Catalytic combustion of diesel soot over perovskite-type catalyst: Potassium titanates

Potassium titanates with a high crystallinity were successfully prepared by the sol-gel method and characterized by XRD, SEM, and BET surface area measurements. K₆Ti₄O₁₁, K₂Ti₂O₅, K₂Ti₄O₉ were found to have better soot oxidation performance compared with Pt/TiO₂ and CeO₂ based catalysts. K₂Ti₂O₅ may be an excellent candidate for soot oxidation due to its high oxidation activity, water-stability, resistance to sulfur poisoning and economical advantages. Certain amount of NO _x can contribute to the catalytic combustion of diesel over potassium titanates, implying that K₂TiO₅ may be a kind of catalyst for simultaneous removal of NO _x and soot.     

Easy synthesis of three‐dimensionally ordered macroporous CuO–CeO2 mixed oxide catalysts and their high activities for the catalytic combustion of soot

Three‐dimensionally ordered macroporous (3DOM) Cu_xCe‐M (x denote the mole ratio of Cu/[Ce + Cu]) oxide catalysts with large pore sizes and interconnected macroporous frameworks were successfully synthesized using a polymethyl methacrylate template method. The 3DOM structure improves the contact efficiency between catalyst and soot, which benefits soot elimination in the low temperature range. The low redox barriers of the 3DOM Cu–Ce solid solution also facilitate the elimination of the soot. The 3DOM Cu_0.1Ce catalysts exhibit the highest catalytic activity with maximum soot oxidation rate temperatures at 375 and 351 °C in the air and NO _x atmosphere, respectively. The NO _x‐TPD results demonstrate that the NO₂ produced in the Ce_0.1Cu‐M sample plays a curial role in improving the soot oxidation performance. Meanwhile, the NO‐DRIFTs reveal that the nitrates stored in the Cu_0.1Ce‐M sample also had a promotional effect on the soot elimination.     

VOCs and carbonaceous particles removal assisted by NOx on alkali0.15/ZrO2 and Csx–M0.1/ZrO2 catalysts (M = Cu or Co)

The effect of alkali metals on the physicochemical characteristics of zirconium oxide and the properties of alkali metals in the oxidation of toluene and/or carbonaceous particles and/or conversion of nitrogen oxides have been studied. We observed that they had an effect on the structural and textural properties of ZrO₂. These solids were tested first in the oxidation of toluene and carbonaceous particles separately and secondly with both pollutants. Whatever the experiments, the sample Cs_0.15/ZrO₂ was found to be the catalyst the most active. The simultaneous removal of toluene and soot shows that the presence of toluene leads to a decrease in the temperature of the maximum soot oxidation rate, particularly with catalysts impregnated of Cs and Cu. The effect of the Cs/Co ratio on NO_x conversion and toluene oxidation was also studied. It was found that the oxidizing properties of NO_x can increase the conversion of toluene. This phenomenon occurs especially in the presence of catalysts with a low amount of alkali metal. For the oxidation of carbonaceous particles on the samples Cs/ZrO₂ impregnated with transition metals, the best performance is obtained for copper, although a decrease of the ratio Cs/Cu leads to a slower oxidation and a shift to higher temperatures.     

Simultaneous soot combustion and NOx reduction over a vanadia-based selective catalytic reduction catalyst

Simultaneous NO_x reduction and soot combustion over a commercial vanadia-based selective catalytic reduction (SCR) catalyst were investigated. Carbon black was used as model soot. The impact of the contact intensity between carbon and catalyst was studied. The experiments appeared as promising results for the utilization of vanadia-based SCR catalysts in SCR on filter system as, in the SCR operating temperature range (250–400 °C), no significant impact of the presence of carbon black on NO_x reduction was observed. However, a decrease in the specific carbon oxidation rate was highlighted. This latter increases with the contact between carbon and catalyst and is attributed to a lack of NO₂, consumed by the fast SCR reaction. At temperatures greater than 400 °C, the contact between carbon particles and the SCR catalyst partially inhibits the NO_x reduction, whereas it exhibits a catalytic effect on the carbon oxidation rate. The tighter the contact between the two materials, the more significant is this behavior. A redox mechanism, which competes with the redox cycle of the SCR mechanism, was proposed. The impregnation of a V-based SCR catalyst with 2 wt % of calcium was also performed. A drastic loss of DeNO_x activity was observed, whereas the effect of the contact between carbon and catalyst was reduced.     

酸性金属氧化物对锰铈氧化物催化剂脱硝温度窗口的调控作用

利用溶胶-凝胶法,采用三种酸性金属氧化物（氧化铌、氧化钨和氧化钼）对锰铈复合氧化物催化剂进行了改性. 测试了催化剂的氮氧化物选择性催化还原（SCR）活性,以筛选对应不同温度窗口的合适酸性氧化物改性剂. 同时评价了催化剂的NO氧化和NH₃氧化活性. 利用X射线衍射、BET比表面积测试、H₂程序升温还原、NH₃/NO_x程序升温脱附和NH₃/NO_x吸附红外光谱等手段对催化剂进行了表征. MnO_x-CeO₂催化剂表现出良好的低温（100-150 ℃）活性. 酸性金属氧化物的添加削弱了催化剂的氧化还原特性,从而抑制了NH₃的活化和NO₂辅助的快速SCR反应. 与此同时,相对高温（250-350 ℃）区NH₃的氧化也受到了抑制,B酸和L酸上的NH₃吸附得以增强. 因此,催化剂的SCR脱硝温度窗口向高温移动,改性效果Nb₂O₅ < WO₃ < MoO₃.     

On the influence of the alumina precursor in Fe-K/Al2O3 structured catalysts for the simultaneous removal of soot and NOx: From surface properties to reaction mechanism

Cordierite-monolith supported Fe-K/Al₂O₃ catalysts were prepared using different alumina precursors. The catalysts were physico-chemically characterized, and their activity in the simultaneous removal of soot (carbon black) and NO_x was assayed with the aim of studying the influence of the particular features of each alumina precursor on the final properties of the different prepared catalyst. Structural and textural characteristics of the catalytic layer were found to be strongly dependent on the type of alumina used, which, in turn, determined the mobility of the alkali compound. This fact together with the weaker interaction of the catalytic phase with the alumina resulted in easier K diffusion and loss in some cases, whereas, on the other hand, a stronger interaction and favorable textural features of the layer resulted in notably enhanced catalytic activity.     

Role of nitrogen dioxide in the oxidation of diesel soot on promoted mixed catalysts with fluorite and perovskite structures

The oxidation of soot on catalysts with the perovskite and fluorite structures (including platinum-promoted catalysts) in the presence and in the absence of NO₂ was studied using in situ IR spectroscopy and temperature-programmed techniques (TPR, TPD, and TPO). It was found that, as a rule, the temperature of the onset of soot oxidation considerably decreased upon the addition of NO₂ to a flow of O₂/N₂, whereas the amount of oxygen consumed in soot oxidation considerably increased. To explain these facts, we hypothesized that the initiation of soot combustion in the presence of NO₂ was related to the activation of the NO₂ molecule through the formation (at a low temperature) and decomposition (at a high temperature) of nitrate structures on the catalyst. Superequilibrium amounts of NO₂ resulted from the decomposition of nitrate complexes immediately on the catalyst for soot combustion. Based on a comparison between catalyst activities and data obtained by TPR and the TPD of oxygen, a conclusion was drawn that the presence of labile oxygen in the catalyst is a necessary but insufficient condition for the efficient occurrence of a soot oxidation reaction in the presence of NO₂. The introduction of platinum as a constituent of the catalyst increased the amount of labile oxygen and, as a consequence, increased the amount of highly reactive nitrate complexes. As a result, this caused a decrease in the temperature of the onset of soot combustion.     

Role of α-Sites in the selective catalytic reduction of NO x with ammonia over Fe-ZSM-5 catalysts

The catalytic properties of Fe-ZSM-5 zeolites with different iron contents have been investigated in the selective catalytic reduction (SCR) of NO _x with ammonia. The observed catalytic properties the zeolites are correlated with the concentration of the iron-containing sites that are stabilized in the zeolite and effect N₂O decomposition (??-sites). The catalysts activated at a high temperature to increase the ??-site concentration (by a factor of 5?C10) are more active in NO _x SCR with ammonia than the unactivated samples. However, the difference between the activities of the activated and unactivated catalysts is well below the difference between the ??-site concentrations in these catalysts. The nonlinear relationship between these parameters is evidence that the ??-sites in Fe-ZSM-5 is not the only factor determining the activity of Fe-ZSM-5 in NO _x SCR with ammonia. The activated catalysts show a low activity in nonselective ammonia oxidation and, accordingly, a high selectivity in the target process at high temperatures.     

Development of the bifunctional catalyst Mn-Fe-Beta for selective catalytic reduction of nitrogen oxides

The catalytic properties of the Mn-Fe-Beta system with Mn contents in the range 0.1–16 wt.% were studied in the selective catalytic reduction (SCR) of NO _x with ammonia. The catalyst structure was investigated using IR spectra of adsorbed NO, temperature-programmed reduction with hydrogen (H₂-TPR), X-ray diffraction analysis, and ESR. The use of manganese as a promoter substantially increases the activity of iron-containing catalysts in the SCR of NO _x with ammonia. At low contents (<2 wt.%), Mn exists in the cation form and the catalytic activity of the Mn-Fe-Beta system does not increase. At a higher content of Mn, clusters MnO _x begin to form, which are highly active in the oxidation of NO to NO₂ and the low-temperature catalytic activity of the Mn-Fe-Beta system increases. The observed increase in the low-temperature catalytic activity in the process of SCR of NO _x with ammonia is related to a change in the reaction route. The MnO _x clusters favor the oxidation of NO and the iron cations facilitate the reaction of “fast” SCR.     

The Effect of Water on the 2-Propanol Oxidation Activity of Co-Substituted LaFe1−xCoxO3 Perovskites

Perovskites are interesting oxidation catalysts due to their chemical flexibility enabling the tuning of several properties. In this work, we synthesized LaFe_1−xCo_xO₃ catalysts by co-precipitation and thermal decomposition, characterized them thoroughly and studied their 2-propanol oxidation activity under dry and wet conditions to bridge the knowledge gap between gas and liquid phase reactions. Transient tests showed a highly active, unstable low-temperature (LT) reaction channel in conversion profiles and a stable, less-active high-temperature (HT) channel. Cobalt incorporation had a positive effect on the activity. The effect of water was negative on the LT channel, whereas the HT channel activity was boosted for x>0.15. The boost may originate from a slower deactivation rate of the Co³⁺ sites under wet conditions and a higher amount of hydroxide species on the surface comparing wet to dry feeds. Water addition resulted in a slower deactivation for Co-rich catalysts and higher activity in the HT channel state.     

Optimized Pt-MnOx interface in Pt-MnOx/3DOM-Al2O3 catalysts for enhancing catalytic soot combustion

The catalysts of three-dimensionally ordered macroporous (3DOM) Al₂O₃-supported core-shell structured Pt@MnO_x nanoparticles (3DOM-Pt@MnO_x/Al₂O₃) were successfully prepared by the gas bubbling-assisted membrane reduction-precipitation (GBMR/P) method. Pt@MnO_x core-shell nanoparticles (NPs) are highly dispersed on the inner surface of 3DOM-Al₂O₃ support. Pt@MnO_x/3DOM-Al₂O₃ catalysts, which combine both advantages of high-efficiency soot-catalyst contact by 3DOM-Al₂O₃ structure and the abundant active sites by the optimized Pt-MnO_x interface, exhibit high catalytic activities for soot combustion, and the catalytic activities are strongly dependent on the thickness of MnO_x shell. Among the catalysts, 3DOM-Pt@MnO_x/Al₂O₃-1 catalyst with optimized Pt-MnO_x interface shows the highest catalytic activity for soot combustion, i.e., its values of T₅₀ and S_CO2^m are 351 °C and 98.6%, respectively. The highest density of Pt-MnO_x active sites for adsorption-activation of gaseous O₂ is responsible for enhancing catalytic activity for soot combustion. Pt@MnO_x/3DOM-Al₂O₃ catalysts are promising to practical applications for the emission reduction of soot particles.     

Rhenium- and ruthenium-containing catalysts for neutralization of automobile exhaust

The rhenium- and ruthenium-containing catalysts are active in the oxidation of CH _x and CO and in the reduction of NO _x . Comparative testing of catalyst samples under laboratory conditions and on an engine stand demonstrated that these catalysts outperform the known commercial catalysts in the neutralization of exhaust gas from automotive gasoline engines. It is, therefore, possible to completely replace expensive Rh and partially replace Pt and Pd with cheaper components—Re and Rh—in the manufacturing of catalytic converters.     

Fe- and Cu-oxides supported on γ-Al2O3 as catalysts for the selective catalytic reduction of NO with ethanol. Part I: catalyst preparation,characterization, and activity

Fe- and Cu-oxides supported on γ-alumina (γ-Al₂O₃; metal loading of 3 mass %) were investigated as alternative catalysts to the conventional Ag-based system in the selective catalytic reduction of NO with ethanol (EtOH-SCR). The catalysts were characterized by elemental analysis, N₂ sorption, X-ray diffraction, temperature-prgrammed desorption of NH₃, temperature-programmed reduction with H2, diffuse reflectance UV-VIS (DR-UV-VIS) spectroscopy, and compared with 3 mass % Ag/γ-Al₂O₃ as a reference catalyst. Catalytic experiments were carried out between 423 K and 773 K in the steady state and by temperature-programmed surface reaction (TPSR) experiments. For all catalysts, the highest NO conversion (900 ppm (ppm = parts of the mixture component per million parts of all mixture components) NO, 900 ppm EtOH, 0.5 vol. % H₂O, 4 vol. % O₂ in He) was found at 573 K. While 84 % of NO were converted over the Ag-based catalysts, only 20–60 % NO conversion was observed for the Fe- and Cu-containing catalysts. Total oxidation of ethanol as an unwanted side reaction occurs over 3 mass % Cu on γ-Al₂O₃ already at 573 K, whereas the highest activity of 3 mass % Fe on γ-Al₂O₃ for this conversion was reached at 743 K. For lower temperatures, partial oxidation of ethanol leads to organic by-products which can act as active intermediates in EtOH-SCR. TPSR experiments show that ethanol reacts over both the Fe- and the Cu-based catalysts to organic by-products, such as ethene or acetaldehyde, which affect the EtOH-SCR reaction.     

Catalytic activity of layered aluminosilicates for VOC oxidation in the presence of NOx

Raw and variously modified layered aluminosilicates have been used as catalysts in the reaction of ethanol oxidation both in the presence and absence of NO_x. In this study, we clearly showed that the conversion of VOC on the modified layered aluminosilicates decreases slightly in the presence of NO_x. However, the presence of NO_x in the reaction mixture did not affect the stability of the used catalysts. Only a small change of selectivity depending on the carrier type as well as on the way of modification was found.     

Catalytic removal of soot particles over MnCo<Subscript>2</Subscript>O<Subscript>4</Subscript> catalysts prepared by the auto-combustion method

Soot removal for exhaust gas from diesel engine has been addressed due to the more stringent legislation and environmental concerns. MnCo₂O₄ catalysts were systematically prepared using glucose as a fuel via the auto-combustion method and applied for soot removal. The as-prepared samples were characterized by X-ray diffraction (XRD), O₂-temperature-programmed oxidation (TPO) reaction and H₂-temperature-programmed reduction reaction (H₂-TPR). The catalytic activities for soot combustion were evaluated by micro activity test (MAT) with a tight contact mode between soot and catalysts. Compared with catalysts prepared by the solid state method without glucose, auto-combustion method in the presence of glucose can decrease the synthetic temperature, avoiding high temperature treatment and sintering. The catalysts prepared with glucose could catalyze soot oxidation effectively and the derived values of T₁₀, T₅₀, and T₉₀ were 326, 408, and 468 °C in a tight contact mode, respectively, showing a significant drop of T₁₀, T₅₀, and T₉₀ by 156, 177, and 178 °C for non-catalytic reaction.     

Synthesis and characterisation of K–Ag/Al2O3 catalysts for CH4-SCR of NOx: effect of SO2

This paper characterizes the integrated activity of fresh and used catalysts on the selective catalytic reduction of NOx using CH₄. The synthesised K–Ag/Al₂O₃ catalysts exhibited a promotional effect on deNOx activity in the presence of SO₂. In addition, 130 h of time-on-stream reactions demonstrated the thermal and mechanical stability of the synthesised materials. A TEM analysis and diffraction patterns demonstrated the sintering of finely dispersed particles to ~0.5 micron size clusters by sulphation. Furthermore, under reaction conditions, the de-sulphation initiated the re-dispersion of the Ag clusters to different sized particles. The TPD studied demonstrated the strong adsorption sites for methane and formation of R–SOx compounds. This surface modification in the SO₂ feed stream is considered to be the reason for the promotional effect on the deNOx reaction.     

The influence of the active component and support nature, gas mixture composition on physicochemical and catalytic properties of catalysts for soot oxidation

Physicochemical and catalytic properties of compositions Fe(Ce)–Mn–O/support (gamma-, theta-, alpha-Al₂O₃, SiO₂ as the support) and Pt/CeO₂/theta-Al₂O₃ for oxidation of soot were characterized. It was established that the phase composition of the initial catalysts depended mainly on the nature of the active component and preparation conditions. Non-isothermal treatment of the soot–catalyst compositions at the temperature up to 1000 °C resulted in a change in the phase composition depending mainly on the final treatment temperature. The catalyst surface area was determined by the support nature. It was established that catalyst activities for oxidation of soot are determined by both catalyst nature and composition of gas mixture. The process of the soot oxidation is thought to involve oxygen from the catalyst surface. The higher proportion of weakly bound surface oxygen, the higher was the catalyst activity. An increase in the oxygen concentration from 5% O₂/N₂ to 15% O₂/N₂ is shown to lead to a decrease of the temperature of the soot oxidation. The influence of the oxygen concentration on the process of soot oxidation becomes weaker in the presence of water vapor. Results showed that the presence of NO in the gas mixture favors a decrease in the oxidation temperature of the soot, the higher being the nitrogen oxide concentration, the more pronounced effect. Introduction of SO₂ in amount of 50 ppm in the gas mixture has no noticeable effect on the process of the soot oxidation. Among the catalysts under study, Fe–Mn–K–O/gamma-Al₂O₃ is most effective to oxidation of the soot at otherwise identical conditions.     

少量CeO2的添加对Pd/La-Al2O3密偶催化剂三效性能的影响

以La改性的Al₂O₃为载体,采用共吸附浸渍法制备了一系列不同CeO₂含量的单Pd密偶催化剂,并对其进行了表征. PdO_x和CeO₂之间的强相互作用改善了Pd⁰再氧化为PdO的能力,同时增强了反应条件下硝酸盐,亚硝酸盐和异氰酸盐在载体上的吸附. 因此适量CeO₂的添加明显改善了新鲜催化剂对HC和NO_x的催化性能,且当CeO₂添加量为2%时催化效果最佳. Pd-Ce界面上PdO_x和CeO₂间强相互作用也使得PdO_x物种在高温时仍能以小颗粒的形式分散在载体上,从而显著地提高催化剂的热稳定性. 经1100 ℃高温老化后,CeO₂ （2%-4%）的存在明显拓宽了HC和NO_x的操作窗口,这对于提高单Pd密偶催化剂在汽车尾气处理上的催化性能有重要意义.     

An XPS study of the oxidation of noble metal particles evaporated onto the surface of an oxide support in their reaction with NO<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>

The interaction of the model catalysts Rh/Al₂O₃, Pd/Al₂O₃, Pt/Al₂O₃, and Pt/SiO₂ with NO _x (mixture of 10 Torr of NO and 10 Torr of O₂) was studied by X-ray photoelectron spectroscopy (XPS). Samples of the model catalysts were prepared under vacuum conditions as oxide films ≥100 Å in thickness on tantalum foil with evaporated platinum-group metal particles. According to transmission electron microscopic data, the platinum-group metal particle size was several nanometers. It was found by XPS that the oxidation of Rh and Pd nanoparticles in their interaction with NO _x occurs already at room temperature. The particles of platinum were more stable: their oxidation under the action of NO _x was observed at elevated temperatures of ～300°C. At room temperature, the interaction of platinum nanoparticles with NO _x hypothetically leads to the dissolution (insertion) of oxygen atoms in the bulk of the particles with the retention of their metallic nature. It was found that dissolved oxygen is much more readily reducible by hydrogen than the lattice oxygen of the platinum oxide particles.     

Mn1-x(Li,Ti)xCo2O4尖晶石型复合氧化物的制备、表征与催化性能

用柠檬酸配位燃烧法合成了Mn_1-x(Li,Ti)_xCo₂O₄系列尖晶石型复合氧化物催化剂，使用FTIR和XRD方法对催化剂结构进行表征，通过程序升温氧化反应(TPO)技术对这些催化剂在模拟柴油机尾气条件下进行同时消除NO_x和柴油碳黑反应的活性评价。结果表明，掺杂Li或Ti后的Mn_1-x(Li,Ti)_xCo₂O₄系列催化剂仍然保持了完整的尖晶石型复合氧化物结构，这些催化剂对同时消除柴油机尾气中的碳黑颗粒和NO_x具有良好的催化性能，其中Li或Ti的掺杂量为x=0.05较佳，结合碳黑燃烧与NO_x还原总的催化效果，Mn_0.95Li_0.05Co₂O₄具有最好的催化活性。