Liquid‐phase hydrogenation of cinnamaldehyde over Cu‐Au/SiO2 catalysts

The synthesis, characterization, and application of silica‐supported Cu‐Au bimetallic catalysts in selective hydrogenation of cinnamaldehyde are described. The results showed that Cu‐Au/SiO₂ bimetallic catalysts were superior to monometallic Cu/SiO₂ and Au/SiO₂ catalysts under identical conditions. Adding a small amount of gold (6Cu‐1.4Au/SiO₂ catalyst) afforded eightfold higher catalytic reaction rate compared to Cu/SiO₂ along with the high selectivity (53%, at 55% of conversion) toward cinnamyl alcohol. Characterization techniques such as x‐ray diffraction, H₂ temperature‐programmed reduction, ultraviolet‐visible spectroscopy, transmission electron microscopy, Fourier‐transform infrared spectra of chemisorbed CO, and x‐ray photoelectron spectroscopy were employed to understand the origin of the catalytic activity. A key genesis of the high activity of the Cu‐Au/SiO₂ catalyst was ascribed to the synergistic effect of Cu and Au species: the Au sites were responsible for the dissociative activation of H₂ molecules, and Cu⁰ and Cu⁺ sites contributed to the adsorption‐activation of C?C and C?O bond, respectively. A combined tuning of particle dispersion and its surface electronic structure was shown as a consequence of the formation of Au‐Cu alloy nanoparticles, which led to the significantly enhanced synergy. A plausible reaction pathway was proposed based on our results and the literature. © 2014 American Institute of Chemical Engineers AIChE J, 60: 3300–3311, 2014     

Methylcyclohexane dehydrogenation on Rh/γ-Al2O3 catalysts

The influence of the Rh loading on the surface properties and catalytic behaviour of Rh/γ-Al₂O₃ catalysts has been studied. The series of catalysts presents differences in metal dispersion, reducibility, surface composition and catalytic activity. All the data reported suggest that the differences in catalytic behaviour in the methylcyclohexane dehydrogenation reaction can be explained in terms of electron-deficient rhodium clusters, essentially when the metal particle size becomes smaller than 15 Å.     

A Chemoselective Hydrogenation of the Olefinic Bond of α,β‐Unsaturated Carbonyl Compounds in Aqueous Medium under Microwave Irradiation

A microwave‐assisted mild and ecofriendly catalytic transfer hydrogenation process was developed to reduce various α,β‐unsaturated carbonyl compounds into the corresponding saturated carbonyl compounds in the presence of silica‐supported palladium chloride as catalyst and a combination of MeOH/HCOOH/H₂O (1 : 2 : 3) as hydrogen source within 22–55 minutes in moderate to excellent yields with 100% chemoselectivity.     

Preparation of γ‐Fe2O3 Catalysts and their deNOx Performance: Effects of Precipitation Conditions

Magnetic γ‐Fe₂O₃ catalysts were prepared by microwave‐assisted coprecipitation utilizing the direct‐titrate and back‐titrate precipitation technique with different precipitants, namely, (NH₄)₂CO₃, NaOH, Na₂CO₃, and NH₄OH, which were evaluated in the selective catalytic reduction of NO_x with NH₃. The optimum γ‐Fe₂O₃ catalyst preparation method was direct titration with NH₄OH as the precipitant, which exhibits high deNO_x efficiency. This direct titration was effective to maintain the proper crystallization degree of γ‐Fe₂O₃, improve the pore structure, and suppress the formation of α‐Fe₂O₃ phase, being advantageous to get tiny and uniform discrete γ‐Fe₂O₃ particles with high activity in selective catalytic reduction. NH₄⁺‐based precipitants in direct titration leads to an increase of the surface O/Fe atom ratio, and more lattice oxygen sites are exposed to the crystal surface.     

Synthesis and characterization of polyimide‐γ‐Fe2O3 nanocomposites

Novel polyimide‐γ‐Fe₂O₃ hybrid nanocomposite films (PI/γ‐Fe₂O₃) has been developed from the poly(amic acid) salt of oxydianiline with different weight percentages (5, 10, 15 wt %) of γ‐Fe₂O₃ using tetrahydrofuran (THF) and N,N‐dimethylacetamide (DMAc) as aprotic solvents. The prepared polyimide‐γ‐Fe₂O₃ nanocomposite films were characterized for their structure, morphology, and thermal behavior employing Fourier transform infrared spectroscopy (FTIR), scanning electron micrograph (SEM), transmission electron micrograph (TEM), X‐ray diffraction (XRD), ¹³C‐NMR, and thermal analysis (TGA/DSC) techniques. These studies showed the homogenous dispersion of γ‐Fe₂O₃ in the polyimide matrix with an increase in the thermal stability of the composite films on γ‐Fe₂O₃ loadings. Magnetization measurements (magnetic hysteresis traces) have shown very high values of coercive force indicating their possible use in memory devices and in other related applications. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 834–840, 2007     

Structural elucidation and iron oxidation states in situ formed β‐Ca3(PO4)2/α‐Fe2O3 composites

A detailed structural analysis on the in situ synthesized β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is demonstrated. Compositional ratios, the influence and occupancy of iron at the β‐Ca₃(PO₄)₂ lattice, oxidation state of iron in the composites are derived from analytical techniques involving XRD, FT‐IR, Raman, refinement of the powder X‐ray diffraction and X‐ray photoelectron spectroscopy. Iron exists in the Fe³⁺ state throughout the investigated systems and favors its occupancy at the Ca²⁺(5) site of β‐Ca₃(PO₄)₂ until critical limit, and thereafter crystallizes as α‐Fe₂O₃ at ambient conditions. Fe³⁺ occupancy at the β‐Ca₃(PO₄)₂ lattice yields a Ca₉Fe(PO₄)₇ structure that is isostructural with its counterpart. A strong rise in the soft ferromagnetic behavior of β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites is obvious that depends on the content of α‐Fe₂O₃ in the composites. Overall, the diverse level of iron inclusions at the calcium phosphate system with a Ca/P ratio of 1.5 yields a structurally stable β‐Ca₃(PO₄)₂/α‐Fe₂O₃ composites with assorted compositional ratios.     

Chemoselective Reduction of α,β‐Unsaturated Carbonyls over Novel Mesoporous CoHMA Molecular Sieves under Hydrogen Transfer Conditions

Chemoselective reduction of α,β‐unsaturated carbonyls to the corresponding alcohols was achieved by a catalytic transfer hydrogenation (CTH) method using cobalt(II)‐substituted hexagonal mesoporous aluminophosphate (CoHMA) molecular sieve catalyst. Further, the catalyst was found to be promising as a heterogeneous catalyst as the yield was practically unchanged after up to six cycles.     

Bio‐Based Hybrid Magnetic Latex Particles Containing Encapsulated γ ‐Fe2O3 by Miniemulsion Copolymerization of Soybean Oil‐Acrylated Methyl Ester and Styrene

This work reports the use of acrylated fatty acid methyl ester (AFAME) as a biomonomer for the synthesis of bio‐based hybrid magnetic particles poly(styrene‐co‐AFAME)/γ‐Fe₂O₃ produced by miniemulsion polymerization. Poly(styrene‐co‐AFAME)/γ‐Fe₂O₃ can be tailored for use in various fields by varying the content of AFAME. The strategy employed is to encapsulate superparamagnetic iron oxide nanoparticles (SPIONs) as γ‐Fe₂O₃ into a styrene/AFAME‐based copolymer matrix. Raman spectroscopy is employed to ensure the formation of the SPIONs (γ‐Fe₂O₃) obtained by a co‐precipitation technique followed by oxidation of Fe₃O₄. The functionalization of SPIONs with oleic acid (OA) is carried out to increase the SPIONs–monomer affinity. The presence of OA on the surface of γ‐Fe₂O₃ is certified by identification of main absorption bands by fourier‐transform infrared spectroscopy (FTIR). Thermal analysis (differential thermogravimetry/differential thermo analysis and differential scanning calorimetry) results of poly(styrene‐co‐AFAME)/γ‐Fe₂O₃ show an increase in AFAME content leading to a lower copolymer glass transition temperature (T _g). Dynamic light scattering (DLS) measurements result in poly(styrene‐co‐AFAME)/γ‐Fe₂O₃ particles with diameter in the range of 100–150 nm. It is also observed by transmission electron microscopy (TEM) and cryo‐TEM techniques that γ‐Fe₂O₃ particles are successfully encapsulated into the poly(styrene‐co‐AFAME) matrix.     

MoO3—Fe2O3 catalysts: Characterization and activity for isopropyl alcohol decomposition

The vapour-phase dehydration and dehydrogenation of isopropyl alcohol (IPA) have been carried out over pure MoO₃ and Fe₂O₃, produced by calcination of ammonium heptamolybdate and of iron (III) nitrate respectively, as well as MoO₃ mixed with 0·5 and 50 mol% Fe₂O₃, prepared from the same materials. All catalysts were calcined in air, in the temperature range 200–600°C for 5 h, and were characterized by thermal analysis (TG, DTA), XRD, IR and S_BET. Surface areas decreased with increasing calcination temperature, and the catalytic activity of the pure oxides MoO₃ and Fe₂O₃, as well as of MoO₃–0.5 mol % Fe₂O₃, increased with their S_BET. The activity of MoO₃–50 mol % Fe₂O₃, which was independent of its S_BET, could be attributed to the increased intensity of terminal Mo—O bonds as shown by IR spectra. The activation energies for the decomposition of IPA over catalysts calcined at 250 and 500°C are tabulated.     

Performance of Pd catalysts supported on nanocrystalline α-Al2O3 and Ni-modified α-Al2O3 in selective hydrogenation of acetylene

Nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ have been prepared by sol–gel and solvothermal methods and employed as supports for Pd catalysts. Regardless of the preparation method used, NiAl₂O₄ spinel was formed on the Ni-modified α-Al₂O₃ after calcination at 1150 °C. However, an addition of NiO peaks was also observed by X-ray diffraction for the solvothermal-made Ni-modified α-Al₂O₃ powder. Catalytic performances of the Pd catalysts supported on these nanocrystalline α-Al₂O₃ and Ni-modified α-Al₂O₃ in selective hydrogenation of acetylene were found to be superior to those of the commercial α-Al₂O₃ supported one. Ethylene selectivities were improved in the order: Pd/Ni-modified α-Al₂O₃–sol–gel > Pd/Ni-modified α-Al₂O₃-solvothermal ≈ Pd/α-Al₂O₃–sol–gel > Pd/α-Al₂O₃-solvothermal  Pd/α-Al₂O₃-commerical. As revealed by NH₃ temperature program desorption studies, incorporation of Ni atoms in α-Al₂O₃ resulted in a significant decrease of acid sites on the alumina supports. Moreover, XPS revealed a shift of Pd 3d binding energy for Pd catalyst supported on Ni-modified α-Al₂O₃–sol–gel where only NiAl₂O₄ was formed, suggesting that the electronic properties of Pd may be modified.     

Catalytic Hydrogenation of Chiral α‐Amino and α‐Hydroxy Esters at Room Temperature with Nishimura Catalyst without Racemization

The hydrogenation of carboxylic acid derivatives at room temperature was investigated. With a mixed Rh/Pt oxide (Nishimura catalyst), low to medium activity was observed for various α‐amino and α‐hydroxy esters. At 100 bar hydrogen pressure and 10% catalysts loading, high yields of the desired amino alcohols and diols were obtained without racemization. The most suitable α‐substituents were NH₂, NHR, and OH, whereas β‐NH₂ were less effective. Usually, aromatic rings were also hydrogenated, but with the free bases of amino acids as substrates, some selectivity was observed. No reaction was found for α‐NR₂, α‐OR, and unfunctionalized esters; acids and amides were also not reduced under these conditions. A working hypothesis for the mode of action of the catalyst is presented.     

Copper‐Catalyzed Cyclization and Azidation of γ,δ‐Unsaturated Ketone O‐Benzoyl Oximes

An intramolecular imination/azidation sequence has been realized through the tetrakis(acetonitrile)copper(I) hexafluorophophate [Cu(CH₃CN)₄PF₆]‐catalyzed reaction of γ,δ‐unsaturated ketone O‐benzoyl oximes with trimethylsilyl azide (TMSN₃). The reaction proceeds via the copper‐mediated N O cleavage and subsequent C N forming 5‐exo cyclization. The thus formed intermediate is then azidated to afford the corresponding dihydropyrrole product. Preliminary mechanistic investigations suggest that the cyclization step does not involve a radical intermediate.

     

Influence of Ru segregation on the activity of Ru–Co/γ-Al2O3 during FT synthesis: A comparison with that of Ru–Co/SiO2 catalysts

γ-Al₂O₃ and SiO₂ supported Co catalysts, with varying amounts of Ru, were prepared and evaluated for Fischer–Tropsch synthesis (FTS). The composition of Ru for optimum activity was found to be support-dependent. The reducible Co₃O₄ was high in the region of 0–1.64 wt.% of Ru in Co/SiO₂ catalysts. Co/γ-Al₂O₃ displayed a maximum for reducible Co species at 0.42 wt.% Ru. Segregation of Ru occurred beyond this composition decreasing the extent of reduction. Co/γ-Al₂O₃ catalysts showed lower activity and olefin selectivity, in spite of higher Co dispersion, than Co/SiO₂ catalysts. The catalytic performance depends on the amount of reducible Co species, which again depends upon the optimum content of Ru.     

Synthesis and Pharmacological Evaluation of α4β2 Nicotinic Ligands with a 3‐Fluoropyrrolidine Nucleus

Nicotinic acetylcholine receptors (nAChRs) play an important role in many central nervous system disorders such as Alzheimer’s and Parkinson’s diseases, schizophrenia, and mood disorders. The α₄β₂ subtype has emerged as an important target for the early diagnosis and amelioration of Alzheimer’s disease symptoms. Herein we report a new class of α₄β₂ receptor ligands characterized by a basic pyrrolidine nucleus, the basicity of which was properly decreased through the insertion of a fluorine atom at the 3‐position, and a pyridine ring carrying at the 3‐position substituents known to positively affect affinity and selectivity toward the α₄β₂ subtype. Derivatives 3‐(((2S,4R)‐4‐fluoropyrrolidin‐2‐yl)methoxy)‐5‐(phenylethynyl)pyridine ( 11 ) and 3‐((4‐fluorophenyl)ethynyl)‐5‐(((2S,4R)‐4‐fluoropyrrolidin‐2‐yl)methoxy)pyridine ( 12 ) were found to be the most promising ligands identified in this study, showing good affinity and selectivity for the α₄β₂ subtype and physicochemical properties predictive of a relevant central nervous system penetration.     

Effects of promoters on catalytic activity and carbon deposition of Ni/γ‐Al2O3 catalysts in CO2 reforming of CH4

Catalytic reforming of methane with carbon dioxide was studied in a fixed‐bed reactor using unpromoted and promoted Ni/γ‐Al₂O₃ catalysts. The effects of promoters, such as alkali metal oxide (Na₂O), alkaline‐earth metal oxides (MgO, CaO) and rare‐earth metal oxides (La₂O₃, CeO₂), on the catalytic activity and stability in terms of coking resistance and coke reactivity were systematically examined. CaO‐, La₂O₃‐ and CeO₂‐promoted Ni/γ‐Al₂O₃ catalysts exhibited higher stability whereas MgO‐ and Na₂O‐promoted catalysts demonstrated lower activity and significant deactivation. Metal‐oxide promoters (Na₂O, MgO, La₂O₃, and CeO₂) suppressed the carbon deposition, primarily due to the enhanced basicities of the supports and highly reactive carbon species formed during the reaction. In contrast, CaO increased the carbon deposition; however, it promoted the carbon reactivity. © 2000 Society of Chemical Industry     

Highly Enantioselective Michael Addition of Cyclic 1,3‐Dicarbonyl Compounds to β,γ‐Unsaturated α‐Keto Esters

A highly enantioselective Michael addition of cyclic 1,3‐dicarbonyl compounds to β,γ‐unsaturated α‐keto esters catalyzed by amino acid‐derived thiourea‐tertiary‐amine catalysts is presented. Using 5 mol% of a novel tyrosine‐derived thiourea catalyst, a series of chiral coumarin derivatives were obtained in excellent yields (up to 99%) and with up to 96% ee under very mild conditions within a short reaction time.     

Chiral Bioinspired Non‐Heme Iron Complexes for Enantioselective Epoxidation of α,β‐Unsaturated Ketones

Chiral bioinspired iron complexes of N₄ ligands based on the ethylenediamine backbone display remarkable levels of enantioselectivity for the first time in the asymmetric epoxidation of α,β‐unsaturated ketones using hydrogen peroxide (up to 87% ee) or peracetic acid as oxidant, respectively. Notablely, isotopic labeling with H₂¹⁸O strongly demonstrated that there is a reversible water binding step prior to generation of the significant intermediate. Besides, the complex [L₂Fe(III)₂(μ‐O)(μ‐CH₃CO₂)]³⁺ usually derived from the decay of the LFe(IV)O species or thermodynamic sinks for a number of iron complexes was identified by HR‐MS. In addition, the possible mechanisms were proposed and LFe(V)O species may be the main active intermediate in the catalytic system.     

Continuous Hydrogenation of Toluene over Sr‐ and PEG800‐Modified Ni/γ‐Al2O3 Catalysts

A series of γ‐Al₂O₃‐supported nickel‐based catalysts were evaluated in continuous hydrogenation of toluene. Sr‐ and poly(ethylene glycol) 800 (PEG800)‐modified Ni/γ‐Al₂O₃ catalysts provided the best activity with high conversion of toluene and selectivity for methylcyclohexane which was ascribed to the addition of Sr and PEG800 during the preparation process, resulting in smaller and highly dispersed Ni species on the surface and in the pores of γ‐Al₂O₃. Furthermore, the formation of SrCO₃ and NiAl₂O₄ is believed to be advantageous for the dispersion and stabilization of the active Ni species, accounting for its good stability.     

SO42−/ZrO2 supported on γ‐Al2O3 as a catalyst for CO2 desorption from CO2‐loaded monoethanolamine solutions

In this work, the composite catalysts, SO₄²/ZrO₂/γ‐Al₂O₃ (SZA), with different ZrO₂ and γ‐Al₂O₃ mass ratios were prepared and used for the first time for the carbon dioxide (CO₂)‐loaded monoethanolamine (MEA) solvent regeneration process to reduce the heat duty. The regeneration characteristics with five catalysts (three SZA catalysts and two parent catalysts) of a 5 M MEA solution with an initial CO₂ loading of 0.5 mol CO₂/mol amine at 98°C were investigated in terms of CO₂ desorption performance and compared with those of a blank test. All the catalysts were characterized using X‐ray diffraction, Fourier transform infrared spectroscopy, N₂ adsorption–desorption experiment, ammonia temperature programmed desorption, and pyridine‐adsorption infrared spectroscopy. The results indicate that the SZA catalysts exhibited superior catalytic activity to the parent catalysts. A possible catalytic mechanism for the CO₂ desorption process over SZA catalyst was proposed. The results reveal that SZA1/1, which possesses the highest joint value of Brφnsted acid sites (BASs) and mesopore surface area (MSA), presented the highest catalytic performance, decreasing the heat duty by 36.9% as compared to the catalyst‐free run. The SZA1/1 catalyst shows the best catalytic performance as compared with the reported catalyst for this purpose. Moreover, the SZA catalyst has advantages of low cost, good cyclic stability, easy regeneration and has no effect on the CO₂ absorption performance of MEA. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3988–4001, 2018     

Preparation of Highly Active Nickel Catalysts Supported on Mesoporous Nanocrystalline γ‐Al2O3 for Methane Autothermal Reforming

Autothermal reforming (ATR) of methane was carried out over nanocrystalline Al₂O₃‐supported Ni catalysts with various Ni loadings. Mesoporous nanocrystalline γ‐Al₂O₃ powder with high specific surface area was prepared by the sol‐gel method and employed as support for the nickel catalysts. The prepared samples were characterized by X‐ray diffraction, Brunauer‐Emmett‐Teller, temperature‐programmed reduction, temperature‐programmed hydrogenation, and scanning electron microscopy techniques. It is demonstrated that the methane conversion increased with increasing in Ni content and that the catalyst with 25 wt % Ni exhibited the highest activity and a stable catalytic performance in the ATR process, with a low degree of carbon formation. Furthermore, the effects of the reaction temperature, the calcination temperature, the steam/CH₄ and O₂/CH₄ ratios, and the gas hourly space velocity on the catalytic performance of the 25 % Ni/Al₂O₃ catalyst were investigated.