A study of the NOx storage catalyst of Ba–Fe–O complex oxide

The complex oxide Ba–Fe–O catalysts were prepared by sol–gel method. The XRD, DTA, NO-TPD, XPS and NSC measurements were used to characterize the structures, NO_x storage property and sulfur resistance ability. It is concluded that when coadsorption of NO and O₂ at 400 °C, the sample calcined at 750 °C possesses high NO_x storage capacity and sulfur resistance. The perovskite type BaFeO₃ and BaFeO_3−x phases are the active centers in the catalyst for NO_x storage.     

On the Effect of Poor Metals (Al, Ga, In) on the NO x Conversion in Ethanol Selective Catalytic Reduction

Alumina-supported indium and gallium oxide catalysts were prepared by excess solvent impregnation, characterized and tested for the reduction of NO _x by ethanol in Lean Burn Conditions. The promotion of alumina by “poor” metals showed an interesting ability to selectively reduce NO _x to N₂.     

Characterization of CeO2–WO3 catalysts prepared by different methods for selective catalytic reduction of NOx with NH3

In this work, cerium–tungsten oxide catalysts were prepared by three methods: single step sol–gel (SG), impregnation (IM), and solid processing (SP). The catalysts were used for selective catalytic reduction (SCR) of NO_x with ammonia over a wide temperature range. The results indicated that the catalysts prepared by the SP and IM methods exhibited better SCR activity than that prepared via the SG method in 175–500 °C. The excellent activity can be attributed to larger surface area, higher surface concentrations of Ce and Ce^3 +, enhanced NO oxidization ability, and greater number of surface acid sites.     

Characterization of uniform,nanodispersed NOx storage catalyst materials synthesized by successive ionic layer deposition

A dispersed phase of barium oxide (BaO) supported on alumina has been shown to be primarily responsible for NO_x storage in practical lean NO_x trap catalysts. Conventional impregnation based catalyst loading techniques generate a mixture of dispersed and less active bulk-like BaO phases on alumina, with the bulk-like phase increasing as weight loading increases. Samples of equivalent BaO weight loading on fused alumina were prepared by successive ionic layer deposition (SILD) and wet impregnation. NO₂ temperature programmed desorption experiments demonstrate that SILD is uniquely capable of selectively synthesizing uniform, nanodispersed BaO rafts with high surface coverage. These nanodispersed SILD structures show remarkable thermal stability under high operating temperatures up to 650 °C.     

Influence of Ageing, Silver Loading and Type of Reducing Agent on the Lean NO x Reduction Over Ag–Al2O3 Catalysts

The influence of ageing temperature, silver loading and type of reducing agent on the lean NO _x reduction over silver–alumina catalysts was investigated with n-octane and bio-diesel (NExBTL) as reducing agent. The catalysts (2 and 6 wt% Ag–Al₂O₃) were prepared with a sol–gel method including freeze drying and the evaluation of NO _x reduction and aging were performed using a synthetic gas-flow reactor. The results indicate a relatively high NO _x reduction for both reducing agents. The hydrothermally treated 6 wt% Ag–Al₂O₃ sample displays a maximum NO _x reduction of 78 % at 350 °C for n-octane as reductant and the corresponding value for NExBTL is 60 %. Furthermore, the catalysts show high durability and an increase in activity for NO _x reduction after ageing at temperatures up to 650 °C, with n-octane as reducing agent.     

NO x Storage at Low Temperature over MnO x –SnO2 Binary Metal Oxide Prepared Through Different Hydrothermal Process

Three MnO _x –SnO₂ catalysts were successfully prepared by hetero-redox, homo-redox and common hydrothermal methods. NO adsorption and desorption were performed to investigate the NO _x storage capacity at 100 °C. All the samples showed good performances on NO _x storage, especially the sample prepared by homo-redox hydrothermal method. The XRD, BET, TPR, XPS measurements were used to characterize the structure of the catalysts. The results revealed that the oxidation state of Mn and the defect oxygen species could be responsible for the high NO _x storage capacity.     

On the Characterisation of Silver Species for SCR of NO x with Ethanol

Reducing of nitrogen oxides (NO _x ) in a lean exhaust gases has become one of the most important environmental concerns. Among the different active phases studied for NO _x reduction reaction, silver-based catalysts supported over alumina show good performances using, as reducing agents, either hydrocarbons or oxygenated compounds. Nevertheless, a good understanding of the mechanism reaction has not been reached yet. This comprehension requires a better characterisation of the silver-based catalysts system. In our study, Ag/Al₂O₃ catalysts showed high efficiency in NO _x reduction using ethanol as reducing agent. The conversion plots, in steady state conditions for the different samples Ag/Al₂O₃ (0.8–3.5% Ag wt), show a great dependance of the activity with the metal loading. The optimal silver loading has been established around 2 wt.% Increasing the silver loading, the temperature of maximal NO _x conversion shifted toward the lower temperatures. According to the literature, a reduced and an oxide phase of silver have been observed by UV–Vis spectroscopy. The ratio between the two phases is changing with the silver loading. However, temperature programmed reduction (TPR) measurements reveal the presence of two types of oxide phases. TPR reveal the coexistence of a silver oxide phase (Ag₂O), according to a production of water in the course of the reaction, and a non-oxygenated phase attributed to isolated Ag⁺ cation. Thus, an original way using TPR measurements has been developed to differentiate the various oxidized phases. The aim of this characterisation is to correlate the catalyst’s activity with the observed silver phases, in order to understand the nature of phase active for NO _x reduction at low temperatures.     

Effect of the Synthesis Method on Alumina Supported Silver Based Catalyst for NO x Selective Reduction by Ethanol

Alumina supported indium oxide, silver or bimetallic Ag–In catalysts with metal loading of ca. 2.5 wt% were prepared by excess solvent impregnation or incipient wetness impregnation. The influence of the impregnation was studied by testing the catalysts in DeNO _x activity with ethanol in Lean Burn Conditions.     

The Stability Study of Au/La-Co–O Catalysts for CO Oxidation

Perovskite oxide LaCoO₃ and the mixture oxides of La₂O₃ + Co₃O₄ were prepared by sol–gel method. Then Au/La–Co–O catalysts were prepared by deposition- precipitation (DP) method and characterized by means of XRD, BET, XPS, TEM and IR. The catalytic performance for CO low-temperature oxidation and stability over these catalysts were compared. The results of experiment showed gold catalysts supported on perovskite oxides have higher catalytic activity and stability than that of supported on the simple oxides.     

Preparation and reaction mechanistic characterization of sol–gel indium/alumina catalysts developed for NO x reduction by propene in lean conditions

The impregnation and sol–gel preparation methods were investigated to develop high activity catalysts and understand the significance of the indium–aluminium interaction on aluminasupported indium catalysts in NO _x reduction with propene. Active In/alumina catalysts with a very high surface area (270 m²/g) and thermal stability were prepared in controlled conditions by sol–gel processing. When Al isopropoxide and In nitrate in ethyl glycol were used as precursors in aqua media, indium atoms were incorporated evenly distributed as a thermally stable form in the aluminium oxide lattice structure. In wet impregnation it was beneficial to use a certain excess of aqueous In solution (volumes of solution : pores = 2 : 1) to have the highest NO _x reduction activity. The catalyst containing dispersed Al on In oxide (58 wt% In, phaseequilibrium preparation method) showed activity at lower temperatures than any other In–Al oxide catalyst or pure In₂O₃. The adsorption of different reaction intermediates on alumina and stable In₂O₃ sites were detected by FTIR studies. In/alumina catalysts have active sites to oxidize NO to NO₂, partially oxidize HC, form the actual reductant which contains N–H or N–C bonding and react with NO to dinitrogen. The cooperation with indium and aluminium was evident even in the mechanical mixture of sol–gel prepared alumina (301 m²/g) and In₂O₃ powders (27 m²/g), where the probability for molecularscale intimate contact between indium and aluminium sites was very low (particle size 10–250 m). Shortlived gaseous intermediates and surface migration are the possible reasons for the high catalytic activities on the two physically separated active sites both necessary for the reaction sequence.     

Selective oxidation of isobutane to methacrolein over MoVTe mixed oxide supported on SBA-3 and SiO2

SBA-3 and SiO₂-supported MoVTe mixed oxide catalysts have been prepared by impregnation and/or direct synthesis methods and tested for selective oxidation of isobutane to methacrolein (MAL). It was found that the supported catalysts showed much higher activity than the bulk MoVTe mixed oxide for the reaction. Among the supported catalysts, better isobutane conversion and MAL yield were achieved on the 3% MoV_0.8Te_0.23O_x/SBA-3 catalyst prepared by the impregnation method. The catalysts were characterized with BET, XRD, Raman, H₂-TPR, XPS and FT-IR of pyridine adsorption. The good performance of the SiO₂ and SBA-3 supported MoV_0.8Te_0.23O_x catalysts was attributed to a combination of different properties: (i) formation of well dispersed active phases on large surface areas of SiO₂ and SBA-3 supports, which is beneficial for the isolation of active site and preventing the further oxidation of unstable reaction intermediate as well as product; (ii) improved activity for hydrogen abstraction of C-H bond of isobutane due to the formation of isolated pseudotetrahedral VO₄ species.     

Preparation of Pd/(Ce1 − xYx)O2/γ-Al2O3/cordierite catalysts and its catalytic combustion activity for methane

A series of (Ce_1 − xY_x)O₂ (x = 0,0.15,0.35,0.5) coatings on γ-Al₂O₃ pre-coated cordierite honeycomb were prepared by sol–gel method, and then palladium was loaded by aqueous solution impregnation deposition with Pd(NO₃)₂ as precursor. The structure and morphology of samples were evaluated and the catalytic combustion activity for methane was also discussed. (Ce_1 − xY_x)O₂ synthesized by sol–gel has a single-phase cubic fluorite structure. Increasing the Y/Ce ratio can significantly improve the inner surface morphology of the honeycomb channels and also the coating mechanical stability, and leads to a considerable improvement in the catalytic activity of the prepared catalysts for methane.     

Effect of the hybrid catalysts preparation method upon direct synthesis of dimethyl ether from synthesis gas

Direct synthesis of DME from synthesis gas attains more attention recently due to higher conversion and lower cost in comparison to dehydration of the methanol. In this work Synthesis gas To Dimethylether (STD) conversion was examined on various hybrid catalysts prepared by seven different methods. These catalysts had the same general form as CuO/ZnO/Al₂O₃ with theoretical weight ratio 31/16/53, respectively. A novel preparation method for hybrid catalyst namely sol–gel impregnation has also been developed which showed better performance in comparison with the other methods. Also, in order to find out the effect of various alumina contents at a fixed CuO/ZnO ratio on the performance of the hybrid catalyst, a series of catalysts with different contents of alumina have been prepared by sol–gel impregnation method. The optimum weight ratio for CuO/ZnO/Al₂O₃ catalyst has been found to be about 2:1:5, respectively. These catalysts characterized by TPR, XRD, XRF, BET, TGA, N₂O absorption. The catalysts performance were tested at 240 °C, 40 bar and space velocity 1000 ml/g_cat.h, with the inlet gas composition H₂/CO/N₂ = 64/32/4 in a micro slurry reactor.     

Influence of Support Preparation Methods on Structure and Catalytic Activity of Co/TiO2-SiO2 for Fischer–Tropsch Synthesis

TiO₂-SiO₂ supports were prepared by various methods including precipitation, impregnation, hydrolysis-reflux and sol–gel, and then cobalt was impregnated on those supports. The properties of various catalysts were characterized by N₂ physisorption, XRD, XPS and TPR. The introduction of TiO₂ led to stronger Co-support interaction, accompanying with the variation of dispersion and reduction degree of cobalt. The catalytic test for F-T synthesis revealed that the addition of TiO₂ improved the performance of catalysts prepared by precipitation, impregnation and hydrolysis-reflux, but had a negative effect with sol–gel method.     

Thermal stability of Pt particles of Pt/Al2O3 catalysts prepared using microemulsion and catalytic activity in NO–CO reaction

Sintering behaviors of the Pt particles of Pt/Al₂O₃ catalyst prepared using different preparation methods (microemulsion, sol–gel, and impregnation methods) were investigated. It was found that the catalyst prepared by microemulsion had a higher resistance to sintering than did the sol–gel and impregnation catalysts. To limit the sintering even more, the catalysts were pressed. The resistance to sintering in all the catalysts was improved by pressing. The pressed microemulsion catalyst was little deactivated in the NO–CO reaction by thermal treatment at 700 °C for 12 h, and had a high activity relative to that of the sol–gel and impregnation catalysts.     

Fundamental Investigations of Thermal Aging Phenomena of Model NOx Storage Systems

Investigations of the aging behavior induced by high temperatures coupled with oxidizing atmosphere of model NO _x storage systems Ba/Al₂O₃ and Ba/CeO₂ are reported in this paper. The samples were prepared, calcined and exposed to temperatures between 500 and 1000 °C in air for 12 h for thermal aging. Samples were characterized with XRD, HRSEM, DSC-TGA-MS and BET analyses. In XRD investigations of all model systems calcined at 500 °C for 2 h, the NO _x storage component was present in form of BaCO₃. The release of CO₂ as a result of the decarbonization of the NO _x storage component at increased temperatures was verified by thermogravimetric investigations. In the case of Ba/Al₂O₃, already during calcination a partial reaction of the NO _x storage component with Al₂O₃ resulting in the formation of barium aluminate was observed. In the model system Ba/CeO₂ the decomposition of the barium carbonate started above 780 °C and the formation of a barium cerium mixed oxide was observed. The presence of the barium containing NO _x storage component has a strong influence on the specific surface area of the model NO _x storage systems. The morphology and crystallite size of CeO₂ modified with the barium containing NO _x storage component exhibited distinct changes compared to the unmodified oxide. The NO _x storage efficiency determined by model gas tests of freshly prepared and engine aged model NO _x storage catalysts correlates well with the above described observations.     

Role of Support in Lean DeNOx Catalysis

FTIR and pulse thermal analysis were applied to investigate catalysts containing Pt (1 wt%)/Ba (17 wt%) supported on -Al₂O₃, SiO₂ and ZrO₂. The aim was to learn how the support material affects the thermal stability of barium carbonate and its activity in the reaction to bulk Ba(NO₃)₂. The lower thermal stability of BaCO₃ in alumina supported samples was found to influence the formation of barium nitrate during the NO _x storage process. Quantification of Ba(NO₃)₂ formed during NO _x storage indicated that for alumina supported catalysts only ca. 30% of barium present in the sample is involved in the storage process. The low thermal stability found for alumina supported barium nitrite excludes its role in the formation of barium nitrate during interaction of NO _x with the catalyst at 300 °C. The studies indicate that -Al₂O₃ plays a major role in influencing the thermal stability of BaCO₃ and Ba(NO₃)₂. This finding seems to be relevant for the higher activity of -Al₂O₃-supported catalysts in NO _x storage reduction reactions.     

Low-temperature catalytic reduction of nitrogen oxides with ammonia over supported manganese oxide catalysts

MnO_x supported on γ-Al₂O₃, TiO₂, Y-ZrO₂ and SiO₂ was prepared by an impregnation and a deposition-precipitation method, and their catalytic activities for the low-temperature selective catalytic reduction (SCR) of NO_x with NH₃3 in the presence of excess O₂ were examined. The catalytic activity of the catalysts prepared by a deposition-precipitation method was higher than that of catalysts prepared by an impregnation method. The activity follows in the order: MnO_x/TiO₂ ≈ MnO_x/γ-Al₂O₃ > MnO_x/SiO₂ > MnO_x/Y-ZrO₂. Supported MnO_x catalysts prepared by a deposition-precipitation method appeared to have an amorphous manganese oxide phase and those prepared by an impregnation method exhibited a crystalline MnO₂ phase, respectively. The addition of SO₂ with H₂O in the feeding gas slightly deactivates the SCR activity of MnO_x/TiO₂ catalysts.     

Loss of NOx storage capacity of Pt–Ba/Al2O3 catalysts due to incorporation of phosphorous

This work aims at determining the effect of the incorporation of P on NO_x storage capacity by NO_x storage-reduction (NSR) catalysts. Different amounts of phosphorous were deposited on a Pt–Ba/Al₂O₃ catalyst (1 wt% Pt and 17 wt% Ba) by impregnation of a phosphate salt. Samples were calcined at 723 K and characterized using X-ray diffraction (XRD), N₂ adsorption isotherms and X-ray photoelectron spectroscopy (XPS). Their NO_x storage capacity was also measured. It was observed that storage capacity decreased almost linearly with the P/Ba ratio and besides at a phosphorous concentration P/Ba ratio of <0.1 deterioration was low. At higher P concentrations (P/Ba ratio = 0.7) the NO_x storage was significantly reduced. It is proposed that the cause of the decline in NO_x retention capacity would be the formation of Ba–P phases (very likely Ba phosphates) at the expense of Ba carbonate or Ba oxide. These new phases would be unable to exchange NO_x.     

Silver supported mesoporous SBA-15 as potential catalysts for SCR NOx by ethanol

Reduction of nitrogen oxides (NO_x) in a lean exhaust gases has become one of the most important environmental concerns. This study compared the performances of DeNO_x and the properties of silver/mesoporous aluminosilica synthesized by different methods. Silver nanoparticles were obtained after calcination of the materials prepared by incipient wetness or by the excess solvent impregnation of Al-SBA-15 support by silver nitrate. On the other hand, the silver nitrate was introduced on the synthesis gel of SBA-15. The solid product was used as support to deposit aluminium. The effect of synthesis method on silver incorporation and the porous structure of the resulting solids has been examined. Some techniques had been applied, such as: elemental analysis, X-ray diffraction (XRD), N₂ sorption measurements and Transmission Electron Microscopy (TEM). The nature of silver species in these catalysts was investigated by XPS measurements, high angle XRD, high resolution TEM and TPR/H₂ (temperature-programmed reduction). The resulting materials were tested in the selective catalytic reduction of NO_x by ethanol in the presence of oxygen. Finally, the effect of H₂ on the DeNO_x activity was also investigated.The impregnation method of Al-SBA-15 by silver nitrate influences the size, the location of the particles and the catalytic activity. To maintain a higher DeNO_x activity, the percentage of aluminium loading and the feed of H₂ gases should be increased.