Moti Herskowitz

Mesoporous alumina catalytic material prepared by grafting wide-pore MCM-41 with an alumina multilayer

Abstract An alumina multilayer grafted on the surface of MCM-41 produced a mesoporous material with the surface chemical functionality of alumina. The starting MCM-41 material (WPMCM) with a wide pore size distribution, a surface area of 858 m 2 /g, an average pore diameter of 8.2 nm and a pore volume of 1.75 cm 3 /g was synthesized by expanding the cetyltrimethylammonium chloride (CTAC) surfactant micelles with mesitylene at a high solubilizant/CTAC ratio of 10. Successive grafting consisting of aluminum butoxide anchoring followed by hydrolysis and calcination steps yielded a gradual increase of the aluminum content in WPMCM. Tetrahedral Al in the silica pore walls and clusters of a separate octahedral Al alumina phase were identified. Four grafting cycles produced a material with a surface area of 542 m 2 /g and a mean pore diameter of 4 nm containing 38 wt.% Al 2 O 3 that displayed chemical surface functionality of pure alumina. The activity of this material in the alkylation of phenol with methanol was 2.3 times higher than the activity of a reference alumina (460 m 2 /g). The highest activity of grafted alumina in cumene cracking and isopropanol dehydration was achieved at 21 wt.% Al 2 O 3 . Independent measurements of surface charging in aqueous solution, of [Mo 7 O 24 ] 6− anions adsorption and of surface acidity indicated that the material grafted with alumina and the reference alumina display similar chemical functionality.

Hierarchical Zeolitic Imidazolate Framework-8 Catalyst for Monoglyceride Synthesis

Metal–organic frameworks (MOFs) are heterogeneous porous catalysts with unprecedented catalytic functionality via coordinatively unsaturated metal nodes, provoked defects, organic functions of linker molecules, and intrinsic chirality. These materials are amenable to catalytic modification by means of encapsulation of nanoparticles, polyoxometalates, and porphyrins. MOFs have been demonstrated as active heterogeneous catalysts for various organic reactions, including acid–base and redox reactions, such as esterification, transesterification, epoxidation, alcoholysis, Knoevenagel condensation, 6] among others. The introduction of a secondary pore system, demonstrated to be advantageous in zeolite catalysis, is still in its infancy in the world of MOFs and might further lift the potential of MOF materials in catalysis. A very challenging area of heterogeneous catalysis is the synthesis of monoglycerides. Monoglycerides are produced according to two major routes: 1) direct esterification of fatty acid with glycerol and 2) transesterification of triglycerides with glycerol. Monoglycerides are popular natural emulsifiers in food and beverages, personal care products, and pharmaceuticals. According to a recent prediction, the global emulsifier market is primed to reach volume sales of 2.6 million metric tons by the year 2017. Industrial monoglyceride production is currently performed at high temperature (493–523 K) using a basic homogeneous catalyst with limited monoglyceride selectivity, owing to formation of diand triglyceride side products and soap. The high reaction temperature bears the risk of deterioration of taste, aroma, and color of the product. Developing a heterogeneous catalytic process at lower temperature for selective monoglyceride production is a major scientific challenge. We discovered nanoparticles of zeolitic imidazolate framework-8 (ZIF-8) transformed into hierarchical material through reaction with fatty acid to be a promising truly heterogeneous catalyst for monoglyceride synthesis. ZIFs possess excellent thermal stability up to 693 K and a tunable pore architecture. The ZIF-8 structure resembles sodalite with 1.16 nm wide cavities connected through 0.34 nm wide windows formed by four-ring and six-ring ZnN4 clusters. ZIF-8 is a promising material for gas separation, as well as for catalytic applications. ZIF-8 exhibits a unique pressure-induced change of pore size and amorphization. It has attractive tribological properties, and guest molecule trapping behavior. Immobilization of catalytically active nanoparticles, such as Pt, Ni, Au, and Co3O4, is a recent avenue in ZIF catalysis. ZIF-8 originally was synthesized via the solvothermal route from inorganic zinc compound and 2-methylimidazole in dimethylformamide (DMF) solvent and temperatures of 358–423 K. Alternative synthesis methods are precipitation from methanol or water solution at room temperature, steam-assisted synthesis, mechanochemical, and ultrasound treatment. Here we report another facile synthesis of ZIF-8 nanomaterial with large specific surface area and micropore volume. Nanosized ZIF-8 was prepared from a synthesis solution 2.2 times more concentrated than usual (see the Supporting Information for Experimental Details). The reproducibility was excellent. Phase purity was confirmed by XRD (Figure 1 a). The XRD pattern can be indexed with cubic unit cell parameter a = 1.710(5) nm, in agreement with literature. IR spectra further confirmed sample purity (Figure S1). SEM revealed a particle size of about 150 nm qualifying as nanomaterial (Figure 1 b). TGA in nitrogen (Figure S2) revealed this ZIF-8 nanopowder is stable till 723 K. The microporous nature of ZIF-8 is apparent from the Type 1 nitrogen adsorption isotherm (Figure 1 c). The BET and Langmuir specific surface area and micropore volume are 1388 m g , 2110 m g 1 and 0.78 cm g , respectively. These are high values for a nanosized ZIF-8 sample given that there were no chemical additives nor excess solvent used in the synthesis. [a] Dr. L. H. Wee, Prof. J. A. Martens Centre for Surface Science and Catalysis KU Leuven Kasteelpark Arenberg 23, Heverlee, B3001 (Belgium) Fax: (+ 32) 163-21998 E-mail : likhong.wee@biw.kuleuven.be johan.martens@biw.kuleuven.be [b] T. Lescouet, Dr. D. Farrusseng Institut de Recherche sur la Catalyse et l’Environnement de Lyon (IRCELYON), University Lyon 1, CNRS 2 Av. Albert Einstein, Villeurbanne, 69626 (France) [c] J. Ethiraj, Dr. F. Bonino, Prof. S. Bordiga NIS Centre of Excellence and INSTM Reference Centre Department of Chemistry, University of Turin Via Quarello 15, Turin, 10135 (Italy) [d] Dr. R. Vidruk, Prof. M. Herskowitz Blechner Center for Industrial Catalysis and Process Development Ben-Gurion University of the Negev Beer-Sheva (Israel) [e] Dr. E. Garrier, Dr. D. Packet Novance Rue les rives de l’Oise, Venette, B.P. 20609 Compiegne, Cedex, 60206 (France) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/cctc.201300581.

Magnetic properties of nanocrystalline La1- xMnO3+δ manganites : Size effects

The magnetic properties of nanocrystalline manganites La1?xMnO3+? with particle size of 20 (LMO20), 25 (LMO25), and 30 nm (LMO30), prepared by the citrate method, have been investigated in the temperature range 5?320?K, magnetic field up to 90?kOe and under quasi-hydrostatic pressures up to 14.5?kbar. The studies involve sequential zero-field-cooled magnetization (M) measurements followed by magnetization measurements during cooling in the same magnetic field (H) and complementary measurements of ac susceptibility. Additional measurements of M versus H were carried out at ambient and applied pressures. All nanoparticles exhibit a paramagnetic to ferromagnetic transition (PFT) at a Curie temperature TC>200?K. It was found that the relative volume of the ferromagnetic phase increases for larger particle size and approaches a value of about 93% for LMO30. The real part of the ac susceptibility of sample LMO20 exhibits strong frequency dependence in a wide temperature range below TC, whereas for sample LMO30 only relatively weak frequency dependence was observed. The magnetization of sample LMO30 exhibits a PFT of second order; the type of transition could not be established for the smaller particles. It was found that an applied pressure enhances the TC of La1?xMnO3+? nanoparticles with a pressure coefficient of dTC/dP?1.9?K?kbar?1 for LMO20 and dTC/dP?1.4?K?kbar?1 for LMO25 and LMO30 samples. Peculiar magnetic memory effects observed for sample LMO20 are discussed.

Selectivity in heterogeneous catalytic processes

Abstract The selectivity of several catalytic systems was studied. Shape selectivity of Pt on carbon-fiber catalysts was demonstrated in the competitive hydrogenation of 1-hexene and cyclohexene and in the parallel dehydrogenation of cyclohexanol to cyclohexanone and phenol. Both reactions were carried out in a gas-phase fixed-bed reactor. Catalysts prepared on carbon fibers, containing pores with small constrictions (5 A) yielded significantly higher rates of hydrogenation of 1-hexene compared to those of cyclohexene and selectively produced cyclohexanone from cyclohexanol. Other catalysts, supported on carbon fibers with large constrictions (7 A) or activated carbon, displayed comparable rates of hydrogenation for both reactants and yielded cyclohexanone as well as phenol from cyclohexanol. Nitration of o -xylene with nitrogen dioxide was carried out in the gas phase over a series of solid acid catalysts packed in a fixed bed. Several zeolites, supported sulfuric acid, and sulfated zirconia were tested. Zeolite H-β was found to be the most active and selective catalyst for the production of 4-nitro- o -xylene. A preliminary kinetic model indicated that the selectivity to 4-nitro- o -xylene increased with decreasing concentration of nitrogen dioxide. Alkylation of phenol with methanol was performed on zeolites, supported sulfuric and phosphoric acids, and sulfated zirconia packed in a fixed-bed. The ratio of o - to c -alkylation, measured at 180°C and methanol to phenol feed molar ratio of unity, ranged from 4 with the supported acids to 2 with zeolite H-β. This ratio decreased with temperature. The ratio of o - to p -cresol changed from about 2 in zeolites in supported sulfuric acid and to 0.5 in phosphoric acid supported on carbon fibers.

Magnetotransport in granular LaMnO3+δ manganite with nano-sized particles

Transport and magnetic properties of compacted LaMnO3+? manganite nanoparticles of an average size of 18?nm have been investigated in the temperature range 5?300?K. The nanoparticles exhibit a paramagnetic-to-ferromagnetic (FM) transition at the Curie temperature TC ~ 246?K. However, the spontaneous magnetization disappears at a higher temperature of about 270?K. It was found that at low temperatures the FM core occupies about 50% of the particle volume. The temperature dependence of the resistivity shows a metal?insulator transition and a low-temperature upturn below the resistivity minimum at T ~ 50?K. The transport at low temperatures is controlled by the charging energy and spin-dependent tunnelling through grain boundaries. It has been found that the charging energy decreases monotonically with increasing magnetic field. The low temperature I?V characteristics are well described by an indirect tunnelling model while at higher temperatures both direct and resonant tunnelling dominates. The experimental features are discussed in the framework of a granular ferromagnet model.

Sustainable Production of Green Feed from Carbon Dioxide and Hydrogen

Carbon dioxide hydrogenation to form hydrocarbons was conducted on two iron-based catalysts, prepared according to procedures described in the literature, and on a new iron spinel catalyst. The CO2 conversion measured in a packed-bed reactor was limited to about 60% because of excessive amounts of water produced in this process. Switching to a system of three packed-bed reactors in series with interim removal of water and condensed hydrocarbons increased CO2 conversion to as much as 89%. The pure spinel catalyst displayed a significantly higher activity and selectivity than those of the other iron catalysts. This process produces a product called green feed, which is similar in composition to the product of a high-temperature, iron-based Fischer–Tropsch process from syngas. The green feed can be readily converted into renewable fuels by well-established technologies.

Selective propane dehydrogenation to propylene on novel bimetallic catalysts

Abstract Platinum catalysts (0.1–0.2% of Pt) supported on corundum and promoted by indium and tin were prepared, characterized by XPS, XRD, TEM and chemisorption and tested in propane dehydrogenation at 500–580°C with steam and hydrogen as diluents. The characteristics of samples based on corundum were compared with catalysts of similar composition supported on θ-alumina. The catalytic performance in steam was superior by far to that in hydrogen. Coking of corundum-supported catalysts decreased by a factor of 30–60 so their stability was much higher than with θ-supported catalyst. For the first time high dispersion and high activity of corundum-based dehydrogenation catalysts are reported.

From macroalgae to liquid fuel via waste-water remediation, hydrothermal upgrading, carbon dioxide hydrogenation and hydrotreating

This article showcases a proof-of-concept in the production of high quality renewable biofuel from algae. Here, we introduce a path combining a number of approaches that, when integrated as a whole, create a process that takes algae grown in waste-water through to a liquid fuel containing fractions ready for blending with regular gasoline, jet fuel and diesel. With the overarching goal of reducing the nitrogen content invariably associated with whole algal biomass, we apply a number of approaches including (i) nutrient starvation to reduce the internal nitrogen of the freshwater alga Oedogonium (ii) continuous co-solvent (10 wt% n-heptane) hydrothermal liquefaction (HTL) to produce a non-polar biocrude containing <1 wt% N; (iii) blending the biocrude with green feed produced from the hydrogenation of CO2 to obtain <0.5 wt% N; (iv) hydrogenation and hydro-isomerization of the blend in two stages over nanodisperse silica-supported Ni2P (achieving 630 ppm N) and acidic zeolite-supported Pt catalysts respectively to produce a synthetic paraffinic mixture (SPM) containing 277 ppm N and 0.12% O. With the incorporation of renewable H2 (which can be from gasification of polar organics produced in the solvent HTL, or other renewable sources) and captured CO2 the process demonstrates a new and technically cohesive approach to the production of renewable, high-quality biofuels for demanding transport applications.

High loading of short W(Mo)S2 slabs inside the nanotubes of SBA-15. Promotion with Ni(Co) and performance in hydrodesulfurization and hydrogenation.

Abstract Layered nanoslabs of a M0S2 and WS2 phases with a well-defined hexagonal crystalline structure were inserted into the nanotubular channels of SBA-15 at loadings up to 60 wt%. Sonication of a slurry containing SBA-15 in a W(Mo)(CO)6-sulfur-diphenylmethane solution yielded an amorphous W(Mo)S2 phase inside the mesopores that was transformed into hexagonal crystalline W(Mo)S2 nanoslabs by further sulfidation. The nanoslabs were distributed exclusively inside the mesopores in a uniform manner (HRTEM, local quantitative microanalysis), without blocking the pores (N2-sorption). The Ni(Co) promoters were introduced into the W(Mo)S2/SBA-15 composites by impregnation from an aqueous solution of nickel (cobalt) acetate. The activity (based on the volume of the catalyst loaded into reactor) of the optimized Ni-W-S/SBA-15 catalyst in hydrodesulfurization (HDS) of dibenzothiophene (DBT) and hydrogenation (HYD) of toluene was 1.4 and 7.3 times higher, respectively, than that of a sulfided commercial CO-MO/Al2O3. The HDS activity of Co-Mo- S/SBA-15 catalyst was 1.2 times higher than that of commercial catalyst. After promotion with Co, the directly introduced M0S2 slabs and M0S2 slabs prepared by sulfidation of Mo- oxide monolayer spread over SBA-15 displayed similar HDS performance.

The role and stability of Li2O2 phase in supported LiCl catalyst in oxidative dehydrogenation of n-butane

This study was aimed at defining the role of active phases in supported LiCl and LiCl–DyCl3 catalysts in the catalytic oxidative dehydrogenation (ODH) of n-butane. LiCl supported on silica displayed the highest activity and selectivity in n-butane ODH compared with other alkali metal halides. Addition of DyCl3 increased the activity. TPO, XRD and Raman light scattering (RLS) data showed that LiCl and DyCl3 formed during the preparation stage were converted to Li2O2 and DyOCl phases, respectively, by calcination in air at >400°C. The results of separate TPR experiments (O2-oxidation–butane reduction) along with XRD, RLS and X-ray photoelectron spectroscopy (XPS) data proved that butane reacts mainly with oxygen species of Li2O2 phase at ODH conditions, probably attributed to [Li+O−] pairs. The proposed functions of chlorine and dynamic oxygen in the ODH of butane are consistent with the activity, selectivity and stability of silica and magnesia-supported catalysts. High thermal stability of Li2O2 in oxidized LiCl catalyst was attributed to the formation of protective Li2O·LiCl surface layer. Deactivation of LiCl/SiO2 catalyst in n-butane ODH is caused by the formation of Li-silicates at reaction conditions while LiCl/MgO display a stable performance.