硅胶固载氧化镓非均相催化合成乙酸丁酯

在氧化镓固载量为20%,500℃焙烧2 h的条件下制备了硅胶固载氧化物型非均相酯化催化剂Ga2O3/S iO2,用于催化合成乙酸丁酯,考察了催化剂用量、n(正丁醇)∶n(乙酸)、环己烷用量、反应时间、带水剂用量和催化剂重复使用性等因素对酯化率的影响。结果表明,该催化剂催化合成乙酸丁酯的适宜反应条件为:乙酸0.2 mol,n(正丁醇)∶n(乙酸)=1.8,催化剂1.25 g,回流反应1 h,酯化率达99.62%。     

Mesoporous silica supports for improved thermal stability in supported Au catalysts

In this work, we present a comprehensive review of our research on the role of mesoporous silica pore architecture, composition of the pore walls (addition of Co or Al), and silica surface chemistry (surface modification by TiO₂) to improve the hydrothermal stability of Au particles. We have found that mesoporous silica architecture plays an important role in improving Au stability, with three dimensional mesoporous architectures being less effective than one dimensional (1-D) pores. The tortuous 1-D pores in aerosol silica were found to be most effective at controlling Au particle size. Since Au particles continue to grow larger than the pore diameter, we conclude that Ostwald ripening must be the dominant sintering pathway for these Au catalysts. These catalysts are active for CO oxidation even after the Au particles have grown large enough to block the pores, suggesting that the thin walls of mesoporous silica provide easy access to gas phase molecules. Further improvements in Au stability and reactivity were obtained by surface modification of the aerosol and MCM-41 silica with TiO₂. After TiO₂ modification of the silica, the Au particles remained smaller than the pore size (< 3 nm) even after three cycles of CO oxidation at temperatures up to 400 °C.     

Selective oxidation of butane on phosphorus-modified silica supported vanadia catalysts

Triethylphosphate impregnation of 2.8 wt% V/SiO₂ and subsequent controlled calcination produced phosphorus-modified supported vanadium catalysts. Phosphorus modification enhanced the yield of maleic anhydride in the partial oxidation of butane. Varying the phosphorus to vanadium atomic ratio from 0 to 2.8 increased the selectivity to maleic anhydride from 0 to approximately 48%. The selectivity was nearly constant up to 20% butane conversion and for different O₂/C₄H₁₀ ratios. The Raman spectra of the phosphorus-modified samples had bands at 1040 and 930 cm^–1, and broad unresolved bands between 580 and 540 cm^–1. It was concluded that the active phases in these samples were -VOPO₄.     

Copper oxide catalysts supported on ceria for low-temperature CO oxidation

Copper oxide catalysts supported on ceria were prepared by wet impregnation method using finely CeO₂ nanocrystals, which was derived from alcohothermal synthesis, and copper nitrate dissolved in the distilled water. The catalytic activity of the prepared CeO₂ and CuO/CeO₂ catalysts for low-temperature CO oxidation was investigated by means of a microreactor-GC system. The samples were characterized using BET, XRD, SEM, HRTEM and TPR.     

Effect of the metal oxide loading on the activity of silica supported MoO3 and V2O5 catalysts in the selective partial oxidation of methane

Precipitated silica catalysts loaded with either MoO₃ (0.2–4.0 wt%) or V₂O₅ (0.2–5.3 wt%) have been studied in the selective partial oxidation of methane to formaldehyde with molecular oxygen at 520 °C. The functionality of the SiO₂ surface towards the formation of HCHO is significantly promoted by V₂O₅, while it is depressed by the MoO₃.     

Photo-electrochemical properties of amorphous WO3 supported on TiO2 hybrid catalysts

In this work, we have carried out ivestigations on photo-electrochemical energy conversion and storage on WO₃/TiO₂ hybrid materials. The band gap excitation of the hybrid WO₃/TiO₂ having an amorphous WO₃ phase led to an effective photo-charging to form a tungsten bronze structure by the intercalation of protons while a reversible discharging through de-intercalation could also be observed.     

Effect of H2S on the hydrogenation of carbon dioxide over supported Rh catalysts

The hydrogenation of CO₂ was studied on supported noble metal catalysts in the presence of H₂S. In the reaction gas mixture containing 22 ppm H₂S the reaction rate increased on TiO₂ and on CeO₂ supported metals (Ru, Rh, Pd), but on all other supported catalysts or when the H₂S content was higher (116 ppm) the reaction was poisoned. FTIR measurements revealed that in the surface interaction of H₂ + CO₂ on Rh/TiO₂ Rh carbonyl hydride, surface formate, carbonates and surface formyl were formed. On the H₂S pretreated catalyst surface formyl species were missing. TPD measurements showed that adsorbed H₂S desorbed as SO₂, both from TiO₂-supported metals and from the support. IR, XP spectroscopy and TPD measurements demonstrated that the metal became apparently more positive when the catalysts were treated with H₂S and when the sulfur was built into the support. The promotion effect of H₂S was explained by the formation of new centers at the metal/support interface.     

An XPS study of dispersion and valence state of TiO2 supported vanadium oxide catalysts

Monolayer vanadium species are mainly in the V(V) valence state, but with XPS a small fraction of V⁴⁺ species are identified. Prolonged analysis treatment increases the V⁴⁺ concentration. With increasing vanadium concentration, a monolayer coverage corresponding to 1 mg V₂O₅ per m² develops, and it contains additional layers with a thickness of about 250 Å at 4 mg V₂O₅ per m², covering 3% of its surface area.     

Oxidative methane conversion to carbon monoxide and hydrogen at low reactor wall temperatures over ruthenium supported on silica

Oxidative methane conversion to carbon monoxide and hydrogen is catalyzed over ruthenium supported on silica at reactor wall temperatures as low as 400° C when the flow rate of reactants (methane and oxygen) is significantly high. The conversion of methane and the yields of carbon monoxide and hydrogen increase with increase in the flow rate of the reactants while oxygen is always completely consumed. Addition of carbon dioxide to the reactant flow can increase the yield of carbon monoxide in the reaction, suggesting that carbon dioxide functions as an oxidant and the actual surface temperature of the catalyst is sufficiently high that thermal conversion of methane via carbon dioxide and water can take place.     

Gold supported CeO2/Al2O3 catalysts for CO oxidation: influence of the ceria phase

A series of low loading gold supported ceria/alumina catalysts have been prepared by the deposition–precipitation method, varying the pH of the synthesis. The catalysts were characterised by means of XRD, TEM, S_BET, XRF and UV–Vis techniques, and their catalytic activity towards CO oxidation in the absence and in presence of water in the stream, were tested. It has been found that in this low loading gold catalysts, where the metallic particles are far away one from another and the oxygen transportation is not the limiting step of the reaction, the electronic properties of the ceria phase and the structure of the metal-support perimeter more than the diameter of the gold nanoparticles is the determinant factor in the catalytic performances of the solid.     

Influence of composition of MgAl2O4 supported NiCeO2ZrO2 catalysts on coke formation and catalyst stability for dry reforming of methane

Dry reforming of methane was studied over Ni catalysts supported on γAl₂O₃, CeO₂, ZrO₂ and MgAl₂O₄ (670 °C, 1.5 bar, 16–20 l CH₄ ml_catalyst⁻¹ h⁻¹). It is shown that MgAl₂O₄ supported Ni catalysts promoted with both CeO₂ and ZrO₂ are promising catalysts for dry reforming of methane with carbon dioxide. Within a certain composition range, the simultaneous promotion with CeO₂ and ZrO₂ has great influence on the amount of coke and the catalyst service time. XRD analyses indicate that formation of crystalline Ce_xZr_1−xO₂ mixed oxide phases occurs on double promotion. In particular, incorporation of low amounts of Zr in the CeO₂ fluorite structure provides stable dry reforming catalysis. As shown with TPR, promotion leads to a higher reduced state of Ni. SEM, XRD and TPR analyses demonstrate that highly dispersed, doubly promoted Ni catalysts with a strong metal-support interaction are essential for stable dry reforming and suppression of the formation of carbon filaments.     

The effect of SO2 on the activity of Pd-based catalysts in methane combustion

The effect of SO₂ on Pd-based catalysts for the combustion of methane has been investigated. It is shown that while SO₂ poisons Al₂O₃- and SiO₂-supported catalysts, pre-treatment of Pd/ZrO₂ by SO₂ enhances the activity substantially.     

Acylation of Benzene over Clay and Mesoporous Si-MCM-41 Supported InCl3, GaCl3 and ZnCl2 Catalysts

Liquid phase acylation of benzene by acyl chloride (e.g., benzoyl chloride, butyryl chloride or phenyl acetyl chloride) over InCl₃, GaCl₃ and ZnCl₂ supported on commercial clays (viz. montmorillonite-K10, montmorillonite-KSF and kaolin) or high silica mesoporous MCM-41 at 80°C has been investigated. The Mont.-K10 and Si-MCM-41 supported InCl₃ and GaCl₃ catalysts showed high activity in the acyation of benzene by benzoyl chloride even in the presence of moisture in the reaction mixture. The redox function of the supported InCl₃, GaCl₃ or ZnCl₂ catalysts seems to play a very important role in the acylation process.     

Room temperature decomposition of N2O in the presence of gaseous oxygen on prereduced Rh supported catalysts

The room temperature decomposition of N₂O over prereduced Rh‐based catalysts (Rh supported on ceria, zirconia and titania–alumina) is studied as a function of the oxygen content in the feed. Results indicate that Rh supported on titania–alumina shows lower degree of inhibition by gaseous oxygen on this reaction, attributed to the role of the metal particle–support interface region in the reaction. The effect of Rh loading and of the reaction temperature are consistent with the hypothesis. This revised version was published online in July 2006 with corrections to the Cover Date.     

Hydrodesulfurization of dibenzothiophene over supported and unsupported molybdenum carbide catalysts

A series of γ-Al₂O₃ supported molybdenum carbides [carbided Mo/γ-Al₂O₃ (MCS), Co-Mo/γ-Al₂O₃ (CMCS), and Ni-Mo/γ-Al₂O₃ (NMCS)] and unsupported molybdenum carbide (MCUS) were prepared by the temperature-programmed carburization of their corresponding molybdenum nitrides with 20 % CH₄/H₂. XRD and SEM studies show that unsupported molybdenum carbide catalyst possesses a typical crystalline Mo₂C (FCC structure), while supported molybdenum carbide catalysts possess highly dispersed surface molybdenum carbide species on an alumina oxide support. The results of dibenzothiophene (DBT) hydrodesulfurization over molybdenum carbide catalysts show that the reactivity is strongly dependent on the type of catalyst. Supported molybdenum carbide catalysts possess a higher reactivity than the unsupported molybdenum carbide catalyst. In addition, Co or Ni promoted, supported molybdenum carbide catalyst possesses a higher reactivity than the unpromoted, supported molybdenum carbide catalyst. The reactivity, which is also dependent on the reaction conditions, increases with increasing reaction temperature and pressure and contact time. The CO uptakes of the molybdenum carbide catalysts correlate well with overall activity (total rate) for DBT hydrodesulfurization. The major reaction product is biphenyl, with cyclohexylbenzene next in abundance regardless of the type of catalysts and reaction conditions. It was also found that the molybdenum carbide catalysts exhibit stable initial reactivity due to the stable and weak acidic characteristics of these catalysts.     

Active and selective copper catalysts supported on alkali-doped silica for the dehydrogenation of cyclohexanol to cyclohexanone

Copper supported on alkali-doped silica was found to be the most effective among various types of copper-containing catalysts tested for the dehydrogenation of cyclohexanol to cyclohexanone. This catalyst could be used with lower copper content than others, and showed the highest conversion and selectivity and good resistance against thermal sintering.     

Combined catalytic partial oxidation and CO2 reforming of methane over supported cobalt catalysts

The combined partial oxidation and CO₂ reforming of methane to synthesis gas was investigated over the reduced Co/MgO, Co/CaO, and Co/SiO₂ catalysts. Only Co/MgO has proved to be a highly efficient and stable catalyst. It provided about 94–95% yields to H₂ and CO at the high space velocity of 105000 mlg^–1h^–1 and for feed ratios CH₄/CO₂/O₂=4/2/1, without any deactivation for a period of study of 110 h. In contrast, the reduced Co/CaO and Co/SiO₂ provided no activity for the formation of H₂ and CO. The structure and reducibility of the calcined catalysts were examined using X-ray diffraction and temperature-programmed reduction, respectively. A solid solution of CoO and MgO, which was difficult to reduce, was identified in the 800°C calcined MgO-supported catalyst. The strong interactions induced by the formation of the solid solution are responsible for its superior activity in the combined reaction. The effects of reaction temperature, space velocity, and O₂/CO₂ ratio in the feed gases (while keeping the C/O ratio constant at 1/1) were investigated over the Co/MgO catalyst. The H₂/CO ratio in the product of the combined reaction increased with increasing O₂/CO₂ ratio in the feed.     

Steam reforming of methanol using Cu-ZnO catalysts supported on nanoparticle alumina

Methanol steam reforming was studied over several catalysts made by deposition of copper and zinc precursors onto nanoparticle alumina. The results were compared to those of a commercially available copper, zinc oxide and alumina catalyst. Temperature programmed reduction, BET surface area measurements, and N₂O decomposition were used to characterize the catalyst surfaces. XRD was used to study the bulk structure of the catalysts, and XPS was used to determine the chemical states of the surface species. The nanoparticle-supported catalysts achieved similar conversions as the commercial reference catalyst but at slightly higher temperatures. However, the nanoparticle-supported catalysts also exhibited a significantly lower CO selectivity at a given temperature and space time than the reference catalyst. Furthermore, the turnover frequencies of the nanoparticle-supported catalysts were higher than that of the commercial catalyst, which means that the activity of the surface copper is higher. It was determined that high alumina concentrations ultimately decrease catalytic activity as well as promote undesirable CH₂O formation. The lower catalytic activity may be due to strong Cu-Al₂O₃ interactions, which result in Cu species which are not easily reduced. Furthermore, the acidity of the alumina support appears to promote CH₂O formation, which at low Cu concentrations is not reformed to CO₂ and H₂. The CO levels present in this study are above what can be explained by the reverse water-gas-shift (WGS) reaction. While coking is not a significant deactivation pathway, migration of ZnO to the surface of the catalyst (or of Cu to the bulk of the catalyst) does explain the permanent loss of catalytic activity. Cu₂O is present on the spent nanoparticle catalysts and it is likely that the Cu⁺/Cu⁰ ratio is of importance both for the catalytic activity and the CO selectivity.     

Supercapacitive properties of a nanowire-structured MnO2 electrode in the gel electrolyte containing silica

Nanowire-structured MnO₂ active materials were prepared by a chemical precipitation method and their supercapacitive properties for use in the electrodes of supercapacitors were investigated by means of cyclic voltammetry in an aqueous gel electrolytes consisting of 1 M Na₂SO₄ and fumed silica (SiO₂). The MnO₂ electrode showed a maximum specific capacitance of 151 F g⁻¹ after 1000 cycles at 100 mV s⁻¹ when using the gel electrolyte containing 3 wt.% of SiO₂, which is higher than 121 F g⁻¹ obtained when using the 1 M Na₂SO₄ liquid electrolyte alone.     

Influence of molybdenum and tungsten additives on the properties of nickel steam reforming catalysts

An introduction of small amounts of molybdenum and tungsten compounds into the nickel catalyst of the steam reforming of methane considerably reduces the detrimental effect of carbon deposit formation, while entailing no change in the catalyst activity.