Bimetallic nickel complexes of trimethyl phenyl linked salicylaldimine ligands: Synthesis, structure and their ethylene polymerization behaviors

Bimetallic salicylaldimine-nickel complexes, 2,4,6-Me₃-1,3-{[NCH–(3′-R-5′-Y-2′-O–C₆H₃)-κ²-N,O]Ni(Ph) (PPh₃)}₂ [R = tert-Bu, Y = Me, 1b; R = Ph, Y = H, 2b] were prepared and their catalytic behaviors of ethylene polymerization were investigated. The bimetallic complex 2b shows higher activities (2.9 × 10⁵ g PE mol⁻¹ Ni h⁻¹) for ethylene polymerization and affords polymer with high molecular weight (M_w = 1.41 × 10⁵) and broad molecular weight distribution (M_w/M_n = 6.1) than its mononuclear matrix, {[(2,6-Me₂C₆H₃)–NCH–(3′-Ph-2′-O–C₆H₃)-κ²-N,O]Ni(Ph)(PPh₃)} (3) (Activity = 5.5 × 10⁴ g PE mol⁻¹ Ni h⁻¹; M_w = 1.86 × 10⁴; M_w/M_n = 2.8).     

Oxidative coupling of methane over Ce4+-doped Ba3 WO6 catalysts: investigation on oxygen species responsible for catalytic performance

Ce⁴⁺ doped Ba₃ WO₆ complex oxides were used as catalysts for methane oxidative coupling (MOC), and characterized by XPS and O₂-TPD-MS techniques. The results indicate that the ratio of electrophilic oxygen species O^– and O ₂ ^– to lattice oxygen on the surface is crucial for C₂ selectivity. By adjusting the relative amount of cations in Ba-W-Ce complex oxides with perovskite superstructure interstitial oxygen species can be created which benefits C₂ selectivity by raising the relative amount of (O^– + O ₂ ^– ) on the surface.     

Improvement of ethylene epoxidation in low-temperature corona discharge by separate ethylene/oxygen feed

In this work, the ethylene epoxidation performance in a low-temperature corona discharge system was improved by initially producing oxygen free radicals prior to the reaction with unactivated ethylene molecules, in which the ethylene was separately fed into the system at various feed positions of the plasma zone. In addition, various operating parameters, including O₂/C₂H₄ feed molar ratio, applied voltage, input frequency, total feed flow rate, and gap distance between pin and plate electrodes, were optimized for the separate feed system. The highest ethylene oxide (EO) yield was achieved under the operating conditions of a C₂H₄ feed position of 0.2 cm, an O₂/C₂H₄ feed molar ratio of 1:2, an applied voltage of 18 kV, an input frequency of 500 Hz, a total feed flow rate of 100 cm³/min, and an electrode gap distance of 10 mm. In comparisons between the separate feed and the mixed feed of C₂H₄ and O₂ under their own optimum conditions, the separate feed provided higher EO selectivity and yield with lower undesired product selectivities and lower power consumption, as compared to the mixed feed. The results confirm that the separate feed with a suitable C₂H₄ feed position has sufficient reaction time with minimum ethylene molecules to be activated which, in turn, can reduce all undesired reactions including cracking, dehydrogenation, hydrogenation, combustion, and coupling reactions of ethylene, resulting in superior ethylene epoxidation performance.     

In situ controlled electrochemical promotion of catalyst surfaces: Pd-catalysed ethylene oxidation

The catalytic activity of polycrystalline Pd films deposited on 8 mol% Y₂O₃-stabilized–ZrO₂ (YSZ), an O^2–-conductor, can be altered reversibly by varying the potential of the Pd catalyst film via the effect of nonfaradaic electrochemical modification of catalytic activity (NEMCA) or electrochemical promotion. The complete oxidation of ethylene was investigated as a model reaction in the temperature range 290–360 °C and atmospheric total pressure. The rate of C₂H₄ oxidation can be reversibly enhanced by up to 45% by supplying O^2– to the catalyst via positive current application. The steady-state rate change is typically 10³–10⁴ times larger than the steady-state rate I/2F of electrochemical supply or removal of promoting oxide ions. The observed behaviour is discussed on the basis of previous NEMCA studies and the mechanism of the reaction.     

Copolymerizations of ethylene with 1–decene over various ansa–metallocene complexes combined with Al( i-Bu) 3/ [CPh 3] [B(C 6F 5) 4] cocatalyst

Copolymerizations of ethylene with 1-decene were carried out with a series of stereospecific metallocene compounds, rac–(EBI)Zr(NMe₂)₂ [ 1, EBI = ethylene–1,2–bis( 1–indenyl)], rac–(EBI)Hf(NMe₂ (2), rac–Me₂Si( 1–C₅H₂–2–Me–4– ^t Bu)₂Zr(NMe₂)₂ (3), ethylidene(cyclopentadienyl)(9-fluorenyl)ZrMe2 [4, Et(Flu)(Cp)ZrMe2] and isopropylidene(cyclopentadienyl)(9–fluorenyl)ZrMe₂ [5, iPr(Flu)(Cp)ZrMe₂], combined with Al(i–Bu)₃/[CPh₃] [B(C₆F₅)₄] cocatalyst. All catalyst systems showed very high copolymerization rates and the 1–decene reactivity decreased in the order of 2 > 5 > 1 4 > 3. The reactivity product of ethylene and 1–decene (r _E x r _D) was below 1 except 3 catalyst, corresponding to random copolymer structures with an alternating character. The melting point (T_m), crystallinity (X_C), intrinsic viscosity ([] and density of the 1–decene/ethylene copolymers decreased markedly with an increase in the 1–decene content, regardless of the type of catalytic system.     

The activation of O2 and the oxidative dehydrogenation of C2H6 over SmOF catalyst

The activation of O₂ over SmOF was studied by in situ laser Raman spectrometry and temperature programmed desorption (TPD). When the hydrogen- and helium-treated (1 h for each gas at 973 K) SmOF sample was cooled to 303 K in oxygen, Raman bands which correspond to the existence of O ₂ ^2– , O ₂ ^n– (2 >n > 1), O ₂ ^– and O ₂ ^- (1 > > 0) species were observed. From 303 to 973 K, there was no O₂ desorption but the Raman bands observed at 303 K reduced in intensity and vanished completely at 973 K, even though the sample was under an atmosphere of oxygen. We suggest that as the sample temperature increased, dioxygen species were converted to mono-oxygen species such as O^– which were undetectable by Raman spectrometry. O₂ desorption occurred above 973 K, giving a TPD-peak at 1095 K. When C₂ H₆ was pulsed over the sample pretreated with oxygen and helium at 973 K, C₂H₄ selectivity was 91.8%. We conclude that the mono-oxygen species is responsible for the oxidative dehydrogenation of ethane to ethene.     

Room temperature photocatalytic oxidation of liquid cyclohexane into cyclohexanone over neat and modified TiO2

The oxidation of liquid cyclohexane by O₂ over UV-illuminated TiO₂ at room temperature has been studied in a static slurry reactor. From the effects of the mass of catalyst, the temperature, the radiant flux, the concentration of C₆H₁₂ (using acetonitrile as a solvent), it is concluded that the reaction is photocatalytic. Using mainly the 365 nm-ray of a mercury-lamp, an initial quantum yield of 0.1 is found for pure cyclohexane and radiant fluxes < ca.5mWcm^–2 (6×10¹⁵ photons s^–1 cm^–2). A high selectivity to cyclohexanone is observed (83%), the other products being cyclohexanol (5%) and CO₂ (12%). The low amount of cyclohexanol is explained by the higher rate of oxidation of this alcohol compared to that of cyclohexane. Smaller oxidation rates are observed when TiO₂ is loaded with 0.5 to 10 wt%Pt and the cyclohexanone/cyclohexanol ratio decreases to ca. 4. Finally, the C₆H₁₂ oxidation has been employed as a test reaction to confirm the detrimental effect of the doping with several tri or pentavalent cations upon the photocatalytic activity of TiO₂.     

Characterization of polypyrrole films incorporating various anions

The conductivity of polypyrrole films has been enhanced by electrochemical post-deposition doping with various anions. The change of conductivity was found to depend on the type and concentration of the anion. Results for the polypyrrole films doped with anions of H₂SO₄, (C₂H₅)₄N(O₃SC₆H₄CH₃), KI, CH₃C₆H₄SO₃H · H₂O (p-toluene sulphonic acid monohydrate), AlCl₃, KBrO₃ and HNO₃ showed that in the case of H₂SO₄, (C₂H₅)₄ N(O₃SC₆H₄CH₃) and CH₃C₆ H₄SO₃ H · H₂O the conductivity can be enhanced by up to a factor of two, from a value of 67 S cm^–1 up to 165, 102 and 95 S cm^–1, respectively. Doping with I^– had a negligible effect on the conductivity which was about 71 S cm^–1, while in the case of AlCl₃, KBrO₃ and HNO₃ the conductivity of the polypyrrole decreased significantly for certain anion concentrations.     

Synthesis, characterization, and catalytic application of copper(I) nitrile cations with perfluorinated weakly coordinating anions

Complexes of the type [Cu(CH₃CN)₄]⁺[A]^– ([A]^– = [B(C₆F₅)₄]^– (1), [B{C₆H₃(CF₃)₂}]^– (2), [(C₆F₅)₃B–C₃H₄N₂–B(C₆F₅)₃]^– (3)) are synthesized and characterized. Their utilization as catalysts in cyclopropanation and aziridination reactions of olefins, forming three membered rings is explored. The compounds are found to catalyze both reactions in moderate to good yields being the best results obtained with compound 1. The more weakly the nitrile ligands are coordinated to the metal center, the better is the catalytic performance of the catalyst.     

Study on an iron–manganese Fischer–Tropsch synthesis catalyst prepared from ferrous sulfate

A systematic study was undertaken to investigate the effects of the initial oxidation degree of iron on the bulk phase composition and reduction/carburization behaviors of a Fe–Mn–K/SiO₂ catalyst prepared from ferrous sulfate. The catalyst samples were characterized by powder X-ray diffraction (XRD), Mössbauer spectroscopy, X-ray photoelectron spectroscopy (XPS) and H₂ (or CO) temperature-programmed reduction (TPR). The Fischer–Tropsch synthesis (FTS) performance of the catalysts was studied in a slurry-phase continuously stirred tank reactor (CSTR). The characterization results indicated that the fresh catalysts are mainly composed of α-Fe₂O₃ and Fe₃O₄, and the crystallite size of iron oxides is decreased with the increase of the initial oxidation degree of iron. The catalyst with high content of α-Fe₂O₃ in its as-prepared state has high content of iron carbides after being reduced in syngas. However, the catalyst with high content of Fe₃O₄ in its as-prepared state cannot be easily carburized in CO and syngas. FTS reaction study indicates that Fe-05 (Fe³⁺/Fe_total = 1.0) has the highest CO conversion, whereas Fe-03 (Fe³⁺/Fe_total = 0.55) has the lowest activity. The catalyst with high CO conversion has a high selectivity to gaseous hydrocarbons (C₁–C₄) and low selectivity to heavy hydrocarbons (C₅₊).     

Ethane‐selective carbon composites CPDA@A‐ACs with high uptake and its enhanced ethane/ethylene adsorption selectivity

Novel composites (CPDA@A‐ACs) of carbonized polydopamine (CPDA) and asphalt‐based activated carbons (A‐ACs) were successfully synthesized, and characterized for adsorption separation of ethane/ethylene. The resulting CPDA@A‐ACs exhibited high Brunauer–Emmett–Teller surface area of 1971 m²/g. The O and N contents on CPDA@A‐ACs are higher than those on A‐ACs due to the introduction of CPDA. Interestingly, CPDA@A‐ACs exhibited great preferential adsorption of ethane over ethylene. Its ethane capacity reached as high as 7.12 mmol/g at 100 kPa and 25°C, and its ethane/ethylene adsorption selectivity became higher compared to A‐ACs, reaching as high as 3.0～20.6 below 100 kPa, significantly superior to the reported ethane‐selective adsorbents. Simulation results revealed the mechanism of enhanced selectivity toward C₂H₆/C₂H₄, and suggested that the surface oxygen functionalities of the composites play predominant role in enhancing ethane/ethylene adsorption selectivity. Fixed‐bed experiments showed that C₂H₆/C₂H₄ mixtures can be well separated at room temperature, suggesting great potential for industrial C₂H₆/C₂H₄ separation. © 2018 American Institute of Chemical Engineers AIChE J, 64: 3390–3399, 2018     

Low methane selectivity using Co/MnO catalysts for the Fischer-Tropsch reaction: Effect of increasing pressure and Co-feeding ethene

CO hydrogenation using cobalt/ manganese oxide catalysts is described and discussed. These catalysts are known to give low methane selectivity with high selectivity to C₃ hydrocarbons at moderate reaction conditions (GHSV < 500 h^–1, < 600 kPa). In this study the effect of reaction conditions more appropriate to industrial operation are investigated. CO hydrogenation at 1–2 MPa using catalyst formulations with Co/Mn = 0.5 and 1.0 gives selectivities to methane that are comparable to those observed at lower pressures. At the higher pressure the catalyst rapidly deactivates, a feature that is not observed at lower pressures. However, prior to deactivation rates of CO + CO₂ conversion > 8 mol/1-catalyst h can be observed. Co-feeding ethene during CO hydrogenation is investigated by the reaction of¹³C0-¹²C₂H₄-H₂ mixtures and a significant decrease in methane selectivity is observed but the hydrogenation of ethene is also a dominant reaction. The results show that the co-fed ethene can be molecularly incorporated but in addition it can generate a C, species that can react further to form methane and higher hydrocarbons.     

Probing the early stages of polymerization of ethylene on a model chromium/silica catalyst by Fourier transform infrared spectroscopy

The nature of the interaction of monomer, and the early stages of growth of oligomers of ethylene on a rather more uniform surface of Cr/SiO₂ catalyst than hitherto studied has been investigated by differenceFTIR spectroscopy using C₂D₄ and C₂H₄ as reactants both with and without subsequent treatment of the catalyst with CO andTHF. The active catalyst was prepared by reaction of vapour phase CrO₂Cl₂ with the vicinal hydroxyls of the silica surface. Three distinct kinds of methylene groups were detected. Arguments are given for assigning the peaks at 2935 and 2860 cm^–1 to CH₂ groups directly bound to the active site and those at 2920 and 2850 to CH₂s in the growing chain well removed from the Cr. The peaks at 2160 and 2165 cm^–1 are attributed to CD₂ groups hydrogen bonded to surface hydroxyls.     

Oxidative coupling of methane over BaF2-TiO2 catalysts

The addition of F^– to Ba-Ti mixed oxide catalysts significantly improves the catalytic performances for the oxidative coupling of methane (MOC), which can achieve high C₂ yields at wide feed composition range and high GHSV. The effect is particularly marked for the BaF_2– TiO₂ catalysts containing more than 50 mol% BaF₂. The C₂ yield of 17% and the C₂ selectivity of > 60% were achieved over these catalysts at 700 ° C. After being on stream for 31 h, the 50 mol% BaF₂-TiO₂ catalysts showed only a 1–1.5% decrease in the C₂ yields. Results obtained by XRD show that various Ba-Ti oxyfluoride phases were formed due to the substitution of F^– to O^2–.     

Effect of pressure on three catalytic partial oxidation reactions at millisecond contact times

The effects of pressure on reactant conversion and product selectivities in three catalytic oxidation systems have been examined at pressures between 1 and > 5 atm. Reaction was sustained autothermally near adiabatic operating conditions at temperatures of 1000°C with residence times over the noble metal catalysts between 10^–4 and 10^–2 s. The three systems investigated were (1) HCN synthesis over Pt-10% Rh gauze catalysts, (2) methane oxidation to synthesis gas (CO and H₂) over rhodium-coated monoliths, and (3) ethane conversion to ethylene over platinum-coated monoliths. We find that selectivities in all three reactions do not change dramatically with approximately a five-fold increase in pressure. This strongly suggests that free radical homogeneous chain reactions are not significant in these processes and that they can be operated reliably above atmospheric pressure. For the synthesis of HCN over Pt-10% Rh gauzes, the selectivity to HCN can be maintained above 0.75 at pressures up to 5.5 atm. Selectivities to synthesis gas (CO and H₂) from a methane-air mixture over a Rh-coated foam monolith at pressures up to 5.5 atm were maintained above 0.90. Over a Pt-coated foam monolith, the selectivity to ethylene from ethane-air and ethane-O₂ mixtures was independent of pressure up to 6.5 atm and conversion rose slightly although it was necessary to maintain constant velocity and residence time over the catalyst to avoid carbon formation.This research was supported by DOE under Grant No. DE-FG02-88ER13878.     

Density functional study of the primary events on TiO2 photocatalyst

Density functional calculations at the B3LYP/6-311G**//B3LYP/6-311G level of theory were used to study the initial process of ethylene degradation on the TiO₂ photocatalyst by adopting the dimeric titanium structure Ti₂O₆H₄ as a model of the catalyst surface. Adsorption energies of water and ethylene were calculated to be 31.9 and 20.4 kcal mol^–1. The photogenerated OH radical does not desorb from the catalyst surface and the further reaction with ethylene proceeds since the adsorption energy was estimated to be 39.3 kcal mol^–1. Our calculation also indicated that under steady illumination, ethylene directly attacks the OH radical bound to the TiO₂ surface even though the surface has vacant sites available for ethylene adsorption.     

Boosting C2H6/C2H4 separation in scalable metal-organic frameworks through pore engineering

The development of ethane (C₂H₆)-selective adsorbents for ethylene (C₂H₄) purification, although challenging, is of prime industrial importance. Pillared-layer metal-organic frameworks (MOFs) possess facilely tunable pore structure and functionality, which means they have excellent potential for high-performance C₂H₆/C₂H₄ separation applications. Herein, we report a family of isostructural pillared-layer MOFs with various metal centers M and co-ligands L, M₂(D-cam)₄L₂ (denoted M-cam-L; M = Cu, Co, Ni; L = pyz, apyz, dabco), with a variety of pore surface properties. All of the M-cam-L materials exhibit preferential adsorption for C₂H₆ over C₂H₄. In particular, Ni-cam-pyz exhibits the highest C₂H₆ capture capacity (68.75 cm³ g⁻¹ at 1 bar and 298 K), Cu-cam-dabco possesses the greatest C₂H₆/C₂H₄ adsorption selectivity (2.3), and the lowest isosteric heat of adsorption is demonstrated for Cu-cam-pyz (20.1 kJ mol⁻¹). Dynamic column breakthrough experiments also confirmed the excellent separation performance of M-cam-pyz and M-cam-dabco materials. The synthesis route of the M-cam-L materials is easily scaled-up under laboratory conditions, and hence this class of MOFs is promising for practical C₂H₄ purification.     

Propane Oxidative Dehydrogenation over Metal Pyrophosphates Catalysts

Metal pyrophosphates (M–P₂O₇, where M is V, Zr, Cr, Mg, Mn, Ni or Ce) have been found to catalyze the oxidative dehydrogenation of propane to propene. The reaction was conducted at 1 atm, 450–550°C and feed flowrate of 75 cm³/min (20 cm³/min propane, 5 cm³/min oxygen and the balance is helium). All catalysts showed increase in degrees of conversion and decrease in olefins selectivity with increase in reaction temperature. At 550°C, MnP₂O₇ exhibited the highest activity (40.7% conversion) and total olefins (C₃H₆ and C₂H₄) yield (29.3%). The other catalysts, indicated by their respective metals, may be ranked (based on olefins yield) as V (16.9%) < Cr (17.5%) < Ce (25.1%) < Zr (26.2%) < Ni (26.8%) < Mg (27.9%). The reactivity of the lattice oxygen was estimated from energy of formation of the corresponding metal oxides. Correlation between the selectivity to propene and the standard energy of formation was attempted. Although there was no clear correlation, the result suggested that the lattice oxygen play a key role in the selectivity-determining step.     

Carbon Monoxide Hydrogenation over Zirconia Supported Ni and Co-Ni Bimetallic Catalysts

Zirconia supported nickel and cobalt-nickel bimetallic catalysts were prepared and characterized for various physico-chemical properties. The hydrogenation of carbon monoxide was studied over these catalysts in the pressure range of 101.3–1654kPa, temperature range of 513–533K, weight hourly space velocity range of 8–14h^–1 and H2/CO mole ratio of 2. Catalysts containing both Co and Ni were found to give higher C₅₊ hydrocarbons selectivity compared to that containing only Ni. A maximum C₅₊ hydrocarbons selectivity of 55wt% was obtained at 655kPa pressure, 523K and 9.6h^–1 of WHSV with catalyst containing 4.03wt% Co and 2.64wt% Ni. The C₂ and C₃ olefin contents of the products decreased with increase in pressure. Improved deactivation behavior of the catalysts was observed when operated at high pressure.     

Uptake of heavy metal ions from aqueous solution using Mg–Al layered double hydroxides intercalated with citrate, malate, and tartrate

Mg–Al layered double hydroxide (Mg–Al LDH) was modified with organic acid anions using a coprecipitation technique, and the uptake of heavy metal ions from aqueous solution by the Mg–Al LDH was studied. Citrate·Mg–Al LDH, malate·Mg–Al LDH, or tartrate·Mg–Al LDH, which had citrate³⁻ (C₆H₅O₇³⁻), malate²⁻ (C₄H₄O₅²⁻), or tartrate²⁻ (C₄H₄O₆²⁻) anions intercalated in the interlayer, was prepared by dropwise addition of a mixed aqueous solution of Mg(NO₃)₂ and Al(NO₃)₃ to a citrate, malate, or tartrate solution at a constant pH of 10.5. These Mg–Al LDHs were found to take up Cu²⁺ and Cd²⁺ rapidly from an aqueous solution at a constant pH of 5.0. This capacity was mainly attributable to the formation of the citrate–metal, malate–metal, and tartrate–metal complexes in the interlayers of the Mg–Al LDHs. The uptake of Cu²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH < citrate·Mg–Al LDH. The uptake of Cd²⁺ increased in the order malate·Mg–Al LDH < tartrate·Mg–Al LDH = citrate·Mg–Al LDH. These differences in Cu²⁺ and Cd²⁺ uptake were attributable to differences in the stabilities of the citrate–metal, malate–metal, and tartrate–metal complexes. These results indicate that citrate³⁻, malate²⁻, and tartrate²⁻ were adequately active as chelating agents in the interlayers of Mg–Al LDHs.