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.     

Environmentally clean synthesis of diphenylmethanes using silica gel-supported ZnCl2 and FeCl3

Lewis acids such as FeCl₃ and ZnCl₂ were supported on silica gel, alumina, zirconia and titania by co-grinding with anhydrous Lewis acids in appropriate proportions in an agate mortar. The catalysts have good shelf life and reusability. Synthesis of diphenylmethanes with these catalysts was studied; silica gel was the best support. © 1998 SCI     

The roles of BrØnsted and Lewis surface acid sites in acid-treated montmorillonite supported ZnCl2 alkylation catalysts

The catalyst known as clayzic (ZnCl₂ supported on acid-treated montmorillonite) exhibits both BrØnsted and Lewis surface acidities. The relative catalytic activities of these two types of acid site have been determined in a range of reactions, by comparing the activities of clayzic with those of related catalysts which exhibit only one type of surface acidity. Acid-treated montmorillonite has been used as the BrØnsted acid catalyst in this comparison, and ZnCl₂ supported on a mesoporous silica has been used as the Lewis acid catalyst. The results confirm that the relative activities of the two types of acid site depend on both the nature of the reaction and the polarity of the reaction medium. They will be of value in optimising the choice of support and the ZnCl₂ loading in clayzic-type catalysts for specific reactions.     

Oxidation of CH4 over Pd supported on TiO2-doped SiO2: Effect of Ti(IV) loading and influence of SO2

Titania-modified silicas with different weight% of TiO₂ were prepared by sol–gel method and used as supports for Pd (1 wt%) catalysts. The obtained materials were tested in the oxidation of methane under lean conditions in absence and in presence of SO₂. Test reactions were consecutively performed in order to evaluate the thermal stability and poisoning reversibility. Increasing amounts of TiO₂ improved the catalytic activity, with an optimum of the performance for 10 wt% TiO₂ loading. Moreover, the titania-containing catalysts exhibited a superior tolerance towards SO₂ by either adding it to the reactants or feeding it as a pure pretreatment atmosphere at 350 °C. Catalysts were characterized by XPS, XRD, FT-IR and BET measurements. According to the structural and surface analyses, the mixed oxides contained Si–O–Ti linkages which were interpreted as being responsible for the enhanced intrinsic activity of supported PdO with respect to PdO on either pure SiO₂ or pure TiO₂. Moreover, the preferential interaction of the sulfur molecule with TiO₂ and the easy SO_x desorption from high surface area silica were the determining factors for the superior SO₂ tolerance of the TiO₂-doped catalysts.     

Silica Gel- and MCM-41-Supported MoS2 Catalysts for HDS Reactions

MCM-41- and silica gel-supported MoS₂ catalysts were prepared. MCM-41 was synthesized and impregnated with precursor, then activated to obtain the active phase. The sol–gel method was used for providing the SiO₂ support as well as for including the catalyst precursors in one single step of preparation. Such catalysts have applications particularly in hydrodesulfurization (HDS) and hydrodenitrogenation (HDN) processes. A comparison of the activities of the catalysts was made. The catalytic activity results showed the method of preparation used in this study was successful in producing very efficient catalysts for the HDS of dibenzothiophene (DBT).A higher selectivity for direct C–S bond cleavage was observed for the MoS₂ catalyst supported on SiO₂ by the sol–gel method. X-ray diffraction studies showed that the catalysts were poorly crystallized with a very weak intensity of the (002) line of 2H-MoS₂.     

Reductive Activation of Dioxygen in Catalytic Systems Including Platinum and Heteropoly Compounds: Oxidation of Cyclohexane

Thermal activation of clayzic catalyst has been thoroughly investigated by calcining anhydrous ZnCl₂ impregnated on Mont-K10 with different ZnCl₂ loadings (0.5-2.0 mmol g^-1) under static or flowing air at 270 °C and also under N₂ flow at different temperatures (150-400 °C). Depending upon the ZnCl₂ loading and calcination temperatures, an appreciable amount of HCl is evolved in the thermal activation, indicating an occurrence of reaction between the ZnCl₂ and the surface hydroxyl groups of the clay (- OH + ZnCl₂ - O - Zn - Cl + HCl), leading to formation of new Lewis acid sites (- O - Zn -Cl). The Cl/Zn ratio, surface area and catalytic activity (in the benzene benzylation by benzyl chloride at 80 °C) of the clayzic formed in the thermal activation are influenced markedly by the ZnCl₂ loading and calcination conditions (temperature and gas atmosphere). The maximum catalytic activity for the clayzic is observed at the optimum ZnCl₂ loading (about 1.0 mmol g^-1) and calcination temperature (about 270 °C). The thermal activation at 270 °C under flowing N₂ led to a most active clayzic catalyst for the benzene benzylation. A temperature-programmed evolution of HCl in the calcination of ZnCl₂/Mont-K10 with different ZnCl₂ loadings from 25 to 400 °C at a linear heating rate of 2 °C min^-1 has also been investigated.     

Study of ruthenium supported on Ta2O5–ZrO2 and Nb2O5–ZrO2 as catalysts for the partial oxidation of methane

Ru-based catalysts supported on Ta₂O₅–ZrO₂ and Nb₂O₅–ZrO₂ are studied in the partial oxidation of methane at 673–873 K. Supports with different Ta₂O₅ or Nb₂O₅ content were prepared by a sol–gel method, and RuCl₃ and RuNO(NO₃)₃ were used as precursors to prepare the catalysts (ca. 2 wt.% Ru). At 673 K high selectivity to CO₂ was found. An increase of temperature up to 773 K produced an increase in the selectivity to syngas (H₂/CO = 2.2–3.1), and this is related with the transformation of RuO₂ to metallic Ru as was determined from XRD and XPS results. At 873 K and with co-fed CO₂ an increase of the catalytic activity and CO selectivity was found. A TOF value of 5.7 s⁻¹ and H₂/CO ratio ca. 1 was achieved over Ru(Cl)/6TaZr. Catalytic results are discussed as a function of the support composition and characteristics of Ru-based phases.     

Unique adsorption and catalytic behavior of H2 and CO over hollow Silica-Rh, -Ir, and -Ru nanocomposites prepared by Reversed Micelle Technique

Hollow silica nano spheres containing Rh, Ir or Ru metal particles were synthesized by Rh(NH₃)₆Cl₃ aq, Ir(NH₃)₃Cl₃ aq or Ru(NH₃)₆Cl₃ aq/NP-6/cyclohexane reversed micelle system. Hydrolysis of TEOS surrounding metal ammine complex crystals inside the micelle caused the formation of the hollow, which contained small metal particles inside and tiny metal clusters in the silica network. The amounts of H₂ adsorption over Rh and Ir nanocomposites were two to three times more in the cases of hollow-SiO₂ catalysts compared with those of non-hollow ones, suggesting the occlusion of hydrogen inside the hollows of Rh–SiO₂ or Ir–SiO₂. CO molecules could also permeate into the silica wall and be adsorbed on the metal clusters in the silica wall after 573 K pretreatment. Especially in the case of Ru nanocomposite the amount of adsorbed CO was much more than that of H₂, suggesting some unique character of Ru metal nanoparticles. After 773 K pretreatment, however, the amount of CO(a) decreased drastically to less than 1/10 of H(a), indicating the densification of Si–O–Si bonds and the formation of ultra-micropores in the silica wall where only H₂ can selectively permeate. Selective formation of methane was observed in the CO–H₂ reaction over these nanocomposite catalysts, provably because of the higher concentration of hydrogen inside the hollow and silica network.     

Kinetics of ethylene polymerization at high temperature with Ziegler–Natta catalysts

A kinetic technique is developed for the study of ethylene polymerization reaction at high temperature with Ziegler–Natta catalysts. The technique is based on the calculation of polymerization rate parameters from the data on ethylene consumption vs. time. It takes into account increase of reaction temperature at the beginning of the reaction. Kinetic data in coordinates “polymerization rate–time” are presented for several pseudohomogeneous catalysts (TiCl₄? AlEt₂Cl, Ti(OiC₃H₇)₄? AlEt₂Cl), heterogeneous catalysts (δ-TiCl₃? AlEt₃, δ-TiCl₃? AlEt₂Cl, TiCl₄/MgCl₂? AlEt₃, TiCl₄/MgCl₂? AlEt₂Cl) and solubilized catalysts (δ-TiCl₃? poly-1-hexene? AlEt₂Cl) at 180°C and reaction pressure 14.6 atm for first 10 min of the reaction. These data are useful for the selection of Ziegler–Natta catalysts for testing in ethylene polymerization reaction in continuous high pressure reactors at short residence times.     

The Adsorption of VO(acac)2 on a Mesoporous Silica Support by Liquid Phase and Gas Phase Modification to Prepare Supported Vanadium Oxide Catalysts

Supported vanadium oxide catalysts are prepared by adsorption and subsequent calcination of the vanadyl acetylacetonate complex on silica by liquid phase and gas phase modification. The influence of the pretreatment temperature and the effect of the solvent in the liquid phase are discussed. Two types of gas phase deposition processes are used: flow-type reactions and vacuum deposition. The bonding mechanism, the influence of pretreatment temperature of the support and the influence of the reaction temperature are investigated by FTIR, XRD, TGA and chemical analysis. After calcination the obtained vanadium oxide layer is characterized by XRD and UV-Vis diffuse reflectance spectroscopy. The gas phase modification enables the creation of well dispersed supported VO_x catalysts. Loadings up to 1.4 mmol g^-1 (7 wt% V) without the formation of a crystalline fraction can be achieved. The selective oxidation of methanol to formaldehyde is used as a probe reaction to assess the catalytic activity and selectivity of the catalysts. It is shown that not the concentration of vanadium species, but their surface configuration is the determining factor in catalytic reactions.     

Synthesis of Zirconium Phosphate,HZr2(PO4)3, in Pores of Silica Beads and Some Ion Exchange Separation Properties of the Composite Obtained

Abstract

Zirconium phosphate, HZr₂(PO₄)₃ (HZP), was synthesized in inner pores of highly porous silica beads, and the ion exchange properties of HZP-loaded silica beads (HZP-SiO₂) thus obtained were examined. The ion exchange properties of HZP-SiO₂ were basically equivalent to those of HZP in the form of powders. Chromatographic lithium isotope separation was attempted using HZP-SiO₂ as column packing material. The heavier isotope was effectively accumulated in the frontal part of the lithium chromatogram. However, the tailing phenomenon was observed at the rear boundary of the chromatogram, and no effective accumulation of the isotope separation effect was observed in the tail.     

Supported TiO2/silica gel as an efficient and inexpensive catalyst for nonsolvent liquid-phase oxidation of cyclohexylamine to cyclohexanone oxime

A benign approach is proposed for the highly efficient synthesis of cyclohexanone oxime through nonsolvent liquid-phase oxidation of cyclohexylamine with dioxygen over supported TiO₂/silica gel. The as-prepared catalyst was characterized by Brunauer–Emmett–Teller (BET), Fourier-transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and X-ray powder diffraction (XRD) analyses. The results indicate that titanium active sites could be grafted on silica gel supports as catalytic centres. Various parameters such as reaction time and reaction temperature were systematically optimized; the results showed that supported 20%TiO₂/silica gel exhibited the best catalytic effect with 63.2% of amine conversion and 86.3% of selectivity to CHO. A possible pathway is proposed for cyclohexylamine oxidation over supported TiO₂/silica gel. The method developed in this study using dioxygen as the oxidant and inexpensive TiO₂/silica gel as an efficient catalyst has incredible industrial application potential for green synthesis of cyclohexanone oxime.     

Hydrodesulphurization performance of NiW/TiO2-Al2O3 catalyst for ultra clean diesel

TiO₂-Al₂O₃ binary oxide supports were obtained by sol–gel methods from Tetra-n-butyl-titanate and pseudoboehmite/aluminium chloride resources. The typical physico-chemical properties of NiW/TiO₂-Al₂O₃ catalysts with different TiO₂ loadings and their supports were characterized by means of BET, XRD and UV–vis DRS, etc. The BET results indicated that the specific surface areas of NiW/TiO₂-Al₂O₃ catalysts were as higher as that over pure γ-Al₂O₃ support, and the pore diameters were also large. The XRD and UV–vis DRS analyzing results showed that the Ti-containing supported catalysts existed as anatase TiO₂ species and the incorporation of TiO₂ could adjust the interaction between support and active metal, and impelled the higher reducibility of tungsten. The hydrodesulphurization (HDS) performance of the series catalysts were evaluated with diesel feedstock in a micro-reactor unit, and the HDS results showed that NiW/TiO₂-Al₂O₃ catalysts exhibited higher activities of ultra deep hydrodesulphurization of diesel oil than that of NiW/Al₂O₃ catalyst. The optimal TiO₂ content of NiW/TiO₂-Al₂O₃ catalysts was about 15 m%, and the corresponding HDS efficiency could reach to 100%. The sulphur contents of diesel products over NiW/TiO₂-Al₂O₃ (from pseudoboehmite/AlCl₃) catalysts with suitable TiO₂ content could be less than 15 ppmw, which met the sulphur regulation of Euro IV specification of ultra clean diesel fuel.     

A green method for solvent-free conversion of epoxides to thiiranes using NH4SCN in the presence of NiFe2O4 and MgFe2O4 magnetic nanocatalysts

Nickel and magnesium ferrite magnetic nanoparticles were fabricated and applied as efficient and reusable catalysts in the solvent-free conversion of various epoxides to the corresponding thiiranes with ammonium thiocyanate under oil bath (60°C) conditions. NiFe₂O₄ and MgFe₂O₄ nanoparticles can catalyze the reactions at short times in high to excellent yields. The catalysts can also be recovered easily using an external magnetic field and be reused four times without any significant loss of activity.     

Dehydrogenation of cyclohexanol to cyclohexanone over Cu/SiO2 catalysts : Dispersion and catalytic activity

Copper catalysts supported on silica (Cu/SiO₂) were prepared by three different methods; incipient wetness, precipitation, and ion exchange. Catalytic properties in the dehydrogenation of cyclohexanol over these catalysts were examined. Copper surface area increased in the order of incipient wetness precipitation ion-exchange method for the catalysis with the same loading of copper. Conversion was mainly dependent on the copper surface area regardless of preparation methods, and selectivity to cyclohexanone was very high for all Cu/SiO₂ catalysts.     

Low-temperature catalytic combustion of chlorobenzene over MnOx–CeO2 mixed oxide catalysts

MnO_x–CeO₂ mixed oxide catalysts prepared by sol–gel method were tested for the catalytic combustion of chlorobenzene (CB), as a model of chlorinated aromatic volatile organic compounds (CVOCs). MnO_x–CeO₂ catalysts with the different ratio of Mn/Ce + Mn were found to possess high catalytic activity for catalytic combustion of CB, and MnO_x(0.86)–CeO₂ was the most active catalyst, on which the complete combustion temperature (T_90%) of chlorobenzene was 236 °C. The stability of MnO_x–CeO₂ catalysts in the CB combustion was investigated. MnO_x–CeO₂ catalysts with high Mn/Ce + Mn ratios present high stable activity, which is related to their high ability to remove Cl species adsorbed and a large amount of active surface oxygen.     

Characterization of zirconium sulfate supported on TiO2 and activity for acid catalysis

A series of Zr(SO₄)₂/TiO₂ catalysts were prepared by impregnation of powder TiO₂ with an aqueous solution of zirconium sulfate. No diffraction line of zirconium sulfate was observed up to 30 wt%, indicating good dispersion of Zr(SO₄)₂ on the surface of TiO₂. The high catalytic activities of Zr(SO₄)2/TiO₂ for both 2-propanol dehydration and cumene dealkylation were related to the increase of acidity and acid strength due to the addition of Zr(SO₄)₂. Zr(SO₄)₂/TiO₂ containing 25% zirconium sulfate and calcined at 400 °C exhibited maximum catalytic activities for 2-propanol dehydration and cumene dealkylation. The catalytic activities for these reactions were correlated with the acidity of catalysts measured by the ammonia chemisorption method. This paper is dedicated to Professor Hyun Ku Rhee on the occasion of his retirement from Seoul National University.     

High activity Ni/MoS2 catalysts obtained from alkylthiometalate mixtures for the hydrodesulfurization of dibenzothiophene

An efficient method for improving the catalytic properties of unsupported Ni/MoS₂ catalysts is mixing thiometalate precursors applying the appropriate precursors and thermal conditions. High active catalysts for the hydrodesulfurization (HDS) of dibenzothiophene (DBT) are prepared by the controlled decomposition of physical mixtures of Ni(diethylentriamine)₂MoS₄ (NDTA-TM) and [(Propyl)₄N)]₂MoS₄ (TPA-TM). The catalysts with a higher content of NDTA-TM are very active with a high selectivity for the direct desulfurization pathway (DDS) due to the synergistic effect of nickel. In addition the presence of a large amount of carbon may produce single-slabs of nickel promoted carbon containing molybdenum sulfides. The activity enhancement is attributed to an increased number of NiMoS active sites originated by the chemical interaction between the precursors NDTA-TM and TPA-TM during the mixing procedure. Furthermore, the carbon content in the final products is related to the enhancement of the activity and the preference of the DDS pathway. The controlled decomposition of mixtures of NDTA-TM + TPA-TM yields catalysts which are about twofold more active than an industrial NiMo/Al₂O₃ catalyst. This improvement may be attributed to an intense interaction of the precursors during the synthesis causing a re-dispersion of nickel atoms from NDTA-TM over the surface of carbon containing molybdenum sulfide provided by the precursor TPA-TM, increasing the amount of active sites. The catalysts from mixtures of (NH₄)₂MoS₄ (A-TM) and NDTA-TM behave similarly to the pure precursors.     

Polystyrene and silica gel supported AlCl3 as highly chemoselective heterogeneous Lewis acid catalysts for Friedel–Crafts sulfonylation of aromatic compounds

Crosslinked polystyrene supported AlCl₃ (Ps–AlCl₃) and silica gel supported AlCl₃ (SiO₂–AlCl₃) have shown to be mild and chemoselective heterogeneous Lewis acid catalysts for the sulfonylation of different kinds of aromatic compounds with p-toluene sulfonyl chloride (TsCl) and benzene sulfonyl chloride (PhSO₂Cl) as sulfonylating agents. These solid acid catalysts are stable (as bench top catalysts) and can be easily recovered and reused without appreciable change in their efficiency.     

Catalytic Properties of Cr2O3 Doped with MgO Supported on MgF2 and Al2O3

Catalytic properties of Cr₂O₃ supported on MgF₂ or Al₂O₃ have been modified by magnesium oxide. The catalysts have been obtained by the co-impregnation method and characterised by: BET, XRD and TPR. As follows from the results, the oxides supported on magnesium fluorine react with each other already at 400 °C, leading to formation of an amorphous spinel-like phase. On the Al₂O₃ support such an MgCr₂O₄ spinel has appeared at much higher temperatures. The addition of magnesium oxide has a significant effect on the activity and selectivity of the catalysts studied in the CO oxidation reaction at room temperature and in the reaction of cyclohexane dehydrogenation. The magnesium–chromium catalysts supported on MgF₂ have been found to show much higher activity and selectivity than the analogous systems supported on Al₂O₃.