Preparation of γ-Al2O3 sorbents loaded with metal components and removal of thiophene from coking benzene

Series sorbents of Cu, Zn, Ni, Ce and Ag metal components supported on γ-Al₂O₃ carrier for removing thiophene from benzene were prepared by conventional and ultrasound-assisted incipient-wetness impregnation method. The static adsorption experiments were carried out in the thiophene-benzene solution with thiophene concentration of 500?mg/L. The results show that the desulfurization activity of all γ-Al₂O₃ sorbents modified by different metal components obviously increase, among which the sorbent modified by silver nitrate has the best performance. The active components of sorbents from Cu, Zn, Ni, Ce nitrates loaded on γ-Al₂O₃ carrier are their oxides. Besides Ag₂O, the products of silver nitrate thermal decomposition in sorbent prepared still have Ag⁰ and Ag–O–Al species. The assistant ultrasound in the process of sorbent preparation can not only shorten the impregnation time, but also enrich the pore structure of sorbent and improve the size and distribution of the Ag species, which is favorable to the removal of thiophene from benzene. The desulfurization capacity of sorbent changes with the Ag content loaded. The sorbent with 15?% quality content of Ag prepared by ultrasound-assisted impregnation method has the highest desulfurization efficiency. It could reduce the thiophene concentration to 1.7?mg/L from 500?mg/L at room temperature and ambient pressure, with the desulfurization efficiency of more than 99?%, when the ratio of sorbent to solution was 1:4?(g/mL).     

Preparation and characterization of W/γ-Al2O3 and Pd–W/γ-Al2O3 catalysts from organometallic precursors. The catalytic activity for NO decomposition

The photochemical reaction of W(CO)₆ with triphenylphosphine (PPh₃) in the presence of γ-Al₂O₃ and Pd/γ-Al₂O₃ has been used to prepare W/γ-Al₂O₃ and Pd–W/γ-Al₂O₃ catalysts. Adsorbed mono- and disubstituted W species have been identified by FTIR spectroscopy. There is evidence of the adsorption of W(CO)_6−x L_x species on both the alumina and the Pd surface. After thermal decomposition and reduction at 573 K the catalysts have been characterized by FTIR spectroscopy of adsorbed NH₃, CO and NO. The retention of W and P suppresses the Lewis acidity of the alumina support. On Pd–W/γ-Al₂O₃, the W is present in a partially reduced state in close association with Pd. This interaction modifies the chemisorptive properties of NO relative to those of the monometallic Pd and W catalysts. In line with these observations the Pd–W/γ-Al₂O₃ catalyst presents an enhanced activity for NO decomposition at 473 K.     

Catalytic Combustion of Styrene over the Binary Mixture of Manganese and Copper Based Catalyst in the Absence and Presence of Water Vapor

MnO _x and MnCu based catalysts prepared by ultrasonic impregnation methods were characterized by XRD, TPR-H₂, XPS and N₂ adsorption and tested for styrene combustion in the presence and absence of water vapor. Results showed that the loading of binary mixtures of manganese oxide and copper oxide on γ-Al₂O₃ increased the ratio of Cu⁺/Cu²⁺ of the defect spinel of Cu_1.5Mn_1.5O_4–x and the reducibility of the catalyst and in this way increased the catalytic activity of the catalysts for styrene combustion. The catalyst MnCu/γ-Al₂O₃ (20%/l) with 20 wt % loading amount and the Mn/Cu ratio of 1 : 1 showed the highest catalytic activity with T₉₀ = 214°C. Water vapor in feed steam decreased the activity of the catalysts MnCu/γ-Al₂O₃ (20%/l) and Mn₂O₃/γ-Al₂O₃ (10%). The catalyst MnCu/γ-Al₂O₃ (20%/l) had more resistant to negative influence of water vapor. Upon addition of 2.94 vol % water vapor to the feed stream a 6.5% decrease in styrene conversion was observed whereas for the catalyst Mn₂O₃/γ-Al₂O₃ (10%) a 14% reduction in conversion at the same condition was recorded. Higher resistance to the negative influence of water vapor could be due to weaker interactions between water molecules and the surface of catalyst.     

Enhancement of the catalytic performances and lifetime of Ni/γ-Al2O3 catalysts for the steam toluene reforming via the combination of dopants: inspection of Cu,Co, Fe,Mn, and Mo species addition

In this work, the influence of metallic dopant addition in 10 wt % Ni/γ-Al₂O₃ catalyst on the material physico-chemical properties and catalytic activity for the toluene steam reforming was studied. Seventeen doped Ni/γ-Al₂O₃ catalysts were synthesized by the sol–gel process. The aim of this study was to determine which elements were the most suitable for the doping of 10 wt % Ni/γ-Al₂O₃ catalysts. The influence of the dopants was studied through different physico-chemical techniques. It appeared that some dopants showed lower catalytic performances due to high carbon deactivation. On the contrary, some dopants increased the resistance to coking while also improving the catalytic activity. Different mechanisms were proposed to explain these modifications of catalytic behavior. Among all doped Ni/γ-Al₂O₃ catalysts, the samples that combined Mn + Mo or Co + Mo dopants showed the best catalytic performances at 650 °C. Both samples showed high toluene reforming activity and low amounts of carbon deposit.     

Thermal stability and glass transition behavior of PANI/γ-Al2O3 composites

Polyaniline/γ-Al₂O₃ (PANI/γ-Al₂O₃) composites were synthesized by in-situ polymerization at the presence of HCl as dopant by adding γ-Al₂O₃ nanoparticles into aniline solution. The composites were characterized by FTIR and XRD. The thermogravimetry (TG) and modulated differential scanning calorimetry (MDSC) were used to study the thermal stability and glass transition temperature (T _g) of the composites, respectively. The results of FTIR showed that γ-Al₂O₃ nanoparticles connected with the PANI chains and affected the absorption characteristics of the composite through the interaction between PANI and nano-sized γ-Al₂O₃. And the results of XRD indicated that the peaks intensity of the PANI/γ-Al₂O₃ composite were weaker than that of the pure PANI. From TG and derivative thermogravimetry (DTG) curves, it was found that the pure PANI and the PANI/γ-Al₂O₃ composites were all one step degradation. And the PANI/γ-Al₂O₃ composites were more thermal stable than the pure PANI. The MDSC curves showed that the nano-sized γ-Al₂O₃ heightened the glass transition temperature (T _g) of PANI.     

Mechanism on The Disproportionating Synthesis of Dichlorodimethyl- silane by ZSM-5(5 T)@γ-Al2O3 Series Core-Shell Catalysts

In view of the wide application of organosilicon bifunctional structure in industry, the most effective disproportionation solution is used by the new catalyst to prepare the largest and the most versatile organic silicon monomer dimethyldichlorosilane. However, there are still remaining doubts on the disproportionation mechanism of the catalyst. The Density Functional Theory (DFT) was used to theoretically calculate the disproportionation mechanism of 5 T clusters ZSM-5@γ-Al₂O₃ series catalysts at the B3LYP/6–311++G(3df, 2pd) level. The properties were verified and the catalytic effects of different active sites pre- and post- modified by AlCl₃ were calculated and compared. The active center of HZSM-5@γ-Al₂O₃ was proton, and that of AlCl₃/ZSM-5@γ-Al₂O₃ changed to lewis acidic center. The presence of the lewis acid center enhances the total activity of the catalyst to some extent. The catalytic activity of the 5 T cluster ZSM-5@γ-Al₂O₃ catalyst modified by AlCl₃ was higher, which was the same as the experimental results.     

Adsorption and catalytic properties of sulfated aluminum oxide modified with cobalt ions

The adsorption properties of sulfated aluminum oxide (9% SO ₄ ^2- /γ-Al₂O₃) and a cobalt-containing composite (0.5%Сo/SO ₄ ^2- /γ-Al₂O₃) based on it are studied via dynamic sorption. The adsorption isotherms of such test adsorbates as n-hydrocarbons (C₆–C₈), benzene, ethylbenzene, chloroform, and diethyl ether are measured, and their isosteric heats of adsorption are calculated. It is shown that the surface sulfation of aluminum oxide substantially improves its electron-accepting properties, and so the catalytic activity of SO ₄ ^2- /γ-Al₂O₃ in the liquid-phase alkylation of benzene with octene-1 at temperatures of 25–120°C is one order of magnitude higher than for the initial aluminum oxide. It is established that additional modification of sulfated aluminum oxide with cobalt ions increases the activity of this catalyst by 2–4 times. It is shown that adsorption sites capable of strong specific adsorption with both donating (aromatics, diethyl ether chemosorption) and accepting molecules (chloroform) form on the surface of sulfated γ-Al₂O₃ promoted by cobalt salt.     

Determination of the maximum monolayer dispersion and dispersed state for WO3 on γ-Al2O3

The maximum monolayer dispersion (the threshold) for WO₃ on γ-Al₂O₃ calcined at 500°, 550°, 600°, and 640°C has been determined quantitatively by XRD (amount of crystalline phase) and XPS (intensity ratios I_w4f/I_Al2). The results show that if the amount of WO₃ loaded is lower than the maximum monolayer dispersion, WO₃ will react with γ-Al₂O₃ to form surface compound due to mutual ionic interaction, and will be dispersed on γ-Al₂O₃ surface as monolayer then. In case the amount is higher than this value, the residual crystalline WO₃ will remain. The maximum monolayer dispersion (threshold) is 0.21 g and 0.20 g WO₃/100 m² γ-Al₃O₃ by XRD and XPS respectively. It agrees with the value (0.189 g WO₃/100 m² or 4.90 × 10^?18 W atoms/m²) calculated from the model on assumption that the WO₃ is dispersed as a closed-packed monolayer on γ-Al₂O₃ surface. Inasmuch as WO₃/γ-Al₂O₃ system is stable up to higher temperature, e.g. 700°C, than MoO₃/γ-Al₂O₃ system, WO₃ seems unfavorable to form new bulk compound with γ-Al₂O₃ at that temperature. However, Al₂(MoO₄)₃ forms perceptibly in MoO₃/γ-Al₂O₃ system at 500°C. Besides, the size of residual crystalline WO₃ in WO₃/γ-Al₂O₃ is much smaller than that of MoO₃ in MoO₃/γ-Al₂O₃. It might be the reason that WO₃/γ-Al₂O₃ catalyst is superior to MoO₃/γ-Al₂O₃ in hydrodesulfurization (HDS) or hydrodenitrogenation (HDN) in some cases.     

A study of Pt–Pd/γ-Al2O3 catalysts for methane oxidation resistant to deactivation by sulfur poisoning

The catalytic oxidation of methane was studied over calcined and reduced Pt–Pd/γ-Al₂O₃ catalysts, in the presence and the absence of SO₂ in the CH₄–O₂ reaction feed. The effect of sulfation (SO₂ + O₂ for 4 h at 500 °C) was also studied on the catalyst resistance to deactivation by sulfur poisoning. Sulfating the calcined Pt–Pd/γ-Al₂O₃ catalysts resulted in a strong deactivation for the CH₄–O₂ reaction. However, the catalytic activity of the reduced-sulfated Pt–Pd/γ-Al₂O₃ catalyst for CH₄–O₂ reaction remained rather unaffected in the presence and in the absence of SO₂ in the reaction feed. XPS analysis revealed, over reduced-sulfated Pt–Pd/γ-Al₂O₃ catalysts, the presence of Pt(0) metallic surface species on which SO₂ interactions may be faster related to Pd surface species. The presence of Pt(0) may be necessary to prevent the interactions between SO₂ and Pd surface species. Long time catalytic tests showed that the activity of a reduced Pt–Pd/γ-Al₂O₃ catalysts for CH₄–O₂ reactions remained rather unaffected despite the presence of SO₂ in the reaction feed.     

Effect of promoters on the catalytic performance of Ni/Al2O3 catalyst for partial oxidation of methane to syngas

The effect of promoters such as Ce, La and Ca on catalytic performance of Ni catalyst was measured in a continuous fixed bed reactor. The effect of promoters on Ni/a-Al₂O₃ catalyst is more significant than on Ni/g-Al₂O₃ catalyst. Ce was proved to be the best promoter among the three promoters tested and the optimum loading of Ce was 1%. The catalyst was characterized by TG, XPS, TPR and XRD techniques. TPR results showed that Ce can improve the reducibility of the Ni/Al₂O₃ catalyst. XRD results indicated that Ce was highly dispersed when its loading was low, but at higher loading it was crystallized into bulk CeO₂, thus, decreased the catalytic activity. This revised version was published online in June 2006 with corrections to the Cover Date.     

Ethanol synthesis from syngas on Mn- and Fe-promoted Rh/γ-Al2O3

The catalytic hydrogenation of CO was studied over Mn- and/or Fe-promoted Rh/γ-Al₂O₃ catalysts. The catalysts were characterized by means of XRD, BET, H₂-TPR·H₂-TPD, XPS and DRIFTS. CO hydrogenation results showed that the doubly Mn- and Fe-promoted Rh/γ-Al₂O₃ catalysts exhibited superior catalytic activity and better ethanol selectivity. The DRIFTS results showed that Mn promoter stabilized the adsorbed CO on Rh⁺ and Fe stabilized adsorbed CO on Rh⁺ and Rh⁰, especially Rh⁰. The fact that doubly Mn- and Fe-promoted Rh/γ-Al₂O₃ owned more (Rhx⁰–Rhy⁺)–O–Fe³⁺·(Fe²⁺) active species was proposed to be a crucial factor accounting for its higher ethanol selectivity.     

Chemical vapor infiltration method for deposition of gold nanoparticles on porous alumina supports

Knudsen’s effusion method with mass spectral analysis of the composition of the gas phase was used to measure the temperature dependence of the saturated vapor of several (CH₃)₂AuL chelate complexes and to determine the thermodynamic parameters of their sublimation. Based on the results of this study, conditions for chemical vapor deposition of gold using dimethylgold(III) chelates were chosen. Gold nanoparticles were synthesized by chemical vapor deposition (infiltration) of (CH₃)₂Au(acac) on porous granules of γ-Al₂O₃ with subsequent calcination in air at 325°C. Particle size and the chemical state of gold in Au/γ-Al₂O₃ systems were evaluated by transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). A vapor infiltration procedure is suggested to prepare metallic gold particles ≤5 nm in diameter from Au/γ-Al₂O₃. It is shown that Au/γ-Al₂O₃ systems obtained by chemical vapor infiltration and containing small gold crystallites possess high catalytic activity in CO oxidation reactions at 40°C.     

电催化氧化法处理苯酚废水的Mn-Sn-Sb/γ-Al2O3粒子电极研制

采用溶胶-凝胶法制备了一系列不同Mn/Sn/Sb比的γ-Al₂O₃负载型粒子电极, 以苯酚为模型污染物考察了粒子电极的催化活性, 并用BET表面积、SEM和XRD等手段, 对粒子电极的微结构、表面形貌及物相进行了表征. 研究表明, 在Sn和Sb含量相同的情况下, Mn与Sn的摩尔比为2∶1时催化活性最高, 其催化活性远远高于某化学物理所提供的Ru/TiO₂粒子电极. 所制粒子电极不仅具有相当高的电催化活性, 而且在使用过程中催化性能稳定, 经5次反复使用后仍具有较高的催化活性. 反应过程中活性组分的流失是粒子电极失活的主要原因, 催化剂表面积炭也可能是粒子电极失活的原因之一.     

KF promoted mesoporous γ-Al2O3 with strong basicity: Preparation,characterization and catalytic activitiy for transesterification to biodiesel

The present paper describes the preparation of KF/M-γ-Al₂O₃, efficient mesoporous solid bases. The procedure involves loading KF into a crystalline mesoporous γ-Al₂O₃ that was synthesized by the self-assembly of poly-4-vinylpyridine (P4VP) with Al³⁺ species. The synthesis is based on the strong acid-base interaction, hydrothermal treatment at 180°C and calcination at 550°C. Characterizations using XRD analysis and low temperature N₂ adsorption indicated that different amounts of KF could be introduced into crystalline mesoporous γ-Al₂O₃ to obtain catalysts with high BET surface areas, large pore volumes and uniform pore size distribution. Based on SEM images, KF/M-γ-Al₂O₃ catalysts have rough surface character and a large nanopore volume. CO₂-TPD curves registered for KF/M-γ-Al₂O₃ contain high temperature peaks, indicating strong basicity of the catalysts. Under the same reaction conditions KF/M-γ-Al₂O₃ catalysts exhibit much better activities for transesterification to biodiesel than KOH, NaOH, H₂SO₄, hydrotalcite and CaO. Enhanced activities appear to arise from strong basisity and large BET surface areas.     

Role of metal Cu species on methyl laurate catalytic hydrogenation to oxygen-containing compounds

The Cu/γ-Al₂O₃ catalysts with different Cu loadings were prepared by impregnation method. The physicochemical properties of these Cu/γ-Al₂O₃ catalysts were characterized by H₂-TPR, XRD, and in-situ XPS. The catalytic hydrogenation performances of methyl laurate over Cu/γ-Al₂O₃ catalysts were studied. The results show that the hydrogenation performances of methyl laurate on Cu/γ-Al₂O₃ catalyst are related to the dispersion, crystallite size, and content of the active component Cu⁰. The 10CA catalyst has the best hydrogenation performances for methyl laurate to produce C₁₂ alcohol. At 300 °C, the conversion of methyl laurate and the selectivity of C₁₂ alcohol are 55.6% and 30.4%, respectively.     

La2O3 promotional effect to Co3O4/γ-Al2O3 catalyst in the oxidative dehydrogenation of ethylbenzene with CO2 as soft oxidant

Co₃O₄/γ-Al₂O₃ catalysts with variable Co₃O₄ loadings (5–20 wt%) and deposition of 15% Co₃O₄ on La₂O₃/γ-Al₂O₃ were prepared by wet impregnation method. La₂O₃-γ-Al₂O₃ support with variable composition of La₂O₃ (2–6 wt%) were prepared by co-precipitation method. All the catalysts were tested for oxidative dehydrogenation of ethylbenzene with CO₂ as soft oxidant. Among the Co₃O₄/γ-Al₂O₃ catalysts, 15% Co₃O₄/γ-Al₂O₃ has shown good performance and hence this catalyst has been chosen to investigate the effect of La₂O₃ species. CO₂ pulse chemisorption data indicate more amount of CO₂ uptake over 15% Co₃O₄/4%La₂O₃/γ-Al₂O₃ catalyst which clearly indicates that this catalyst exhibits good performance in ethylbenzene dehydrogenation with CO₂ as soft oxidant because of reverse water gas shift reaction. Temperature programmed reduction studies indicate that the Co₃O₄ catalysts follow two step reduction mechanism from Co₃O₄ to CoO and then to Co and La₂O₃ promotional effect is visible through facile reduction of Co₃O₄ species. La₂O₃ doping has a vital influence in getting enhanced ethylbenzene conversion, styrene yield and alleviates catalyst deactivation compared to that of unpromoted Co₃O₄/γ-Al₂O₃ catalyst. TGA studies indicate the presence low amount coke deposition during time-on-stream over 15% Co₃O₄/4%La₂O₃/γ-Al₂O₃ catalyst compared to 15% Co₃O₄/γ-Al₂O₃ catalyst.     

A theoretical and experimental XAS study of monolayer dispersive supported CuO/γ-Al2O3 catalysts

The local structures of supported CuO/γ-Al₂O₃ monolayer dispersive catalysts with different CuO loadings have been investigated by EXAFS and multiple scattering XANES simulations. The EXAFS results show that the first nearest neighbors around the Cu atoms in the CuO/γ-Al₂O₃ catalysts are similar to that of the polycrystalline CuO powder, which is independent of the CuO loadings. Moreover, the Cu K-XANES FEFF8 calculations for CuO reveal that the monolayer-dispersed CuO species are of small distorted (CuO₄)_mⁿ⁺ clusters, which is mainly composed of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support. We consider that the CuO species for the CuO/γ-Al₂O₃ catalysts with loadings of 0.4 and 0.8 mmol/100 m² are distorted (CuO₄)_mⁿ⁺ clusters composed mainly of a distorted CuO₆ octahedron incorporated in the surface octahedral vacant sites of the γ-Al₂O₃ support after calcinations at high temperature in air for a few hours. On the contrary, for the CuO/γ-Al₂O₃ with loading of 1.2 mmol/100 m², the local structure of Cu atoms in CuO/γ-Al₂O₃ is similar to that of polycrystalline CuO powder.     

Methane conversion under cold plasma over Pd-containing ionic liquids immobilized on γ-Al2O3

Pd-containing ionic liquid (IL) l-hexyl-3-methylimidazolium tetrafluoroborate (C₆MIMBF₄) immobilized on γ-Al₂O₃ (Pd-IL/γ-Al₂O₃) was prepared and characterized by Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET) analysis. The influences of C₆MIMBF₄ loading and Pd on methane conversion to C₂ hydrocarbons under cold plasma were investigated. FTIR and SEM analyses indicated that C₆MIMBF₄ had been successfully immobilized on γ-Al₂O₃ and the C₆MIMBF₄ showed excellent stability under cold plasma. The results of BET and methane conversion showed that with the increase in immobilization amount of C₆MIMBF₄ onto γ-Al₂O₃, the specific surface area and pore volume of IL/γ-Al₂O₃ decreased, while the selectivity and yield of C₂ hydrocarbons increased. The selectivity of C₂ hydrocarbons was 94.6% when the loading of C₆MIMBF₄ was 40%, and the percentage of C₂H₄ in C₂ hydrocarbons was as high as 64% when using Pd-IL/γ-Al₂O₃ as a catalyst with no conventional thermal reduction treatment. Optical emission spectra (OES) from the cold plasma reactor during methane conversion were also studied. The results indicated that the intensity of the C₂, CH, H, and C active species from methane and hydrogen decomposition increased when IL/γ-Al₂O₃ or Pd-IL/γ-Al₂O₃ was introduced into the plasma system. Based on the analyses of the gas product and OES spectra, it can be concluded that the surface catalyzed reactions between plasma and ionic liquid were very important for the reduction of Pd²⁺ and the formation of C₂H₄     

Catalytic dehydrogenation of propane to propylene over highly active PtSnNa/γ-Al_2O_3 catalyst

This paper reports a new fabrication method of the PtSnNa/γ-Al₂O₃ catalyst through ball milling, which is more stable and active than the commercial catalyst.