Group VI Metal Research Articles

Photoluminescence properties of SnO2 nanoparticles doped with group VI elements (Cr, Mo, W) synthesized by pulsed laser ablation in liquid

Tin oxide nanoparticles (SnO2 NPs), both pure and doped with Group VI (G6) metal ions (Cr+3, Mo+5, and W+6), were synthesized using pulsed laser ablation in liquid. This study aimed to investigate the effect of G6 doping on the electronic properties of SnO2 NPs, with an emphasis on enhancing their photoluminescence for optoelectronic applications. Transmission electron microscopy revealed well-crystallized samples with diameters of 3–6 nm, indicating quantum-confinement effects. The optical band gap, determined by UV–Vis spectroscopy, was reduced from 5.1 eV (undoped) to 4.9 eV (Cr-doped) due to defect states, while increasing to 5.3 eV and 5.7 eV for Mo- and W-doped SnO2, respectively, due to the Moss-Burstein effect. The photoluminescence spectra exhibited a redshift, with strong red emission around 700 nm, which was up to 90 % more intense than that of the undoped SnO2. This enhancement was attributed to the 2E→4A2 transition and increased defect states.

Exploring Ligand Effects on Structure, Bonding, and Photolytic Hydride Transfer of Cationic Gold(I) Bridging Hydride Complexes of Molybdocene and Tungstenocene.

A diverse family of heterobimetallic bridging hydride adducts of the type [LAu(μ-H)2MCp2][X] (L = 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene, IPr; 1,3-bis(1-adamantyl)imidazole-2-ylidene, IAd; 1,3-bis(2,6-di-iso-propylphenyl)-5,5-dimethyl-4,6-diketopyrimidinyl-2-ylidene, DippDAC; triphenylphosphine, PPh3; 2-di-tert-butylphosphino-2',4',6'-triisopropylbiphenyl, tBuXPhos; X = SbF6-, BF4- or TfO-) was synthesized by reacting group VI metallocene dihydrides Cp2MH2 (Cp = cyclopentadienyl anion; M = Mo, W) with cationic gold(I) complexes [LAu(NCMe)][X]. Trimetallic [L'Au2(μ-H)2WCp2][X]2 and tetrametallic [L'Au2{(μ-H)2WCp2}2] [X]2 complexes (L' = rac-2,2'-bis(diphenylphosphino)-1,1'-binaphthalene or bis(diphenylphosphinomethane)) were obtained by reacting digold [L'{Au(NCMe)}2][X]2 with Cp2WH2 in a 1:1 and a 1:2 stoichiometry. Accessing such a broad structural diversity allowed us to pinpoint roles played by the ancillary ligands and group VI metals on the bonding properties of this family of bridging hydrides. In particular, a clear effect of the ligand on the interaction energy and electronic structure was observed, with important implications on photolytic reactivity. UV or visible light irradiation, indeed, leads to the selective cleavage of the heterobimetallic Au(μ-H)2M arrangement and formation of molecular gold hydrides. The photolysis was found to be chromoselective (wavelength-dependent), which can be ascribed to different charge redistributions upon excitation to the first (Kasha's reactivity) and higher (anti-Kasha's reactivity) excited states.

Unveiling the intrinsic rhenium effect in Tungsten

Body-centered cubic refractory metals, as a class of critical structural materials, are often restricted by poor low-temperature toughness, which is a common, undesirable phenomenon that continues to be the focus of intense research. Historically, rhenium (Re) has been considered the most promising alloying element in improving ductility and reducing the ductile-to-brittle transition (DBT) temperature of group-VI metals, known as the “Re effect”. However, whether this is indeed possible remains uncertain so far. Here, in the modelled W-xRe (x = 0, 3, 5, 10 wt.%) alloys, we reveal that only in a limited temperature range of 50 °C∼200 °C does the Re softening occur, imparting a positive but small effect on fracture toughness. At higher temperatures (>300 °C), the dynamic interactions between Re solutes and dislocations produce profuse jogs and sessile loops that strongly hinder dislocation motion and cause hardening. The resultant difficulty in plastic flow significantly degrades the high-temperature (>300 °C) toughness of W-Re alloys, leading to an undesirable increase of the DBT temperature, which shifts higher with increasing Re content. Our discovery of the solution softening-to-hardening transition, including its dislocation mechanism, clarifies the intrinsic effect of Re on the toughness of recrystallized W alloy, providing essential knowledge for the compositional design of refractory alloys in general.

ОСОБЕННОСТИ ФОРМИРОВАНИЯ РЕАКЦИОННОЙ МАССЫ И СТРУКТУРЫ МЕТАЛЛИЧЕСКИХ ПОРОШКОВ ПРИ ВОССТАНОВЛЕНИИ СЛОЖНЫХ ОКСИДНЫХ СОЕДИНЕНИЙ ТУГОПЛАВКИХ МЕТАЛЛОВ V И VI ГРУПП ПАРАМИ ЩЕЛОЧНОЗЕМЕЛЬНЫХ МЕТАЛЛОВ

The features of the formation of the reaction mass and the structure of powders of refractory metals of group V (Ta, Nb) and group VI (Cr, W, Mo, MoCr, MoW) formed during the reduction of complex oxide compounds: Mg4Ta2O9, Mg4Nb2O9, MgCr2O4, MgWO4, CaWO4, MgMoO4, CaMoO4, MgW0.3Mo0.7O4, Cr2(MoO4)3, Cr2WO6 with alkaline earth metal vapors (Mg, Ca) was studied. It was determined that after reduction under certain conditions of compounds containing metals of group VI, a spatial separation of products takes place, which consists in the fact that the bulk of the oxide of the reducing metal is located outside the reaction zone . It was shown that powders of both pure metals and alloys have a mesoporous structure. The specific surface area of metal powders is many times greater than the specific surface area of precursor powders

Sulfur coordination engineering of molybdenum single-atom for dual-functional oxygen reduction/evolution catalysis

Oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) catalysis are required in metal-air batteries and an efficient dual-functional single-atom catalyst (SAC) is still lacking. This is partly because of the limited synthesis strategies to modify the coordination environment of metal centers in SACs. Herein, we report a genetic strategy, transformation from thiometallate anions in the precursor to metal-sulfur bonding in carbon, producing hollow-sphere-structured Mo SAC with O/N/S co-coordination as an efficient ORR/OER dual-functional catalyst. The MoS 4 2− -doped polydopamine have O/S co-coordination for Mo, which converts into S/O/N co-coordination in carbon during pyrolysis. We established that coordination engineering, specifically S coordination, could boost the ORR catalysis of Mo SAC. The low ORR half-wave potential (E 1/2 ) and small Tafel slope are among the best of Mo-based non-noble metal catalysts. The OER overpotential of 303 mV at 10 mA cm −2 is significantly lower than that of commercial IrO 2 , and Pt/C. Assembled Zn-air batteries can work steadily for 90 h without significant voltage decay. Our strategy can be extended to the synthesis of other group-V and group-VI metal hollow SACs with an S coordination, such as W.

Synthesis of [(CO)5MS=CFcCH3] and exploration of the nature of M-S vs. M-O bonds in [(CO)5ME=CFcCH3]; (M = Cr, Mo, W and E = O, S) complexes

Photolysis of a methanol solution containing substituted alkyne, group VI metal hexacarbonyl and P4S10 at low temperature under an inert atmosphere leads to metal-sulfur coordinated complexes of chromium, molybdenum, and tungsten. The structure of pentacarbonylthioacetylferrocene-S-chromium (1) is confirmed by single crystal x-ray diffraction study and both the complexes (1 and 2) are confirmed using IR and NMR spectral studies. The sulfur-coordinated metal carbonyl complexes are thought to be formed by the initial activation of metal carbonyl with acetylenic ligand which then rearranges into metal coordinated thioacetylferrocene by dithiophosphoryl radical (formed in situ by reaction of P4S10 and methyl alcohol under photolytic condition). The stability of pentacarbonylthioacetylferrocene of group VI metal complexes are further compared with their acetylferrocene derivatives of Group VI metal complexes using DFT studies. Density functional theory was performed on six complexes [(CO)5ME=CFcCH3] (where M = Cr, Mo and W; while E = O and S) to assess their geometry and electronic structure aspects. Natural bonding orbital (NBO) and energy-decomposition analysis (EDA) were carried out to probe the nature and strength of the M-E interactions. NBO and EDA analysis predict M-E bond strength in the following order: Cr-E < Mo-E < W-E. The M-E bond covalency increases as we move down the group from Cr, Mo to W, which rationalizes the observed trends in the M-E bonds. While comparing the nature of the E (O and S) linkage in bonding, we found that -S analogue shows exceptionally robust σ and π interactions compared to the -O analogue. The reasonably strong M-S interactions resulted in the isolation of these -thio analogues.

Materials selection for nuclear applications in view of divacancy energies by comprehensive first-principles calculations

We investigated formation and binding energies of di-vacancy in 51 type pure metals with bcc, fcc, and hcp structures to understand the clustering and dissolution of vacancies in metals by means of a comprehensive first-principles study. First, mono- and di-vacancy formation energies as the first (1nn) and second (2nn) nearest neighbor were compared using three typical functionals. Comparing with other Groups, the formation energies of mono- and di-vacancy reach the maximum in Group VI metals whose d-band is half filled. The interaction between two vacancies is attractive in most metals and the energy difference between the 1nn and 2nn configurations is obvious. We predicted the relationships of di-vacancy formation energy with melting temperature and cohesive energy and discussed vacancy clustering and void formation in metals by the binding energy and dissolution energy of vacancies and their clusters. The present work provides the fundamental data of di-vacancy in metals and a theoretical guideline for nuclear materials selection and design.

Completing the triad: synthesis and full characterization of homoleptic and heteroleptic carbonyl and nitrosyl complexes of the group VI metals.

Oxidation of M(CO)6 (M = Cr, Mo, W) with the synergistic oxidative system Ag[WCA]/0.5 I2 yields the fully characterized metalloradical salts [M(CO)6]+˙[WCA]− (weakly coordinating anion WCA = [F-{Al(ORF)3}2]−, RF = C(CF3)3). The new metalloradical cations with M = Mo and W showcase a similar structural fluxionality as the previously reported [Cr(CO)6]+˙. Their reactivity increases from M = Cr < Mo < W and their syntheses allow for in-depth insights into the properties of the group 6 carbonyl triad. Furthermore, the reaction of NO+[WCA]− with neutral carbonyl complexes M(CO)6 gives access to the heteroleptic carbonyl/nitrosyl cations [M(CO)5(NO)]+ as salts of the WCA [Al(ORF)4]−, the first complete transition metal triad of their kind.

Calcium Vapor Reduction of Group V and VI Metal Oxide Compounds

We have studied calcium vapor reduction of Group V and VI metal oxide compounds (Ta2O5, Nb2O5, WO3, MoO3, MgWO4, MgMoO4, and CaMoO4) at temperatures from 800 to 860°C and residual argon pressures from 5 to 10 kPa. The products of the reduction of the Group V metal compounds had the form of a homogeneous mixture corresponding to the reaction stoichiometry. After the reduction of the Group VI compounds under similar conditions, we observed spatial separation of the reaction products: most of the reductant metal oxide was located beyond the reaction zone. In the initial stage of the reduction of MgWO4 and MgMoO4, calcium substitutes for magnesium in these compounds. Together with calcium oxide, the magnesium oxide forms a layer on the surface of the reactants. Analysis of our results suggests that the calcium vapor reduction of the Group VI metal oxide compounds is likely to follow the electronically-mediated reaction mechanism.

New 1,2,3-triazole based bis- and trisphosphine ligands: synthesis, transition metal chemistry and catalytic studies.

The syntheses and transition metal chemistry of triazole-based bis- and tris-phosphines, 5-(diphenylphosphanyl)-1-(2-(diphenylphosphanyl)phenyl)-4-phenyl-1H-1,2,3-triazole (2), 5-(diphenylphosphanyl)-4-(2-(diphenylphosphanyl)phenyl)-1-phenyl-1H-1,2,3-triazole (5), 1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (6) and 5-(diphenylphosphanyl)-1,4-bis(2-(diphenylphosphanyl)phenyl)-1H-1,2,3-triazole (7), are described. Bisphosphines 5 and 6 show versatile coordination behavior due to the presence of at least four donor atoms. The reactions of 5 and 6 with group VI metal carbonyl derivatives were found to be highly sensitive to the reaction conditions. Bisphosphine 5 upon treatment with [M(CO)4(piperidine)2] (M = Mo and W) yielded both P,P and P,N coordinated complexes [M(CO)4(5)] [M = Mo-κ2-P,N (8); W-κ2-P,N (9); Mo-κ2-P,P (10); W-κ2-P,P (11)], whereas 6 afforded only P,N coordinated complexes [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Mo(CO)4] (12) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}W(CO)4] (13). The reactions of 5 with [M(COD)Cl2] (M = Pd and Pt) yielded κ2-P,P chelate complexes 14 and 15, respectively, whereas the treatment of 6 with [Pd(COD)Cl2] at ambient temperature resulted in the formation of a rare fused six-membered PCP pincer complex [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}PdCl] (16). Similar reactions of 6 with [NiCl2(DME)] and [Pt(COD)Cl2] in the presence of LiHMDS yielded [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}NiCl] (17) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}PtCl] (18), respectively. The reaction between 6 and [M(COD)Cl]2 (M = Rh and Ir) produced cationic complexes [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Rh(C8H12)]Cl (19) and [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))CH}-κ2-P,N}Ir(C8H12)]Cl (20), respectively, whereas the reaction with [Rh(acac)(CO)2] resulted in a pincer complex [{o-Ph2P(C6H4){1,2,3-N3C(o-Ph2P(C6H4))C}-κ3-P,C,P}Rh(CO)] (21). The structures of most of the compounds have been determined by single crystal X-ray analyses. The fused six-membered PCP palladium pincer complex 16 is found to be an excellent catalyst for the Mizoroki-Heck coupling reaction.

Theoretical study on the M-H···π interactions between metal hydrides and inorganic benzene B3X3H3(X = O, S, Se)

In this work, we conducted ab initio calculations to evaluate the properties of M-H···π interactions between the metal hydrides MH (M = Li, Na, MgH, CaH, NiH, CuH, ZnH) and inorganic benzenes B3X3H3 (X = O, S, Se). Unlike benzene, inorganic benzene B3X3H3 (X = O, S, Se) supports a large area of positive molecular electrostatic potential above and below the molecule, which acts as a Lewis acid and interacts with the H atom of metal hydride. MP2/6–311++G(d, p) results show that these intermolecular interactions exhibit the characteristics of close shell noncovalent interactions. The electrostatic interaction significantly contributes to stabilizing the complexes. The M-H···π interaction’s strength is associated with the property of group VI atom and metal hydride. X’s atomic number decreasing and the H of MH becoming more negative facilitate stronger interaction. Furthermore, the addition of substituent on the B3O3Y3 (Y = F, Cl, CN, OH, and CH3) significantly impacts the π-hole of inorganic benzene and thus modulates these M-H···π interactions. More elongation and blueshift of the MH bonds upon complexation were found for electron-withdrawing substituents. Analysis of σ and π orbital separation indicates that the π-attractor’s position relative to the B atom in the inorganic benzene changes with different substituents. The M-H···π interaction’s strength is primarily dependent on the π-electron density, not σ-electron density.

Molybdenum Dioxide in Carbon Nanoreactors as a Catalytic Nanosponge for the Efficient Desulfurization of Liquid Fuels

AbstractThe principle of a “catalytic nanosponge” that combines the catalysis of organosulfur oxidation and sequestration of the products from reaction mixtures is demonstrated. Group VI metal oxide nanoparticles (CrOx, MoOx, WOx) are embedded within hollow graphitized carbon nanofibers (GNFs), which act as nanoscale reaction vessels for oxidation reactions used in the decontamination of fuel. When immersed in a model liquid alkane fuel contaminated with organosulfur compounds (benzothiophene, dibenzothiophene, dimethyldibenzothiophene), it is found that MoO2@GNF nanoreactors, comprising 30 nm molybdenum dioxide nanoparticles grown within the channel of GNFs, show superior abilities toward oxidative desulfurization (ODS), affording over 98% sulfur removal at only 5.9 mol% catalyst loading. The role of the carbon nanoreactor in MoO2@GNF is to enhance the activity and stability of catalytic centers over at least 5 cycles. Surprisingly, the nanotube cavity can selectively absorb and remove the ODS products (sulfoxides and sulfones) from several model fuel systems. This effect is related to an adsorptive desulfurization (ADS) mechanism, which in combination with ODS within the same material, yields a “catalytic nanosponge” MoO2@GNF. This innovative ODS and ADS synergistic functionality negates the need for a solvent extraction step in fuel desulfurization and produces ultralow sulfur fuel.

Formation of Hydrocarbon Nanoscale Microemulsions Containing Group VI Metals and Catalytic Cracking of Final Systems

Regularities of the catalytic cracking of petroleum fractions in the presence of metal sulfides formed in situ from microemulsion of the “oil fraction–aqueous solution of transition metal salt” type are studied. The conditions of formation of microemulsions containing particles of the dispersed phase with a size less than 140 nm are found. The main features of thermolysis of these systems are ascertained, and the phase composition of the resulting materials is identified. The intensification of catalytic cracking by molybdenum and tungsten sulfides at expense of internal hydrogen resources is studied. This effect makes itself evident as an increase in the feedstock conversion by 6.0–7.6%; the yield of gas and the gasoline fraction increases by 2.1–2.5 and 5.6–6.1%, respectively.

Reaction Mechanism for the Hydrogen Evolution Reaction on the Basal Plane Sulfur Vacancy Site of MoS2 Using Grand Canonical Potential Kinetics.

We develop the grand canonical potential kinetics (GCP-K) formulation based on thermodynamics from quantum mechanics calculations to provide a fundamental basis for understanding heterogeneous electrochemical reactions. Our GCP-K formulation arises naturally from minimizing the free energy using a Legendre transform relating the net charge of the system and the applied voltage. Performing this macroscopic transformation explicitly allows us to make the connection of GCP-K to the traditional Butler-Volmer kinetics. Using this GCP-K based free energy, we show how to predict both the potential and pH dependent chemistry for a specific example, the hydrogen evolution reaction (HER) at a sulfur vacancy on the basal plane of MoS2. We find that the rate-determining steps in both acidic and basic conditions are the Volmer reaction in which the second hydrogen atom is adsorbed from the solution. Using the GCP-K formulation, we show that the stretched bond distances change continuously as a function of the applied potential. This shows that the main reason for the higher activity in basic conditions is that the transition state is closer to the product, which leads to a more favorable Tafel slope of 60 mV/dec. In contrast if the transition state were closer to the reactant, where the transfer coefficient is less than 0.5 we would obtain a Tafel slope of almost 150 mV/dec. Based on this detailed understanding of the reaction mechanism, we conclude that the second hydrogen at the chalcogenide vacant site is the most active toward the hydrogen evolution reaction. Using this as a descriptor, we compare it to the other 2H group VI metal dichalcogenides and predict that vacancies on MoTe2 will have the best performance toward HER.

Synthesis of Dimethyl Phenylphosphonates Catalyzed by Group VI Metal(0) Hexacarbonyls

The coupling of dimethyl phosphite and iodobenzene occurs in the presence of catalytic amounts of homoligand carbonyl complexes of chromium subgroup metals to form dimethyl phenylphosphonate in yields of 50–73% depending on the metal.

Stabilization of Hydroxy Tautomeric Form of Dimethyl Phosphite in the Coordination Sphere of Carbonyl Complexes of Group VI Metals

The interaction of dimethyl phosphite with hexacarbonyls of the chromium group metals in a nonpolar solvent has afforded metal(0) σ4,λ4-(dimethyl phosphite)pentacarbonyls containing a hydroxy tautomeric form of dimethyl phosphite in the coordination sphere. Hydrogen of the phosphite OH group in the metal(0) σ4,λ4-(dimethyl phosphite)pentacarbonyls exhibited a significant acidity, strongest for the chromium complexes. Due to the significant acidity of the phosphite hydroxyl, the metal(0) σ4,λ4-(dimethyl phosphite)-pentacarbonyls are intermediates in the electrophilic version of the Pudovik reaction.

Inductive modulation of tris(phosphinomethyl)phenylborate donation at group VI metals via borate phenyl substituent modification.

A series of zerovalent group VI metal complexes of tris(diisopropylphosphinomethyl)phenylborate ([PhB(CH2PiPr2)3]-, PhBPiPr3), including [PPN][M(CO)3(PhBPiPr3)] (M = Cr, Mo, W) and the first bimetallics in which PhBPiPr3 serves as a bridging ligand via binding M(CO)3 units at the three phosphorus atoms and the borate phenyl substituent, have been synthesized and fully characterized. Two new tris(phosphinomethyl)borates featuring 3,5-dimethylphenyl and 3,5-bis(trifluoromethyl)phenyl borate substituents were prepared as crystallographically characterized thallium salts, and metallated giving their inaugural transition metal complexes [PPN][M(CO)3(((3,5-Me)C6H3)BPPh3)] and [PPN][M(CO)3(((3,5-CF3)C6H3)BPPh3)]. A comparative ν(CO) infrared spectroscopic analysis and examination of half wave potentials assessed by cyclic voltammetry supports a ligand donor ranking of Tp > PhBPiPr3 ≥ Cp > PhBPPh3 > triphos. For these anionic complexes, in which a lower electrostatic contribution to zerovalent metal-PhBPR3 binding is likely operative relative to that present in the zwitterionic complexes most commonly prepared with tris(phosphinomethyl)borates, PhBPR3 ligands do not function as strongly donating scorpionates. Nevertheless, PhBPPh3 is a substantially stronger donor than triphos towards zerovalent M(CO)3; the half wave potentials of [Et4N][M(CO)3(PhBPPh3)] are ∼340 mV lower than those of M(CO)3(triphos). The potentials of the ((3,5-Me)C6H3)BPPh3 group VI metal tricarbonyl anions are more negative than those of the corresponding ((3,5-CF3)C6H3)BPPh3 group VI metal tricarbonyl anions by ∼50 mV, suggesting a modest, yet rational, tuning of PhBPPh3 donation via inductive modulation of the borate anion charge.

On the kinetics and mechanism of the conversion of Cr(CO)5(κ1-P-dppm) to Cr(CO)4(κ2-P,P′-dppm) (dppm = 1,2-diphenylphosphinomethane): an alternative hypothesis

The data from a previously reported kinetic evaluation dealing with the conversion of Cr(CO)5(κ1-P-dppm) (1: dppm = 1,2-diphenylphosphinomethane) into the corresponding chelated complex Cr(CO)4(κ2-P,P′-dppm) (2), via CO loss, is re-evaluated. The conclusion is that the process is more likely to involve a rate-determining step that is first-order in [Cr(CO)5(κ1-P-dppm)], as opposed to the previously reported zero-order model as proposed. This implies CO loss from 1, by presumably either an I d or more likely a Dissociative (D: S N 1-type) mechanism, leads to 2. This hypothesis is compared and contrasted to reported data and comparisons are made to similar processes involving related Group VI metal carbonyl species. $$ \mathop {{\text{Cr}}\left( {\text{CO}} \right)_{5} (\upkappa^{1} -P-dppm) + \Delta }\limits_{{\mathbf{1}}} \to \mathop {{\text{Cr}}\left( {\text{CO}} \right)_{4} (\upkappa^{2} -P,P^{{\prime }} {\text{-dppm}}) + {\text{CO}}}\limits_{{\mathbf{2}}} $$

Use of Improved Orbitals for CCSD(T) Calculations for Predicting Heats of Formation of Group IV and Group VI Metal Oxide Monomers and Dimers and UCl6.

The prediction of the heats of formation of group IV and group VI metal oxide monomers and dimers with the coupled cluster CCSD(T) method has been improved by using Kohn-Sham density functional theory (DFT) and Brueckner orbitals for the initial wave function. The valence and core-valence contributions to the total atomization energies for the CrO3 monomer and dimer are predicted to be significantly larger than when using the Hartree-Fock (HF) orbitals. The predicted heat of formation of CrO3 with CCSD(T)/PW91 is consistent with previous calculations including high-order corrections beyond CCSD(T) and agrees well with the experiment. The improved heats of formation with the DFT and Brueckner orbitals are due to these orbitals being closer to the actual orbitals. Pure DFT functionals perform slightly better than the hybrid B3LYP functional due to the presence of exact exchange in the hybrid functional. Comparable heats of formation for TiO2 and the second- and the third-row group IV and group VI metal oxides are predicted well using either the DFT PW91 orbitals, Brueckner orbitals, or HF orbitals. The normalized clustering energies for the dimers are consistent with our previous work except for a larger value predicted for Cr2O6. The prediction of the reaction energy for UF6 + 3Cl2 → UCl6 + 3F2 was significantly improved with the use of DFT or Brueckner orbitals as compared to HF orbitals.

One-pot synthesis of canola oil based biolubricants catalyzed by MoO3/Al2O3 and process optimization study

Research on the formulations of vegetable oils into biolubricants has gained significant interest due to their promising lubricity and eco-friendly properties. The epoxidation of unsaturated groups in vegetable oil followed by epoxide ring opening by acetic anhydride provides vicinal di-O-acetylated glyceryl fatty acid esters as a stable and potential biolubricant. The present study is emphasized on the development of a single and novel heterogeneous catalyst for both the reaction steps (epoxidation and di-O-acetylation) to produce biolubricants from canola oil and canola biodiesel (methyl fatty acid esters). Group VI metal oxides (Cr, W and Mo) impregnated on aluminium oxide were prepared and screened for their catalytic activity on the epoxidation and vicinal di-O-acetylation steps. MoO3/Al2O3 was found to be the most effective catalyst for the epoxidation of canola oil and canola biodiesel, and its further conversion to corresponding vicinal di-O-acetylated derivatives (biolubricants). The response surface methodology (RSM) was employed for optimizing the process conditions and statistical analysis for both the reaction steps separately. Based on the process optimization study, 10wt% MoO3/Al2O3 was found to be the best catalyst for 100% conversion of unsaturated groups to the epoxide and its further conversion to vicinal di-O-acetylated products in one-pot synthesis. All the products were confirmed by 1H NMR and mass spectrometry. The physico-chemical characterization of MoO3/Al2O3 was carried out to evaluate and understand the properties required for effective catalysis. This study discloses MoO3/Al2O3 as a promising catalyst for the synthesis of biolubricants from vegetable oils.