertheless, a 100% N 2 O conversion could be achieved at 800 K under simulated conditions of tail gas from nitric acid plant. Moreover, Co/MgO catalyst exhibited quite good durability and no obvious activity loss was observed in the 100 h stability test.
Catalysis Communications, 2011
A series of Co-Mn-Al mixed oxides was prepared by a thermal treatment of coprecipitated layered double hydroxide precursors modified with different amount of potassium (0-3 wt.%) and tested in N 2 O catalytic decomposition. Chemical analysis, XRD, XPS, surface area measurements, SEM, and contact potential difference measurements were used for bulk and surface characterization of the catalysts. The Co-Mn-Al mixed oxide with 1.1-1.8 wt.% K exhibited the highest conversion of N 2 O and minimum value of the catalyst surface work function. Direct correlation between the work function values and the activity of the catalysts demonstrates that N 2 O decomposition over K-promoted Co-Mn-Al mixed oxides proceeds via the cationic redox mechanism and controlled modification of surface electronic properties provides the essential factor for catalyst optimization.
Ammonia decomposition activity over Ni/SiO2 catalysts with different pore diameters
International Journal of Hydrogen Energy, 2014
Ni-loaded catalysts Pore diffusion Kinetic study Knudsen diffusion a b s t r a c t Ammonia decomposition over Ni-loaded SiO 2 catalysts (Ni/SiO 2 ) was observed in a fixedbed reactor at different temperatures (ranging from 773 to 973 K) and ammonia feeding rates (ranging from 1200 to 18,000 h À1 ). As support materials, several porous and inert SiO 2 particles with different mean pore diameters ðdÞ ranging from 7.7 to 34.8 nm were used to clarify the effect of pore diameter on the kinetic parameters for catalytic ammonia decomposition. The Ni/SiO 2 catalyst with the smallest pores, d ¼ 7.7 nm, showed the highest activity at temperatures below 923 K, while the activity of this catalyst at 973 K was lower than that of catalysts with larger pores. Kinetic analysis indicated that the activation energy for d ¼ 7.7 nm was significantly decreased at higher temperatures, suggesting the occurrence of strong diffusion resistance of ammonia molecules in the pores. Our experiments also confirmed that almost complete decomposition of ammonia could be achieved over Ni/SiO 2 with d ¼ 26.7 nm at 973 K and a gas hourly space velocity as high as 42,000 h À1 .
Applied Catalysis A: General, 1996
A series of coprecipitated Ni/A1203 catalysts containing 0-25 wt.-% Ni were examined for total surface area, total pore volume, metal surface area, CO 2 adsorption and CO 2 methanation activity in order to study the relation between metal content, structure and catalyst activity. Coprecipitated Ni/A1203 catalysts are found to be efficient promoters for methanation. Methanation activity is dependent on the nickel content and the degree of CO 2 adsorption at the reaction considered. Although A1203 does not exhibit methanation activity, it is found to be active for CO 2 adsorption. Reverse spillover increases methane production per unit nickel surface particularly for catalysts with low Ni loadings.
Applied Catalysis B: Environmental, 2009
A series of catalysts was prepared by thermal treatment (500 8C) of the coprecipitated Co-Mn-Al layered double hydroxide (Co:Mn:Al molar ratio of 4:1:1) doped with various amount of potassium (0-3 wt%). Obtained spinel-like mixed oxides were characterized by powder X-ray diffraction, X-ray photoelectron spectroscopy, BET surface area measurements, temperature-programmed H 2 reduction, and temperature-programmed CO 2 and NH 3 desorption. The prepared catalysts were tested for N 2 O decomposition to determine the effect of K addition on the catalytic activity in the presence of O 2 , NO x and H 2 O. An optimum K content of ca. 0.9-1.6 wt% was found to achieve a high catalytic activity in the presence of O 2 and H 2 O, while the non-modified Co-Mn-Al mixed oxide was the most active catalyst in the presence of O 2 and NO x. The addition of potassium to the Co-Mn-Al mixed oxide apparently results in a modification of both electronic properties of active metals and acid-base function of the catalyst surface.