Synthesis of pyridine and picolines over modified silica-alumina and ZSM-5 catalysts

In the reaction of acetaldehyde, formaldehyde and ammononia over HZSM-5 (Si/Al-280), PbZSM-5 and WZSM-5 catalysts at 420°C, 0.5 h^–1 weight hourly space velocity, the total yields of pyridine and 3-picoline obtained were 58.2, 42.8 and 78.3 wt.% based on aldehydes, respectively. In the reaction of acetaldehyde and ammonia over typical Pb–SiO₂–Al₂O₃ (20% PbO), W–SiO₂–Al₂O₃ (10% W), Pb–Cr–SiO₂–Al₂O₃ (F) and Pb–Cu–SiO₂–Al₂O₃ (E) catalysts at 420°C, 0.5 h^–1 W.H.S.V., the yields of 2- and 4-picolines obtained were 51.1, 66.1, 80.6 and 53.7 wt.%, respectively.IICT Communication No. 3421, — dedicated to Dr. A.V. Rama Rao on his 60th birthday.     

Influence of the Charge Transfer Capacity of Alkali and Alkaline Earth Metals as Promoters in Thehydrogenation of Phenol over Palladium and Nickel Catalysts

The gas phase hydrogenation (523-573 K) of phenol has been studied over 1 wt.% Pd/Al₂O₃ and 1 wt.% Ni/SiO₂ catalysts doped with Group I and II promoter oxides. A direct correlation between catalytic activity and the charge transfer capacity of the promoters is presented where hydrogenation is favored by increasing electron donation from the promoter. The Pd catalysts generated cyclohexanone (selectivity > 97%) as the predominant product; selectivity was unaffected by the presence of the alkali or alkaline earth dopants. The Ni system exhibited appreciable hydrogenolysis behavior and charge transfer from the dopants limited the degree of hydrodeoxygenation to favor complete hydrogenation to cyclohexanol.     

浸渍法制备的Pd-MnO_x/γ-Al_2O_3催化剂及不同载体对地表O_3降解的影响(英文)

在γ-Al2O3载体上用等体积浸渍法浸渍Pd、MnOx活性组分,然后涂覆于堇青石基体上制备Pd-MnOx/γ-Al2O3整体式催化剂.分别用X射线衍射(XRD)、H2-程序升温还原(H2-TPR)、低温N2吸附-脱附及X射线光电子能谱(XPS)对制备的催化剂进行表征.研究了Pd、MnOx浸渍顺序对催化剂活性、氧化还原性能及织构性质的影响.实验结果表明,Pd、MnOx共浸渍较分别浸渍制备的催化剂活性好,Pd和MnOx之间存在一定的协同作用.考察了不同载体如La-Al2O3、SiO2、γ-Al2O3和Zr-Al2O3对催化剂活性、氧化还原性能、织构性质及表面电子性能的影响.研究表明,以La-Al2O3或SiO2为载体的催化剂活性最好,即,14°C时O3转化率为82%,完全转化温度为36°C.γ-Al2O3载体次之,Zr-Al2O3载体较差.不同载体制备的催化剂中MnOx的氧化还原性能顺序为:PdMnOx/SiO2Pd-MnOx/La-Al2O3Pd-MnOx/γ-Al2O3Pd-MnOx/Zr-Al2O3.     

Effect of the oxidation state of manganese in the manganese oxides used in the synthesis of Mn-substituted cordierite on the properties of the product

Catalysts based on Mn-substituted cordierite 2MnO · 2Al₂O₃ · 5SiO₂ have been synthesized using different manganese oxides (MnO, Mn₂O₃, and MnO₂) at a calcination temperature of 1100°C. The catalysts differ in their physicochemical properties, namely, phase composition (cordierite content and crystallinity), manganese oxide distribution and dispersion, texture, and activity in high-temperature ammonia oxidation. The synthesis involving MnO yields Mn-substituted cordierite with a defective structure, because greater part of the manganese cations is not incorporated in this structure and is encapsulated and the surface contains a small amount of manganese oxides. This catalyst shows the lowest ammonia oxidation activity. The catalysts prepared using Mn₂O₃ or MnO₂ are well-crystallized Mn-substituted cordierite whose surface contains different amounts of manganese oxides differing in their particle size. They ensure a high nitrogen oxides yield in a wide temperature range. The product yield increases with an increasing surface concentration of Mn³⁺ cations. The highest NO_x yield (about 76% at 800–850°C) is observed for the MnO₂-based catalyst, whose surface contains the largest amount of manganese oxides.     

Characterization of La-promoted Ni/Al2O3 catalysts for hydrogen production from glycerol dry reforming

In the current paper, dry (CO₂)-reforming of glycerol, a new reforming route, was carried out over alumina (Al₂O₃)-supported, non-promoted and lanthanum-promoted nickel (Ni) catalysts. Both sets of catalysts were synthesized via a wet co-impregnation procedure. Physicochemical characterization of the catalysts showed that the promoted catalyst possessed smaller metal crystallite size, hence higher metal dispersion compared to the virgin Ni/Al₂O₃ catalyst. This was also corroborated by the surface images captured by the FESEM analysis. From temperature-programmed calcination analysis, the derivative weight profiles revealed two peaks, which represent a water elimination peak at a temperature range of 373 to 473 K followed by nickel nitrate decomposition from 473 to 573 K. In addition, BET surface area measurements gave 85.0 m²·g⁻¹ for the non-promoted Ni catalyst, whilst the promoted catalysts showed an average of 1% to 6% improvement depending on the La loadings. Significantly, reaction studies at 873 K showed that glycerol dry reforming successfully produced H₂. The 2%La-Ni/Al₂O₃ catalyst, which possessed the largest BET surface area, gave an optimum H₂ generation (9.70%) at a glycerol conversion of 24.5%.     

Catalytic ketonization over oxide catalysts, Part VI.a Cross-ketonization of aliphatic and aromatic esters

Activity of 20 wt.% MO₂/Al₂O₃ catalysts, where M = Mn, Ce and Zr has been studied in cross-ketonization of ethyl esters of aliphatic and aromatic acids in a flow system. Pentan-3-one and tridecan-7-one were formed in ketonization of pure aliphatic esters, ethyl propanoate and ethyl heptanoate. Benzene was obtained instead of diphenylmethanone as the product of ethyl benzoate transformations. Only two ketones, dialkyl and aralkyl, were obtained from the cross-ketonization of a mixture of aliphatic and aromatic esters. The highest yield of 1-phenyl-1-heptanone (70%) from ethyl heptanoate and ethyl benzoate was reached at 698 K in the presence of MnO₂/Al₂O₃ catalyst. Under similar conditions cross-ketonization of a mixture of ethyl propanoate and ethyl benzoate led to 1-phenyl-1-propanone (60% at 673 K).     

Catalytic Reactions of n-Propanol and n-Butanol with Hydrogen Sulfide

The transformations of n-propanol and n-butanol in an H₂S atmosphere at T = 300–350°C and P = 0.1 MPa in the presence of acid–base catalysts were studied. Only alcohol dehydration with the release of alkenes occurred at a high rate on catalysts with strong proton sites (tungstosilicic and tungstophosphoric acids on SiO₂ or a decationized high-silica zeolite), whereas alcohol thiolation with the formation of alkanethiols also occurred on catalysts with Lewis acid sites (Al₂O₃; NaX; MgO; Cr/SiO₂; and Al₂O₃ modified with W, K, Na, K₂WO₄, or Na₂WO₄). The rate of reaction decreased with decreasing strength of Lewis acid sites and with increasing strength of basic sites; however, the selectivity of thiol formation increased. Alumina modified with alkaline additives was the most selective catalyst. In the presence of this catalyst, an alcohol selectively reacted with H₂S to form an alkanethiol, and the alkanethiol underwent partial decomposition with the release of an alkene and H₂S at a long contact time.     

Styrene polymerization in the presence of the CpTiCl3/Al2O3–SiO2/MAO catalytic system

Syndiotactic polymerization of styrene in the presence of heterogenized hemititanocene catalysts CpTiCl₃/Al₂O₃–SiO₂/MAO (Cp = cyclopentadienyl; MAO = methylaluminoxane) showed that the yield and selectivity of this reaction depend on the support composition, i.e. on the Al₂O₃ content in the support. The most active catalysts contained Al₂O₃ in a quantity of 50 to 70 wt%. Despite a relatively lower selectivity of 75–59%, the amount of syndiotactic polystyrene in the presence of those catalysts was the greatest. Copyright © 2002 John Wiley & Sons, Ltd.     

Hydrogenolysis of hexane on supported rhodium catalysts

Hexane was reacted in mixtures with excess hydrogen on 5% Rh on different supports: Al₂O₃ and SiO₂, the latter catalyst in two states: after reduction at 603 K (LT) and after a prereduction at 1253 K (HT). The main reaction was hydrogenolysis. The catalysts were characterized with the fragment composition at different temperatures and hydrogen pressures. Two surface states could be distinguished: one with more hydrogen favored single rupture, the other with less hydrogen preferred multiple fragmentation. The transition between these states could be rather abrupt, as the surface hydrogen availability changed. The tendency to produce multiple fragments increased in the order Rh/Al₂O₃< Rh/SiO₂-LT < Rh/SiO₂-HT.     

Electron Paramagnetic Resonance Study on Supported Molybdenum Catalysts. Part 1: Interaction of Molybdenum Oxide with Silica and Signal Anlsotropy

The effects of reduction, evacuation and adsorbate adsorption on Mo/SiO₂ catalysts prepared by impregnation were studied by means of the electron paramagnetic resonance (EPR) technique. Pentavalent molybdenum species in the overlayer (Mo₀⁵⁺, g? = 1.941, g| = 1.895) and at the interface (Mo_i⁵⁺, g? = 1.952, g| = 1.866) between MoO₃ and SiO₂ were distinguished in the EPR spectra; they were observed from samples reduced at T < 573 K and T > 573 K respectively. The difference in their nature reflected the extent of their interaction with the support. Mo₀⁵⁺ existed in the MoO3 overlayer of the catalyst and interacted only weakly with the support. Mo_i⁵⁺ from the Mo ions connected directly to SiO₂ was affected strongly by the support. The anisotropic factor of the measured Mo_i⁵⁺ signals increased with the extent of support interaction. Superoxide ions (O₂, g₁ = 2.016, g₂ = 2.011, g₃ = 2.006) were found upon oxygen adsorption on samples evacuated at temperatures above 573 K. The observed O₂ may exist at the interface between MoO₃ and the support.     

Bifunctional catalysis of Mo/HZSM-5 in the dehydroaromatization of methane with CO/CO2 to benzene and naphthalene

The catalytic dehydrocondensation of methane to aromatics such as benzene and naphthalene was studied on the Mo carbide catalysts supported on micro- and mesoporous materials such as HZSM-5 (0.6 nm) and FSM-16 (2.7 nm). The Mo catalysts supported on H-ZSM-5 having appropriate micropores (0.6 nm size) and Si/Al ratios (20-70) exhibit higher yields (90-150 nmol/g-cat/s) and selectivities (higher than 74% on the carbon basis) in methane conversion to aromatic products such as benzene and naphthalene at 973 K and 1 atm, although they are drastically deactivated because of substantial coke formation. It was demonstrated that the CO/CO₂ addition to methane effectively improves the catalyst performance by keeping a higher methane conversion and selectivities of benzene formation in the prolonged time-on-stream. The oxygen derived from CO and CO₂ dissociation suppresses polycondensation of aromatic products and coke formation in the course of methane conversion. XAFS and TG/DTA/mass-spectrometric studies reveal that the zeolite-supported Mo oxide is endothermally converted under the action of methane around 955 K to nanosized particles of molybdenum carbide (Mo₂C) (Mo-C, coordination number = 1,R- 2.09 å; Mo-Mo, coordination number = 2.3–3.5;R = 2.98 å). The SEM pictures showed that the nanostructured Mo carbide particles are highly dispersed on and inside the HZSM-5 crystals. On the other hand, it was demonstrated by IR measurements of pyridine adsorption that the Mo/HZSM-5 catalysts having the optimum SiO₂/Al₂O₃ ratios around 40 show the maximum Brönsted acidity among the catalysts with the SiO₂/Al₂O₃ ratios of 20–1900. There is a close correlation between the activity of benzene formation in the methane aromatization and the Brönsted acidity of HZSM-5 due to the bifunctional catalysis.     

On the characterization of surface VOx-species by XPS: layered oxidic systems as model catalysts

Summary The influence of the support on vanadia, immobilized on Au, SiO₂, Al₂O₃ and TiO₂, suitable for the selective catalytic reduction (SCR) of nitric oxide by ammonia has been investigated. The layered oxidic substrates, which are deposited onto gold coated silicon wafers, represent model systems for the surfaces of technical SCR catalysts, that are suitable for surface science investigations. The oxidation states of the surface vanadia species immobilized on these samples have been studied by XPS after well-defined sample treatment in both oxygen and hydrogen atmospheres at 573 K and 723 K. From the observed shifts of the V 2p_3/2 binding energies, and from peak deconvolution, vanadia layers on gold, silica and alumina are found to exhibit characteristics similar to those of bulk vanadia. This behavior is characterized by the relative stability against a reductive atmosphere at 573 K. Changes in the oxidation states of the surface vanadia species are prominent only after treatment at 723 K. Titania exhibits a unique support interaction with vanadia which allows the reduction of vanadia at temperatures as low as 573 K. This fact may contribute to the outstanding performance of VO_x/TiO₂ in the selective reduction of nitric oxide by ammonia in waste gases.     

Effect of ultra-fine gold particle addition to metal oxides in ethylene oxidation

Oxidation of ethylene was carried out over alumina-supported metal oxide catalysts and highly dispersed gold catalysts, respectively, under atmospheric pressure. The ethylene was completely oxidized to produce carbon dioxide and water with both metal oxide and gold catalysts. The activity of gold catalyst prepared by deposition method was much higher than that of supported metal oxide catalysts. Ultra-fine gold particles on Co₃O₄ were more active than on Al₂O₃. Fe₂O₃/Al₂O₃ and MnO₂/Al₂O₃ catalysts were more active than MoO₃/Al₂O₃ catalyst. The activity of the supported metal oxide catalysts was greatly enhanced by addition of gold particles. It was therefore considered that gold particles promote dissociative adsorption of oxygen and the adsorbed oxygen reacts with adsorbed ethylene on support adjacent to the active site.     

Nonoxidative methane conversion into aromatic hydrocarbons on tungsten-containing pentasils

The effects of the tungsten concentration and of the method of tungsten introduction into ZSM-5 pentails with different SiO₂/Al₂O₃ molar ratios on the acidity and the activity of the resulting catalysis in nonoxidative methane conversion into aromatic hydrocarbons are considered. The catalysts obtained from the SiO₂/Al₂O₃ = 40 pentasil and a nanosized tungsten powder are the most active and the most stable. The maximum methane conversion and the highest yield of aromatic hydrocarbons are achieved on the zeolite containing 8.0 wt % tungsten nanopowder.     

Nature of condensation products in but-1-ene aromatization on high-silica zeolite catalyst

The aromatization of but-1-ene on the H-form of pentasil-type zeolite catalyst (SiO₂/Al₂O₃ = 54) is studied in the temperature range from 573 to 723 K. It is shown that in the range of 623 to 723 K, the liquid phase consists mainly of aromatic hydrocarbons. The results from differential thermal and X-ray diffraction analyses show that graphite-like depositions can form in zeolite channels during the conversion of but-1-ene on the H-form of zeolite catalyst at 673 K and more than 20 h. The activity of the catalyst remains virtually the same.     

Fischer–Tropsch Synthesis by Carbon Dioxide Hydrogenation on Fe-Based Catalysts

Impregnated and co-precipitated, promoted and unpromoted, bulk and supported iron catalysts were prepared, characterized, and subjected to hydrogenation of CO₂ at various pressures (1–2 MPa) and temperatures (573–673 K). Potassium, as an important promoter, enhanced the CO₂ uptake and selectivity towards olefins and long-chain hydrocarbons. Al₂O₃, when added as a structural promoter during co-precipitation, increased CO₂ conversion as well as selectivity to C₂₊ hydrocarbons. Among V, Cr, Mn and Zn promoters, Zn offered the highest selectivity to C₂–C₄ alkenes. The different episodes involved in the transformation of the catalyst before it reached steady-state were identified, on the co-precipitated catalyst. Using a biomass derived syngas (CO/CO₂/H₂), CO alone took part in hydrogenation. When enriched with H₂, CO₂ was also converted to hydrocarbons. The deactivation of impregnated Fe–K/Al₂O₃ catalyst was found to be due to carbon deposition, whereas that for the precipitated catalyst was due to increase in crystallinity of iron species. The suitability of SiO₂, TiO₂, Al₂O₃, HY and ion exchanged NaY as supports was examined for obtaining high activity and selectivity towards light olefins and C₂₊ hydrocarbons and found Al₂O₃ to be the best support. A comparative study with Co catalysts revealed the advantages of Fe catalysts for hydrocarbon production by F–T synthesis.     

Phosphorus pentoxide supported on silica gel and alumina (P2O5/SiO2, P2O5/Al2O3) as useful catalysts in organic synthesis

Phosphorus pentoxide supported on silica gel or alumina (P₂O₅/SiO₂, P₂O₅/Al₂O₃) has been used in many organic transformations as versatile solid catalysts. These catalysts have received considerable attention as an inexpensive, eco-friendly, highly reactive, easy to handle and non-toxic acid catalyst for various organic transformations, affording the corresponding products in excellent yields and high selectivity. In this review, some applications of these catalysts in organic reactions are discussed.     

Highly Selective Aldol Condensation Using Amine-functionalized SiO2-Al2O3 Mixed-oxide under Solvent-free Condition

A series of amine catalysts supported on mesoporous molecular sieves SiO₂/Al₂O₃ with trimethoxysilylpropylamine [(CH₃O)₃Si(CH₂)₃NH₂] loading varying from 3 mmol to 6 mmol were synthesized by impregnation method. The aldol condensation of various aromatic aldehydes and 1‐heptanal was used to test the acid‐base cooperativity of amine‐functionalized SiO₂/Al₂O₃. The effects of solvent, reaction temperature, benzaldehyde to 1‐heptanal molar ratio, different supports (SiO₂, Al₂O₃ and SiO₂‐Al₂O₃), catalyst amount and recyclability of the catalyst were investigated. Sample containing 5 mmol amine loaded showed highest benzaldehyde conversion (100%) and selectivity (97%) for jasminaldehyde.     

Enantioselective properties of asymmetric supported Ni and Ni-Co catalysts in the hydrogenation reaction of ethyl acetoacetate

The influence of the metal content on the support, the conditions of the preparation of the catalysts, and the reaction conditions on the enantioselectivity of the liquid-phase hydrogenation reaction of ethyl acetoacetate in the presence of Ni and Ni-Co catalysts supported on Al₂O₃ and SiO₂, and modified by RR(+)-tartaric acid, was investigated. The maximal optical yield (66–76%) was obtained for the 20% Ni/Al₂O₃ catalyst.     

Fe- and Cu-oxides supported on γ-Al2O3 as catalysts for the selective catalytic reduction of NO with ethanol. Part I: catalyst preparation,characterization, and activity

Fe- and Cu-oxides supported on γ-alumina (γ-Al₂O₃; metal loading of 3 mass %) were investigated as alternative catalysts to the conventional Ag-based system in the selective catalytic reduction of NO with ethanol (EtOH-SCR). The catalysts were characterized by elemental analysis, N₂ sorption, X-ray diffraction, temperature-prgrammed desorption of NH₃, temperature-programmed reduction with H2, diffuse reflectance UV-VIS (DR-UV-VIS) spectroscopy, and compared with 3 mass % Ag/γ-Al₂O₃ as a reference catalyst. Catalytic experiments were carried out between 423 K and 773 K in the steady state and by temperature-programmed surface reaction (TPSR) experiments. For all catalysts, the highest NO conversion (900 ppm (ppm = parts of the mixture component per million parts of all mixture components) NO, 900 ppm EtOH, 0.5 vol. % H₂O, 4 vol. % O₂ in He) was found at 573 K. While 84 % of NO were converted over the Ag-based catalysts, only 20–60 % NO conversion was observed for the Fe- and Cu-containing catalysts. Total oxidation of ethanol as an unwanted side reaction occurs over 3 mass % Cu on γ-Al₂O₃ already at 573 K, whereas the highest activity of 3 mass % Fe on γ-Al₂O₃ for this conversion was reached at 743 K. For lower temperatures, partial oxidation of ethanol leads to organic by-products which can act as active intermediates in EtOH-SCR. TPSR experiments show that ethanol reacts over both the Fe- and the Cu-based catalysts to organic by-products, such as ethene or acetaldehyde, which affect the EtOH-SCR reaction.