Catalytic Combustion Of Diesel Soot Research Articles

On the effect of La–Cr–O– phase composition on diesel soot catalytic combustion

A series of samples of La–Cr–O– perovskites were designed as catalysts for diesel soot combustion. They were prepared by using co-precipitation method, at ambient temperature using ammonia followed by a hydrothermal treatment (T = 200 °C, P = 20 atm, t = 24 h). All the chromium-containing precursors were then calcined at high temperature to develop the oxide catalyst. Two phase composition 86%LaCrO3–(14%) La2CrO6 or 94%LaCrO3–6%La2O3 were formed depending on the atmosphere of calcination (oxygen or hydrogen respectively) used. Their respective BET surface areas were 1.1 and 6.5 m2 g−1. Highly crystalline, pure phase of LaCrO3 and La2CrO6 powders were also prepared, with BET area of 4 and 3 m2 g−1, respectively. The crystalline structure and properties of all samples were characterised by X-ray diffraction (XRD), using Rietveld refinement, and temperature-programmed reduction (TPR) techniques. O2-TPD measurements performed on all samples showed the presence of suprafacial, weakly chemisorbed oxygen only for LaCrO3, which contributes actively to soot combustion. TPR study performed on all catalysts showed that while pure LaCrO3 and La2O3 samples did not reduce, the biphasic catalysts showed the presence of oxygen depletion peaks characteristic of lattice oxygen mobility in the samples at ca. 665 °C. Catalytic combustion of diesel soot was studied over all catalysts. The results showed that pure LaCrO3 exhibited significant catalytic activity which was sensitively affected by the modifier La2CrO6 or La2O3.

Catalytic Combustion of Diesel Soot on Co−Sr−K Catalysts

The catalytic activities of Co3O4, Sr(NO3)2, Co−Sr, and Co−Sr−K catalysts were studied, and the effect of the contact mode on the soot onset ignition temperature and soot oxidation rate was also discussed. All the catalysts were characterized by X-ray diffraction and thermogravimetry/differential scanning calorimetry. The catalytic activities were evaluated by a soot oxidation reaction using the temperature-programmed reaction system. The soot onset ignition temperature is 370 °C for Co−Sr catalysts with molar ratios of 1:1 and 2:1, which is the same as that of pure Co3O4. The Co−Sr catalysts containing KNO3 can greatly lower the soot onset ignition temperature. The catalytic activity of pure Co3O4 and Sr(NO3)2 is affected by catalysts−soot contact intensity, which has nearly no effect on the soot onset ignition temperature and soot oxidation rate for Co−Sr catalysts with appropriate ratios. The cooperation of Co3O4 and Sr(NO3)2 can accelerate the soot oxidation rate and reduce the effect of the soot−cata...

Catalytic combustion of diesel soot: Deactivation by SO2 of copper and potassium nitrate catalysts supported on alumina

Abstract The SO2 poisoning of Cu KNO3/Al2O3 catalysts used in the catalytic combustion of diesel soot with NO/O2 feed has been studied in this work. Fresh catalysts show temperatures of maximum combustion rate (Tmax) at about 470, 375 and 368 °C for Cu/Al2O3, KNO3/Al2O3 and Cu KNO3/Al2O3 respectively. Poisoned catalysts decrease the activity and techniques of vibrational spectroscopy (FTIR) and temperature programmed reduction (TPR) suggest the KNO3 loss and the formation of potassium sulfate in the mentioned poisoned catalysts.

Diesel soot combustion on potassium promoted hydrotalcite-based mixed oxide catalysts

KNO3 or K2CO3 supported Mg–Al hydrotalcite-based mixed oxide catalysts were investigated for the catalytic combustion of diesel soot. The activity of the catalysts before and after reactions with soot was conducted under the flow of air and high purity He gas. It has been found that K shows a great promotion of the catalytic activity, and deactivation was not detected after the reaction with soot in a muffle furnace in a static air atmosphere. The active phases were examined by XRD. The high activity is found to be due to an interaction between K and Mg(Al), which may weaken the Mg(Al)–O bonds, thus facilitating the mobility of the O species.

Study of the catalytic combustion of diesel soot over nanometric lanthanum-cobalt mixed oxide catalysts

Co3O4, NiCo2O4 and LaCo2O4catalysts were synthesizedby the citric acid-ligated method. These catalysts containing Co-oxide active components can largely lower the temperature of soot combustion under tight contact conditions. Under the conditions of loose contact NiCo2O4 cannot promote soot combustion, but LaCo2O4 can effectively promote soot combustion because the nanometric perovskite-type catalyst LaCoO3produced in the LaCo2O4sample.

Surface characterization of Co,K/La2O3 catalysts used for the catalytic combustion of diesel soot

AbstractCatalysts of Co,K/La2O3 have been prepared by wet impregnation. The samples have been calcined at 400°C and 700°C and have been characterized for phase composition using x‐ray diffraction and Fourier transform infrared spectroscopy. The XPS analysis of the samples has been obtained by examination of the O 1s, K 2p, C 1s and La 3d spectral regions. The XPS data are discussed with respect to the calcination temperatures and the soot combustion performed in the spectrometer reaction chamber. Analysis of the XPS data indicates considerable carbonation of the surfaces of all samples, even after burning the soot. The K/La2O3 solid presents the highest content of surface carbonated species, showing the highest catalytic activity for soot combustion. Interaction of the catalysts with CO2 is studied by temperature‐programmed desorption and microbalance experiments. Kinetic studies and surface characterization of the potassium‐containing samples suggest that an appropriate surface potassium concentration is necessary for a synergetic action between potassium and lanthanum. In the cobalt‐containing catalysts calcined at 700°C, an increase is observed in the concentration of the outer‐layer perovskite species when the potassium content increases, following the same tendency observed in the bulk. Such LaCoO3 species would limit the reaction of lanthanum with CO2. Copyright © 2003 John Wiley & Sons, Ltd.

Catalytic combustion of diesel soot on Co, K supported catalysts

Catalysts containing 12% Co and 4.5% K, supported on MgO and CeO 2 have been studied for diesel soot catalytic combustion. It has been found that this reaction occurs by a redox mechanism when Co and K are deposited on any of the above-mentioned supports. On MgO-supported catalysts, CoO x species are responsible for the supply of oxygen by a redox reaction. In this catalyst, K plays different roles, one of them being the stabilization of the CoO x particles. On CeO 2-supported catalysts, Co does not significantly improve the activity of the K/CeO 2 catalyst, since in this case the support itself displays redox properties. XPS analyses indicate that the oxygen availability on the surface is much higher on CeO 2 than on MgO. On both CeO 2 and MgO-supported catalysts, K might provide a route for CO 2 release through a carbonate intermediate species. The presence of NO in the gas phase improves the catalytic activity for soot elimination. NO is oxidized to NO 2 on the Co, K/CeO 2 catalyst, and NO 2 is a stronger oxidizing agent than O 2, therefore decreasing the temperature needed to burn the soot.

Catalytic combustion of diesel soot on Co,K/MgO catalysts. Effect of the potassium loading on activity and stability

Co,K/MgO catalysts with 12 wt% of Co and 1.5, 4.5 and 7.5 wt% of K, calcined at 400°C are active for the combustion of diesel soot. Among them, the one containing 4.5 wt% of K is that which burns soot at the lowest temperature (378°C). Coincidentally, this is the catalyst presenting the highest K/Mg and K/O surface ratios in XPS measurements. When the calcination temperature is increased at 500°C, both the solid containing 4.5% of K and the one containing 1.5% as well as the unpromoted catalyst (Co/MgO) noticeably lose activity due to the formation of a solid solution (Co, Mg). However, the solid with the highest K content (7.5 wt%) presents a similar activity at different calcination temperatures (400°C, 500°C and 700°C). It has been found that the activity of these solids is directly related to the reducibility of cobalt, thus indicating that the reaction is carried out by a redox mechanism. Potassium plays different roles in these catalysts: (i) it increases the catalyst–soot contact by increasing surface mobility, (ii) it preserves the reducibility and dispersion of cobalt by improving stability against thermal treatments, and (iii) it favors the oxidation of soot by consuming the carbon to form carbonate species during soot combustion. It was also found that soot with a higher content of sulfur (1050 ppm) is more efficiently burned than that containing low amounts of sulfur (70 ppm). However, the severe sulfation of the catalyst leads to a noticeable loss of activity. In experiments of carbon monoxide oxidation, it was found that conversion is practically total between 400°C and 500°C under the conditions used in this work. The direct impregnation of the soot with either Co or Co and K, showed lower combustion temperatures if compared with the mechanical mixtures of soot and Co/MgO or Co,K/MgO, suggesting that the soot–catalyst contact poses a physical limitation on the oxidation activity. This important result suggests that the soot–catalyst contacting problem is the main difficulty to be overcome in order to obtain useful catalysts. All research effort towards developing catalyst formulations will be unable to reduce the temperature for combustion until this problem is solved.

Microwave-assisted catalytic combustion of diesel soot

The concept of oxidizing diesel soot in a microwave-assisted catalytic trap was demonstrated. Comparisons were made to experiments using electric heating with and without catalysts to understand the influence of microwave irradiation on catalysis. The complex permittivities of the three materials (diesel soot, catalyst and support) involved in such a system were measured and the feasibility of using this combination of materials in diesel soot burn-off was evaluated, based upon these measured data. It was found that iron and copper were the most active catalysts in lowering the ignition temperature of diesel soots, while palladium was a necessary component in achieving more complete combustion. The iron-containing catalyst was also very effective and energy-efficient at low microwave input. A non-thermal or microwave enhancement effect was observed which further decreased the ignition temperature by more than 200°C. It was also found that the more vigorous burning of diesel soot by microwave heating led to an increase in carbon monoxide in the combustion products, because of the difference in the heating mechanism. However, when palladium was used, the same completeness of combustion as in electric heating could be achieved.

Catalytic combustion of diesel soot over metal oxide catalysts

The activity of different metal oxides in the catalytic combustion of a diesel soot having a high amount of adsorbed hydrocarbons has been investigated and tested in a TPO apparatus. Two different steps have been observed. The first is related to the combustion of hydrocarbons adsorbed on soot and the second one to the combustion of the graphitic solid fraction. A high surface area Fe 2O 3 was found to be the most active catalyst for the oxidation of hydrocarbons, whereas V 2O 5 was also able to promote the combustion of graphitic carbon. The oxidation of the hydrocarbon fraction has been correlated with the surface area and the strength of the metal-oxygen bond of the metal oxide. The combustion of graphitic carbon is favoured instead on metal oxides having a low melting point. The effect of platinum addition to γ-alumina has been also investigated. Spillover of activated oxygen from Pt to the support has been postulated to take into account the promotion of the oxidation of graphitic carbon.

Catalytic combustion of carbon particulate

The catalytic combustion of carbon particulate was investigated with the aim of developing a catalyst for the abatement of soot in diesel exhausts. In the presence of a Cu/V/K based catalyst a strong increase of the rate of carbon combustion and a marked decrease of the apparent activation energy were observed. The carbon reactivity showed a linear dependence upon the initial ratio of the mass of catalyst to the mass of carbon and a square root dependence upon the oxygen partial pressure. However, catalytic combustion of diesel soot and partially graphitized carbon black confirmed previous results obtained for other carbon materials. In particular, kinetic data follow a model proposed for the catalytic combustion of amorphous carbon black [1]. An extension of this model, incorporating the influence of carbon-catalyst contact on the catalyst performances, has been presented.

Catalytic combustion of soot deposits from diesel engines

The catalytic combustion of diesel soot under the influence of metal oxides and metals has been studied. The catalytically active materials, dispersed on a carrier of γ-alumina, have been studied in order to simulate the conditions in a catalytic particulate trap. A mixture of soot and catalyst was placed in a flow reactor and a gas mixture containing 6% oxygen, 7% water and balance of nitrogen was led through it at a flow-rate of 90 l/h. The combustion rate was determined between 573 and 698 K. The results showed that V 2O 5 is the most active catalyst for the combustion of diesel soot whereas oxides of copper, manganese and chromium as well as the metals silver and platinum are active in the combustion of hydrocarbons that desorb from the diesel soot upon heating. Catalytically active materials sensitive to sulphur poisoning are deactivated immediately during the experiments as large amounts of SO 2 are released from the diesel soot when heated. The results indicate that V 2O 5 is not sensitive to sulphur poisoning. This study shows that a catalyst for the combustion of diesel soot should be based on V 2O 5.

Combustion of soot deposits from diesel engines on mixed oxides of vanadium pentoxide and cupric oxide

The catalytic combustion of diesel soot has been studied under the influence of mixed oxides of V 2O 5 and CuO on a carrier of γ-alumina. A mixture of diesel soot and catalyst was placed in a flow reactor and a gas mixture containing 10% oxygen, 7% water and balance of nitrogen was led through it at a flow-rate of 90 l/h. The combustion rate of the soot was determined between 573 and 698 K. The results showed that a mixed oxide of V 2O 5 and CuO with a molar fraction of 0.9 in vanadium has the highest activity. Small amounts of platinum (<0.1 wt.-%) dispersed on the metal oxide phase through decomposition of H 2PtCl 6 in a reducing atmosphere enhance the catalyst's ability to combust hydrocarbons and carbon monoxide greatly. In addition, the catalyst is not sensitive to sulphur poisoning. A catalyst for the combustion of diesel soot should therefore be based on a mixed oxide of V 2O 5 and CuO, promoted with small amounts of platinum.