Steps Of Catalyst Preparation Research Articles

Oxovanadium(IV)‐salophen covalently immobilized on silica‐coated Fe3O4 nanoparticles: A magnetically recoverable nanocatalyst for the selective oxidation of sulfides

The current study introduces an approach toward the development of heterogeneous, magnetically recoverable oxovanadium(IV)‐salophen complex to employ in the selective oxidation of sulfides using H2O2 as oxidant. A salophen ligand containing hydroxyl functional group was synthesized, which is conducive to successful, covalent immobilization of metal complex onto the silica‐modified Fe3O4 magnetic nanoparticles (SMNPs). This type of metal anchoring is achieved through an intermolecular condensation reaction. The in‐depth investigation on the catalyst (Fe3O4@SiO2@VO(salophen)) productivity and lifetime in the oxidation of a wide range of linear and aromatic sulfides is well represented and discussed. The use of the current catalyst in the selective oxidation of prototype substrate (methyl phenyl sulfide) resulted in an appreciable increase in the selectivity toward the desired sulfoxide (92%) and conversion rate (95%) compared with similar studies, reported to this day. Analytical techniques such as field emission scanning electron micrograph (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD) analysis, and inductively coupled plasma optical emission spectrometer (ICP‐OES) provided data on structural/compositional characterization of materials in catalyst preparation steps.

A Mechanistic Approach to Liquid‐Assisted Mechanochemical Synthesis of 5‐Aryl/Spiro‐[1,2,4]‐triazolidine‐3‐thiones

Abstract1,3‐dimethylbarbituric acid‐H2O mediated liquid assisted mechanochemical route has been developed for the synthesis of a wide array of 5‐aryl/spiro‐1,2,4‐triazolidine‐3‐thiones, via in situ generation of benzylidene/alkylidene barbiturates, followed by tandem, base‐driven Michael addition reaction and rearrangement of the pyrimido[4,5‐e][1,2,4]triazepine intermediate. The method is an application of mechanochemistry in organic synthesis. It is efficient, easy to follow and avoids the tedious steps of catalyst preparation and chromatographic separation. Moreover, the protocol is compared to “on‐water”, room temperature approach and the reaction mechanism has been revisited with the aid of experiments.

Formation Mechanism of Carbon-Supported Hollow PtNi Nanoparticles via One-Step Preparations for Use in the Oxygen Reduction Reaction

Hollow Pt-based nanoparticles are known to possess the properties of high electrocatalytic activity and durability. Nonetheless, their practical applications as catalytic materials are limited because of the requirement for exhaustive preparation. In this study, we prepared carbon-supported hollow PtNix (x = the moles of the Ni precursor to the Pt precursor in the catalyst preparation step) catalysts using a one-step preparation method, which substantially reduced the complexity of the conventional method for preparing hollow Pt-based catalysts. In particular, this hollow structure formation mechanism was proposed based on extensive characterizations. The prepared catalysts were examined to determine if they could be used as electrocatalysts for the oxygen reduction reaction (ORR). Among the investigated catalysts, the acid-treated hollow PtNi3/C catalyst demonstrated the best ORR activity, which was 3 times higher and 2.3 times higher than those of the commercial Pt/C and acid-treated particulate PtNi3/C catalysts, respectively.

CATALYTIC ACTIVITY OF VANADIUM OXIDE DOPED WITH PALLADIUM NANOPARTICLES ON OXIDATION OF 5-HYDROXYMETHYLFURFURAL

2,5-Furan dicarboxylic acid (FDCA) is a bio-based chemical used as a feedstock for a wide range of industrial applications - particularly the bioplastic industries. It is derived from 5-hydroxymethylfurfural (HMF) through a reaction of oxidation using either homogeneous or heterogeneous catalysts. According to the advantages of heterogeneous catalysts, this research aims to seek a novel catalyst type with high selectivity and high activity. We performed an investigation of the synergic effect of palladium nanoparticles and V2O5 catalysts on catalytic oxidation of HMF and physicochemical properties. A commercial vanadium oxide powder (V2O5) was doped with 1 wt.% palladium nanoparticles (Pd NPs). The Pd NPs were prepared by the colloid-chemical reduction method. Two different synthesis processes were performed base on the consequence of the combination of colloid-chemical reduction and immobilization steps, herein stepwise (ST) and simultaneous (SI) process. For the ST process, Pd NPs were reduced and then immobilized on V2O5 powder. During the SI process, the reduction and immobilization steps took place simultaneously. Physical and chemical properties of a prepared catalyst such as morphology, particle size distribution, and chemical structure and composition were characterized using various techniques, e.g. TEM, BET, X-ray diffraction, UV-vis spectrophotometer. It was distinctly found the synergic effect between Pd NPs and V2O5 catalysts on the surface catalytic activity of HMF oxidation and catalytic selectivity. The Pd NPs incorporated catalysts (ST and SI processes) gave catalytic activity at 63%, which are 2-fold in catalytic activity in comparison with bare V2O5 catalysts as well as they were selective to FDCA up to 19-24%. The step of catalyst preparation slightly influenced on catalytic activity and yield of FDCA; however, it did alter particle size distribution of Pd NPs and surface characteristics

Interface tuning of Cu+/Cu0 by zirconia for dimethyl oxalate hydrogenation to ethylene glycol over Cu/SiO2 catalyst

An efficient ZrO2–doped Cu/SiO2 catalyst was fabricated through hydrolysis precipitation method (HP) and used to produce ethylene glycol (EG) through dimethyl oxalate (DMO) hydrogenation. The states for zirconia on copper catalyst and roles in DMO hydrogenation were investigated through various characterization tools, including N2 physical adsorption, XRD, H2–TPR, Methyl glycolate–TPD–MS, XPS, XAES as well. Compared with common ammonia evaporation and co–precipitation methods used in catalyst preparation, this HP method is found to effectively suppress the agglomeration and further size growth of copper nanoparticles by enhancing the interactions between copper and zirconia species. More importantly, uniform distribution of ZrO2 dopant is achieved due to the pseudo-homogeneous reactions in the mixing step of catalyst preparation. A proper amount of zirconium dopant helps achieve the desirable proportion of Cu+/(Cu++Cu0) for surface copper species, especially promotes the production of Cu+ species originated from Cu–ZrO2 species at the interface of copper and zirconia particles. In comparison with Cu+ species formed from copper phyllosilicates reduction, the Cu+ sites derived from Cu–ZrO2 species show higher adsorption ability of MG, an important intermediate species in ethylene glycol production. These adsorbed MG molecules further react with atomic hydrogen shifted from adjacent metallic copper surface, leading to a higher catalytic behavior. For the EG production via DMO hydrogenation, the turnover frequency (TOF) normalized by Cu0 species on CuZr/SiO2 catalyst is 1.8 times than that of traditional Cu/SiO2 counterpart. Due to the enhanced synergy effect between Cu+ and Cu0 active sites, a lower activation energy of ester hydrogenation on this ZrO2–doped Cu/SiO2 catalyst is believed to be responsible for the significant improvement.

Catalytic activity of maghemite supported palladium catalyst in nitrobenzene hydrogenation

A maghemite supported palladium catalyst was prepared and tested in nitrobenzene hydrogenation. The catalyst support was made by a newly developed combined technique, where sonochemical treatment and combustion have been used. As a first step, maghemite nanoparticles were synthesized. Iron(II) citrate was treated in polyethylene glycol by high-intensity ultrasound cavitation to get a homogeneous dispersion, then the product was combusted. The produced powder contained maghemite nanoparticles with 21.8 nm average particle size. In the second step of catalyst preparation, the magnetic nanoparticles were dispersed in the ethanolic solution of palladium(II) nitrate. The necessary energy for the reduction of Pd2+ ions was achieved in the “hot spots” by acoustic cavitation, thus catalytically active palladium was formed. The prepared maghemite supported Pd catalyst have been tested in nitrobenzene hydrogenation at three different temperatures (283 K, 293 K and 303 K) and constant pressure (20 bar). At 293 K and 303 K, the conversion and selectivity of nitrobenzene was above 99% and 96%, respectively. However, the selectivity was only 73% at 273 K because the intermediate species (azoxybenzene and nitrosobenzene) have not been transformed to aniline. All in all, the prepared catalyst is successfully applied in nitrobenzene hydrogenation and easily separable from the reaction media.

Iron ore as precursor for preparation of highly active χ-Fe5C2 core-shell catalyst for Fischer-Tropsch synthesis

This work describes a novel method for the preparation of active and stable Fe-based catalyst from an iron ore, which was chemically treated with oxalic acid to obtain a mixture of iron oxides and oxalate. It was found that under CO atmosphere at 350 °C, this mixture can be effectively transformed into active iron carbide phase (χ-Fe5C2), which is highly desirable for FTS. The catalysts were characterized by SEM, TEM, TGA, Raman, XRD, BET, and CO-TPR-MS. The catalytic performance was evaluated under FTS conditions (280 °C, H2 / CO = 1, P =20 bar) and GHSV = 12 N L gcat−1 h−1 for 100 h. The results showed that the CO conversion (66.8%) was higher on the oxalic acid-treated iron ore than in the untreated iron ore (46.5%), obtaining a high C5+ hydrocarbon selectivity (> 60.0%) in all cases. The proposed method significantly reduced the catalyst preparation steps using an inexpensive and abundant raw material for the sustainable preparation of very active and stable Fe-based catalysts for the FTS.

Analysis of particle breakage during the preparation steps of Co/Al2O3 catalysts

Fischer–Tropsch reaction is applied to produce ultra-clean fuels based on the synthesis gases. Supported cobalt catalysts are used for Fischer–Tropsch synthesis due to their high stability and good catalytic activity. These catalysts are generally prepared by wet chemical methods which involve impregnation, drying and calcination. A new approach to the analysis of degradation of catalysts under thermal stress during the various steps of catalyst preparation has been applied to the support (γ-Al2O3) and to the catalysts (10 wt% Co/Al2O3). Low particle damages occur when the catalyst is prepared by impregnation. Thus, a rate of about 1 wt% of fine particles with sizes less than 63 µm has been quantified. However, the effect of temperature during drying at 100 °C and calcination at 400 °C becomes significant: a degradation rate of 2% and 5% is noted for temperatures of 100 °C and 400 °C, respectively. These results show particle degradation through cleavage and fragmentation. These mechanisms result in the initial heterogeneous structure (fractures and cracks) of the support which reduces the mechanical resistance of the catalyst and initiates the rupture of the particles under an increase in temperature. To describe the particle breakage, a numerical approach was implemented under thermal stresses on modeled Co/Al2O3 ring particles. Calculations were performed using COMSOL Multiphysics® (Structural Mechanics Module) following a 2D geometry. The effect of temperature, crack height (radial and axial components) and porosity on the particle breakage were studied. The results obtained highlighted the solid breakage at high temperature (calcination phase), high-size cracks and low porosity.

Pt stabilization on Pt/SBA-15 through surface modification using MPTMS for sulfuric acid decomposition in SI cycle to produce hydrogen

Catalysts for the sulfuric acid (SA) decomposition, one of three reactions in Sulfur–Iodine (SI) cycle to produce hydrogen, should be active and stable in wide temperature ranges of 650–850 °C. Pt based catalysts are explored for SA decomposition, but they suffered from the severe Pt loss at the high temperature of 850 °C. Uniform platinum nanoparticles (NPs) are physically trapped within mesopores of the mesoporous SBA-15 prepared in a “one pot” method (Ptx.x-NTS, x.x: loaded Pt wt%). Other Pt catalysts are prepared to stabilize Pt particles using 3-mercaptopropyletrimethoxysilane (MPTMS) as a stabilizing agent (Ptx.x-TS, x.x: loaded Pt wt%). The co-assembly method in the one pot is based on the I+M–S+ scheme in which S+ (Protonated block copolymer) and I+ (Cationic inorganic precursor) are assembled together through the M– (PtCl6-) mediator. The MPTMS containing thiol group is used to modify the cationic precursors (I+) in order to hold the Pt nanoparticles in meso-channels as the reduced platinum metal is easy to bond with thiol groups. The prepared samples are characterized by XRD, TEM, CO Chemisorption, N2 adsorption desorption, and ICP-OES techniques. The TEM images show that the small Pt NPs of an average size of 7.0 (±0.84 nm) are uniformly dispersed within the mesopores on the mesoporous SBA-15. The thiol stabilized Pt-TS catalysts display the exceptional catalytic stability for sulfuric acid decomposition at the high temperature of 850 °C for 50 h. The overall average metal loss is 67% for the Pt2.0-NTS for 50 h at 76,000 mL.gcat−1.h−1, while it is 16% for the Pt2.0-TS. The metal loss of Pt/SBA-15 is significantly suppressed by the surface functionalization using MPTMS in the catalyst preparation step.

Correlation of Sol–Gel Alumina‐Supported Cobalt Catalyst Processing to Cobalt Speciation, Ethanol Steam Reforming Activity, and Stability

AbstractThe effect of sol–gel alumina characteristics on the supported Co catalyst properties was investigated at the different steps of catalyst preparation. Porous alumina with variable surface reactivity were prepared from the sol–gel transition and the spinodal decomposition induced by polymers. The hydrophobicity of polymer or the calcination temperature controls the amount of the hydroxyl groups. The dried catalysts are composed of cobalt alumina hydrotalcite‐like compounds up to 64 %. After calcination, higher proportions of CoAl2O4 are observed in the alumina presenting a greater content of hydroxyl and hydrotalcite. The Co speciation during activation investigated by Quick X‐ray absorption spectroscopy evidences that both Co3O4 and CoAl2O4 are first fully reduced to CoO and then partially transformed into point‐like Co0 nucleus. The catalysts were highly active in the ethanol steam reforming reaction; however, coke deposition leads to deactivation. This deleterious effect was minimized for catalysts operating with a CoO/Co0 ratio close to 1:3.

Activation and In Situ Ethylene Polymerization on Silica-Supported Ziegler–Natta Catalysts

The structural, vibrational, and electronic properties of silica-supported Ziegler–Natta catalysts industrially relevant for polyethylene production were investigated in detail by means of a multitechnical approach at each step of catalyst preparation, including precatalyst activation. In the precatalyst, the TiClx phase is grafted mainly to the silica surface and almost independent of the supported MgClx phase. However, the subsequent activation by means of an aluminum–alkyl compound causes important changes to both the supported MgClx phase and the TiClx phase. The resulting catalyst is entirely reconstructed so that most of the titanium sites are detached from the silica surface and in interaction with a highly dispersed MgCl2 phase, thus mimicking the most famous and highly investigated Ziegler–Natta catalysts (not silica-supported). For the first time, the catalyst performances were monitored by means of in situ FT-IR spectroscopy in transmission mode, simulating industrially significant polymerizati...

Polymeric Material Application for The Production of Ceramic Foam Catalyst

Ceramic foams are prepared as positive images corresponding to a plastic foam structure which exhibits high porosities (85–90%). This structure makes the ceramic foams attractive as a catalyst in a dry reforming process, because it could reduce a high pressure drop problem. This problem causes low mass and heat transfers in the process. Furthermore, the reactants would shortly contact to catalyst surface, thus low conversion could occur. Therefore, this research addressed the preparation of dry reforming catalysts using a sol-gel catalyst preparation via a polymeric sponge method. The specific objectives of this work are to investigate the effects of polymer foam structure (such as porosity, pore sizes, and cell characteristics) on a catalyst performance and to observe the influences of catalyst preparation parameters to yield a replica of the original structure of polymeric foam. To accomplish these objectives industrial waste foams, polyurethane (PU) and polyvinyl alcohol (PVA) foams, were used as a polymeric template. Results indicated that the porosity of the polyurethane and polyvinyl alcohol foams were about 99% and 97%. Their average cell sizes were approximate 200 and 50 micrometres, respectively. The cell characteristics of polymer foams exhibited the character of a high permeability material that can be able to dip with ceramic slurry, which was synthesized with various viscosities, during a catalyst preparation step. Next, morphology of ceramic foams was explored using scanning electron microscopy (SEM), and catalyst properties, such as; temperature profile of catalyst reduction, metal dispersion, and surface area, were also characterized by H2TPR and H2-TPD techniques, and BET, respectively. From the results, it was found that metal-particle dispersion was relatively high about 5.89%, whereas the surface area of ceramic foam catalysts was 64.52 m 2 /g. Finally, the catalytic behaviour toward hydrogen production through the dry reforming of methane using a fixed-bed reactor was evaluated under certain operating conditions. The approaches from this research provide a direction for further improvement of marketable environmental friendly catalyst production.

High density and taper-free boron doped Si1−xGex nanowire via two-step growth process

The authors study Au catalyzed chemical vapor growth of Si1−xGex alloyed nanowires in the presence of diborane, serving as a dopant precursor. Our experiments reveal that introduction of diborane has a significant effect on doping and morphology. Boron exposure poisons the Au catalyst surface, suppresses catalyst activity, and causes significantly tapered wires, as a result of conformal growth. The authors develop here a two-step method to obtain high density and taper-free boron doped Si1−xGex alloy nanowires. The two-step process consists of: (1) growth of a small undoped Si1−xGex section and (2) introduction of diborane to form a boron doped Si1−xGex section. The catalyst preparation step remarkably influences wire yield, quality and morphology. The authors show that dopant-ratio influences wire resistivity and morphology. Resistivity for high boron doped Si1−xGex nanowire is 6 mΩ-cm. Four probe measurements show that it is possible to dope Si1−xGex alloy nanowires with diborane.

ChemInform Abstract: Advances in the Surface Characterization of Heterogeneous Catalysts Using ToF‐SIMS

AbstractReview: 52 refs.

Advances in the surface characterization of heterogeneous catalysts using ToF-SIMS

This paper provides a critical review on the applications of time-of-flight secondary ion mass spectrometry (ToF-SIMS) in heterogeneous catalysis, with a particular emphasis on the examples published during the last decade. The covered areas include supported metal oxide catalysts, supported metal catalysts, electrocatalysts for oxygen-reduction reaction and organometallic clusters as precursors for the preparation of heterogeneous catalysts. The molecular specificity and surface sensitivity of ToF-SIMS have been shown to be extremely useful in the surface characterization of heterogeneous catalysts, in particular in the areas of assessing the formation of new compounds or interactions between different components (e.g. active phase–active phase or active phase–support), providing more precision on the structure of surface species, monitoring the different steps of catalyst preparation and/or activation, etc. In some cases, ToF-SIMS is able to provide unique molecular information that is unattainable with other conventional techniques and thus give a more precise characterization of the heterogeneous catalysts. Finally, the advantages and limitations of ToF-SIMS with respect to other more conventional techniques such as XPS are also discussed.

Improvement of the neodymium catalyst preparation step in isoprene rubber production

The results of pilot tests of a tubular reactor of the diffuser-confuser type in modification of neodymium chloride isopropanol complex in turbulent flows were presented. The new procedure leads to reduced catalyst consumption, as well as to increased average molecular weights and narrowed molecular weight distribution of cis-1,4-polyisoprene.

A Soft Chemistry Route to Selective Nickel‐Based Nanocatalysts with Faceted Morphologies

A one pot synthesis of alumina supported faceted nickel nanoparticles is carried out following a simple, inexpensive, and sustainable pathway. Tailoring the different chemical steps of catalyst preparation allow the faceted morphology to be maintained while reducing the organic leftover. Moreover, this work shows the key role of the halide ions on the nanoparticles shaping that occurs during the reduction step under H2. The predominant role of the {111} facets on the performance of the resulting supported nanocatalysts is also demonstrated. Indeed, catalytic tests in selective hydrogenation of polyunsaturated hydrocarbons performed for both faceted nanocatalysts and reference Ni show a clear selectivity enhancement for the former. The positive impact of {111} faceted Ni catalysts on hydrogenation selectivity is of particular interest to reduce the purification steps after the catalyzed reaction.

Convenient in situ generation of a chiral bis-N-heterocyclic carbene palladium catalyst and its application in enantioselective synthesis

To simplify catalytic reactions employing chelating bisNHC–metal complexes, studies were conducted to elucidate conditions for the in situ generation of a chiral chelating bisNHC–palladium catalyst from the corresponding diimidazolium salt. The method provides a convenient entry to catalytic reactions and eliminates catalyst preparation steps. In addition to the in situ prepared catalyst, for comparative purposes, isolable species were synthesized and characterized by NMR spectroscopy, combustion analysis, and single-crystal X-ray diffraction. Employing C2-symmetric ligands derived from trans-9,10-Dihydro-9,10-EthanoAnthracene-11,12-diyl (DEA) and trans-9,10-Dihydro-9,10-EthanoAnthracene-11,12-diylMethanediyl (DEAM), diNHC–Pd complexes were synthesized and tested for activity in enantioselective arylboronic acid addition to cyclic enones.

Physical mixing of metal acetates: a simple, scalable method to produce active chloride free bimetallic catalysts

We have prepared supported gold, palladium and gold–palladium bimetallic catalysts by the physical mixing of the acetate salts of the metals followed by a simple heat treatment. The use of the acetates as the metal precursor eliminates chloride from the catalyst preparation step. Extensive characterisation shows the formation of bimetallic alloy particles. These catalysts are extremely active for alcohol oxidations and the direct formation of hydrogen peroxide.

Quantitative determination of average rhodium oxidation state by a simple XANES analysis

Quantitative determination of average rhodium oxidation state for supported rhodium catalyst was examined by using Rh L3-edge XANES (X-ray absorption near-edge structure) spectra. A series of Rh-loaded SiO2 catalysts (Rh2Ox/SiO2) containing different amount of Rh metal and Rh2O3 phases were prepared, and the average oxidation number (x) was determined by the amount of CO2 formed during CO reduction treatment as the final step of catalyst preparation. L3-edge XANES spectra of these samples were recorded, and the white line area intensity of the spectra was evaluated. A good linear relationship was confirmed between the white line area intensity and the average oxidation number (x), indicating that the oxidation state of Rh species in structurally unknown Rh samples could be quantitatively determined by a simple L3-edge XANES analysis. The effect of the oxidation number (x) on the Rh2Ox/SiO2-catalysed CO oxidation was discussed, in order to demonstrate a utility of this method in a catalytic study.