Catalytic decomposition of methylene chloride by sulfated oxide catalysts

Catalytic decomposition of methylene chloride in air with a concentration of 959 ppm and temperature ranges from 160 to 275°C were studied. Three different sulfated oxide catalysts, TiO₂(SO₄), ZrO₂(SO₄), CeO₂(SO₄) were prepared and their activities and selectivities were measured. The catalytic activity decreased in the order: TiO₂(SO₄) > ZrO₂(SO₄) > CeO₂(SO₄). Complete catalytic decomposition of methylene chloride was achieved at low temperature (275°C) over a sulfated titanium dioxide catalyst. The oxygen adsorption (pick-up) and the acidity values of three catalysts showed the same trend as their activities. The presence of water (2% in volume) in the feed stream reduced the activities remarkably and raised the activation energies for the decomposition reaction. The selectivities among all three catalysts were similar, with HCl, CO and CO₂ being the products. A bifunctional catalyst comprising sulfated titanium dioxide with copper oxide was developed to improve the selectivity of catalytic oxidation of methylene chloride towards carbon dioxide.     

Cu-Mn氧化物催化N_2O直接分解性能

分别以Cu(NO_3)_2·3H_2O和50%Mn(NO_3)_2水溶液为铜源和锰源,K_2CO_3为沉淀剂,采用沉淀法和共沉淀法制备单一Cu、Mn氧化物催化剂和Cu-Mn-O复合氧化物催化剂,用于催化N_2O直接分解反应,并利用N_2物理吸附-脱附、XRD、FT-IR和TPR等进行表征。结果表明,单一Cu和Mn氧化物分别以体相CuO和Mn2O_3物相形式存在,Cu-Mn-O复合氧化物中除形成CuMn_2O_4尖晶石物相外,还有一定量小晶粒CuO,较单一氧化物具有更加优异的还原性能,表现出较高的催化N_2O直接分解活性。在空速10 000 h~(-1)和N_2O体积分数0.1%条件下,Cu-Mn-O复合氧化物催化剂可在440℃催化N_2O完全分解,分别较单一Cu和Mn氧化物催化剂降低了40℃和60℃。     

Catalytic combustion of volatile organic compounds on gold/iron oxide catalysts

Catalytic oxidation of 2-propanol, methanol, ethanol, acetone and toluene was investigated on coprecipitated Au/Fe₂O₃ catalysts in the presence of excess of oxygen. Gold catalysts have been found to be very active in the oxidation of tested volatile organic compounds (VOCs). The high activity of these systems has been related to the capacity of highly dispersed gold to weaken the Fe–O bond thus increasing the mobility of the lattice oxygen which is involved in the VOCs oxidation probably through a Mars–van Krevelen reaction mechanism.     

Catalytic decomposition of nitrous oxide over perovskite type solid oxide solutions and supported noble metal catalysts

The catalytic decomposition of nitrous oxide to nitrogen and oxygen has been investigated over various solid oxide solutions (SOS), La_0.8Sr_0.2MO_3– (M=Cr, Fe, Mn, Co or Y), La_1.8Sr_0.2CuO_4– and supported Pd, Pt catalysts. The reaction was carried out in a gradientless recycle reactor at 1 atm pressure with a feed gas containing about 0.5% N₂O (in helium). Among the various solid solutions, La_0.8Sr_0.2CoO_3– showed a maximum N₂O conversion of 90% at 600C. The order of activity observed for N₂O decomposition was La_0.8Sr_0.2CoO_3–>La_0.8Sr_0.2FeO_3–>La_1.8Sr_0.2CuO_4–> La_0.8Sr_0.2MnO_3–La_0.8Sr_0.2CrO_3–La_0.8Sr_0.2YO_3–. The activity of La_0.8Sr_0.2CoO_3– was compared with supported Pd, Pt and also with unsubstituted LaCoO₃ catalysts under similar reaction conditions. Among all the catalysts tested in this study, Pd/Al₂O₃ showed the lowest light-off temperature for N₂O decomposition. The activity of La_0.8Sr_0.2CoO_3– was found to be comparable to Pd/Al₂O₃ catalyst at temperatures above 500 C. The influence of added oxygen (about 4%) in the feed was examined over La_0.8Sr_0.2CoO_3– and Pd/Al₂O₃ catalysts and only in the case of cobalt catalyst was the conversion of N₂O decreased by 13%. By choosing varied sintering conditions, La_0.8Sr_0.2CoO_3– of different BET surface areas were prepared and the light-off temperature was found to decrease with increase in surface area. The results obtained over solid solutions are discussed on the basis of the cation mixed valency and oxygen properties of the catalyst.     

负载型钴锰复合金属氧化物催化剂催化分解N_2O

以ZrO_2为载体,采用浸渍法制备负载型钴锰复合金属氧化物催化剂,研究催化剂活性组分负载量、Co与Mn物质的量比、焙烧条件及含H_2O气氛对N_2O转化率的影响。结果表明,催化剂最佳制备条件为:活性组分Co负载质量分数3%,Co与Mn物质的量比为1∶1,焙烧升温速率2℃·min-1,焙烧温度900℃。该条件制备的负载型钴锰复合金属氧化物催化剂在反应温度850℃时,N_2O转化率达98.7%。当反应气氛中H_2O体积分数小于20%条件下,850℃时N_2O转化率高于90%,表明催化剂具有较强的抗水性能。     

Methane decomposition over ceria modified iron catalysts

The catalytic behaviour of ceria supported iron catalysts (Fe–CeO₂) was investigated for methane decomposition. The Fe–CeO₂ catalysts were found to be more active than catalysts based on iron alone. A catalyst composed of 60 wt.% Fe₂O₃ and 40 wt.% CeO₂ gave optimal catalytic activity, and the highest iron metal surface area. The well-dispersed Fe state helped to maintain the active surface area for the reaction. Methane conversion increased when the reaction temperature was increased from 600 to 650 °C. Continuous formation of trace amounts of carbon monoxide was observed during the reaction due to the oxidation of carbonaceous species by high mobility lattice oxygen in the solid solution formed within the catalyst. This could minimise catalyst deactivation caused by carbon deposits and maintain catalyst activity over a longer period of time. The catalyst also produced filamentous carbon that helped to extend the catalyst life.     

Catalytic properties of supported tungsten oxide catalysts

Catalytic properties of the WO₃-MgF₂ preparations obtained by the impregnation (I-series) and coprecipitation (C-series) method have been determined in acid environment. Various tungsten complexes causing the Lewis and Broensted acidity have been observed by IR spectroscopy. For catalysts of the I-series the isolated tungsten species were responsible for the activity in acid reactions, whereas for the C-series preparations the polymerized oxide was also involved.     

Catalytic decomposition of nitric oxide by perovskites

Catalytic decomposition of nitric oxide has been studied for nearly a century, using materials ranging from noble metals to alkaline earth metal oxides, without much success. Only since about last fifteen years some progress in finding promising materials has been made. Of the numerous catalyst systems studied, very few show tangible decomposition rates : copper substituted zeolites, silver-cobalt mixed oxides, some perovskites, and supported noble metals. Although at 773 K the rates of decomposition over zeolites are two to three orders higher than those over remaining systems, these materials have very low thermal stability, above 773 K. In this respect, perovskites have much higher potential, although so far no composition exhibiting practical decomposition rates has been found. Systematic study of the effect of composition on the performance should help to advance the complete understanding of this important reaction. In this paper a current state of art is outlined, and some latest preliminary results for new specially formulated perovskites are presented.     

Catalytic decomposition of nitrous oxide over Fe-BEA zeolites: Essential components of iron active sites

The catalytic decomposition of N₂O was investigated over Fe-BEA zeolites treated with various methods such as reduction, steaming and dissolution with potassium nitrate and nitric acid solutions in order to deduce the essential components of the active sites for the decomposition. The iron species were characterized by XPS, XANES, ESR, NO adsorption, and linear sweep voltammetry. The reduction-treated Fe-BEA zeolite with the large amounts of Fe(II) and Fe(III) species showed the highest activity. On the contrary, the dissolution treatment with the potassium nitrate solution seriously deteriorated the catalytic activity of the Fe-BEA zeolite by agglomerating iron oxide clusters and interaction between iron and potassium atoms. The catalytic roles of Fe(II)/Fe(III) species and the negative effect of potassium on the catalytic activity of the Fe-BEA zeolites were discussed.     

Study of the ammonia decomposition over iron catalysts

The decomposition of ammonia is a reaction associated with the process of the nitriding of metals. The kinetics of the ammonia decomposition on iron catalysts has been studied using a differential reactor with internal mixing. The balance between the inlet and outlet ammonia quantity has been used to determine the degree of conversion. The rate of ammonia decomposition could be described by the following expression: r = k₀ exp (Ea/RT)pNH₃. The activation energy of the ammonia decomposition process has been found for samples with potassium as E _a= 96 kJ/mol, for samples without potassium as E _a= 87 kJ/mol. This revised version was published online in July 2006 with corrections to the Cover Date.     

Catalytic decomposition of nitrous oxide over Ru-exchanged zeolites

We report that ultrastable faujasite-based ruthenium zeolites are highly active catalysts for N₂O decomposition at low temperature (120–200°C). The faujasite-based ruthenium catalysts showed activity for the decomposition of N₂O per Ru³⁺ cation equivalent to the ZSM-5 based ruthenium catalysts at much lower temperatures (TOF at 0.05 vol.-% N₂O: 5.132 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-HNaUSY at 200°C versus 5.609 × 10⁻⁴ s⁻¹ Ru⁻¹ of Ru-NaZSM-5 at 300°C). The kinetics of decomposition of N₂O over a Ru-NaZSM-5 (Ru: 0.99 wt.-%), a Ru-HNaUSY (Ru: 1.45 wt.-%) and a Ru-free, Na-ZSM-5 catalyst were studied over the temperature range from 40 to 700°C using a temperature-programmed micro-reactor system. With partial pressures of N₂O and O₂ up to 0.5 vol.-% and 5 vol.-%, respectively, the decomposition rate data are represented by: −dN₂O/dt=itk(P_N2O) (P_O2)^−0.5 for Ru-HNaUSY, −dN₂O/dt=k(P_N2O) (P_O2)^−0.1 for Ru-NaZSM-5, and −dN₂O/dt=k(P_N2O)^−0.2 (P_O2)^−0.1 for Na-ZSM-5. Oxygen had a stronger inhibition effect on the Ru-HNaUSY catalyst than on Ru-NaZSM-5. The oxygen inhibition effect was more pronounced at low temperature than at high temperature. We propose that the negative effect of oxygen on the rate of N₂O decomposition over Ru-HNaUSY is stronger than Ru-NaZSM-5 because at the lower temperatures (<200°C) the desorption of oxygen is a rate-limiting step over the faujasite-based catalyst. The apparent activation energy for N₂O decomposition in the absence of oxygen is much lower on Ru-HNaUSY (E_a: 46 kJ mol⁻¹) than on Ru-NaZSM-5 (E_a: 220 kJ mol⁻¹).     

Methane combustion over unsupported iron oxide catalysts

Bulk iron oxide, prepared by precipitation and by the citrates method, has been studied as an alternative catalyst for methane combustion. While hematite was the dominant phase in all the samples prepared, significant differences were observed regarding the activity and stability of the catalysts, depending on the preparation method. The catalysts prepared by precipitation presented higher surface areas and lower light-off temperatures. Catalyst deactivation is due to sintering under reaction conditions, and becomes more severe if the operating temperature exceeds the calcination temperature used in catalyst preparation. The best performance in terms of stability and steady-state conversion was obtained with the catalyst prepared by precipitation and calcined at 600°C.     

Alkali-metal promoted rhodium-on-alumina catalysts for nitrous oxide decomposition

Catalytic activity of γ-alumina supported rhodium catalysts in nitrous oxide decomposition into dinitrogen and dioxygen has been determined, the total conversion being reached at 450 °C. Rhodium is present at alumina surface in three forms: metal particles, Rh₂O₃ and rhodium zero valent atoms interacting with oxygen ions at the metal/support interface. Linear dependence of the catalytic activity on rhodium dispersion has been found. Deposition of alkali metal cations: Li, Na, K and Cs as promoters at the surface of alumina results in a considerable increase of rhodium dispersion and hence catalytic activity. The effect of promoters depends strongly on the speciation of alkali metals and rhodium used in the preparation of the catalyst. Both alkali metal cations and rhodium compete for the same OH groups at the alumina surface. The electronegativity of alkali metal oxides is much greater than that of alumina and their deposition increases the negative charge of surface oxide ions hindering the diffusion of rhodium and preventing the growth of its larger particles.     

Catalytic decomposition of ammonia over fly ash supported Ru catalysts

Fly ash (FA), an industrial waste material, has been treated by physical and chemical methods. These materials were then employed as supports for preparation of Ru-based catalysts for H₂ generation from ammonia decomposition. The physicochemical properties of the supports and Ru-based catalysts were characterised using several techniques. The results revealed that the surface area of FA could be enhanced and thus improved the dispersion of Ru particles, resulting in higher catalytic activity. Ru/FA-800 exhibits the highest conversion due to higher surface loading of Ru, stronger NH₃ adsorption and least acid sites.     

Catalytic decomposition of dibenzothiophene sulfones over layered double hydroxide catalysts

The object of the present study is to apply layered double hydroxide catalysts to remove sulfur dioxide from sulfone compounds, by-products of Oxidative Desulfurization (ODS). The effects of Mg/Al ratio, aging temperature, and calcination on the characteristics of the layered double hydroxide catalysts were investigated through the BET surface area, XRD, SEM, and temperature-programmed desorption of CO₂. The layered double hydroxide catalyst with an Mg/Al ratio of 2 or 3 and with an aged temperature of 150 °C was found to be optimal for the decomposition of dibenzothiophene sulfone. It has since been ascribed to a well-developed LDH structure and has the greatest amount of base site. The optimized layered double hydroxide catalysts were found to have high activity and stability during the catalytic removal of sulfur dioxide from sulfones that were in ODS diesel.     

Catalytic nitroxidation of para-xylene over chromium oxide based catalysts

The synthesis of para-tolunitrile (PTN) and terephthalonitrile (TPN) by reacting nitrogen monoxide with para-xylene was studied in presence of three chromium oxide catalysts. The Cr₂O₃—Al₂O₃ catalyst was prepared under the form of aerogel or xerogel and shows excellent selectivities in nitriles along with good stability. However, the unsupported Cr₂O₃ catalyst showed much less performance and, in particular, produced no TPN. The beneficial action of alumina was explained in terms of stabilization of the Cr⁵⁺ species. Kinetic results seemed to indicate a redox-type mechanism of the reaction. Moreover the PTN was shown to be an intermediate in TPN formation.     

Catalytic valorization of bioethanol over Cu-Mg-Al mixed oxide catalysts

The conversion of ethanol into 1-butanol and 1,1-diethoxyethane was studied over Cu-Mg-Al mixed oxide catalysts obtained from LDH precursors. The optimum yields are obtained for Cu loadings comprised between 5 and 10 at.%. A reaction scheme accounting for the main and secondary reaction products is proposed. The influences of the reaction temperature and of the reaction time on the catalytic performances have also been investigated. The negative effect of water, a by-product of the reaction, on this transformation was evidenced.     

Ce-Zr-V-O复合氧化物对二氯甲烷催化燃烧性能

用共沉淀法制备不同铈锆比及V掺杂量的Ce-Zr-V-O复合氧化物催化剂,在常压固定床反应器上对复合氧化物催化剂用于二氯甲烷催化燃烧的活性进行评价,采用BET、XRD、XPS和H₂-TPR等方法对复合氧化物催化剂进行表征。结果表明,V与Ce-Zr形成了Ce-Zr-V-O固溶体,V掺杂提高了催化剂的比表面积和孔径,形成了更多的晶格缺陷和活性中心,使催化剂具有更高的催化活性和稳定性。n(Ce)∶n(Zr)∶n(V)=7∶3∶0.5时,Ce_0.7Zr_0.3V _0.05 O _2-λ催化剂活性最好,小于300 ℃,连续反应200 h,二氯甲烷转化率大于98%。