The financial grant from the Blechner fund and other grants from competitive sources are aimed at providing support for the Blechner Center research program. Five to eight proposals have been submitted every year to various agencies and foundations, some of them international, to fund the research. The rate of funding is satisfactory.
Catalytic performance of novel nanocrystalline MgO, Al2O3 and transition metal oxides in green acid/base and redox reactions
The catalytic activity of inorganic ionic crystals in many organic reactions is determined by low-coordinated surface ions (LCSI) located at the crystal steps, edges or corners. Areas of atomic disorder formed at the interface of crystal grains - grain boundaries (GB) - were theoretically predicted to be additional important source of LCSI active sites in solid catalysts. However, experimental implementation of LCSI in GB areas for catalytic applications was hampered by the lack of techniques for controlled formation of GB in high-surface-area nanocrystalline ionic solids and for determination of their contribution to the LCSI content. This study demonstrates how these limitations can be overcome by controlled forming/characterization of GB in nanocrystalline MgO, γ-Al2O3 and CrOx phases. The surface chemical functionality of ionic nanocrystals and their catalytic activity can be controlled by quantitative alteration of nanocrystals interface using chemical, pressure-assisted or thermal densifications. The stabilization of atomic disorder in GB areas was confirmed by more accurate density functional theory (DFT) calculations, showing formation of crystallographic disordered ions available on the surface of GB areas, reaching a width of up to 7 atomic layers. This increased the surface basicity of MgO material by as much as 8 times, yielding a major enhancement of catalytic activity in test reactions. It was shown for the first time that production of renewable green fuels can be achieved in condensation reaction of ethanol using densified MgO material as catalyst. Areas with atomic disorder were formed also at the GB of nanostructured alumina. It was demonstrated that the surface acidity and catalytic activity of nanocrystalline γ-alumina in isopropanol dehydration can be controlled over an order of magnitude altering the interface of the primary nanocrystals by chemical and thermal densification of alumina aerogel. The increase of surface activity due to formation of LCSI was confirmed by XPS, NH3-TPD, Al27 NMR and FTIR of adsorbed pyridine techniques. H2-TPR experiments showed higher reduction capability of the surface Cr ions in the chemically densified Cr2O3 sample. Densified material possessed higher kinetic constant and higher specific catalytic activity in butane oxidation reaction, being important in VOC combustion processes. This is a result of the densification creating larger amounts of LCSI at the grain boundary areas
Deoxygenation of Triglycerides Via Decarboxylation/Decarbonylation Pathway
The production of renewable fuels and the attempt to move the market dependence away from fossil-based energy sources has been expanding worldwide driven by increasing of petroleum prices, government mandates and incentives, as well as commitments to greenhouse gas reduction. Renewable liquid alkanes can be produced by catalytic deoxygenation reaction of vegetable oils. There are three known pathways for deoxygenation of triglycerides/fatty acids: decarbonylation (removal of oxygen as CO), decarboxylation (removal the oxygen as CO2) and hydrodeoxygenation (removal the oxygen as water).
The present research examined catalytic deoxygenation of Methyl decanoate as a model of ester in order to divert the reaction to decarbonylation/decarboxylation pathway and reduce the amount of water produces. Four different catalysts were tested: Pd/C, Ni/Al2O3, Ni2P/SiO2, Ni12P5/SiO2. Hexadecane used as a solvent. The reaction was performed in a continuous trickle bed reactor at 300 oC and different pressures: 5, 10 and 20 bar.
It was found that decreasing the reaction pressure increases the selectivity to decarbonylation/decarboxylation pathway, while increasing the pressure increases the efficiency of the hydrodeoxygenation pathway.
Fe-Carbide-Oxide-Carbon phases in Catalyst for Hydrogenation of CO2 to Liquid Fuels
Renewable energy, one of the major subjects concerning human kind in the last decade; huge investments are made by governments, Energy companies and academia in this subject, still current (and near future) technology doesn't provide an alternative to fossil fuels for the heavy transportation sector. Last decade advances in GTL (Gas Too Liquid) technology and photoelectric water splitting to hydrogen and oxygen, lead to a renew interest in the possibility of "recycling" CO2 to liquid fuels. Despite the fact that CO2 hydrogenation was first studied at the 80', many question marks exist regarding the reaction pathway, composition and activity of the catalyst during the synthesis. The idea behind this synthesis is the combination of two well-known reactions: the Fischer-Tropsch Synthesis (FTS) and the Reverse Water-Gas Shift (RWGS). The only known catalyst who demonstrated promising performance is the Fe based catalyst, but unfortunately its activity is possible due to a complex phase system in the catalyst. To add on this, the supposed reaction pathway didn't received sufficient evidence and a strong correlation between phase composition and morphology to the catalyst activity wasn't demonstrated.
The purpose of this work was to try to answer does questions and to build a basic understanding for future work. To answer these questions a steady-state operation at three different phase composition were investigated. This was achieved by initiating the reaction from three different catalytic precursors: metallic iron (α-Fe), iron oxide (Fe3O4/Fe2O3) and iron carbide (χ-Fe5C2). From catalytic activity, composition and morphology analysis at steady-state, strong evidence of two step reaction pathway and catalytic phase-activity correlation ware demonstrated. Furthermore, a model of phase self-assembly (composition and morphology) at reaction conditions of the most active steady-state composition was suggested for the first time.
Catalyst activity was determined according to conversion of CO2 and selectivity towards CO, CH4 and C5+, this was achieved using on-stream GC analysis of the gas phase and GC-MS analysis of the liquid phase.
The catalyst composition was determined by conventional wide-angle XRD, exposed catalytic phases and surface composition were determined by XPS and XPS depth profile analysis. Morphology and the assembly of the catalyst phases at steady-state were determined using TEM-EELS at energy filtering imaging mode.
Molten Salt Synthesis of LaMnO3 Perovskite: Effect of Preparation Conditions
Perovskite type oxides such as LaMnO3 are an interesting class of oxides potentially applied in combustion of volatile organic compounds . Most of the methods used for their preparation involve a calcination step at high temperature (often higher than 800°C), required for solid-state diffusion and reaction. Consequently, large crystal size and low specific surface area are usually obtained. Therefore, the potential applications of these materials as catalysts are limited. Molten salt offers a unique liquid medium for the perovskite formation process. It enhances the mass transport and reduces the required synthesis temperature. Furthermore, the interactions of molten salt with perovskite precursors allow control of the morphological and structural properties of the obtained materials. In this work pure LaMnO3 perovskite nanocrystallites were successfully synthesized, for the first time, in molten NaCl-KCl and LiCl-KCl eutectic mixtures. The synthesis included heating the La-nitrate, Mn-nitrate and salt mixtures in an alumina crucible above the salt's melting temperature (657ºC for NaCl-KCl, 353°C for LiCl-KCl) for a short time (10 min to 3 hours). This procedure yielded a pure LaMnO3 phase integrated in the fused salt matrix. Washing with hot water removed the salts completely yielding pure perovskite nanocrystals. The synthesis without molten salt yielded several byproducts in addition to the LaMnO3 phase. This shows the significant effect of the molten salt on the preparation of LaMnO3. The effect of temperature, metal-to-salt ratio, perovskite precursors (oxides vs. nitrates) and salt type (mixtures of LiCl, NaCl, KCl, CaCl2) on the properties (investigated by XRD, SEM and nitrogen adsorption) and catalytic performance in butane combustion of the obtained materials will be presented.
Catalytic wet hydrogen peroxide oxidation (CWHPO) with rare earth (RE) orthoferrites of perovskite structure
The chemical industry produces large amounts of wastewater each year. The contaminants in wastewater cause environmental damage to both animal and human populations. In some cases, biological treatment may be used to decompose the pollutants in the wastewater, but in others organic pollutants are toxic to the bacteria population and preliminary treatment is required to decompose them. In addition, chemical treatment such as a catalytic filter placed on the sewage line for decomposition of wastewater can bring an industrial solution.
Catalytic wet hydrogen peroxide oxidation (CWHPO) of organic wastewater contaminants using hydrogen peroxide as the oxidant is an attractive technology for treating wastewater. This technology deals with the removal of organic carbon at atmospheric pressure and temperatures of <100°C.
The research goal was to test and understand the effect of varying the rare earth (RE) metal in perovskites with the formula RE-FeO3 on the catalytic activity in CWHPO of phenol, to find a more efficient and stable catalyst for CWHPO. The second target was minimization of iron and RE metal leaching – by finding a more stable form of RE-Perovskite.
The effectiveness and stability of the perovskites with the formula RE-FeO3 in CWHPO are functions of the natures of both metals. By varying the type of RE ion, the dimensions of unit cell varies; those changes in unit cell dimension are expected to be a result of variations in the RE-O and Fe-O bonding that should lead to changes in catalytic performance.
Experimental results showed that as the RE cationic radius decreases the catalytic activity and catalyst stability in CWPO increases. In addition it was observed that as catalyst surface area increases, the TOC conversion increases.
Results can be attributed to the increase of Fe(2P3/2) binding energy (BE) in RE-perovskite as the RE cationic radius decreases, leading to increased ionic character of the Fe-O bond which causes higher efficiency in the redox cycles.
DFT calculations of the interaction energies between NixP ( x = 2-3) and sulfur compounds during adsorption and hydrodesulfurization of S-organics
The crystalline structures of the two nickel phosphides with Ni/P ratios of 2 and 3 were verified by DFT calculations. It was shown that the most abundant planes exposed by equilibrated nanocrystals of these phases to the external reacting molecules are (001) and (101) for Ni2P and Ni3P, respectively. Calculation the distributions of densities of states (DOS) for electrons in these phases demonstrated that nickel in Ni3P phase possess an order of magnitude higher metallicity compared with that in Ni2P phase. The collected information about the states of atoms in NxP bulk phases forms a basis for calculation the energies of their surface interaction with S-organic compounds in presence and absence of hydrogen. These will be used for comparison with data about adsorption capacity/rate of hydrodesulfurization activity of corresponding nickel phosphides collected at Blechner Center.
Catalytic air wet oxidation of organic pollutants in wastewater with Mn-Ce and Ru/Ce-Zr catalysts
Testing the Mn-Ce-oxide catalyst with surface area of 300 m2/g in CWO of aniline (AN, 800 ppm) revealed high initial activity of the material: 90% AN conversion at 140°C and LHSV = 20 h-1. The catalyst quickly deactivated by more than 90% of initial activity in the first 50 h of run. It was found that the reason for deactivation in this case is colloidization and leaching-out of catalysts nanoparticles from the reactor due to strong adsorption of AN molecules. This problem was solved by acidification of AN-H2O solution with HCl at HCl/AN molar ratio of 1.2 (pH = 2.3). Neutralization of basic AN molecules depressed their strong adsorption and catalyst colloidization. In presence of HCl the AN was fully converted to N2 and NH4+ ions with TOC conversion of 91-92% at 140°C and LHSV=5h-1. No catalyst deactivation was observed running the acidified AN solution for 212 h. The pH of outcoming water was 6.4-6.6 due to removal of not reacted HCl by stripping in oxygen flow.
The ruthenium promoted Ce/Zr mixed-oxide catalysts applied in the catalytic wet oxidation of dibromoneopentyl glycol (DBNPG) demonstrated much higher catalytic activity relative to the Mn/Ce based catalysts. At 120–140°C and LHSV = 20 h-1 the Ru/Ce/Zr catalyst (surface area 38 m2/g) successfully removes 90% of DBNPG at a high dehalogenation extent caused primarily by the formation of Br-1.
Tailoring the shape and assembling mode of catalytic phases embedded in mesostructured silica matrices
Insertion of catalytic phases inside the pores of mesostructured host matrices allows a simultaneous control of catalytic phase size and assembling modes: nanoparticles ensemble, nanowires or coating layers. The catalytic activity follows the catalytic phase surface area in cases when the specific activity of catalytic phase is constant at that size range. This behavior alters in cases when the diminishing of catalytic phase size and/or changing the shape significantly affect its specific activity in a selected reaction. The available information about the directing the catalytic phase to proper assembling modes: surface layer and nanowires, created in mesostructured host matrices and in corresponding nanocasts and their effects on catalytic performance of catalytic phases was analyzed. The theoretical considerations of these issues were accepted as a Chapter in a monograph “Ordered mesoporous solids: Recent Advances and Prospects" Edited by M.Tsapatsis, Elsevier, Physical Science Books, Amsterdam.
Multiwall carbon nanotubes and nanofibers decorated with nickel nanoparticles as hydrogenation catalysts
The Ni/MWCNT composite prepared by direct injection of benzene-alcohol solution of nickel acetylacetonate into high-temperature reactor (680-780°C) followed by insertion of benzene vapor as a carbon source was characterized with XRD, HRTEM, N2-adsorption-desorption, TGA, Raman spectroscopy and TPR methods. It was found that this material contains three types of Nio nanoparticles: large 70-120 nm crystallites at the ends of MWCNT, nanoparticles of 20-30 nm at the external surface of MWCNT and 4-5 nm nanocrystals inside the MWCNT channels. The as-synthesized Ni/MWCNT material displays the minimal catalytic activity due to relatively low metal dispersion and hindered accessibility of the metal surface inside the channels. Removal of 'parent" nickel followed by decoration of the external surface of MWCNT with nickel nanoparticles by carbonylation-ion exchange-H2 reduction or sonochemical deposition yields catalysts with 10-17 times higher catalytic activity in hydrogenation of chloroacetophenone. The sonochemical deposition from the Ni-carbonyl solution in decaline yields directly the metallic nickel phase with the highest dispersion - crystal size 4 nm, and highest catalytic activity. It was established that the activity of metallic nickel phase in these catalytic materials is limited by sintering of metal nanoparticles. Another possible activity is the limitation-partial encapsulation of nickel nanoparticles in the graphitic body at the external surface of MWCN.
Inorganic ultrafiltration membranes with pore size tailored in range of 2-6 nm for water purification
The 200 nm channels in anodic alumina (AOA) membrane were filled with two mesostructured silica materials: amorphous SiO2-gel and mesostructured silica MCM-48 at loadings of ~25 wt%. The uniform filling of the membrane channels volume with mesoporous materials was proven by pore size distributions and SEM micrographs. The SiO2-filled membranes displayed pore sizes and surface areas of 4-6 nm / 15-20 m2/g and 2-3 nm /75-160 m2/g, for SiO2-gel and MCM-48 fillers, respectively. These characteristics are favorable for high performance of the membrane in ultrafiltration purification of wastewater that requires their stability in aqueous media. In both cases the pore structure and surface area of the fillers alters as a result of contacting with water. Even MCM-48 filler stable in water for at least 10 days as a powder, alters its pore structure inside the membrane as a result of contacting with water. The fillers hydrophobization approach is under development aiming at protecting their pore structure inside the channels in aqueous media.
Synthesis of proton-enriched Cs-salts of heteropolyacids with P, Si and Al central atoms in Keggin polyanions by nanocasting approach
It was demonstrated that replacement of P(5+) central ion in Keggin polyanions of H3PW12O40-heteropolyacid with Si (4+) and Al(3+) increases its activity in homogeneous MTBE synthesis and isopropanol dehydration proportionally to increasing of the amount of protons in its molecule from 3 to 5. The nanocasting approach using SiO2-gel with surface area of 400 m2/g as a hard template allowed synthesizing the Cs-salts of H3PW12O40-heteropolyacid containing 1.7 and 2 Cs-ions per molecule with the surface area 18-45 m2/g. The classical co-precipitation approach gives only Cs2HPW12O40 with the very low surface area of 1 m2/g. The nanocasting protocol was optimized and expanded for using the templates with higher surface area: SBA-15 (800 m2/g) and MCM-48 (1300 m2/g) stable in polar solvents. The work will be extended applying the developed approach to the Cs-salts of Si- and Al-based heteropoly-acids.
Creation of coordinative unsaturated active sites at the grain boundaries of MgO nanocrystallites
The opportunity for creation of intercrystalline grain boundaries in nanostructured magnesia obtained by dehydration of magnesia aerogel was proven by materials densification. Filling the pores of aerogel with additional magnesia nanoparticles or its densification by pressurizing the material increases the amount of intercrystalline contacts favoring the counterdiffusion of metal and oxygen ions at the contact interface during their thermal dehydration. This creates the 0.5-0.7 nm thick areas with disordered atomic layers (HRTEM) that are visible at XR-diffractograms as amorphous magnesia phase. Formation of coordinatively unsaturated oxygen atoms at the MgO nanocrystals grain boundaries strongly (by a factor of 7) increases the surface concentration of strong basic sites responsible for catalytic transformations of organic molecules (indicator titration). The surface concentration of basic sites and amount of formed amorphous MgO phase correlate with the MgO nanocrystals aggregation ratio. The latter was calculated by dividing the crystal size controlled theoretical surface area by measured BET surface area controlled by nanocrystalls aggregation. The collected information presents for the first time a firm basis for quatitative investigation the effects of grain boundaries in nanocrystalline metal oxides on their performance in practical catalytic reactions.
Deep and ultradeep desulfurization of refractory sulfur compounds
Deep and ultradeep desulfurization of refractory sulfur compounds in HAGO and synthetic solvents (ref.1, 3, 5, 9, 12, 14, 19, 27, 34, 35, 41) and hydroprocessing of Israeli shale oil (ref. 6, 7, 8) have been studied extensively in the framework of the long-range program supported by the Israeli Oil Refineries. Two routes to desulfurization: cracking and hydrogenation were identified and quantified. Routine catalyst preparation methods using different supports, including high-surface area MCM-41, did not produce high-performance desulfurization catalysts. Novel methods based on fundamental work, like ultrasonication controlled deposition-precipitation appears to yield improved performance. Study of the process aspects published in several papers is instrumental in the design of improved processes. The combined study of catalytic and reactor issues form the basis for new leads into novel catalytic systems that are currently being investigated.
Studies of olefin production from light paraffins
by oxidative dehydrogenation (ref. 4, 13, 29, 33, 34) and dehydrogenation (ref. 17, 23, 32) supported by Technip Benelux (the Netherlands) were the basis for a number of patents. Detailed fundamental investigation of rare earth-lithium-halogen catalytic systems identified routes for olefins production and correlated the catalytic activity with the catalyst properties/ structure. Dehydrogenation catalysts were tested under different conditions. Advantage of steam addition was pointed out. Novel catalysts supported on low surface area a-alumina displayed unexpected high performance (ref. 32). CoNx catalyst supported on alumina displayed good performance in oxidative dehydrogenation of light paraffins at low temperature (ref. 40, 44).
Catalytic processing for production of intermediates and fine chemicals
has been mostly done as exploratory research or in industrial projects. The published work covers dehydrogenation of methoxyisopropanol on bimetallic Cu-Zn catalysts (ref. 10), nitration of o-xylene by nitrogen dioxide and alkylation of phenol with methanol on zeolites (ref. 11) and ammoxidation of p-cresol to p-hydroxy-benzonitrile on high performance boria-phosphoria supported catalysts (ref. 25). The latter introduced catalysts that displayed performance significantly better than catalysts published in the literature. Testing of the SnCl4 catalyst anchored on silica in Prins condensation of isobutene with formaldehyde yielded high activity and selectivity (ref. 30). Anchoring the catalyst on MCM-41 displayed a particularly high activity compared with silica (ref. 31). High performance in anisole acylation with acetic anhydride and with propionylchloride was measured with sulfated zirconia and silica-supported Nafion catalysts.
Study of advanced catalytic materials
has received increasing emphasis (ref. 2, 16, 18, 20, 21, 28, 30, 31, 43, 44, 45, 46). Functionalized MCM materials have become a specifically important topic of research. Grafted alumina was prepared and tested in several representative reactions (ref. 28). Extensive characterization quantified the acidity type and strength and activity in sample reactions (ref. 28, 45). Nanocrystals of zeolite beta stabilized in alumina matrix displayed high performance in hydrocarbons cracking and hydrocracking reactions (ref. 16). Short (<5 nm) nanoslabs of WS2 and MoS2 located inside the nanotubes of mesostructured silica SBA-15 perpendicular to their axis and promoted with Ni or Co at high loading (>45 wt.%) display ~ 2 times higher activity in hydrodesulfurization of dibenzothiophene compared with the same sulfide phases at regular loadings on commercial amorphous silica and γ- alumina (ref. 43). WS2 slabs with increased sticking number at the surface of silica gel display enhanced hydrogenation activity in aromatics saturation (ref. 35). Stabilizing the small nanocrystals of tetragonal ZrO2 (< 2.5-4.5 nm) exclusively inside the nanotubes of mesostructured silica SBA-15 at high loadings > 45 wt.% yields after sulfatation an acidic material with 1.5-2.5 higher activity in acid-catalyzed reactions compared with commercial bulk sulfated zirconia. Chromia aerogel (600-735 m2/g) modified with Pt and Ce or Ce-Mn display 10 times higher activity and better low-temperature performance in VOC (ethylacetate) combustion compared with a standard Pt/alumina catalyst (ref. 43).
The heterogenization of homogeneous metal complexes
has been studied. Different methods were employed to combine the advantages of homogeneous (high activity and selectivity) and heterogeneous catalysis (simple separation and recycling of catalysts). Several chiral and chiral complexes such as Rh-DuPHOS, Ru-BINAP and Wilkinson's catalyst were successfully occluded in polymer matrixes without previous modification and tested in representative hydrogenation reactions [20, 38, 39]. Ionic liquids were also used to heterogenize variety of transition metal complexes in mono- and biphasic systems. Several symmetric and asymmetric reductions of functionalized ketone and carbon-carbon double bonds as well as aerobic oxidations of aromatic and aliphatic alcohols have been successfully performed with recycling of the complex in ionic liquids-containing systems [36, 41].
Modeling and simulation studies related to analysis and design of advanced aftertreatment systems of diesel exhaust gases
(needed to fulfill the proposed future EURO 5 emission limits) are conducted. The work is done in the framework of two consortia funded as RTD projects of the 5th Framework Program of the European Union. Advanced modeling and simulation tools are applied to guide, analyze and apply the experimental work of several academic and industrial partners.
Ultradeep adsorption-desulfurization of gasoline with Ni/Al-SiO2 sorbent: effect of ethanol addition
Addition of 3 wt% ethanol to gasoline increased strongly the adsorption rate of S-organics on Ni/Al-SiO2 material and its sulfur capacity enabling ultradeep adsorptive desulfurization to < 0.5 ppm residual sulfur with sulfur capacity of 2-3 wt% in absence of external hydrogen source. Three potential ways of improving desulfurization performance of Ni-sorbent in presence of ethanol and its decomposition products were considered: - formation of nickel carbide (Ni3C) phase with reactivity toward S-organic compounds higher than that of metallic nickel - reduction of carbon deposits in presence of hydrogen - formation of nickel sulfide nanoparticles in presence of H2/H2S vs. epitaxial nickel sulfide layer that blocks the surface of metallic nickel in absence of EtOH (hydrogen). Based on catalysts characterization data (N2-adsorption, XRD, EDX, HRTEM, XPS, AES depth profile anal.) it was concluded that the effect of ethanol on the desulfurization performance is a result of the two last phenomena. They take place due to participation of hydrogen evolved by catalytic decomposition of ethanol in two processes: adsorption of S-organics and formation of nickel sulfide phases.
Exploratory programs are more focused, aimed at producing preliminary results that could be exploited in industrial applications.
The current programs are divided according to criteria adopted at the Blechner Center:
Modeling of surface complexes as active sites in porous solids
· Aerobic Oxidations of alcohols with immobilized ruthenium complexes
· Functionalized polymers immobilized in mesostructured silicas - optimization functional groups concentration
Development of novel catalysts materials.
· Transition metal-based catalytic phases dispersions stabilized inside silica nanotubes – structure, assembling and functionality
· Development and testing the nanostructured transition metal oxides in combustion of halogenated VOC.
· High-surface area nanostructured MnOx-based catalysts promoted by transition metal oxides, alkaline and noble metals for catalytic wet oxidation
Modeling and Simulation of Advanced Catalysts and Reactors Structures.
· Multifunctional operation of catalytic systems in ionic liquids
· Modeling and simulation of aftertreatment systems
Details about industrial projects are confidential. The Blechner Center has developed methods and infrastructure that enhance its capability to conduct industrial projects:
· Dedicated personnel ensures short response time
· Extensive hands-on experience in catalyst preparation, characterization and testing
· Proven capability for the development of novel catalytic processes
· Proprietary technology and software for scale-up of heterogeneous catalytic processes
A hydrogenation process developed at the Blechner Center has been applied in industry. The Blechner Center developed the process from bench scale to the commercial unit through all scale up stages. The development of three other processes has been essentially completed at the bench scale and are expected to be scaled up in the near future.
