Hydrodechlorination of chlorophenols over Pd catalysts supported on zeolite Y,MCM-41 and graphene

Hydrodechlorination (HDC) reaction of chlorophenols was carried out using Pd catalysts supported over zeolite Y, MCM-41 or graphene. Pd-MCM-41 and Pd-Y zeolite were prepared by impregnation and ion-exchange method, respectively. Pd-graphene (Pd-G) was prepared by hydrazine hydrate reduction of palladium ion dispersed on graphene oxide. The catalysts were characterized by several analytical tools such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDS). These catalysts were subjected to HDC reaction of chlorophenols, such as 4-chlorophenol (4-CP), 2,4-dichlorophenol (2,4-DCP), 2,6-dichlorophenol (2,6-DCP) and 3,4-dichlorophenol (3,4-DCP). The reaction rate of HDC of chlorophenols catalyzed by Pd catalysts with various solid bases, such as KF/Al₂O₃ (alumina), sodium acetate (NaOAc) and K₂CO₃ was compared. First, Pd-MCM-41 and Pd-Y catalysts were compared. 2,4- and 3,4-DCPs were completely decomposed within 6 h, in the case of Pd-MCM-41 with NaOAc. Using Pd-Y instead of Pd-MCM-41 with NaOAc, much faster decomposition was observed. Faster decomposition of 4-CP and DCPs was observed with NaOAc base than K₂CO₃ or KF/Al₂O₃ under the same condition. In the case of Pd-Y with KF/Al₂O₃, slower decomposition of 4-CP and DCPs was observed. These base effects were interpreted using the solubility of NaCl and KCl in alcohol and the basic sites of KF/Al₂O₃. Because the solubility of NaCl is known to be larger than KCl solubility in alcohol, byproduct NaCl could be easily dissolved and ionized in solvents. For Pd-Y with KF/Al₂O₃, the small pore size of Y zeolite can interfere with the diffusion of HCl to KF/Al₂O₃ basic site. Second, three catalysts, including Pd-graphene, were compared. 2,4-DCP was decomposed within 2 h using Pd-G with either K₂CO₃, NaOAc or KF/Al₂O₃. Pd-G catalyst showed the highest catalytic activity among Pd-G, Pd-MCM-41 and Pd-Y catalysts. The high activity and stability of the Pd-G could be attributed to the strong metal–support interaction with an electron-deficient site and a critical Pd particle size (ca. 3.5 nm) of Pd-G nanocatalyst with a stronger resistance to the deactivation and good affinity toward aromatic organic molecules, especially phenols. The progress of HDC reaction was monitored by gas chromatography with flame ionization detection (GC/FID), and a feasible degradation process could be explained by analyzing the degradation products such as phenol, cyclohexanone and cyclohexanol from resulting GC chromatograms. The effect of reaction temperature on HDC in Pd-G catalyst was also discussed. In conclusion, Pd-G is an efficient catalyst for decomposition of chlorophenols and can be applied to remediation of chlorophenol-contaminated water under mild conditions.     

新型介孔分子筛KIT-1加氢脱硫催化剂的研究

制备了新型的结构排列无序的介孔分子筛KIT-1和负载Ni, Mo的KIT-1加氢脱硫催化剂。实验结果表明MoO3较易分散在KIT-1的表面,而NiO则容易在其表面形成小晶粒。与以MCM-41和NaY分子筛为载体的Ni, Mo催化剂相比, KIT-1负载催化剂具有较高的加氢脱硫催化活性,因为KIT-1载体具有相互交错的三维孔道结构, 有利于反应物和产物的扩散, 而不容易受孔道堵塞的影响。     

载体性质对Pd催化剂加氢脱硫性能的影响

以Si O2、全硅MCM-41(Si-MCM-41)、通过机械混合Si-MCM-41与ZSM-5得到的Z-MCM-41-M以及通过在ZSM-5外部包覆MCM-41制备得到的Z-MCM-41四种材料为载体,制备了四种负载型Pd催化剂。采用XRD、HRTEM、N2吸附-脱附、NH3-TPD手段对Pd催化剂进行了表征;以二苯并噻吩(DBT)为模型化合物,在固定床反应器上对四种催化剂的加氢脱硫(HDS)活性、加氢路径选择性和加氢裂化活性进行了考察,研究了不同类型载体对Pd催化剂加氢脱硫性能的影响。结果表明,载体的性质会显著影响负载型Pd催化剂的加氢脱硫性能。载体的比表面积对负载型Pd催化剂加氢脱硫活性影响不大,但是HYD路径的选择性与载体的孔道结构有关;具有介孔孔道结构有利于加氢路径选择性的提高。酸性载体负载的Pd催化剂表现出较好加氢脱硫活性和加氢选择性,这与氢溢流有关。介孔材料的孔道结构与微孔沸石的酸性有机结合,所得到的Z-M CM-41复合材料是是潜在的贵金属Pd加氢脱硫催化剂优良载体,可有效提升其加氢脱硫活性。     

Beta zeolite colloidal nanocrystals supported on mesoporous MCM-41

Zeolite-based composite materials prepared by the embedding of the beta zeolite nanophase from aqueous colloidal solution into matrices of preformed Si(Al)MCM-41 mesoporous molecular sieves have been characterized by different methods (XRD, SEM, FTIR, N2 adsorption, and TPD of NH3). Their potential as catalysts for toluene disproportionation has been compared to mechanical mixtures of freeze-dried nanobeta crystallites with Si(Al)MCM-41 mesoporous materials. It is found that the zeolite catalyst efficiency is not substantially changed by the presence of mesopores belonging to the matrix. It is suggested that formation of intergrown aggregates from the colloidal nanobeta particles provides own highly developed textural mesoporosity that makes the contribution of the diffusional alleviation of the support negligible.     

The studies of hydrodesulfurization activity over molybdenum catalysts supported on Al-MCM-41 modified by lanthanum

A series of lanthanum modified Al-MCM-41 substrates served as supports to prepare the Mo/La-Al-MCM-41 catalysts. The catalysts were characterized by XRD, BET, FT-IR, XPS, TPR and TPD, and their catalytic activities were determined for thiophene hydrodesulfurization (HDS).     

Size effects in the CO-oxidation over supported Pd particles

Low pressure CO oxidation was studied over small supported Pd particles by means of static secondary ion mass spectrometry (SSIMS). The SSIMS spectra of adsorbed layers on Pd particles with diameters below ～7nm contained, besides other species, Pd _n X⁺ ions (X=C, O, CO;n=1–3). In experiments with Pd films, Pd _n C⁺ species were much less abundant or even absent from the mass spectra. We conclude that CO decomposed in appreciable amounts only on Pd particles. No significant influence of the support material (mica, MgO,α-Al₂O₃) was seen and posthumous TEM analysis revealed well defined particle morphologies with largely (111) and (100) facets. At total pressures below 10^?4 Pa, the relative carbidic intensities Pd _n C⁺/Pd _n ⁺ , which were taken as proportional to the carbon surface concentrations, first increased with increasing temperatures and then decreased after they passed a maximum at T=400–440 K. The smaller the particle size, the more intense were the maxima. For T ?440 K, carbon was removed from the surface via reaction with oxygen. Strong hysteresis effects in the C_ad and CO_ad concentrations occurred during temperature variation measurements. The Pd _n C⁺/Pd _n ⁺ ratios displayed maxima during heating but not during cooling. While the Pd _n CO⁺/Pd _n ⁺ ratios were always high at 300 K and always low at T>550 K, they were more intense in the medium temperature range when subjecting the samples to heating. These hysteresis effects are discussed in terms of asymmetric adsorption and reaction behaviour of CO/O₂ mixtures, involving inhibition of CO₂ formation by adsorbed carbon and carbon monoxide.     

含镍Y沸石的硫化及加氢脱硫性能

本文制备了不同形态的含镍Y沸石, 研究了温度, 时间和H~2S浓度对含镍Y沸石硫化的影响, 发现负载型含镍Y沸石最易硫化, 离子交换型次之, 骨架型最难硫化。考察了沸石表面硫化物物种的热稳定性和水热稳定性。指出高温下沸石脱附的水蒸汽能使硫化物发生水解, 导致催化剂失硫。用XRD, IR和化学分析等方法对硫化的含镍沸石催化剂进行表征, 硫化后沸石表面形成的NiS~x有可能是属正交晶系的Ni~7S~6化合物。对噻吩加氢脱硫反应, 硫化的含骨架镍Y沸石无催化活性, 硫化的离子交换型含镍Y沸石活性比负载型含镍Y沸石高5-6倍左右, 因其酸性较强。催化剂表面酸性位和硫化镍活性位共存, 对噻吩加氢脱硫反应是有利的。     

Reduction of benzylideneaniline over supported Pd catalysts

In this work we have carried out a study on the liquid phase hydrogenation of benzylideneaniline, using dihydrogen over various supported Pd catalysts. Benzyl-ideneaniline reduction can be classified as insensitive to the catalyst structure. On the other hand, no compensating effect has been observed in performing the reaction over different supported Pd catalysts.

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Hydrogenolysis of glycerol over HY zeolite supported Ru catalysts

An enhanced active and selective catalyst consisting of ruthenium supported on dealuminated HY zeolite has been prepared by a wet impregnation method. It was found that BET surface area of Ru/HY catalysts significantly increases after HCl treatment. This treatment also increases the concentration of strong acid sites in the catalyst. The hydrogenolysis of glycerol over 5 wt% Ru/HY catalyst was investigated at 190-220 ℃, an initial H2pressure of 3-6 MPa, and in 20 wt% glycerol aqueous solution. The results indicate that HCl treated Ru/HY catalyst shows higher activity compared with the untreated Ru/HY catalyst, and that the glycerol hydrogenolysis efficiency is influenced by the porosity and acidity of the support. A selectivity to 1,2-PDO of 81.3% at a glycerol conversion of 60.1% under 3 MPa H2pressure and 220 ℃ for 10 h was achieved over the modified Ru/HY catalyst with a 1.0 mol/L HCl treatment. It has also been shown that a longer reaction time, a higher temperature and a higher H2pressure have the positive effects on the glycerol hydrogenolysis efficiency of the enhanced Ru/HY.     

Development of a novel molecularly imprinted polymer for the retention of 4,6-dimethyldibenzothiophene

Several molecularly imprinted polymers (MIPs) for the retention of 4,6-dimethyldibenzothiophene (4,6-DMDBT) were prepared. The first was a polymer prepared non-covalently with methacrylic acid and ethylene glycol dimethacrylate polymerized in the presence of 4,6-DMDBT. After extraction of 4,6-DMDBT, the selectivity of the imprinted polymer was evaluated by HPLC and compared to a non-imprinted control polymer prepared without 4,6-DMDBT. The imprinted polymer retained 4,6-DMDBT slightly longer than the control polymer. The second polymer was prepared using nickel (II)-methacryloylhistidinedihydrate monomer which was combined with 4,6-DMDBT, and polymerized with ethylene glycol dimethacrylate. This is a novel use of this monomer for retention of sulfur-containing organic compounds. Selectivity for 4,6-DMDBT was much greater in this polymer compared to the first, and retention in acetonitrile was more than three times greater on the imprinted polymer compared to a control polymer. Results indicate the potential use of this novel MIP for the removal of organosulfur compounds from fuel.

Hydrocarbons from synthesis gas over Pd supported on silica-alumina catalyst

We have studied the operational conditions which allow the synthesis gas to hydrocarbon transformation in only one step using Pd supported over an amorphous silica-alumina catalyst. The increase of temperature, pressure and time factor favors carbon monoxide conversion. Methanol synthesis reaction can be considered as the limiting step of the overall process. The product distribution is governed by the reaction medium (type and distribution of active sites and the presence of hydrogen).     

Photocatalytic activity of different morphology BiPO_4 supported on zeolite

Highly efficient sheet-like Bi PO_4/zeolite and ball-flower-like Bi PO_4/zeolite had been successfully synthesized by a standard hydrothermal method.The addition of assistant reagent in the hydrothermal system is promising to obtain special morphology.The assistant reagent(EDTA) acts as a growth modifier of crystal.The possible formation mechanisms of sheet-like Bi PO_4/zeolite and ball-flower-like Bi PO_4/zeolite were schematically discussed.A detailed study of sheet-like Bi PO_4/zeolite and ball-flower-like Bi PO_4/zeolite impacted on the photodecoloration methylene blue(MB) solution showed that the composite had a highly reusable and stable property for long-run photocatalytic application.     

Toluene total oxidation over Pd and Au nanoparticles supported on hydroxyapatite

The total oxidation of toluene was carried out in a series of catalytic systems composed of either palladium or gold, as active phase, with hydroxyapatite as supports. The influence of different parameters on the catalytic reactivity was investigated: the type of support, the active phase content, the preparation method, and the nature of the active phase. Hydroxyapatite supports, impregnated by the active phase, showed better reactivities than that of the classical alumina one. Moreover, low palladium content (0.25 wt%) is enough to get high toluene conversions at low temperatures. Two preparation methods were used to introduce the active phase on the support: the conventional wet impregnation and the nanoparticle deposition achieved by impregnation of a colloidal suspension of the noble metal using the surfactant HEA16Cl. Introducing palladium by either of these methods leads to similar catalytic efficiencies. In addition to this, palladium is much more active than gold, gold was not probably present under the form of highly dispersed nanoparticles. X-ray Photoelectron Spectroscopy (XPS) evidenced PdO presence on the surface of all our catalysts. Palladium impregnated on apatite by conventional method showed an improvement of catalytic reactivity after 13 h under reacting mixture, probably because of Pd(0) formation besides PdO. As a result and after a literature survey, our catalysts could be classified among the most reactive systems towards total oxidation of toluene.     

Oxidation with MnO2 supported on Y,FAU zeolite

MnO₂ supported on Na-Y,FAU prepared as described in a previous paper has been tested for selective oxidation of benzyl alcohol to benzaldehyde. Experimental results have shown that oxidation is selective and stoichiometric under the conditions used, but the adsorption of the substrate and/or the product on the zeolite support decreases the yield of benzaldehyde.

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Catalytic activity of palladium supported on mesoporous modified Y-zeolite in methane combustion

Palladium-based catalysts were prepared by the ion-exchange method with dealuminated HY zeolite as support. The support dealumination was realised using acid solution of HNO₃, HCl or H₂SiF₆. The high activity of prepared catalysts for methane combustion was observed. This activity was dependent on the Al concentration, structural and textural properties of the support changed after the dealumination. Especially, Pd loaded on supports developing a second pore system, and having the highest Si/Al ratio, was more active than that on unmodified supports. It was also expected that the active sites in the methane combustion, which are suspected to be PdO, were influenced by the acidic properties of the support.     

Simple preparation and catalytic activity of Pd particles dispersed mesoporous carbons from poly(VDC/MA) containing Pd and Y compounds

We report a simple preparation of Pd particles dispersed mesoporous carbons. The carbons were prepared by steam activation of carbonized vinylidene chloride/methyl acrylate copolymer (poly(VDC/MA)) containing yttrium acetylacetonate (Y(acac)(3)) and palladium acetylacetonate (Pd(acac)(2)). The resulting carbons consist of high contents of mesopore and uniformly dispersed fine Pd particles. We measured the catalytic activities of the carbons obtained for hydrogenation of methyl linoleate. The Pd particles dispersed in mesoporous activated carbons obtained from poly(VDC/MA) containing both Y(acac)(3) and Pd(acac)(2) showed high catalytic activities, compared with the microporous activated carbon obtained from poly(VDC/MA) containing only Pd(acac)(2). Especially Pd particles dispersed in mesoporous carbons exhibited excellent selectivity for hydrogenation of diene (methyl linoleate) to monoene (methyl oleate).     

Catalytic performances of heteropoly compounds supported on dealuminated ultra-stable Y zeolite for liquid-phase esterification

Carboxylic ester is one of the important fine chemicals, which is usually synthesized with various mineral acids as catalysts, such as H2SO4, HF, H3PO4, etc. But these liquid catalysts are toxic, corrosive and often hard to be recovered from the reaction …     

Hydrogenation of chloronitrobenzenes over Pd and Pt catalysts supported on cationic resins

Liquid phase hydrogenation of chloronitrobenzene isomers (x-CNB x = 2, 3, 4) to the corresponding chloroanilines (x-CAN) at mild reaction conditions (0.6 MPa, 25°C, diethyl ether-methanol as solvents) over palladium and platinum catalysts containing 1 mass % of metal on trimethylammonium functionalized poly{styrene-co-divinylbenzene} (Dowex-D) was studied. The average selectivities to x-CAN over Pd/D-Cl and Pd/D-OH catalysts were 72 % and 42 %, respectively, at the x-CNB conversion of about 80 %. The average selectivities of 81 % and 84 % were achieved using Pt/D-Cl and Pt/D-OH, respectively, at the x-CNB conversion of approximately 90 %, whereas the average starting reaction rates were 1.2 × 10^?3 mol g^?1 s^?1 and 2.6 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of platinum), respectively. Under similar reaction conditions, using palladium catalysts supported on a resin with anionic groups anchored to polymeric chains at the average reaction rate equal to 3.8 × 10^?3 mol g^?1 s^?1 (hydrogen consumption rate per mass of palladium), the selectivities from 85 % (2-CAN and 3-CAN) to 95 % (4-CAN) were achieved (Kratky et al., 2002).