Activity and acidity of Nb2O5-MoO3 and Nb2O5-WO3 in the Friedel-Crafts alkylation

Nb₂O₅ loaded on the supports and mixed with oxides was studied to investigate the activity and acidity for Friedel-Crafts benzylation of anisole. From the study on the loaded catalysts, a preliminary conclusion for the selection of metal oxide was obtained; namely, such an acidic oxide as silica was suitable for the support of Nb₂O₅. Then, MoO₃ and WO₃ were mixed with Nb₂O₅, and prominent high catalytic activity and acidities were observed. Both oxides of Nb₂O₅-MoO₃ and Nb₂O₅-WO₃ showed almost similar behavior with respect to characterization and catalytic activity. Surface area increased, X-ray diffraction (XRD) and Raman bands were lost, acid sites, both Brønsted and Lewis characters generated, and surface acid site density was as high as 2–4 nm⁻². The acid sites were generated on the amorphous metal oxides consisting of Nb and Mo or W oxides, different in nature from those of Nb₂O₅ calcined and un-calcined, and active for Friedel-Crafts benzylation.     

η-Al2O3与γ-Al2O3在CS2催化水解反应中的性能比较

通过制备高纯度的前驱体湃铝石获得了η-Al₂O₃材料,采用XRD验证了η-Al₂O₃与γ-Al₂O₃在晶相结构上的差异,比较了两者的表面形貌、织构及酸碱性能,结果显示,η-Al₂O₃与γ-Al₂O₃的比表面积相当,但η-Al₂O₃具有更弱的弱碱位和较少的强碱位,并拥有丰富的中等强度酸性位。将η-Al₂O₃与γ-Al₂O₃作为催化剂应用于CS₂水解反应,结果表明,在(200~450) ℃测试温度范围内,η-Al₂O₃催化剂对CS₂的水解活性始终优于γ-Al₂O₃,两种催化剂上CS₂反应的浓度效应也明显不同,推测与它们的酸碱性质影响了对CS₂的吸附能力有关,导致两者催化CS₂水解反应遵循了不同的机制。     

NO reduction by CH4 in the presence of O2 over La2O3 supported on Al2O3

Dispersing La₂O₃ on δ- or γ-Al₂O₃ significantly enhances the rate of NO reduction by CH₄ in 1% O₂, compared to unsupported La₂O₃. Typically, no bend-over in activity occurs between 500° and 700°C, and the rate at 700°C is 60% higher than that with a Co/ZSM-5 catalyst. The final activity was dependent upon the La₂O₃ precursor used, the pretreatment, and the La₂O₃ loading. The most active family of catalysts consisted of La₂O₃ on γ-Al₂O₃ prepared with lanthanum acetate and calcined at 750°C for 10 h. A maximum in rate (mol/s/g) and specific activity (mol/s/m²) occurred between the addition of one and two theoretical monolayers of La₂O₃ on the γ-Al₂O₃ surface. The best catalyst, 40% La₂O₃/γ-Al₂O₃, had a turnover frequency at 700°C of 0.05 s⁻¹, based on NO chemisorption at 25°C, which was 15 times higher than that for Co/ZSM-5. These La₂O₃/Al₂O₃ catalysts exhibited stable activity under high conversion conditions as well as high CH₄ selectivity (CH₄ + NO vs. CH₄ + O₂). The addition of Sr to a 20% La₂O₃/γ-Al₂O₃ sample increased activity, and a maximum rate enhancement of 45% was obtained at a SrO loading of 5%. In contrast, addition of SO⁼₄ to the latter Sr-promoted La₂O₃/Al₂O₃ catalyst decreased activity although sulfate increased the activity of Sr-promoted La₂O₃. Dispersing La₂O₃ on SiO₂ produced catalysts with extremely low specific activities, and rates were even lower than with pure La₂O₃. This is presumably due to water sensitivity and silicate formation. The La₂O₃/Al₂O₃ catalysts are anticipated to show sufficient hydrothermal stability to allow their use in certain high-temperature applications.     

The role of lanthana loading on the catalytic properties of Pd/Al2O3-La2O3 in the NO reduction with H2

The role of La₂O₃ loading in Pd/Al₂O₃-La₂O₃ prepared by sol–gel on the catalytic properties in the NO reduction with H₂ was studied. The catalysts were characterized by N₂ physisorption, temperature-programmed reduction, differential thermal analysis, temperature-programmed oxidation and temperature-programmed desorption of NO.

The physicochemical properties of Pd catalysts as well as the catalytic activity and selectivity are modified by La₂O₃ inclusion. The selectivity depends on the NO/H₂ molar ratio (GHSV = 72,000 h⁻¹) and the extent of interaction between Pd and La₂O₃. At NO/H₂ = 0.5, the catalysts show high N₂ selectivity (60–75%) at temperatures lower than 250 °C. For NO/H₂ = 1, the N₂ selectivity is almost 100% mainly for high temperatures, and even in the presence of 10% H₂O vapor. The high N₂ selectivity indicates a high capability of the catalysts to dissociate NO upon adsorption. This property is attributed to the creation of new adsorption sites through the formation of a surface PdO_x phase interacting with La₂O₃. The formation of this phase is favored by the spreading of PdO promoted by La₂O₃. DTA shows that the phase transformation takes place at temperatures of 280–350 °C, while TPO indicates that this phase transformation is related to the oxidation process of PdO: in the case of Pd/Al₂O₃ the O₂ uptake is consistent with the oxidation of PdO to PdO₂, and when La₂O₃ is present the O₂ uptake exceeds that amount (1.5 times). La₂O₃ in Pd catalysts promotes also the oxidation of Pd and dissociative adsorption of NO mainly at low temperatures (<250 °C) favoring the formation of N₂.     

Coprecipitated iron-containing catalysts (Fe-Al2O3, Fe-Co-Al2O3, Fe-Ni-Al2O3) for methane decomposition at moderate temperatures: Part II. Evolution of the catalysts in reaction

Coprecipitated Fe-Al₂O₃, Fe-Co-Al₂O₃ and Fe-Ni-Al₂O₃ catalysts is shown to be very efficient in carbon deposition during methane decomposition at moderate temperatures (600–650 °C). The carbon capacity of the most efficient bimetallic catalysts containing 50–65 wt.% Fe, 5–10 wt.% Co (or Ni) and 25–40 wt.% Al₂O₃ is found to reach 145 g/g_cat. Most likely, their high efficiency is due to specific crystal structures of the metal particles and formation of optimum particle size distribution. According to the TEM data, catalytic filamentous carbon (CFC) is formed on them as multiwall carbon nanotubes (MWNTs). The phase composition of the catalysts during methane decomposition is studied using a complex of physicochemical methods (XRD, REDD, Mössbauer spectroscopy and EXAFS). Possible mechanisms of the catalyst deactivation are discussed.     

Comparison of catalytic activity and selectivity of Pd/(OSC + Al2O3) and (Pd + OSC)/Al2O3 catalysts

The effect of the Pd addition method into the fresh Pd/(OSC + Al₂O₃) and (Pd + OSC)/Al₂O₃ catalysts (OSC material = Ce_xZr_1−xO₂ mixed oxides) was investigated in this study. The CO + NO and CO + NO + O₂ model reactions were studied over fresh and aged catalysts. The differences in the fresh catalysts were insignificant compared to the aged catalysts. During the CO + NO reaction, only small differences were observed in the behaviour of the fresh catalysts. The light-off temperature of CO was about 20 °C lower for the fresh Pd/(OSC + Al₂O₃) catalyst than for the fresh (Pd + OSC)/Al₂O₃ catalyst during the CO + NO + O₂ reaction. For the aged catalysts lower NO reduction and CO oxidation activities were observed, as expected. Pd on OSC-containing alumina was more active than Pd on OSC material after the agings. The activity decline is due to a decrease in the number of active sites on the surface, which was observed as a larger Pd particle size for aged catalysts than for fresh catalysts. In addition, the oxygen storage capacity of the aged Pd/(OSC + Al₂O₃) catalyst was higher than that of the (Pd + OSC)/Al₂O₃ catalyst.     

Ni/Al_2O_3催化剂的CO_2-TPD表征

Ni/Al_2O_3催化剂是甲烷二氧化碳重整反应制取合成气研究最多、最具应用潜力的一种催化剂。通过对催化剂进行CO_2-TPD研究,考察还原态Ni/Al_2O_3催化剂的CO_2脱附特性。结果表明,浸渍法制备的Ni/Al_2O_3催化剂CO_2脱附曲线呈现双峰,分别在(60~65)℃和(350~380)℃出现高低温两个活性位;高温CO_2吸附量为3.0 cm~3·g~(-1),低温CO_2吸附量为24.0 cm~3·g~(-1)。催化剂的CO_2吸附量与其Ni含量无关。考察选用不同载体的CO_2脱附行为,发现以Al_2O_3为载体的催化剂CO_2吸附量是MgO和SiO_2为载体催化剂的2~4倍,以TiO_2为载体的催化剂几乎不吸附CO_2。     

Physico-chemical characteristics and CO oxidation studies over Pd/(Mn2O3 + SnO2) catalyst

The mixed oxide catalyst (Mn₂O₃ + SnO₂) prepared by the coprecipitation method has been impregnated with Pd metal and it's catalytic behaviour for CO oxidation reaction has been investigated. In the coprecipitated material, Mn₂O₃ and SnO₂ were found to crystallise at 875 K and 1175 K, respectively, which are significantly higher than the crystallisation temperatures of individual oxides prepared under similar conditions. Results of catalytic oxidation of CO, carried out using the pulse method for the mixed oxide system and the individual oxides, suggest significant synergistic effects between these two oxides. The impregnation of palladium metal facilitated CO oxidation and the catalyst Pd/(Mn₂O₃ + SnO₂) was found to be quite effective for CO oxidation even at room temperature. Further, the CO disproportionation has been observed on palladium sites in the temperature range 350 to 400 K for the individual oxide systems.     

Role of CeO2 in Ni/CeO2–Al2O3 catalysts for carbon dioxide reforming of methane

Ni catalysts supported on γ-Al₂O₃, CeO₂ and CeO₂–Al₂O₃ systems were tested for catalytic CO₂ reforming of methane into synthesis gas. Ni/CeO₂–Al₂O₃ catalysts showed much better catalytic performance than either CeO₂- or γ-Al₂O₃-supported Ni catalysts. CeO₂ as a support for Ni catalysts produced a strong metal–support interaction (SMSI), which reduced the catalytic activity and carbon deposition. However, CeO₂ had positive effect on catalytic activity, stability, and carbon suppression when used as a promoter in Ni/γ-Al₂O₃ catalysts for this reaction. A weight loading of 1–5 wt% CeO₂ was found to be the optimum. Ni catalysts with CeO₂ promoters reduced the chemical interaction between nickel and support, resulting in an increase in reducibility and stronger dispersion of nickel. The stability and less coking on CeO₂-promoted catalysts are attributed to the oxidative properties of CeO₂.     

A comparative study of the partial oxidation of methane to formaldehyde on bulk and silica supported MoO3 and V2O5 catalysts

The mechanism of the partial oxidation of methane to formaldehyde with O₂ has been investigated on bulk and differently loaded silica supported (4–7 wt%) MoO₃ and (5–50 wt%) V₂O₅ catalysts at 600–650°C in a pulse reactor connected to a quadrupole mass spectrometer. The reaction rate and product distribution in the presence and in the absence of gas-phase O₂ have been evaluated. On bare SiO₂, low and medium loaded silica supported MoO₃ and V₂O₅ catalysts the reaction proceeds via a concerted mechanism involving the activation of gas-phase oxygen on the reduced sites of the catalyst surface as proved by the direct correlation between catalytic activity and density of reduced sites evaluated in steady-state conditions, while on highly loaded catalysts as well as on bulk MoO₃ and V₂O₅ the reaction rate drops dramatically and the reaction pathway via redox mechanism becomes predominant. The results indicate that the surface mechanism is essentially more effective than the redox mechanism enabling also a higher selectivity to HCHO.     

ZrO2/SiO2- and La2O3/Al2O3-supported platinum catalysts for CH4/CO2 reforming

Surface-phase ZrO₂ on SiO₂ (SZrOs) and surface-phase La₂O₃ on Al₂O₃ (SLaOs) were prepared with various loadings of ZrO₂ and La₂O₃, characterized and used as supports for preparing Pt/SZrOs and Pt/SLaOs catalysts. CH₄/CO₂ reforming over the Pt/SZrOs and Pt/SLaOs catalysts was examined and compared with Pt/Al₂O₃ and Pt/SiO₂ catalysts. CO₂ or CH₄ pulse reaction/adsorption analysis was employed to elucidate the effects of these surface-phase oxides.

The zirconia can be homogeneously dispersed on SiO₂ to form a stable surface-phase oxide. The lanthana cannot be spread well on Al₂O₃, but it forms a stable amorphous oxide with Al₂O₃. The Pt/SZrOs and Pt/SLaOs catalysts showed higher steady activity than did Pt/SiO₂ and Pt/Al₂O₃ by a factor of three to four. The Pt/SZrOs and Pt/SLaOs catalysts were also much more stable than the Pt/SiO₂ and Pt/Al₂O₃ catalysts for long stream time and for reforming temperatures above 700 °C. These findings were attributed to the activation of CO₂ adsorbed on the basic sites of SZrOs and SLaOs.     

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.     

The mechanism of SO2 effect on NO reduction with propene over In2O3/Al2O3 catalyst

An In₂O₃/Al₂O₃ catalyst shows high activity for the selective catalytic reduction of NO with propene in the presence of oxygen. The presence of SO₂ in feed gas suppressed the catalytic activity dramatically at high temperatures; however it was enhanced in the low temperature range of 473–573 K. In TPD and FT-IR studies, the formation of sulfate species on the surface of the catalyst caused an inhibition of NO_X adsorption sites, and the absorbance ability of NO was suppressed by the presence of SO₂, and the amount of ad-NO₃⁻ species decreased obviously. This leads to a decrease of catalytic activity at higher temperatures. However, addition of SO₂ enhanced the formation of carboxylate and formate species, which can explain the promotional effect of SO₂ at low temperature, because active C₃H₆ (partially oxidized C₃H₆) is crucial at low temperature.     

Surface properties and reactivity of Cu/γ-Al2O3 catalysts for NO reduction by C3H6: Influences of calcination temperatures and additives

The influences of calcination temperatures and additives for 10 wt.% Cu/γ-Al₂O₃ catalysts on the surface properties and reactivity for NO reduction by C₃H₆ in the presence of excess oxygen were investigated. The results of XRD and XPS show that the 10 wt.% Cu/γ-Al₂O₃ catalysts calcined below 973 K possess highly dispersed surface and bulk CuO phases. The 10 wt.% Cu/γ-Al₂O₃ and 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalysts calcined at 1073 K possess a CuAl₂O₄ phase with a spinel-type structure. In addition, the 10 wt.% La–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses a bulk CuO phase. The result of NO reduction by C₃H₆ shows that the CuAl₂O₄ is a more active phase than the highly dispersed and bulk CuO phase. However, the 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K possesses significantly lower reactivity for NO reduction than the 10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K, although these catalysts possess the same CuAl₂O₄ phase. The low reactivity for NO reduction for 10 wt.% Mn–10 wt.% Cu/γ-Al₂O₃ catalyst calcined at 1073 K is attributed to the formation of less active CuAl₂O₄ phase with high aggregation and preferential promotion of C₃H₆ combustion to CO_x by MnO₂. The engine dynamometer test for NO reduction shows that the C₃H₆ is a more effective reducing agent for NO reduction than the C₂H₅OH. The maximum reactivity for NO reduction by C₃H₆ is reached when the NO/C₃H₆ ratio is one.     

Performance and characterization of Ru/Al2O3 and Ru/SiO2 catalysts modified with Mn for Fischer–Tropsch synthesis

Mn effect and characterization on γ-Al₂O₃-, -Al₂O₃- and SiO₂-supported Ru catalysts were investigated for Fischer–Tropsch synthesis under pressurized conditions. In the slurry phase Fischer–Tropsch reaction, γ-Al₂O₃ catalysts showed higher performance on CO conversion and C₅⁺ selectivity than -Al₂O₃ and SiO₂ catalysts. Moreover, Ru/Mn/γ-Al₂O₃ exhibited high resistance to catalyst deactivation and other catalysts were deactivated during the reaction. From characterization results on XRD, TPR, TEM, XPS and pore distribution, Ru particles were clearly observed over the catalysts, and γ-Al₂O₃ catalysts showed a moderate pore and particle size such as 8 nm, where -Al₂O₃ and SiO₂ showed highly dispersed ruthenium particles. The addition of Mn to γ-Al₂O₃ enhanced the removal of chloride from RuCl₃, which can lead to the formation of metallic Ru with moderate particle size, which would be an active site for Fischer–Tropsch reaction. Concomitantly, manganese chloride is formed. These schemes can be assigned to the stable nature of Ru/Mn/γ-Al₂O₃ catalyst.     

Influence of the co-feeding of CO, H2, CO2 or H2O in the partial oxidation of methane over Ni and Rh supported catalysts

The influence of the addition of 5 vol.% of carbon monoxide, hydrogen, carbon dioxide or water to the feed of partial oxidation of methane was investigated over Ni/γ-Al₂O₃ and Rh/γ-Al₂O₃ catalysts. In addition to catalytic tests, thermodynamic calculations were performed to predict the effect of these gas co-feeds. Compared to the thermodynamic trends, differences in the influence of the co-feeding on catalytic performances were observed between both catalysts. Co-feeding of CO, H₂, CO₂ or H₂O can modify the oxidation state and dispersion of the metal component of the catalysts during reaction, and as a consequence, their performances. Changes in catalysts can be due to dynamic processes occurring during reaction. It is suggested to take these processes into account in a more complex kinetic equation for the reactions involved.     

K2CO3/γ-A12O3催化剂在棉籽油制备生物柴油中的应用

利用等体积浸渍法制备K₂CO₃/γ-A1₂O₃负载型固体碱催化剂,应用于棉籽油和甲醇酯交换反应制备生物柴油。对催化剂使用前的保存条件、水分、重复使用性能、游离脂肪酸影响以及失活和再生进行了分析。结果表明,固体催化剂K₂CO₃/γ-Al₂O₃具有较好的抗水性,酸度对催化剂影响明显,重复使用4次未经活化的催化剂,催化活性明显降低,催化剂应密封保存。K₂CO₃/γ-A1₂O₃负载型固体碱催化剂经济实惠且催化效果良好。     

The deposition of γ-Al2O3 layers on ceramic and metallic supports for the preparation of structured catalysts

Deposition of γ-Al₂O₃ washcoats onto Aluminium and FeCrAlloy^® supports in the form of slabs and onto -Al₂O₃ tubes was performed according to a two-step procedure involving: (a) deposition of a bohemite primer, (b) deposition of the γ-Al₂O₃ layer, both by dip coating into powder dispersions in HNO₃ aqueous solutions. We present herein data concerning the effects of the major preparation variables (HNO₃ and H₂O concentrations in the dispersion, withdrawal velocity, drying temperature, number of dipping cycles, calcination temperature) on the deposited coating load and on the adherence of the washcoat. Based on a rheological characterisation of the γ-Al₂O₃ dispersions, we propose also a correlation between their apparent viscosity and the washcoat load. Finally, we briefly illustrate the activity in catalytic combustion reactions of structured Pd-based catalysts prepared according to the investigated washcoating methods.     

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.     

Ce1−xCuxO2−x/Al2O3/FeCrAl catalysts for catalytic combustion of methane

A series of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts (x = 0–1) were prepared. The structure of the catalysts was characterized using XRD, SEM and H₂-TPR. The catalytic activity of the catalysts for the combustion of methane was evaluated. The results indicated that in the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts the surface phase structure were the Ce_1−xCu_xO_2−x solid solution, -Al₂O₃ and γ-Al₂O₃. The surface particle shape and size were different with the variety of the molar ratio of Ce to Cu in the Ce_1−xCu_xO_2−x solid solution. The Cu component of the Ce_1−xCu_xO_2−x/Al₂O₃/FeCrAl catalysts played an important role to the catalytic activity for the methane combustion. There were the stronger interaction among the Ce_1−xCu_xO_2−x solid solution and the Al₂O₃ washcoats and the FeCrAl support.