Nature Of Active Species Research Articles

Nature of surface active centers in activation of peroxydisulfate by CuO for degradation of BPA with non-radical pathway

Nowadays, the nature of active species and the role of peroxydisulfate (PDS) was still unclear in advance oxidation systems based on activation of PDS by CuO with non-radical pathway. In this paper, a sheet like CuO containing two kinds of Cu2+ was prepared, one of which was electron deficient Cu2+ (Cu2+-h). The CuO/PDS system showed extraordinarily utilization of PDS (172.3%) for BPA degradation (after four cycles of PDS). The main degradation mechanism was dominated by non-radical pathway. SO4•- was not involved in the reaction. Cu2SO5 complex was identified as active species, which originated from PDS and two kinds of CuOx on surface of CuO. An electron deficient center [Cu(III)EDC] formed in Cu2SO5 due to the combination of Cu2+-h and PDS directly. [Cu(III)EDC] could capture electronics from pollutants and H2O, leading to the degradation of BPA and the formation of •OH. PDS was locked by two CuOx units in Cu2SO5, which explained the trace consumption during the reaction.

Theoretical perspective on mononuclear copper-oxygen mediated C–H and O–H activations: A comparison between biological and synthetic systems

Dioxygen activations constitute one of core issues in copper-dependent metalloenzymes. Upon O 2 activation, copper-dependent metalloenzymes such as particulate methane monooxygenases (pMMOs), lytic polysaccharide monooxygenases (LPMOs) and binuclear copper enzymes PHM and DβM, are able to perform various challenging C–H bond activations. Meanwhile, various copper-oxygen core containing complexes have been synthetized to mimic the active species of metalloenzymes. Dioxygen activation by mononuclear copper active site may generate various copper-oxygen intermediates, including Cu(II)-superoxo, Cu(II)-hydroperoxo, Cu(II)-oxyl as well as the Cu(III)-hydroxide species. Intriguingly, all these species have been invoked as the potential active intermediates for C–H/O–H activations in either biological or synthetic systems. Due to the poor understanding on reactivities of copper-oxygen complex, the nature of active species in both biological and synthetic systems are highly controversial. In this account, we will compare the reactivities of various mononuclear copper-oxygen species between biological systems and the synthetic systems. The present study is expected to provide the consistent understanding on reactivities of various copper-oxygen active species in both biological and synthetic systems. Reactivities of various mononuclear copper-oxygen have been compared between the synthetic and biological systems, showing that all species are reactive toward O–H activations but only [CuO] + species could be responsible for C–H activations in monooxygenases.

Towards a greater olefin share in polypropylene cracking – Amorphous mesoporous aluminosilicate competes with zeolites

For plastic waste cracking the path for production of high olefins yield without loose in gasoline fraction is an intriguing option. Among the commercial FAU zeolites of different properties and mesoporous HAlMCM-48 materials, the catalysts of polypropylene (PP) cracking being able to operate in low-temperature regime was searched. The aim was to investigate the effects of the presence of mesopore system in the context of internal and external acidic features on PP cracking. The advanced operando FT-IR and UV–vis characterization coupled with GC and MS analysis offered insight into the nature of active species during cracking reaction as well as into the nature of coke deposit formed after reaction. The results for series of FAU zeolites were faced with mesoporous HAIMCM-48 as the catalyst of similar cracking competence, as it will be documented.

Synergistic Effect of Different Species in Stannic Chloride Solution on the Production of Levulinic Acid from Biomass

Metal chloride has shown high potential in biomass conversion to valuable chemicals, but the nature of active species and the corresponding performances on each successive reaction step need further elucidation. In this work, SnCl4 was found to exhibit satisfactory catalytic activity, achieving 64.6 mol % yield of levulinic acid from corncob residue. The levulinic acid obtained could be further converted to more valuable ethyl levulinate with 85% yield without any extra catalyst addition. In water medium, the hydrolysis of SnCl4 resulted in the formation of stannic oxide, H+ and Cl–, which showed a synergistic effect and all contributed to levulinic acid production. It was demystified that Cl– promoted cellulose hydrolysis, and the formed H+ as Bronsted acid mainly contributed to cellulose hydrolysis and fructose dehydration, as well as HMF decomposition to levulinic acid. Sn(IV) species facilitated both glucose-to-fructose isomerization and fructose consumption yielding undesirable polymers, but exhibite...

The activity of titanium silicalite-1 (TS-1): Some considerations on its origin

The high activity of titanium silicate (TS-1) in oxidations with hydrogen peroxide is the result of different factors, directly referable to the MFI structure. The configuration of Ti site (tetrahedral), the nature of active species (Ti-OOH) and the nature of the surface (hydrophobic) are the three factors that are immediately apparent. Hydrophobicity alone, however, cannot fully explain certain catalytic performances and trends in the oxidation of the olefins, without envisaging a major involvement of porosity. Actually, the molecular dimensions of pores (ca. 0.55 nm), normally perceived as just a drawback for the limits set to the range of potential substrates, play a relevant and positive role in TS-1 catalysis. The purpose of the paper is to illustrate and discuss these issues, with supporting evidences mostly taken from the oxidation of olefins and alkanes.

Polymerization of olefins with single-site catalyst anchored on amine-functionalized surface of SBA-15

Mesoporous silica SBA-15 functionalized with amine or nitrile group have been synthesized and (n-BuCp)2ZrCl2 and methylaluminoxane (MAO) were subsequently immobilized on the functionalized SBA-15 for the further evaluation as a catalyst of ethylene polymerization. Five silanes such as 3-aminopropyltrimethoxysilane(1NS), N-[(3-trimethoxysilyl)propyl]ethylenediamine(2NS), N1-[3-(trimethoxysilyl)propyl]diethylenetriamine(3NS), and 4-(triethoxysilyl)butyronitrile(1NCy), 1-(3-triethoxysilylpropyl)-2-imidazoline(2NIm) were compared as functional groups for the immobilization (n-BuCp)2ZrCl2 and methylaluminoxane (MAO). Zr contents in the final supported catalysts were observed to be strongly dependent on the nitrogen content on the surface of functionalized SBA-15, indicating the more Zr could be immobilized due to the interaction between (n-BuCp)2ZrCl2 and amine or nitrile groups presented on the surface of SBA-15. 2NIm, 2NS and 3NS were shown to interact with (n-BuCp)2ZrCl2 strongly compared to 1NCy and 1NS due to larger number of amine groups and formation of stable active species. The ethylene homo- and copolymerization activities of (n-BuCp)2ZrCl2 supported on the amine or nitrile-functionalized SBA-15 were increased with an increase in the nitrogen and Zr content in the supported catalyst. The electron-donating effect of the amine or nitrile surface group on the surface toward the (n-BuCp)2ZrCl2 was expected to be a significant parameter in consideration of the higher activity of ethylene homopolymerization and ethylene-1-hexene copolymerization. SBA-15/1NCy/(n-BuCp)2ZrCl2 also showed different chemical compositional distribution of ethylene-1-hexene copolymer compared to the others, meaning change in nature of active species. It would result from different electric environment of nitrile group from amine one. It also revealed that the resulting polymer particle prepared supported (n-BuCp)2ZrCl2 on the amine or nitrile-functionalized SBA-15 was more regular and larger in particle size than that of no functionalized SBA-15.

Electron Paramagnetic Resonance investigation of the nature of active species involved in carbon black oxidation on ZrO2 and Cu/ZrO2 catalysts

Abstract To identify the nature of active paramagnetic species involved in the carbon black (CB) oxidation, an Electron Paramagnetic Resonance (EPR) study of (CB–ZrO 2 ) and (CB–Cu/ZrO 2 ) loose contact mixtures treated under argon flow has been undertaken. In the presence of pure zirconia catalysts, it was found that ZrO 2 interacts with CB and can be reduced into Zr 3+ formed in tetragonal phase of this oxide support. In parallel, several EPR signals assigned to carbonaceous radicals were detected: i) carbonaceous radicals on CB surface, ii) radicals located at the CB–ZrO 2 interface and iii) oxygen deficit carbonaceous radicals observed at high treatment temperature. The carbonaceous signals disappeared completely after CB oxidation in agreement with a regeneration of the catalyst treated under air. For copper supported on zirconia catalysts, oxygen surrounding isolated Cu(II) species and oxygen from tetragonal ZrO 2 lattice are involved in carbon black oxidation. The phenomenon is reversible and this catalyst is also regenerated by air. Carbonaceous radical signals were also observed for (CB–Cu/ZrO 2 ) mixture and their intensity decrease versus temperature appeared in good agreement with the better activity of Cu/ZrO 2 compared to pure ZrO 2 .

Structure and reactivity of copper iron pyrophosphate catalysts for selective oxidation of methane to formaldehyde and methanol

The structure of copper iron pyrophosphate catalysts prepared with various atomic ratios of metals and different pretreatment conditions was studied by using XRD, FT-IR, DR UV–vis and H 2-TPR techniques. The preparation methods modify the phase composition, oxidation state and reducibility of the patterns. The catalytic properties in the selective oxidation of methane to formaldehyde and methanol were examined in both, pulse and flow reactors, using O 2 and/or N 2O oxidizing agents. The oxidants used impact the onset of methane conversion, the primary oxidation products formation and the methane conversion. The highest single-pass yield of useful oxygenates (1.8%) was achieved with N 2O over the Cu/Fe ≅ 1:2 pyrophosphate catalyst which consists mainly of the crystalline Fe IIFe III 2(P 2O 7) 2 and copper containing nanodomains. Enhanced interaction and cooperation between these phases leading to a synergic effect of Cu and Fe has been emphasized. The Cu II and Fe III species of the above structure can be reduced more easily but at similar temperatures than those in the crystalline CuFe 2(P 2O 7) 2. Pulse reaction studies indicate that the lattice oxygen of the catalyst could react with methane molecules producing formaldehyde and methanol and replenishment of the lattice oxygen by N 2O takes place rather readily and rapidly. The nature of active species, methane conversion and oxygenates selectivity remained almost unchanged during the time on stream.

Investigation on the nature of active species in the CeCl 3-doped sodium alanate system

CeCl 3-doped NaAlH 4 was directly synthesized in hydrogenation process using NaH/Al with 2 mol% CeCl 3 under ball-milling. X-ray diffraction was utilized to unveil the nature of cerium during NaAlH 4 synthesis process and succedent cycling. It is found that, CeCl 3 is reduced in the ball-milling process and following cycles, causing the formation of NaCl and Al–Ce alloy with a structure of CeAl 4. The catalytic enhancement arising upon doping the ball-milled CeAl 4 alloy is quite similar to that achieved in the CeCl 3-doped sodium alanate. Because the CeAl 4 dopant does not consume the effective hydrogen storage component, the CeAl 4-doped NaAlH 4 exhibits more hydrogen storage capacity. Moreover, CeCl 3-doped NaAlH 4 and CeAl 4-doped NaAlH 4 exhibit similar apparent activation energies estimated from Kissinger's method, suggesting the reactions are all determined by the same rate-limiting step. These results clearly demonstrate that the in situ formed CeAl 4 acts as active species to catalyze the reversible dehydriding/rehydriding of NaAlH 4.

DRIFT Studies of Adsorbed CO Over Sulfided K–Rh–Mo/Al2O3 Catalysts: Detection of Rh–Mo–S Phase

Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy was used to study the nature of active species in K–Rh–Co–MoS2/Al2O3 catalyst by means of probing with CO molecule. The effects of K addition to Rh and interaction between Mo and Rh were studied with varying K and Mo loadings over 1 wt% Rh/Al2O3 catalyst. In sulfided Rh–Mo/Al2O3, the formation of Rh–Mo–S phase was evidenced first time by a band at 2,095 cm−1. The introduction of Co to K–Rh–MoS2/Al2O3 catalyst showed the existence of both Rh and Co promoted MoS2 sites, but the CO absorption frequencies in DRIFT spectra are significantly at lower side compared to Co free Rh–Mo catalyst. The stabilities of CO band from Rh and Co promoted and unpromoted MoS2 sites are studied at different temperatures. When activated carbon used as support, bands for both promoted and unpromoted MoS2 sites were appeared, but the intensity of these bands were decreased largely compared to alumina based catalyst, resulted from the coverage of added K not only on the support surface but also on the active metal components due to the neutral nature of activated carbon.

The nature of active species in catalytic systems based on non-heme iron complexes, hydrogen peroxide, and acetic acid for selective olefin epoxidation

The catalytic systems [(BPMEN)FeII(CH3CN)2](ClO4)2/H2O2/CH3OOH and [(TPA)FeII(CH3CN)2](ClO4)2/H2O2/CH3OOH, where BPMEN = N,N′-dimethyl-N,N′-bis(2-pyridylmethyl)-1,2-diaminoethane and TPA = tris(2-pyridylmethyl)amine, provide selective olefin epoxidation. Proton NMR studies showed that the mononuclear iron(IV) oxo complexes [(L)FeIV=O]2+, with L = BPMEN or TPA, are present in the cited catalytic systems. These intermediates are the decomposition products of the acylperoxo complexes [(L)FeIII-O3CCH3]2+. Such a complex was observed by the 2H NMR technique at low temperatures. The [(L)FeIV=O]2+ and [(L)FeV=O]3+ oxo complexes are possible active species in the studied catalytic systems.

A review of liquid-phase catalytic hydrodechlorination

This survey was aimed at introducing the effect of light organochlorinated compound emissions on the environment, particularly on water, air, soil, biota and human beings. The characteristics and advantages of liquid phase catalytic hydrodechlorination as a technology for degrading these chlorinated compounds is also outlined and the main catalysts used in the hydrodechlorination process are described. Special emphasis is placed on palladium catalysts, their activity, the nature of active species and deactivation. The effect of several parameters is introduced, such as HCl, solvent, base addition and type of reducing agent used. The main results of kinetic studies, reactors used and the most important survey conclusions are presented.

An explanation for experimental behavior of hybrid metallocene silica-supported catalyst for ethylene polymerization

JMCA“An explanation for experimental behavior of hybrid metallocene silica-supported catalyst for ethylene polymerization” Sı́lvia Rodrigues, Fernando Silveira, J.H.Z. dos Santos, M.L. Ferreira. This work presents the results of homopolymerization of ethylene using an hybrid system ( n BuCp) 2 ZrCl 2 –Cp 2 ZrCl 2 , soluble and supported on silica. The catalytic systems were analyzed by RBS, DRIFTS and EXAFS and polyethylenes (PE) by GPC and DSC. EHMO calculations allow us to conclude that Cp 2 ZrCl 2 has a strong affinity by AIS plane, whereas ( n BuCp) 2 ZrCl 2 shows similar affinity for both silica planes. Formation of active site at surface. This work presents the results of homopolymerization of ethylene using an hybrid system ( n BuCp) 2 ZrCl 2 –Cp 2 ZrCl 2 , supported on silica. The catalytic systems were analyzed by RBS, DRIFTS and EXAFS and polyethylenes (PE) by GPC and DSC. The catalytic activities and the polymer properties showed dependence on the different ratio used ( n BuCp) 2 ZrCl 2 /Cp 2 ZrCl 2 at the preparation step. Theoretical studies permit us to conclude that the metallocenes interact with the surface in different ways. Depending on the addition order and the molar ratio between both metallocenes, distribution and nature of active species would be different. Possibility of binuclear active sites with different propagation and termination constants is analyzed and discussed. EHMO calculations allow us to conclude that Cp 2 ZrCl 2 has a strong affinity by AIS plane, whereas ( n BuCp) 2 ZrCl 2 shows similar affinity for both silica planes.

Studies on the nature of active species in W(CO) 6/CCl 4/ hν system as applied to metathesis polymerisation reactions

Irradiation of W(CO) 6 in CCl 4 generates an ‘active species’ which has the ability to polymerise alkynes and strained cyclic olefins via a metathesis pathway. The precipitate formed after 2 h of irradiation is active for polymerisation. The involvement of metal carbene in the polymerisation of norbornene was proved by in situ 1H-NMR study and by the end-capping reaction. IR studies showed the presence of carbonyl and chlorine ligands around the tungsten centre.

Plasma assisted chemical vapour deposition of boron nitride coatings from using BCl 3–N 2–H 2–Ar gas mixture

Boron Nitride coatings have been deposited by plasma-assisted chemical vapour deposition (PACVD) from BCl 3/N 2/H 2/Ar gas mixtures in a hot wall capacitively coupled radio-frequency (13.56 MHz) reactor. The nature of active species in the plasma during deposition was determined by Optical Emission Spectroscopy (OES) and Mass Spectrometry (MS). The plasma characterisation was performed as follows: first, an Ar/H 2 plasma was studied in order to understand the influence of molecular hydrogen in the discharge mixture. Then the two precursors N 2 and BCl 3 were added and the new gas mixture studied. Finally the deposition plasma was investigated. These characterisations were correlated to the microstructure and c-BN concentrations determined by Scanning Electron Microscopy (SEM) and Fourier Transformed Infrared Spectroscopy (FTIR). The study demonstrates the major role of atomic hydrogen on the possible mechanisms leading to BN deposition: —the introduction of hydrogen in Ar/N 2 controls the nature of the NH x (from N to NH 3) species in the gas phase. These results are correlated to the relative amount of NH groups in the films, —by a modification of the excitation state of the plasma (n e, T e) the introduction of H 2 can increase the dissociation rate of the boron precursor BCl 3 and, reacting with chlorine, leads to the formation of HCl. This corresponds to an increase in the growth rate of the coatings. Finally, BN samples containing 5% of cubic phase were treated by Ar, Ar/H 2 and Ar/Cl 2 plasmas. These post treatments demonstrated that ion assisted preferential etching of h-BN by H or Cl atoms could be used to obtain large concentrations of c-BN coatings and possibly offer a new route for deposition of low stress cubic boron nitride.

ChemInform Abstract: Nature of Active Species in Copper‐Based Catalysts and Their Chemistry of Transformation of Nitrogen Oxides

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Nitrogen precursors in metalorganic vapor phase epitaxy of (Al,Ga)N

Among the difficulties in achieving high quality epitaxial nitrides, the choice of the most suitable nitrogen source remains an open question. NH 3 has been widely used but requires a very high V III ratio and provides a very low concentration of N species other than itself during decomposition. Though the understanding of the MOVPE processes required more refined methods than an equilibrium thermodynamic analysis, the minimization of the Gibbs free energy of the gaseous system at the growth temperature provides pertinent information about the nature of active species. Such a thermodynamic analysis brings some insight into the efficiency of nitrogen precursors. Species produced by thermal decomposition of a standard N precursor as NH 3 are compared to those obtained with N 2H 4 and N(C 2H 5) 3. Preliminary experiments using N(C 2H 5) 3 as nitrogen precursor are reported. The epitaxial growth of AlN on sapphire has been achieved whereas the tentative growth of GaN results in the deposition of Ga droplets. N precursors like N(C 2H 5) 3, although suitable for the deposition of nitrides does not provide significant improvements, in comparison with NH 3. Thermal activation (using a hot filament) or microwave production of active N species seems to provide a significant proportion of highly reactive chemical species.

Study of catalytic activity of nitro substituted ironporphyrins

ortho-Nitrophenyl meso-substituted ironporphyrins (FeP) and their corresponding μ-oxo dimers were studied as catalyst in the oxidation of cyclohexane by iodosylbenzene (PhIO). The cyclohexanol yield versus FeP concentration plot indicate the nature of active species. For (FeTNPP)Cl and (FeDNPP)Cl the active species is Fe IV(O)P +· ( 1). For unhindered (FeMNPP)Cl, the involvement of PFe IVOFe IV(O)P +· ( 2) explains results. The catalytic activity of dimeric species (FeMNPP) 2O and (FeDNPP) 2O were surprisingly high, being as good as the monomeric ones. There is evidence of species 2 for these dimer catalysts. The oxidation reaction conditions were studied. We observed that the concentration of the catalyst, stirring method, ratio of iodosylbenzene/catalyst and presence of air can affect the cyclohexanol yields. (FeMNPP)Cl and (FeMNPP) 2O as catalysts can be seen as good P-450 model systems due to their stability, efficiency and selectivity toward cyclohexanol. The electron withdrawing effect of the substituents on the meso-phenyl rings of the porphyrin overwhelms the steric one in the catalytic activity, since only one ortho-nitro group is almost as efficient as the tetra- ortho-nitro substituted FeP. This work contributes to the understanding of the catalytic activities of unhindered ironporphyrins.

Ring-opening polymerization of cycloolefin induced by tungsten porphyrinates

Polymerization reactions of cyclopentene, cyclooctene and cyclododecene have been carried out in presence of catalytic systems based on tungsten tetraphenylporphyrinate, under inert atmosphere at room temperature, in aromatic solvents. The catalyst precursor was prepared by interaction of WCl 6 with free tetraphenylporphyrin in CCl 4 and characterized by spectroscopic methods (e.g. UV—Vis etc.). Spectroscopic studies on the interaction between the catalytic components or with the monomer, as well as kinetic results, molecular weight distribution and polymer microstructure indicated a high stability and efficiency of the catalytic systems employed. This catalyst allowed polyalkenamers with monomodal and narrow molecular weight distribution to be obtained. The polypentenamer displayed a block and/or alternate distribution of the carbon—carbon double bond dyads and high trans configuration. Data obtained under the above conditions gave information concerning the nature of active species during the initiation and propagation reactions.

Nature of active species in the living cationic polymerization of vinyl ethers initiated by hydrogen halide/zinc halide systems

The living polymerization of chloroethyl vinyl ether is studied. The kinetic results are fully consistent with a reaction pathway involving rapid exchanges (with respect to the polymerization rate) between terminal halides. Two mechanisms of halide exchange can be considered