Catalytic Precursors Research Articles

Kinetics of CO2 methanation using a Fe-bearing blast furnace sludge as catalytic precursor

The catalytic activity of a blast furnace sludge (BFS) with important Fe content, was experimentally evaluated in the methanation of CO2. The effect of temperature (265–320 °C), total pressure (1–5 bar), partial pressures of H2 (12–30 kPa), CO2 (0.5–3.0 kPa) and H2/CO2 ratio (4–25) on CO2 conversion and selectivity towards CH4 and CO were studied. The experimental assays were carried out in a laboratory differential reactor. The favorable effect of temperature, total pressure and H2/CO2 ratio on methane formation was demonstrated. In addition, the catalyst exhibited a stable activity during prolonged reaction times, a valuable characteristic for its industrial application.The reaction mechanism of CO2 hydrogenation using this BFS-catalyst was studied under a strict kinetic regime. Different reaction paths were considered, from which kinetic expressions were derived using the Langmuir-Hinshelwood methodology and the Levenberg-Marquardt algorithm. The latter, for evaluation of the resulting kinetic/adsorption parameters. By applying the corrected Akaike information criterion (AICc), the rate controlling step was established. This corresponds to the hydrogenation of adsorbed CH, with surface CO as the main intermediary of methane formation. From the experimental data, an activation energy of 86.5 kJ/mol was calculated.This article can be considered as a first step for future processes of scaling and optimization of CO2 methanation using a waste from the steel production industry.

Porous clay nanoarchitectures as supports for heterogenized nickel complexes in catalytic reactions of ethylene oligomerization

Linear alpha-olefins (LAOs) are high-value intermediates for fine chemicals and petrochemicals. The main process for obtaining these products is from olefin oligomerization. The use of heterogenized catalytic systems based on anchoring of organometallic precursors on inorganic materials has the advantages of increasing the selectivity of the reaction and the possibility of reusing the catalyst. In this work, porous clay nanostructures with bi (2D) and three-dimensional (3D) structures were synthesized to act as catalytic supports. A Ni-β-diimine organometallic complex was anchored to these materials giving rise to heterogenized nickel complexes that were tested as catalytic precursors for the ethylene oligomerization reaction, and they were compared with the analogous complex in homogeneous medium. The results showed the influence of the heterogenization of the materials on the thermal stability of the catalyst and the selectivity of the products. Also, the results demonstrated a noticeable influence of the different structures of the materials on catalytic activity. The best result was obtained with the catalyst anchored on the support with a 3D structure, presenting a T.O.F. (turnover frequency) of 754 × 10 ³ h−1. Finally, this material was subjected to recycling tests that qualitatively showed that the catalyst can be reused while maintaining a high selectivity of 95% for alpha-olefins.

Effect on water consumption by metallic impurities into electrolyte of lead-acid batteries

Because of the continuous increment of the use of recycled lead in the manufacturing of Lead-Acid Batteries (LABs), the presence of metallic impurities in the batteries has also increased. These impurities have a high impact in this industry as they can be catalytic precursors of the secondary reactions that occur in the LAB performance: the Hydrogen Evolution Reaction (HER) and Oxygen Evolution Reaction (OER). When the secondary reactions are catalyzed, the water consumption of a battery might be increased. In this way, negative effects such as the decrease of high-temperature durability and the increase of self-discharge could occur, even the safety of the battery itself could be jeopardized. Due to these facts, the aim of the present research work was to develop a quick-low-cost system that measured the effect of metallic impurities in the LAB electrolyte. This system consisted of a three electrode cell, able to detect low concentration effect of metallic impurities in the battery electrolyte, applying the Cyclic Voltammetry (CV) technique. In addition, a qualitative study was carried out comparing the catalytic impurity effect on HER in two different systems: a three electrode cell and a 2 V/ 1 Ah lead-acid mono cell. The following impurities were studied at different concentrations: nickel, bismuth, zinc, silver and selenium. The results show that the study by CV allows detecting the effect of impurities qualitatively at low concentrations of all impurities studied, except zinc. Furthermore, it was observed that an increment in the concentration of nickel and selenium in the LAB electrolyte leads to a noticeable increase in HER both in the three electrode and 2 V/ 1 Ah cell systems.

Systematic study on the properties of nickel aluminate (NiAl2O4) as a catalytic precursor for aqueous phase hydrogenolysis of glycerol

A systematic study for determining the maximum amount of nickel incorporated into the γ-Al2O3 structure to form NiAl2O4 was performed, and its behavior as a catalytic precursor for obtaining Ni/γ-Al2O3 catalysts for glycerol hydrogenolysis and cyclohexane conversion as a model reaction was investigated. The catalysts were prepared with 2, 10, 18, and 33 wt%Ni and characterized by N2 physisorption, TPR, XRD-Rietveld refinement, XPS, CO chemisorption, and SEM-EDS. NiAl2O4 was detected by XRD for all catalytic precursors, and NiO was only detected for the solid containing 33 wt%Ni. TPR analysis of catalytic precursors and catalysts showed that the insertion of Ni into the γ-Al2O3 structure is a reversible process. TPR and XRD results indicated that the maximum amount of Ni that can be incorporated into the NiAl2O4 structure is probably 20 wt%Ni. A tetragonal model with I41/amd space group symmetry adjusted to the description of NiAl2O4 structure in Rietveld refinement. XRD, CO chemisorption, and SEM images showed that exsolution of Ni from NiAl2O4 led to the formation of uniformly sized Ni0 particles for catalysts containing 2 and 10 wt%Ni. For 18 and 33 wt%Ni, SEM-EDS results showed larger Ni0 particles and the formation of gridshell type structures, with the alumina covering the Ni particles. XPS analysis showed that the nature of the Ni0 sites depended on if they are obtained entirely from Ni exsolution from NiAl2O4 or from exsolution combined with the reduction of excess NiO, which affected the catalytic activity for cyclohexane conversion. For glycerol hydrogenolysis, the activity decreased with the increase of Ni content. In this case, the formation of the gridshell could be the determining factor affecting the catalytic activity, especially in liquid-phase reactions.

The Effect of Titanium Tetra-Butoxide Catalyst on the Olefin Polymerization.

The purpose of this study was to assess the ability of titanium Ti(IV) alkyloxy compounds supported by organic polymer polyvinyl chloride (PVC) to polymerize ethylene by feeding triethylaluminium (TEA) as a cocatalyst. Additionally, the impacts of the molar ratio of [Al]/[Ti] on the catalytic activities in ethylene’s polymerization and of the comonomer through utilization of diverse quantities of comonomers on a similar or identical activity were studied. The optimal molar ratio of [Al]/[Ti] was 773:1, and the prepared catalyst had an initial activity of up to 2.3 kg PE/mol Ti. h. when the copolymer was incorporated with 64 mmol of 1-octene. The average molecular weight (Mw) of the copolymer produced with the catalysts was between 97 kg/mol and 326 kg/mol. A significant decrease in the Mw was observed, and PDI broadened with increasing concentration of 1-hexene because of the comonomer’s stronger chain transfer capacity. The quick deactivation of titanium butoxide Ti(OBu)4 on the polymers was found to be associated with increasing oxidation when supported by the catalyst. The presence of Ti(III) after reduction with the aluminum alkyls cleaves the carbon-chlorine bonds of the polymer, producing an inactive polymeric Ti(IV) complex. The results show that synergistic effects play an important role in enhancing the observed rate of reaction, as illustrated by evidence from scanning electron microscopy (SEM). The diffusion of cocatalysts within catalytic precursor particles may also explain the progression of cobweb structures in the polymer particles.

Copper-Catalyzed Tandem Cross-Coupling and Alkynylogous Aldol Reaction: Access to Chiral Exocyclic α-Allenols.

An enantioselective copper-catalyzed tandem cross-coupling/alkynylogous aldol reaction has been developed. The tetrasubstituted allenoates containing both central and axial chirality have been obtained in moderate to good yields and excellent enantio- and diastereoselectivity. Distinct from the previous use of Cu(I) salts, this protocol features the use of copper(II) salts as a catalytic precursor in this asymmetric cross-coupling reaction.

Dual Cobalt and Photoredox Catalysis Enabled Redox‐Neutral Annulation of 2‐Propynolphenols

AbstractA hydroxyl‐assisted, organophotoredox/cobalt dual catalyzed annulation of 2‐propynolphenols to form 2‐hydroxymethyl‐benzo[b]furans was developed by employing 1,2,3,5‐tetrakis(carbazol‐9‐yl)‐4,6‐dicyanobenzene (4CzIPN) as photosensitizer and CoCl2(PPh3)2/5,5′‐dimethyl‐2,2′‐bipyridine as cobalt catalytic precursor. Various substrates and functional groups were tolerated. The practical applications of this reaction were further demonstrated by enlarged gram‐scale and various derivations for complex heterocycles. Primary mechanistic studies suggested the involvement of cobalt‐hydride mediated hydrogen atom transfer (HAT) process.magnified image

Improved reversible dehydrogenation properties of Mg(BH4)2 catalyzed by dual-cation transition metal fluorides K2TiF6 and K2NbF7

Two dual-cation transition metal fluorides K2TiF6 and K2NbF7 are introduced into Mg(BH4)2 by ball-milling to catalyze the dehydrogenation of Mg(BH4)2. According to the DSC and TPD results, the onset dehydrogenation temperature of Mg(BH4)2 doped with K2TiF6 and K2NbF7 are remarkably reduced to 105.4 and 118.0 °C, respectively. Meanwhile, both the K2TiF6 and K2NbF7 catalyzed systems can release more than 6.4 wt% H2 under 280 °C, showing an improvement in dehydrogenation kinetics. In addition, the reversible capacity of the Mg(BH4)2–3%K2TiF6 system is 2.7 wt% at 280 °C in 250 min, which is enhanced comparing to that of pristine Mg(BH4)2. X-ray diffraction, Fourier-transformed infrared and 11B nuclear magnetic resonance investigations reveal that the K2TiF6 actually acts as a catalytic precursor to react with Mg(BH4)2, forming active hydrides of KBH4 and TiH2, which further serve as catalyzing agents to facilitate the re-generation of Mg(BH4)2 from intermediates under moderate conditions.

Transfer Hydrogenation of Levulinic Acid to γ‐Valerolactone and Pyrrolidones Using a Homogeneous Nickel Catalyst

AbstractWe report a well‐defined homogeneous nickel‐based catalyst using the complex [dippeNi(COD)] (dippe=1,2‐bis(diisopropyl phosphino)ethane) as a catalytic precursor with high activity in the hydrogenation of levulinic acid (LVA) to yield γ‐valerolactone (GVL) under relatively mild conditions (4 h, 120 °C); formic acid (FA) is the transfer hydrogenation agent in a dehydrogenation‐hydrogenation process. Under optimized conditions, GVL was obtained with excellent yield (>99 %) and selectivity (>99 %). The Ni‐catalyst was assessed in the LVA hydrogenation with a variety of primary amines using an excess of FA (4 eq) as hydrogen donor at 15 h and 170 °C to produce 2‐pyrrolydones with excellent yield (>99 %) and fair to good selectivity (from 68 to 92 %).

A novel heterogenized Ni/β-diimine/SBA-15 complex applied for catalytic ethylene oligomerization

Catalytic oligomerization of ethylene performed with the sterically hindered β-diimine ligand 2-(2,6-diisopropylphenyl)-amine-4-(2,6-diisopropylphenyl)-imine-2-pentene covalently ancored on SBA-15 mesoporous support employing the alkosilane 3-chloropropyltrimetoxysilane (CPTMS) for the first time. This material was tested as catalytic precursors for ethylene oligomerization processes and was characterized using various techniques such as small-angle XRD, elemental analysis, 1H and 29Si NMR, N2 sorption, gas chromatograph and flame atomic absorption spectroscopy. The heterogenized complex demonstrated an increase in selectivity for the products of interest (α-C4).

Molybdenum (VI) Complexes Containing Pyridylimine Ligands: Effect of the Imine Nitrogen Substituent in the Epoxidation Reaction

AbstractA series of pyridylimine ligands with variations of the substituent at the imine nitrogen were synthesized and coordinated to the [MoCl2O2] core. The novel molecular structures of the complexes were fully characterized by 1H and 13C NMR, FT‐IR, ESI, EA, and X‐ray crystallography, and their catalytic activity was studied for the epoxidation of alkenes using tert‐butyl hydroperoxide (TBHP) as the oxidant. The new complexes showed excellent catalytic activity and fine selectivity in the epoxidation reaction compared with similar homogeneous molybdenum complexes. The results demonstrated that there is a significant change in the catalytic performance, depending on the alkyl arm on the structure of the pyridilimine ligand. The catalytic results indicated that complex [MoCl2O2(L)] (L: N‐(2‐Pyridinylmethylene)‐1‐tert‐butylimine) C5 is the best catalytic precursor in the epoxidation of cyclohexene (TON: 92920 and TOF: 30974 h−1).

Electrospinning as a route to advanced carbon fibre materials for selected low-temperature electrochemical devices: A review

Electrospinning is a versatile fabrication method for synthesising mesostructured nanofibrous mats and has been explored in this review for the following electrochemical energy storage devices: redox flow batteries, fuel cells, metal air batteries and supercapacitors. Electrospinning has been proven as a highly versatile fabrication method for producing nano-structured fibres with controllable morphology, of both the fibres themselves and the void structure of the mats. Additionally, it is possible to use heteroatom doped polymers or to include catalytic precursors in the electrospinning solution to control the surface properties of the fibres. These factors make it an ideal method for the production of electrodes and flow media for a variety of electrochemical devices, enabling reduction in mass transport and activation overpotentials and therefore increasing efficiency. Moreover, the use of biomass as a polymer source has recently gained attention for the ability to embed sustainable principles in the materials of electrochemical devices, complementing their ability to allow an increase in the use of renewable electricity via their application. In this review, the historical and recent developments of electrospun materials for application in redox flow batteries, fuel cells, metal air batteries and supercapacitors are thoroughly reviewed, including an overview of the electrospinning process and a guide to best practice. Finally, we provide an outlook for the emerging use of this process in the field of electrochemical energy devices with the hope that the combination of tailored microstructure, surface functionality and computer modelling will herald a new era of bespoke functional materials that can significantly improve the performance of the devices in which they are used.

Epimerization of isosorbide catalyzed by homogeneous ruthenium-phosphine complexes: A new step towards an industrial process

An efficient process for obtaining isoidide by catalytic epimerization of isosorbide using HRu(CO)Cl(PPh3)3/Xantphos (1/1) as organometallic catalyst without hydrogen is reported. The epimerization of isosorbide led to a thermodynamic equilibrium mixture containing 37% isosorbide, 57% isoidide and 6% isomannide in 1 h at 170 °C in tert-amyl alcohol. The same proportions were reached by using the catalytic precursor HRu(CO)Cl(PPh3)3 associated with sulfonated phosphines to isomerize isosorbide without solvent. Interestingly, the reaction can be also performed in a biphasic system (isosorbide/toluene) with the same catalytic activity. In this case, the mixture of isohexides was easily separated from toluene catalytic phase. Thus, by adding in each time a new isosorbide layer, nine successive cycles were performed without a loss of the catalytic activity. A scale-up leading to isomerize 1.3 Kg of isosorbide using only 0.2 g of ruthenium was also performed showing the potentiality of this biphasic catalytic system for an industrial application.

Ni-β-diimine complex heterogenized in delaminated ITQ-2 zeolite as catalytic precursor for ethylene oligomerization

A heterogenized nickel catalytic precursor was synthesized and applied in ethylene oligomerization catalytic reactions. For this, a β-diimine ligand was covalently anchored to the delaminated ITQ-2 zeolite and the metal complexed. The homogeneous nickel complex was synthesized in order to compare the effect of catalyst heterogenization on the reaction. The synthesized materials were characterized by several techniques, such as 1H NMR, solid-state 29Si CP-MAS-NMR, FTIR, TGA, N2 adsorption, flame atomic absorption spectroscopy, elemental analysis and X-ray absorption spectroscopy (XAS). The heterogenized catalytic precursor showed similar catalytic activity and higher selectivity for the target products to its homogeneous complex counterpart. The higher stability of the nickel centers under oxidative handling conditions was demonstrated by the XAS measurements. It was possible to reuse the catalytic precursor twice in oligomerization reactions despite the loss of catalytic activity ascribed to the presence of an excess of co-catalyst. Notwithstanding, it was demonstrated that Al-containing delaminated zeolites are promising materials for anchoring β-diimine-based catalytic precursors in comparison with mesoporous materials due to their higher acidity, which improves the intrinsic catalytic activity (turnover frequency, TOF) due to the higher nickel electron withdrawing capacity provided by the acidic support.

Synthesis of 3-Alkylideneisoindolin-1-ones via Sonogashira Cyclocarbonylative Reactions of 2-Ethynylbenzamides.

Cyclocarbonylative Sonogashira reactions of ortho-ethynylbenzamides have been investigated. The process is carried out under CO pressure, in the presence of a very small amount of PdCl2(PPh3)2 (0.4 mol %) as a catalytic precursor and without the need for a Cu salt as the co-catalyst. 2-Ethynylbenzamide reacted successfully with iodoarenes bearing electron-withdrawing and electron-donating groups, giving rise to different classes of compounds depending on the solvent used. On the contrary, N-(4-chlorophenyl)-2-ethynylbenzamide afforded exclusively polyfunctionalized isoindolinones with high stereoselectivity toward (E) isomers.

Toward Amines, Imines, and Imidazoles: A Viewpoint on the 3d Transition-Metal-Catalyzed Homogeneous Hydrogenation of Nitriles

Mn-, Fe-, Co-, and Ni-based catalytic precursors have been reported for the homogeneous 3d transition-metal-catalyzed hydrogenation of nitriles. We present herein a critical assessment of such repo...

Cyclopalladated Compounds with Polyhalogenated Benzylphosphanes for the Mizoroki‐Heck Reaction

Nine partially halogenated benzylphosphanes ArXCH2PR2 (ArX = 3,6‐dichlorophenyl, 3,6‐difluorophenyl and 3,4,5‐trifluorophenyl; R = Ph, Cy, iPr) have been prepared and reacted with palladium acetate to obtain the cyclometallated dimers [Pd(µ‐OAc)(κ2‐C,P‐ArXCH2PR2)]2. The acetate bridge has been exchanged by bromide using lithium bromide and the obtained dimers have been thoroughly characterised. The dimers with the non‐halogenated phosphanes PhCH2PR2 (R = Ph, iPr) have also been prepared. Treatment with norbornadiene in the presence of silver tetrafluoroborate has furnished the cationic mononuclear complexes [Pd(κ2‐C,P‐ArXCH2PR2)(nbd)]BF4 as stable solids. These complexes and some of the bromide dimers have been used as catalytic precursors in the Mizoroki‐Heck reaction between bromobenzene and butyl acrylate. The complexes efficiently catalyse this transformation and important differences of activity are found depending on the ligand. In general, fluorinated phosphanes give more active systems than chlorinated analogues.

Self-Assembled, Highly Positively Charged, Allyl-Pd Crowns: Cavity-Pocket-Driven Interactions of Fluoroanions.

A series of dodecanuclear highly positively charged homo- and heterometallamacrocycles [{Pd(η3 -2-Me-C3 H4 )}6 (4-PPh2 py)12 {M2 (tpbz)}3 ]18+ (M=Pd, Pt; tpbz=1,2,4,5-tetrakis(diphenylphosphanyl)benzene were synthesized by the quantitative self-assembly of {Pd(η3 -2-Me-C3 H4 )}+ , {M2 (tpbz)}4+ and 4-PPh2 py moieties in 2:1:4 molar ratio. The cationic assemblies were obtained as salts of different fluorinated anions with diverse sizes and electronic properties, namely BF4 - , PF6 - , SbF6 - and CF3 SO3 - . The new crown-like metallamacrocycles showed remarkable differences in their NMR spectra due to the presence of the different counteranions. On the basis of the observed variations, the metallacycles have been tested as catalytic precursors in allylic alkylation reactions. The anion-dependent activity and selectivity has been analysed and compared with that of the corresponding monometallic allylic corners [Pd(η3 -2-Me-C3 H4 )(4-PPh2 py)2 ]X (X=BF4 - , PF6 - , SbF6 - , CF3 SO3 - ). DFT calculations have been employed in order to help to the interpretation of the experimental data and to model the anion-crown interactions.

Photocatalytic Degradation of 2,4-Dichlorophenol on NiAl-Mixed Oxides Derivatives of Activated Layered Double Hydroxides

Advanced oxidation processes such as photocatalysis have assumed enormous importance in the scientific field as viable sustainable alternatives to be applied to the elimination of persistent organic pollutants present in water reservoirs for human consumption. Persistent organic compounds like pesticides that belong to the chlorophenol family are a global public health priority since they are associated with serious diseases like cancer and can even cause death at low concentrations of prolonged exposure. This work proposes the use of activated Ni/Al layered double hydroxides as photocatalysts for the degradation of 2,4-dichlorophenol. The study variables associated with the properties of the catalysts were the Ni/Al metal ratio as well as the synthesis conditions. To determine the structural properties of catalytic precursors and catalysts, the techniques of XRD, FTIR, UV-DR, DGTA, TPD, SEM-EDS and TEM were used. The photodegradation tests were carried out in a Bach type reactor with a high energy uv lamp. The results of the photocatalytic degradation of 2,4-dichlorophenol in aqueous solution showed good photocatalytic activity with a degradation efficiency of up to 94% attributed to the presence of Ni in the crystalline and amorphous structures of NiO–NiAl2O4 oxides by means of a combined oxidation-reduction mechanism due to the effect of holes and superoxide and hydroxyl radicals not associated with the memory effect of reconstruction of layered double hydroxides.

Non-Pt Nanofibrous Catalysts for an ORR PEM Fuel Cell Cathode

Electrospun nanofibrous catalysts made of non-Platinum group metal (non-PGM), low cost precursors are studied for the ORR to be applied in a PEM fuel cell cathode. Optimizing the structure of proton exchange membrane (PEM) fuel cell cathodes is essential to reduce the high cathode loadings (1 to 6 mg of catalyst per cm2), used for non-PGM catalysts to compensate for the lower activity against standard Pt catalysts. Electrospinning is used to shape the catalytic precursors in a network of nanofibers to study the effect of the electrospun architecture with respect to fuel cell performance.