Impact of copper on the performance and sulfur tolerance of barium-based NOx storage-reduction catalysts

The presence of sulfur in automotive exhaust is known to be detrimental to lean-NO_x traps as SO₂ is oxidized to SO₃ that competes with NO₂ for sites on the trap and is difficult to remove. In this study the effect of adding Cu to the prototypical Pt–BaO/γ-Al₂O₃ formulation on the system's tolerance for sulfur was investigated. It was found that in the absence of sulfur, Cu decreases the performance in terms of both NO_x storage capacity and reduction of NO_x to N₂ during regeneration. In the presence of SO₂, Cu provides a significant improvement in sulfur tolerance so that, after sulfur exposure, the storage capacity of the Cu-modified material can exceed that of the baseline material. The sulfur tolerance afforded by Cu is attributed to a moderation in the activity for SO₂ oxidation resulting from the formation of a Pt–Cu bimetallic phase. The propensity for NO oxidation is also modified, but to a lesser effect. Evidence for the bimetallic phase is provided by temperature-programmed reduction (TPR) and electron microscopy. The impact of SO₂ on the Cu-modified material is greater during the regenerative reduction cycle. In this case, the results suggest that sulfur blocks Pt and possibly Cu sites and that the sulfur is not removed by oxidation during the subsequent storage cycle. Hence, activity lost during the reduction cycle is not restored. In contrast, sulfur that blocks Pt sites on the baseline material during the reduction cycle is subsequently oxidized and desorbs from the Pt, restoring the activity. However, some of the resulting SO₃ reacts with the BaO to form BaSO₄, and there is a partial loss of storage capacity.     

Oxidative dehydrogenation of n-butane and 1-butene on undoped and K-doped VOx/Al2O3 catalysts

The oxidative dehydrogenation (OXDH) of n-butane and 1-butene on undoped and K-doped alumina-supported vanadia catalysts has been studied. The low selectivity to OXDH products on alumina-supported vanadia catalysts is a consequence of the isomerization of olefins (low temperatures) and the formation of carbon oxides (high temperatures) on acid sites. The presence of potassium results in a decrease of the number of acid sites and a higher selectivity to OXDH products from both n-butane and 1-butene. Infrared spectroscopy data of 1-butene adsorbed on the catalysts suggest the presence of different adsorbed species: (i) O-containing species on the undoped catalyst, or (ii) adsorbed butadiene on K-doped catalyst. A reaction network including parallel and consecutive reactions is proposed.     

Physicochemical surface and catalytic properties of CuO–ZnO/Al2O3 system

A series of CuO–ZnO/Al₂O₃ solids were prepared by wet impregnation using Al(OH)₃ solid and zinc and copper nitrate solutions. The amounts of copper and zinc oxides were varied between 10.3 and 16.0 wt% CuO and between 0.83 and 7.71 wt% ZnO. The prepared solids were subjected to thermal treatment at 400–1000°C. The solid–solid interactions between the different constituents of the prepared solids were studied using XRD analysis of different calcined solids. The surface characteristics of various calcined adsorbents were investigated using nitrogen adsorption at −196°C and their catalytic activities were determined using CO-oxidation by O₂ at temperatures ranged between 125°C and 200°C.

The results showed that CuO interacts with Al₂O₃ to produce copper aluminate at ≥600°C and the completion of this reaction requires heating at 1000°C. ZnO hinders the formation of CuAl₂O₄ at 600°C while stimulates its production at 800°C. The treatment of CuO/Al₂O₃ solids with different amounts of ZnO increases their specific surface area and total pore volume and hinders their sintering (the activation energy of sintering increases from 30 to 58 kJ mol⁻¹ in presence of 7.71 wt% ZnO). This treatment resulted in a progressive decrease in the catalytic activities of the investigated solids but increased their catalytic durability. Zinc and copper oxides present did not modify the mechanism of the catalyzed reaction but changed the concentration of catalytically active constituents (surface CuO crystallites) without changing their energetic nature.     

Study of n-hexane isomerization on mixed Al2O3–ZrO2/SO4 catalysts

Mixed oxides of alumina and zirconia having a relative composition of 50, 80 and 100% Zr₂O were synthesized by means of sol–gel methods. The catalysts were sulfated with H₂SO₄ 1N, and were loaded with 0.3% Pt metal using the incipient wetness technique. The characterization of the physicochemical properties was carried out using XRD, N₂-adsorption at 78 K, and SEM. The catalytic properties of the Al₂O₃–ZrO₂ series were studied by means of dehydration of 2-propanol at 180°C and isomerization of n-hexane at 250°C, 1 atm. The sulfated solids presented a high surface acidity and a limited crystallinity, together with high activity for alcohol dehydration (i.e. 2-propanol). On the other hand, the Al₂O₃–ZrO₂ solid solutions (i.e. those having a 20–80% composition) turned out to be the most active ones for the isomerization of n-hexane.     

Role of supported metals in the selective reduction of nitrogen monoxide with hydrocarbons over metal/alumina catalysts

The promoting effect of supported metals on alumina catalyst was investigated for the reduction of nitrogen monoxide in oxygen-rich atmospheres. For NO reduction with propene over impregnated CoO/A1₂O₃, the first reaction step was found to be the oxidation of NO to NO₂ probably catalyzed by dispersed cobalt species. The next reaction step, which is the reaction of NO₂ with propene to form N₂, was considered to take place on the alumina surface. Although the activity of impregnated FeO/A1₂O₃ was low because of the presence of large iron oxide particles catalyzing propene oxidation with dioxygen, FeO/A1₂O₃ prepared with sol-gel method showed excellent deNO_x activity.     

Influence of support acid pretreatment on the behaviour of CoOx/γ-alumina monolithic catalysts in the CH4-SCR reaction

The effect of treatment with different mineral acids (H₂SO₄, H₃PO₄, HNO₃ and HCl) on the activity of monolithic CoO_x/γ-Al₂O₃ catalysts in the reduction of nitric oxide with methane in the presence of oxygen (CH₄-SCR of NO_x) was studied. Their behaviour in the methane oxidation reaction in both the presence and absence of NO_x was determined in order to interpret the results in terms of intrinsic activity and competition between both processes. Depending on the nature of the acid used, significant differences were observed in the catalytic activities which were related to the textural states, surface acidities and the nature of the detected species. The best results were obtained after treatment with H₂SO₄, which increased the activity towards NO_x elimination compared to the other catalysts. This behaviour was attributed not only to an increase in surface acidity but also to the stabilisation of the active Co²⁺ species, thus avoiding the formation of Co₃O₄ spinel that is responsible for the strongly adsorbed NO_x species that lead to NO₂ formation which increase the rate of the undesired methane oxidation reaction at high temperatures.     

CoMo/MgO–Al2O3 supported catalysts: An alternative approach to prepare HDS catalysts

Three different supports were prepared with distinct magnesia–alumina ratio x = MgO/(MgO + Al₂O₃) = 0.01, 0.1 and 0.5. Synthesized supports were impregnated with Co and Mo salts by the incipient wetness method along with 1,2-cyclohexanediamine-N,N,N′,N′-tetraacetic acid (CyDTA) as chelating agent. Catalysts were characterized by BET surface area, Raman spectroscopy, SEM-EDX and HRTEM (STEM) spectroscopy techniques. The catalysts were evaluated for the thiophene hydrodesulfurization reaction and its activity results are discussed in terms of using chelating agent during the preparation of catalyst. A comparison of the activity between uncalcined and calcined catalysts was made and a higher activity was obtained with calcined MgO–Al₂O₃ supported catalysts. Two different MgO containing calcined catalysts were tested at micro-plant with industrial feedstocks of heavy Maya crude oil. The effect of support composition was observed for hydrodesulfurization (HDS), hydrodemetallization (HDM), hydrodeasphaltenization (HDAs) and hydrodenitrogenation (HDN) reactions, which were reported at temperature of 380 °C, pressure of 7 MPa and space-velocity of 1.0 h⁻¹ during 204 h of time-on-stream (TOS).     

Enhanced activity of metal oxide-doped Ga2O3–Al2O3 for NO reduction by propene

Effect of additives, In₂O₃, SnO₂, CoO, CuO and Ag, on the catalytic performance of Ga₂O₃–Al₂O₃ prepared by sol–gel method for the selective reduction of NO with propene in the presence of oxygen was studied. As for the reaction in the absence of H₂O, CoO, CuO and Ag showed good additive effect. When H₂O was added to the reaction gas, the activity of CoO-, CuO- and Ag-doped Ga₂O₃–Al₂O₃ was depressed considerably, while an intensifying effect of H₂O was observed for In₂O₃- and SnO₂-doped Ga₂O₃–Al₂O₃. Of several metal oxide additives, In₂O₃-doped Ga₂O₃–Al₂O₃ showed the highest activity for NO reduction by propene in the presence of H₂O. Kinetic studies on NO reduction over In₂O₃–Ga₂O₃–Al₂O₃ revealed that the rate-determining step in the absence of H₂O is the reaction of NO₂ formed on Ga₂O₃–Al₂O₃ with C₃H₆-derived species, whereas that in the presence of H₂O is the formation of C₃H₆-derived species. We presumed the reason for the promotional effect of H₂O as follows: the rate for the formation of C₃H₆-derived species in the presence of H₂O is sufficiently fast compared with that for the reaction of NO₂ with C₃H₆-derived species in the absence of H₂O. Although the retarding effect of SO₂ on the activity was observed for all of the catalysts, SnO₂–Ga₂O₃–Al₂O₃ showed still relatively high activity in the lower temperature region.     

Synthesis, characterization and catalytic properties of NiMo/Al2O3–MCM-41 catalyst for dibenzothiophene hydrodesulfurization

Ni–Mo/Al₂O₃–MCM-41 supported catalysts have been investigated for modification of MCM-41 by using sol–gel alumina incorporation method. Different catalysts were synthesized with variation of Si/Al molar ratios of 10, 50, 100 and 200. High specific surface area ordered meso-porous solid (MCM-41) was synthesized by using organic template method. In order to modify the low acidity of silica solid, the surface of MCM-41 was modified by incorporation of alumina. The surface acidity of solids modified significantly with variation of alumina content in the supports. The sol–gel method of alumina incorporation was used, which does not modify extensively the pore characteristics of MCM-41 material during the preparation of Al₂O₃–MCM-41. The X-ray diffraction intensities indicated that alumina as well as MCM-41 were present in the synthesized supports. Additionally, the hydrothermal stability of the Al₂O₃–MCM-41 materials was maintained up to 873 K using sever conditions like 100% water vapor stream. The catalytic activity of the catalysts was tested in the hydrodesulfurization (HDS) of dibenzothiophene (DBT). Selectivity was oriented mainly to the production of biphenyl (BP) and for high Si/Al ratios toward cyclohexylbenzene (CHB) and showed a higher conversion and better selectivity to hydrogenation (cyclohexylbenzene).     

Hydrogenation of naphthalene on NiMo- Ni- and Ru/Al2O3 catalysts: Langmuir–Hinshelwood kinetic modelling

The importance of the hydrodearomatisation (HDA) is increasing together with tightening legislation of fuel quality and exhaust emissions. The present study focuses on hydrogenation (HYD) kinetics of the model aromatic compound naphthalene, found in typical diesel fraction, in n-hexadecane over a NiMo (nickel molybdenum), Ni (nickel) and Ru (ruthenium) supported on trilobe alumina (Al₂O₃) catalysts. Kinetic reaction expressions based on the mechanistic Langmuir–Hinshelwood (L–H) model were derived and tested by regressing the experimental data that translated the effect of both naphthalene and hydrogen concentration at a constant temperature (523.15 and 573.15 K over the NiMo catalyst and at 373.15 K over the Ni and Ru/Al₂O₃ catalysts) on the initial reaction rate. The L–H equation, giving an adequate fit to the experimental data with physically meaningful parameters, suggested a competitive adsorption between hydrogen and naphthalene over the presulphided NiMo catalyst and a non-competitive adsorption between these two reactants over the prereduced Ni and Ru/Al₂O₃ catalysts. In addition, the adsorption constant values indicated that the prereduced Ru catalyst was a much more active catalyst towards naphthalene HYD than the prereduced Ni/Al₂O₃ or the presulphided NiMo/Al₂O₃ catalyst.     

臭氧催化氧化深度处理炼油废水催化剂的开发

以金属硝酸盐为原料,采用等体积浸渍法制备了CuMnCo/γ - Al2O3催化剂,通过臭氧催化氧化中试试验装置,对炼油厂废水的二级处理出水进行深度研究.累计1000h的反应结果表明,在保证出口COD为100 mg·L-1以下,炼油废水的CODCr平均去除率达到60.3％.通过物理吸附、热重-差热、扫描电镜、X射线衍射和...     

Oxidation behaviour and catalytic properties of Pd/Al2O3 catalysts in the total oxidation of methane

A series of Pd/Al₂O₃ catalysts with a wide range of mean Pd particle sizes (ca. 2–30 nm in diameter) was prepared by using various precursors (H₂PdCl₄, Pd(NO₃)₂ and Pd(AcAc)₂) and pre-treatments. The mean particle size of reduced samples was determined by H₂ chemisorption. The catalytic activity in methane oxidation under lean burn conditions was measured. The oxidation of reduced samples was studied at 300 °C. The extent of oxidation was found to decrease with increasing mean particle size. While small particles (<5 nm) oxidised very rapidly, the oxidation of large particles (ca. >15 nm) proceeded via a two-step process, being first fast and then slow. The decomposition of oxide species was studied by temperature-programmed experiments under vacuum. Two distinct oxidised species with different stability were evidenced depending on the particle size. Oxidised species in larger particles were found of lower stability than in smaller ones. A correlation between the existence of distinct types of oxide species and catalytic properties in methane oxidation was discussed.     

A comparison between β- and USY-zeolite-based hydrocracking catalysts

Two series of zeolite-based hydrocracking catalysts were prepared to study the effects of the support type, preparation method and metal loading on catalyst properties and hydrocracking activity for hydrotreated vacuum gas oil (HT-VGO). The support used was γ-Al₂O₃ and β-zeolite in the first series and γ-Al₂O₃ and USY-zeolite in the second series. Nickel and tungsten were loaded as active metals on these supports. The prepared catalysts were characterized as to their surface area, pore volume, thermal stability, reducibility and acidity characteristics. The characterization results revealed that catalysts displayed significant differences in properties dependent on the preparation method and the type of support used. Catalysts from both series showed promising results for HT-VGO hydrocracking in the batch reactor. A correlation exists between the reducibility of oxidic form and the hydrogenation activity of the sulfided form of the catalysts. The higher the reducibility, the higher the hydrogenation activity. Catalysts prepared on mixed supports gave higher amounts of saturates.     

Palladium–vanadium interaction in binary supported catalysts

We have studied the activity and selectivity of Pd/γ-Al₂O₃, VO_x/γ-Al₂O₃ and Pd–VO_x/γ-Al₂O₃ catalysts for the decomposition of NO and the reduction of NO with CO. Pd–VO_x/γ-Al₂O₃ catalysts were prepared by anchoring Pd(AcAc)₂ on VO_x/γ-Al₂O₃. Characterization of the binary samples by hydrogen chemisorption and TPR measurements indicated that the reduction of VO_x is enhanced by a close contact with palladium and that partially reduced vanadia decorate noble metal particles. This palladium–vanadium interaction alters the catalytic properties of palladium: the activity for NO decomposition is higher for the binary sample and, for the NO–CO reaction, both the activity and the selectivity to N₂ increase when vanadium is in contact with palladium.     

纳米CuO/CoFe2O4-TiO2模拟太阳光降解亚甲基蓝的性能

采用溶胶-凝胶法制备CuO/CoFe2O4粒子,并与P25复合制备纳米催化剂CuO/CoFe2O4-TiO2.通过模拟太阳光催化降解亚甲基蓝,对催化剂活性进行研究,采用SEM、TEM、XRD和UV-Vis DRS方法对催化剂进行表征.结果表明,CuO/CoFe2O4粒子均匀分散在P25微粒表面,平均粒径为60 nm.并...     

Fischer–Tropsch synthesis on monolithic catalysts of different materials

Monolithic structures made of cordierite, γ-Al₂O₃ and steel have been prepared as catalysts and tested for Fischer–Tropsch activity. The monoliths made of cordierite and steel were washcoated with a 20 wt.% Co–1 wt.% Re/γ-Al₂O₃ Fischer–Tropsch catalyst whereas the γ-Al₂O₃ monoliths were made by direct impregnation with an aqueous solution of the Co and Re salts resulting in a loading of 12 wt.% Co and 0.5 wt.% Re. The activity and selectivity of the different monoliths were compared with the corresponding powder catalysts.

Higher washcoat loadings resulted in decreased C₅₊ selectivity and olefin/paraffin ratios due to increased transport limitations. The impregnated γ-Al₂O₃ monoliths also showed similar C₅₊ selectivities as powder catalysts of small particle size (38–53 μm). Lower activities were observed with the steel monoliths probably due to experimental problems.     

Reactivity of Ru-based catalysts in the oxidation of propene and carbon black

The relationship between the state of Ru on different supports and catalytic activity in the oxidation of propene and carbon black was investigated for catalysts prepared by different impregnation methods. It is demonstrated that the addition of ruthenium to ceria (CeO₂), alumina (Al₂O₃) and ceria–alumina significantly improves the reactivity: the temperature of carbon black oxidation decreases by 100–140 °C. It is also shown that the addition of Ru to the different supports is very beneficial for the total oxidation of propene. Temperature programmed reduction (TPR) experiments of the catalysts showed that the oxygen species of ruthenium oxides are reduced at low temperatures which is the main reason of its high reactivity in oxidation reactions.     

添加Ni对Cu基催化剂乙炔选择性加氢性能的影响

采用等体积浸渍法制备了Cu/Al_2O_3及Cu-Ni/Al_2O_3催化剂,将其应用于乙炔选择性加氢反应。结果表明,与Cu/Al_2O_3催化剂相比,Cu-Ni/Al_2O_3催化剂的加氢活性及乙烯选择性(当反应出口尾气中乙炔物质的量分数减少到0.003%时)明显提高。通过对Cu与Ni的浸渍顺序考察发现,先浸渍Ni制得的Cu-Ni/Al_2O_3催化剂活性有所下降,但乙烯选择性提高;通过对Ni含量的考察发现,当Ni质量分数为2%时,催化剂性能最佳。     

Tailoring of alumina surfaces as supports for NiMo sulfide catalysts in the ultra deep hydrodesulfurization of gas oil: case study of TiO2-coated alumina prepared by chemical vapor deposition technique

The present paper gives a detailed review of the different studies under investigation in our laboratory concerning the use of TiO₂ and TiO₂–Al₂O₃ composites prepared by chemical vapor deposition (CVD) as support for sulfide catalysts in the HDS of dibenzothiophene (DBT) derivatives. The supports investigated here are: TiO₂ (from Degussa, 50 m²/g), Al₂O₃ (Nikki, 186 m²/g) and TiO₂–Al₂O₃ supports prepared by CVD of TiCl₄ on alumina. Using several characterization techniques, we have demonstrated that the support composite presents a high dispersion of TiO₂ over γ-Al₂O₃ without forming precipitates up to ca. 11 wt.% loading. Moreover, the textural properties of the support composite are comparable to those of alumina. XPS investigations of Mo and NiMo catalysts supported on the different carriers show that Mo-oxide species exhibit a higher degree of sulfidation on the surface of TiO₂ and TiO₂–Al₂O₃ than on alumina. The HDS tests of 4,6-DMDBT under mild operating conditions (573 K, 3 MPa) show that sulfide catalysts supported on the composite support (ca. 11 wt.%) are more active than those supported on to TiO₂ or Al₂O₃. This higher HDS catalytic activity is attributed to the promotion of the hydrodesulfurization pathway, whereby the pre-hydrogenation of one of the aromatic rings adjacent to the thiophenic one may reduce the steric hindrance caused by the two methyl groups adjacent to the sulfur atom during the C–S bond cleavage.     

Carbon black oxidation in the presence of Al2O3, CeO2, and Mn oxide catalysts: An EPR study

Carbon black oxidation in the presence of CeO₂, Al₂O₃ and manganese oxide catalysts has been studied in tight contact conditions. In the presence of manganese based catalysts, the temperature gain is about 275 °C compared to the non-catalysed carbon black oxidation. The contribution of the manganese species to enhance the reactivity of carbon black oxidation has been evaluated by EPR technique. For Mn/Ce + CB mixtures the Mn²⁺ content considerably increases consequently to tight milled treatment indicating the reduction of some manganese species with higher oxidation states into Mn²⁺ ions. This phenomenon can be considered as the first step in the carbon black oxidation mechanism in the presence of Mn/Ce catalysts.