Coload Research Articles

Steam Reforming of Ethanol over CoMg/SBA-15 Catalysts

Hydrogen production through steam reforming of ethanol (SRE) over Mg modified Co-based catalysts supported on mesoporous SBA-15 was studied herein to evaluate the catalytic activity and the behavior of coke deposition. The CoyMgx/SBA-15 catalysts are obtained according to the steps of consecutive impregnation of Mg (x = 5 and 10 wt%) to be incorporated on SBA-15 and then follow the loading of Co (y = 10 and 20 wt%) using the incipient wetness impregnation method. The catalysts are characterized by using X-ray diffraction (XRD), temperature programmed reduction (TPR), transmission electron microscopy (TEM) and BET techniques. Also, the spent catalysts are further characterized by using XRD and TEM. The catalytic activity of the SRE is evaluated in a fixed-bed reactor under 22,000 h-1 GHSV and with an H2O/EtOH molar ratio of 13. All the CoyMgx/SBA-15 catalysts present a mesoporous structure, even after the SRE reaction. The optimum catalyst of Co20Mg5/SBA-15-H650 comes from the high loading of Co and high reduction temperature pretreatment, which show a high catalytic activity and stability at 550°C with a hydrogen yield (YH2) up to 5.78 and CO selectivity around 3.10%.

Separation of Mo from Chloride Leach Liquors of Petroleum Refining Catalysts by Ion Exchange

Separation of molybdenum from the synthetic chloride leach liquors of spent hydrodesulphurization catalysts was studied by employing cationic (Diphonix) and anionic resins (AG1-x8). The composition of the solution was Mo 394 ppm, Co 119 ppm and Al 1782 ppm. In the HCl concentration range from 1 to 6 kmol/m3, the loading of Co and Al was negligible. As the concentration of HCl increased, the loading percentage of Mo by AG1-x8 increased, while that by Diphonix decreased. The Mo in the loaded AG1-x8 was successfully eluted by using NaOH solution. In terms of the possibility of producing Mo compound from the eluant, AG1-x8 was found to be better than Diphonix. The loading capacity of AG1-x8 for molybdenum was determined. Column experiments verified that it was possible to separate Mo from Co and Al by ion exchange with AG1-x8. [doi:10.2320/matertrans.M2013141]

Performance of a Carboxydothermus hydrogenoformans-immobilizing membrane reactor for syngas upgrading into hydrogen

Hydrogen conversion of CO by a pure culture of Carboxydothermus hydrogenoformans was investigated and optimized in a lab-scale hollow fiber membrane bioreactor (HFMBR). The reactor was operated under strict anaerobic, extremely thermophilic (70 °C) conditions with a continuous supply of gas, for four months. Reactor performance was evaluated under various operational conditions, such as liquid velocity (vliq) (13, 65 and 130 m h−1), temperature (70, 65, and 60 °C), CO pressure (from 1 to 2.5 atm) and CO loading rate (from 1.3 to 16.5molLrxr−1d−1). Overall, results indicated a relatively constant H2 yield of 92 ± 4% (mol mol−1) regardless of the operational condition tested. Permeation across the colonized membrane was improved by three orders of magnitude as compared to the abiotic membrane, because of dissolved CO concentration was constantly maintained low in the liquid on the shell side of the membrane as continually depleted by the microorganisms. Once the biofilm was sufficiently developed, a maximum CO conversion activity of 0.44 mol CO g−1 volatile suspended solid (VSS) d−1 was achieved at a pCO of 2 atm or above and a vliq of 65 m h−1. However, this highest activity represented only 15% of the maximal activity potential of the strain under non-limiting conditions, attributed to the low concentration of dissolved CO (0.01–0.07 mM) present in the HFMBR liquid. Higher vliq (130 m h−1) produced shearing stress, which detached a significant portion of the biofilm from the membrane, and/or prevented less sessile growth (57% total biomass as biofilm, as opposed to 84–86% at lower vliq). One may deduce from this work that the volumetric CO conversion performance of such a membrane bioreactor would be at the most in the range of 5molCOLrxr−1d−1. Overall, the CO conversion performance in the HFMBR was biokinetically limited, when not limited by gas–liquid mass transfer. Additionally, over time, membrane fouling and aging decreased membrane permeability such that the CO transfer rate would be the most limiting factor in the long run.

Transition Metal Sulfide Hydrogen Evolution Catalysts for Hydrobromic Acid Electrolysis

Mixed metal sulfides containing combinations of W, Fe, Mo, Ni, and Ru were synthesized and screened for activity and stability for the hydrogen evolution reaction (HER) in aqueous hydrobromic acid (HBr). Co- and Ni-substituted RuS(2) were identified as potentially active HER electrocatalysts by high-throughput screening (HTS), and the specific compositions Co(0.4)Ru(0.6)S(2) and Ni(0.6)Ru(0.4)S(2) were identified by optimization. Hydrogen evolution activity of Co(0.4)Ru(0.6)S(2) in HBr is greater than RuS(2) or CoS(2) and comparable to Pt and commercial Rh(x)S(y). Structural and morphological characterizations of the Co-substituted RuS(2) suggest that the nanoparticulate solids are a homogeneous solid solution with a pyrite crystal structure. No phase separation is detected for Co substitutions below 30% by X-ray diffraction. In 0.5 M HBr electrolyte, the Co-Ru electrode material synthesized with 30% Co rapidly lost approximately 34% of the initial loading of Co; thereafter, it was observed to exhibit stable activity for HER with no further loss of Co. Density functional theory calculations indicate that the S(2)(2-) sites are the most important for HER and the presence of Co influences the S(2)(2-) sites such that the hydrogen binding energy at sufficiently high hydrogen coverage is decreased compared to ruthenium sulfide. Although showing high HER activity in a flow cell, the reverse reaction of hydrogen oxidation is slow on the RuS(2) catalysts tested when compared to platinum and rhodium sulfide, leaving rhodium sulfide as the only suitable tested material for a regenerative HBr cell due its stability compared to platinum.

Tunable poly(2-acrylamido-2-methyl-1-propan sulfonic acid) based microgels with better catalytic performances for Co and Ni nanoparticle preparation and their use in hydrogen generation from NaBH4

Poly(2-acrylamido-2-methyl-1-propansulfonic acid) (p(AMPS))-based microgel is prepared for metal nanoparticle preparation of Co and Ni and then used in hydrolysis of NaBH4. The Co(II) ions from different anion-containing sources is used for loading of p(AMPS) and used in Co nanoparticle preparation. It is found that loading of Co(II) into p(AMPS) is in the order of Cl− > CH3COO− > NO3− as well as the formed corresponding particles. The porous p(AMPS) microgel is prepared and used in metal nanoparticle preparation and porous p(AMPS) can load more Co(II) than p(AMPS)–silica and bare p(AMPS). The Co nanoparticle-containing composites also give catalytic performances in that order. The activation energy for hydrolysis of NaBH4 by p(AMPS)–Co microgel composites is calculated as 29.80 kJ/mol, that is as low as Ru nanoparticle-containing bulk p(AMPS) hydrogels. It is further revealed that the microgels based on p(AMPS) are versatile, can be used repeatedly up to five times without any loss of catalytic activity (only about 3%) and with no loss in conversion.

Deciphering heavy metal contamination zones in soils of a granitic terrain of southern India using factor analysis and GIS

Soil contamination by heavy metals has been a major concern for last few decades due to increase in urbanization and industrialization. The main objective of this research was to identify the heavy metal contaminated zones in the study area. Twenty five soil samples collected throughout the agriculture, residential and industrial areas were analysed by X-ray Fluorescence Spectrometer (XRF) for trace metals and major oxides. These metals can affect the quality of soil and infiltrate through the soil, thereby causing groundwater pollution. Based on the chemical analysis of major oxides (SiO2, Al2O3, Fe2O3, MnO, MgO, CaO, Na2O, K2O, TiO2, and P2O5) and their distribution; it is observed that these soils are predominantly siliceous type with slight enrichment of alumina component in the study area. Correlation matrix (CM) and factor analysis (FA) is employed to the heavy metal variables, viz., Ba, Cr, Cu, Ni, Pb, Rb, Sr, V, Y, Zn and Zr of the soil to determine the dominant factors contributing to the soil contamination in the area. In the analysis, five factors emerged as significant contributors to the soil quality. The total contribution of these five factors is about 90%. The contribution of the first factor is about 45% and has significant positive loadings of Co, Cr, Cu, Ni and Zn. The contribution of second factor is 22% and has significant positive loadings of Rb, Sr and Y. The contribution of third, fourth and fifth factors is 10, 8 and 5% and show positive loadings for lead, molybdenum and barium respectively to the soil contamination. The spatial variation maps deciphering different zones of heavy metal concentration in the soil were generated in a GIS (geographic information system) based environment using ArcGIS 9.3.1. The results reveal that heavy metal contamination in the area is mainly due to anthropogenic activities.

Assessment of toxic heavy metal loading in topsoil samples within the vicinity of a limestone quarry in South Western Nigeria

Loading of Pb, Cd, Cr, Cu, Co, Mn, Ni, Zn, and Fe in topsoil samples (TS) collected from the vicinity of limestone quarry in South Western Nigeria was investigated. Thirty TS were sampled within ½ km radius from exploration area and 5 background samples from undeveloped area 10 km away from the study area. Limestone rock samples (RK) were also analyzed for metals’ content. All samples were pretreated and leached with appropriate acid solutions for some properties. All leachates were analyzed with atomic absorption spectrophotomer (AAS) technique. Soil pH ranged from 6.65 to 8.23, sand from 55.8 to 75.0%, silt from 16.6 to 34.6%, clay from 8.43 to 13.6%, and organic matter from 0.97 to 4.84%, respectively. These properties compared with those of background samples. Rock samples (RK) showed high Fe and Mn enrichment. Metals levels (mg/kg) in TS with background levels in parenthesis ranged as follows: 11.5 to 27.7 (10.5) Pb, 0.28 to 3.18 (0.55) Cd, 12.1 to 17.4 (5.50) Cr, 80.6 to 55.8 (3.81) Cu, 8.93 to 23.5 (11.1) Co, 262 to 710 (637) Mn, 6.34 to 17.4 (6.10) Ni, 36.0 to 620 (24.4) Zn, and 6585 to 13440 (4563) Fe. The elevated enrichment suggests influence from exploration activities. Residual phase showed highest enrichment for all metals possibly, because of high sand content. Positive correlations were shown between all metals, except Mn and Cd that were negative. Geoaccumulation index rating showed <0 for Mn denoting uncontamination, while others ranged from 1 to 2 indicating moderate contamination.

Insights into the Temperature‐Dependent “Breathing” of a Flexible Fluorinated Metal–Organic Framework

The framework expansion and contraction upon carbon dioxide uptake was studied in a partially fluorinated metal-organic framework, FMOF-2. The results show framework expansion and contraction (breathing) as a function of pressure and temperature. Even at temperatures as low as -30 °C, two phase transitions seem to take place with a pressure step (corresponding to the second transition) that is greatly dependent on temperature. This behavior is described by the model proposed by Coudert and co-workers showing that the material seems to undergo two phase transitions that are temperature-dependent. The isosteric heats of adsorption at high pressures show a minimum that is concurrent with the region of CO(2) loadings where the second pressure step occurs. It was deduced that these lower enthalpy values are a consequence of the energy cost related to the expansion or reopening of the framework. Lastly, the large and reversible breathing behavior may be a product of the combination of the high elasticity of zinc (II) coordination and the apparent high flexibility of the V-shaped organic building block.

Time-Dependent CO2 Sorption Hysteresis in a One-Dimensional Microporous Octahedral Molecular Sieve

The development of sorbents for next-generation CO(2) mitigation technologies will require better understanding of CO(2)/sorbent interactions. Among the sorbents under consideration are shape-selective microporous molecular sieves with hierarchical pore morphologies of reduced dimensionality. We have characterized the non-equilibrium CO(2) sorption of OMS-2, a well-known one-dimensional microporous octahedral molecular sieve with manganese oxide framework. Remarkably, we find that the degree of CO(2) sorption hysteresis increases when the gas/sorbent system is allowed to equilibrate for longer times at each pressure step. Density functional theory calculations indicate a "gate-keeping" role of the cation in the tunnel, only allowing CO(2) molecules to enter fully into the tunnel via a highly unstable transient state when CO(2) loadings exceed 0.75 mmol/g. The energy barrier associated with the gate-keeping effect suggests an adsorption mechanism in which kinetic trapping of CO(2) is responsible for the observed hysteretic behavior.

CoxCu1−x(DDOP)(OH2)(NO3)](NO3): hydrogen bond-driven distortion of cobalt(ii) by solid solution ‘network mismatch’

Late-first row transition metal nitrate complexes of the tetradentate N-donor ligand cis-3,5-bis[(2-pyridinyleneamino]-trans-hydroxycyclohexane (DDOP) adopt a mono-cationic [M(DDOP)(H(2)O)(NO(3))](+) structure (M = Co, 1; Cu, 2; Zn, 3) in which the DDOP ligand occupies the equatorial plane. The complexes are essentially isostructural and isomorphous, allowing the Co(II) and Cu(II) complexes to co-crystallize in mixed-metal solid solutions with the formula [Co(x)Cu(1-x)(DDOP)(NO(3))(H(2)O)](NO(3)), where x = 0.4 (4), 0.1 (5), and 0.7 (6). For 4, structural and magnetochemical analysis indicate that the geometry of the octahedral Co(II) complex distorts to match that of the dominant Jahn-Teller distorted Cu(II) center. Magnetic susceptibility data of octahedral Co(II) are sensitive to ligand geometry distortions and have been analyzed accordingly, comparing 4 to the reference systems 1 and 2. Bond valence calculations have been used to estimate the relative stabilities of the six hydrogen bonded networks, suggesting that the stretching of the Co(II) coordination sphere 4 in is assisted by adoption of the most stable hydrogen bonded network; but that in 6 this is overcome by a higher loading of Co. This family of complexes therefore represent predictable metal-based tectons which can help probe the influence of secondary non-covalent interactions over metal coordination geometries and properties.

Formation of methotrexate-PLLA-PEG-PLLA composite microspheres by microencapsulation through a process of suspension-enhanced dispersion by supercritical CO2

BackgroundThe aim of this study was to improve the drug loading, encapsulation efficiency, and sustained-release properties of supercritical CO2-based drug-loaded polymer carriers via a process of suspension-enhanced dispersion by supercritical CO2 (SpEDS), which is an advanced version of solution-enhanced dispersion by supercritical CO2 (SEDS).MethodsMethotrexate nanoparticles were successfully microencapsulated into poly (L-lactide)-poly(ethylene glycol)-poly(L-lactide) (PLLA-PEG-PLLA) by SpEDS. Methotrexate nanoparticles were first prepared by SEDS, then suspended in PLLA-PEG-PLLA solution, and finally microencapsulated into PLLA-PEG-PLLA via SpEDS, where an “injector” was utilized in the suspension delivery system.ResultsAfter microencapsulation, the composite methotrexate (MTX)-PLLA-PEG-PLLA microspheres obtained had a mean particle size of 545 nm, drug loading of 13.7%, and an encapsulation efficiency of 39.2%. After an initial burst release, with around 65% of the total methotrexate being released in the first 3 hours, the MTX-PLLA-PEG-PLLA microspheres released methotrexate in a sustained manner, with 85% of the total methotrexate dose released within 23 hours and nearly 100% within 144 hours.ConclusionCompared with a parallel study of the coprecipitation process, microencapsulation using SpEDS offered greater potential to manufacture drug-loaded polymer microspheres for a drug delivery system.

Catalytic oxidation of gas-phase mercury over Co/TiO2 catalysts prepared by sol–gel method

Abstract Co/TiO 2 catalysts prepared by sol–gel method were studied for gas-phase mercury oxidation in this paper. Experimental results revealed that the optimal loading of Co was 7.5%, which yielded more than 90% oxidation efficiency within the temperature range of 120–330 °C. The high activity was mainly attributed to the enrichment of well dispersed Co 3 O 4 . We also found that oxygen performed a key role in mercury oxidation process, while HCl could corrode the oxidized mercury and release it to gas phase. Thereafter, a modified Mars–Maessen mechanism was proposed and the possible simultaneous oxidization of NO and mercury was studied.

An FTIR Spectroscopic Study on the Effect of Molecular Structural Variations on the CO2 Absorption Characteristics of Heterocyclic Amines

Herein, the reaction between CO(2) and piperidine, as well as commercially available functionalised piperidine derivatives, for example, those with methyl-, hydroxyl- and hydroxyalkyl substituents, has been investigated. The chemical reactions between CO(2) and the functionalised piperidines were followed in situ by using attenuated total reflectance (ATR) FTIR spectroscopy. The effect of structural variations on CO(2) absorption was assessed in relation to the ionic reaction products identifiable by IR spectroscopy, that is, carbamate versus bicarbonate absorbance, CO(2) absorption capacity and the mass-transfer coefficient at zero loading. On absorption of CO(2) , the formation of the carbamate derivatives of the 3- and 4-hydroxyl-, 3- and 4-hydroxymethyl-, and 4-hydroxyethyl-substituted piperidines were found to be kinetically less favourable than the carbamate derivatives of piperidine and the 3- and 4-methyl-substituted piperidines. As the CO(2) loading of piperidine and the 3- and 4-methyl- and hydroxyalkyl-substituted piperidines exceeded 0.5 moles of CO(2) per mole of amine, the hydrolysis of the carbamate derivative of these amines was observed in the IR spectra collected. From the subset of amines analysed, the 2-alkyl- and 2-hydroxyalkyl-substituted piperidines were found to favour bicarbonate formation in the reaction with CO(2) . Based on IR spectral data, the ability of these amines to form the carbamate derivatives was also established. Computational calculations at the B3LYP/6-31+G** and MP2/6-31+G** levels of theory were also performed to investigate the electronic/steric effects of the substituents on the reactivity (CO(2) capture performance) of different amines, as well as their carbamate structures. The theoretical results obtained for the 2-alkyl- and 2-hydroxyalkyl-substituted piperidines suggest that a combination of both the electronic effect exerted by the substituent and a reduction in the exposed area of the nitrogen atom play a role in destabilising the carbamate derivative and increasing its susceptibility to hydrolysis. A theoretical investigation into the structure of the carbamate derivatives of these amines revealed shorter NC bond lengths and a less-delocalised electron distribution in the carboxylate moiety.

Investigation of CO2 capture mechanisms of liquid-like nanoparticle organic hybrid materials via structural characterization

Nanoparticle organic hybrid materials (NOHMs) have been recently developed that comprise an oligomeric or polymeric canopy tethered to surface-modified nanoparticles via ionic or covalent bonds. It has already been shown that the tunable nature of the grafted polymeric canopy allows for enhanced CO(2) capture capacity and selectivity via the enthalpic intermolecular interactions between CO(2) and the task-specific functional groups, such as amines. Interestingly, for the same amount of CO(2) loading NOHMs have also exhibited significantly different swelling behavior compared to that of the corresponding polymers, indicating a potential structural effect during CO(2) capture. If the frustrated canopy species favor spontaneous ordering due to steric and/or entropic effects, the inorganic cores of NOHMs could be organized into unusual structural arrangements. Likewise, the introduction of small gaseous molecules such as CO(2) could reduce the free energy of the frustrated canopy. This entropic effect, the result of unique structural nature, could allow NOHMs to capture CO(2) more effectively. In order to isolate the entropic effect, NOHMs were synthesized without the task-specific functional groups. The relationship between their structural conformation and the underlying mechanisms for the CO(2) absorption behavior were investigated by employing NMR and ATR FT-IR spectroscopies. The results provide fundamental information needed for evaluating and developing novel liquid-like CO(2) capture materials and give useful insights for designing and synthesizing NOHMs for more effective CO(2) capture.

Near-infrared spectroscopy monitoring of cerebral oxygen during assisted ventilation

Background:Changes in the arterial partial pressure of CO2 (PaCO2) has a direct though transient effect on the cerebral vasculature and cerebral circulation. Decreased PaCO2 levels lead to vasoconstriction and can result in dangerously low levels of cerebral perfusion that resolve in 4–6 h. It is currently believed that perfusion abnormalities contribute to intraventricular hemorrhage (IVH) and periventricular leukomalacia (PVL) in the neonate. PaCO2-induced vasoconstriction may contribute to the pathology of IVH and PVL.Methods:Near-infrared spectroscopy [NIRS; (INVOS cerebral/somatic oximeter; Somanetics Corporation, Troy, MI, USA)] was utilized to determine changes in regional oxygenation (rSO2) of the brain in response to changes in ventilation in isoflurane anesthetized newborn piglets.Results:Changes in cerebral rSO2 correlated significantly with end-tidal CO2 levels and to blood flow in the common carotid artery. This correlation was significant during baseline conditions, after periods of CO2 loading and during periods of hypothermia.Conclusions:The results of the study demonstrate the utility of NIRS to accurately reflect changes in cerebral oxygenation and flow to the brain in response to changes in CO2 levels in anesthetized, ventilated neonatal piglets. The use of NIRS may provide an early alert of low levels of cerebral blood flow and brain oxygenation, potentially helping in preventing the progression of IVH or PVL in the neonate.

Synthesis of WC hard materials using coated powders

Nickel and cobalt were used as binder materials for tungsten carbide powders (WC) hard materials. Ni and Co binder were added individually to the WC powder by two different methods namely, mechanical mixing and chemical electroless coating. In this study WC powders of grain sizes 0.3–1.0 μm were electroless coated with either nickel or cobalt. The loading of either Ni or Co coating was 13 wt.%. The electroless-coating method conditions of both Ni and Co on WC powders are described. The coated powders were cold compacted and sintered in vacuum at different sintering temperatures. For comparison, identical materials compositions were prepared by mixing the powders constituents mechanically, compacted and sintered under the same conditions. The prepared powders and sintered materials were investigated using X-ray diffraction (XRD) and scanning electron microscope (SEM). The results revealed that coated WC materials have smaller values of porosity and more homogeneous microstructure while other properties, such as transverse rupture strength, and hardness exhibit greater values than those produced using mixing elemental powders. It is possible to outline the benefits of coated powder approach in the following: high homogeneity and better distribution of binder materials within WC hard materials, higher density and good interfacial bonding, capability of using fine powders, and possibility of using small alloying and/or reinforcement additions in a more uniform manner.

Kinetics of Removal of Carbon Dioxide by Aqueous Solutions of N,N-Diethylethanolamine and Piperazine

N,N-Diethylethanolamine (DEEA) is a very promising absorbent for CO(2) removal from gaseous streams, as it can be prepared from renewable resources. Aqueous mixtures of DEEA and piperazine (PZ) are attractive for the enhancement of CO(2) capture, due to the high CO(2) loading capacity of DEEA and high reactivity of PZ. In the present work, for the first time, the equilibrium and kinetic characteristics of the CO(2) reaction with such mixtures were considered. Kinetic data were obtained experimentally, by using a stirred cell reactor. These data were interpreted using a homogeneous activation mechanism, by which the investigated reaction was considered as a reaction between CO(2) and DEEA in parallel with the reaction of CO(2) with PZ. It is found that, in the studied range of temperatures, 298-308 K, and overall amine concentrations, 2.1-2.5 kmol/m(3), this reaction system belongs to the fast pseudo-first-order reaction regime systems. The second-order rate constant for the CO0 reaction with PZ was determined from the absorption rate measurements in the activated DEEA solutions, and its value at 303 K was found to be 24,450 m(3)/(kmol s).

Artificial Neural Network Aided Screening and Optimization of Additives to Co/SrCO3 Catalyst for Dry Reforming of Methane under Pressure

An artificial neural network aided methodology succeeded to improve the catalytic performance of Co/SrCO3 for dry reforming of methane at 1 MPa, 1023 K, SV = 100 000 mL/h/g, feed composition = CH4/CO2/N2 = 45/45/10. CH4 conversion after 100 h time on stream was enhanced from 18% with Co/SrCO3 to 33% with the optimum Co/SrCO3, and CH4 conversion was constant from 10 to 100 h with the optimum catalyst, whereas it decreased gradually with Co/SrCO3. Reduction of carbon deposition after 100 h run (from 18.6% with Co/SrCO3 to 5.8% with the optimum) contributes to the stability of the optimum catalyst. In the first step of the optimization, new additives to the Co/SrCO3 catalyst were screened by using an artificial neural network (ANN). Catalytic activities of 10 mol % CO + 1 mol % X/Sr3 (X = B, K, Sc, Mn, Zn, Nb, Ag, Nd, Re, or Tl) and 16 physicochemical properties of these 10 elements were used as training data of the ANN, and the effect of each additive among 53 elements was predicted by the trained ANN. From the prediction and experimental verification, no better additive than the training data was found. Hence, high CO yield was obtained by Re addition, and CO yield gradually increased by Nd addition. Then, the loading of Co, Re, and Nd was optimized by means of design of experiment (DOE) and ANN for higher performance in the second stage of the optimization. The optimum catalyst was decided as 4.3 mol % Co, 2.2 mol % Nd, and 2.3 mol % Re supported on SrCO3, and it showed the remarkable performance.

Surface oxidation of Co 2+ and its dependence on ligand coordination number in silica polyamine composites

Coordination of CoCl 2 solutions to the silica polyamine composite, WP-1, made with the branched polymer polyethylenimine ( PEI) shows irreversible binding resulting from surface oxidation of the Co 2+–Co 3+. This is not the case for the silica polyamine composite BP-1 made with the linear polymer polyallylamine where reversible binding and no oxidation is observed. These observations suggested that oxidation of the cobalt was related to the greater coordination number available with the branched polyamine relative to the linear polyamine. A study of the kinetics of cobalt binding to WP-1 indicated initial loading of Co 2+ at relatively low coordination number followed by desorption of Co 2+ leading to oxidation and irreversible binding. Exclusion of oxygen from the composite-cobalt solution mixtures resulted in irreversible binding at a level that was 14% of the initial experiments. These observations prompted us to undertake a study to elucidate the coordination number around cobalt in the case of the branched polymer PEI. Towards this end, we have synthesized the model complexes [(tren)Co(H 2O) 2] 3+3Cl − (tren = tris(2,2′,2″aminoethyl)amine) and [(dien)Co(H 2O) 3] 3+3Cl − (dien = diethylenetriamine). The UV–Vis spectra of these model complexes were compared with Co 3+ coordinated to PEI in solution and it was concluded that the UV–Vis spectrum of the tren complex was closer to that observed for the solution UV–Vis spectrum of Co 3+–PEI. These data indicated that coordination of four amines was needed to drive surface oxidation under ambient conditions. In order to further elucidate the coordination number of a metal coordinated to the surfaces of WP-1 and BP-1, we reacted these composites with the probe molecule [Ru(CO) 3(TFA) 3] −K + (TFA = trifluoroacetate) (1) where the carbonyl stretching frequencies could be used as a measure of coordination number and geometry of the adsorbed complex. The IR of this complex on WP-1 indicated a monocarbonyl species while the IR of this complex on BP-1 indicated the presence of dicarbonyl species on the surface. These data are consistent with a coordination number of four amines in the case of WP-1 and the coordination of two amines in the case of BP-1 based on our previous studies of the solution coordination chemistry of the 1. Subsequent 13C CPMAS solid-state NMR on 13CO enriched samples of the 1 adsorbed onto BP-1 and WP-1 were consistent with the IR data.

Novel and efficient cobalt encapsulated SBA-15 catalysts for the selective oxidation of cyclohexane

Co-SBA-15 catalysts were synthesized by direct synthesis and post-synthetic impregnation methods at two different loadings of Co viz., 1.2 and 2 wt%. The structure of SBA-15 was found to remain intact even after the incorporation of Co in either of the two methods of catalyst preparation, which was confirmed by low-angle XRD. The existence of Co 2+ species were confirmed by characteristic absorption bands of Co in the UV–vis spectra and XPS results. The encapsulation of Co in SBA-15 was found to be highly advantageous in yielding significant amounts of the desired products viz., cyclohexanone and cyclohexanol in the oxidation of cyclohexane in liquid phase without using any solvent under moderate pressure of O 2 at 433 K. The catalysts showed high turn over numbers towards the oxidation of cyclohexane to cyclohexanone and 2%CoSYN (2 wt% Co-SBA-15) catalyst showed a maximum of 9.4% conversion of cyclohexane and 78% selectivity towards the formation of cyclohexanone.