Catalyst Precursors For Oxidation Research Articles

Revealing the structural evolution of CuAg composites during electrochemical carbon monoxide reduction

Comprehending the catalyst structural evolution during the electrocatalytic process is crucial for establishing robust structure/performance correlations for future catalysts design. Herein, we interrogate the structural evolution of a promising Cu-Ag oxide catalyst precursor during electrochemical carbon monoxide reduction. By using extensive in situ and ex situ characterization techniques, we reveal that the homogenous oxide precursors undergo a transformation to a bimetallic composite consisting of small Ag nanoparticles enveloped by thin layers of amorphous Cu. We believe that the amorphous Cu layer with undercoordinated nature is responsible for the enhanced catalytic performance of the current catalyst composite. By tuning the Cu/Ag ratio in the oxide precursor, we find that increasing the Ag concentration greatly promotes liquid products formation while suppressing the byproduct hydrogen. CO2/CO co-feeding electrolysis and isotopic labelling experiments suggest that high CO concentrations in the feed favor the formation of multi-carbon products. Overall, we anticipate the insights obtained for Cu-Ag bimetallic systems for CO electroreduction in this study may guide future catalyst design with improved performance.

Microwave‐Assisted Synthesis of Cobalt‐Based Selenides as Catalyst Precursors for the Alkaline Water Oxidation

When used to promote the oxygen evolution reaction (OER), transition‐metal chalcogenides convert into oxyhydroxide/(hydr)oxide catalysts, the performance of which depends on the properties of the precursor. The present study aims to explore these effects for cobalt and cobalt–iron selenides (CoSe n and Co1Fe1Se n ) prepared using a simple microwave‐assisted method, in comparison to a reference material synthesized by high‐temperature reaction of CoO x H y with Se vapors. Physical characterization of the microwave‐synthesized CoSe n demonstrates their sheet‐like morphology and identifies Co3Se4 as the major phase, which is essentially completely transformed into CoOOH during the OER. The temperature during the microwave‐assisted CoSe n synthesis affects the crystallinity, the electrochemically active surface area, and thereby the performance of the resulting catalysts. Further improvements in the activity are achieved by combining cobalt with iron into a bimetallic Co1Fe1Se n precursor, which transforms in situ into a CoOOH + FeOOH composite and sustains the OER rate of 100 mA cm−2 (33 A g−1) at an overpotential of ≈ 0.31 and 0.26 V at 24 ± 2 and 80 ± 1 °C, respectively. Satisfactory stability of the Co1Fe1Se n ‐derived electrodes is demonstrated through a 4‐day‐long test at 80 ± 1 °C and 100 mA cm−2.

Review on the Chemistry of [M(NH3)n](XO4)m (M = Transition Metal, X = Mn, Tc or Re, n = 1–6, m = 1–3) Ammine Complexes

The preparation of ammine complexes of transition metals having oxidizing anions such as permanganate and perrhenate ions is a great challenge due to possible reactions between ammonia and oxidizing anions during the synthesis of these materials. However, it has an important role in both the development of new oxidants in organic chemistry and especially in the preparation of mixed-metal oxide catalyst precursors and metal alloys for their controlled temperature decomposition reactions. Therefore, in this paper, synthetic procedures to prepare ammonia complexes of transition metal permanganate, pertechnetate, and perrhenate (the VIIB group tetraoxometallates) salts have been comprehensively reviewed. The available data about these compounds’ structures and spectroscopic properties, including the presence of hydrogen bonds that act as redox reaction centers during thermal decomposition, are given and evaluated in detail. The nature of the thermal decomposition products has also been summarized. The available information about the role of the ammine complexes of transition metal permanganate salts in organic oxidation reactions, such as the oxidation of benzyl alcohols and regeneration of oxo-compounds from oximes and phenylhydrazones, including the kinetics of these processes, has also been collected. Their physical and chemical properties, including the thermal decomposition characteristics of known diammine (Ag(I), Cd, Zn, Cu(II), Ni(II)), triammine (Ag(I)), and simple or mixed ligand tetraammine (Cu(II), Zn, Cd, Ni(II), Co(II), Pt(II), Pd(II), Co(III)), Ru(III), pentaammine (Co(III), Cr(III), Rh(III) and Ir(III)), and hexaammine (Ni(II), Co(III), Cr(III)) complexes of transition metals with tetraoxometallate(VII) anions (M = Mn, Tc and Re), have been summarized. The preparation and properties of some special mixed ligand/anion/cation-containing complexes, such as [Ru(NH3)4(NO)(H2O)](ReO4)2, [Co(NH3)5(H2O)](ReO4)2, [Co(NH3)5X](MnO4)2 (X = Cl, Br), [Co(NH3)6]Cl2(MnO4), [Co(NH3)5ReO4]X2 (X = Cl, NO3, ClO4, ReO4), and K[Co(NH3)6]Cl2(MnO4)2, are also included.

Ni–Mo sulfide nanosized catalysts from water-soluble precursors for hydrogenation of aromatics under water gas shift conditions

Abstract The unsupported catalysts were obtained during hydrogenation by in situ high-temperature decomposition (above 300 °C) of water-soluble metal precursors (ammonium molybdate and nickel nitrate) in water-in-oil (W/O) emulsions stabilized by surfactant (SPAN-80) using elemental sulfur as sulfiding agent. These self-assembly Ni–Mo sulfide nanosized catalysts were tested in hydrogenation of aromatics under CO pressure in water-containing media for hydrogen generation through a water gas shift reaction (WGSR). The composition of the catalysts was determined by XRF and active sulfide phase was revealed by XRD, TEM and XPS techniques. The calculations based on TEM and XPS data showed that the catalysts are highly dispersed. The surfactant was found to affect both dispersion and metal distribution for Ni and Mo species, providing shorter slab length in terms of sulfide particle formation and stacking within high content of NiMoS phase. Catalytic evaluation in hydrogenation of aromatics was performed in a high-pressure batch reactor at T = 380–420 °С, p(CO) = 5 MPa with water content of 20 wt.% and CO/H2O molar ratio of 1.8 for 4–8 h. As shown experimentally with unsupported Ni–Mo sulfide catalysts, the activity of aromatic rings depends on the substituent therein and decreases as follows: anthracene>>1-methylnaphthalene≈2-methylnaphthalene>1,8-dimethylnaphthale-ne>>1,3-di-methylnaphthalene>2,6-dimethylnaphthalene≈2,3-dimethylnaphthalene>2-ethyl-naphthalene. The anthracene conversion reaches up to 97–100% for 4 h over the whole temperature range, while for 1MN and 2MN it doesn’t exceed 92 and 86% respectively even at 420 °С for 8 h. Among dimethyl-substituted aromatics the higher conversion of 45% was achieved for 1,8-dimethylnaphthalene with 100% selectivity to tetralines at 400 °С for 6 h. Similar to 1- and 2-methylnaphtalenes, the hydrogenation of asymmetric dimethyl-substituted substrate carries out through the unsubstituted aromatic ring indicating that steric factors influence on the sorption mechanism over active metal sites. The catalysts were found to be reused for at least six cycles when the hydrogenation is sulfur-assisted preventing metal oxide formation. It was established, that at the first 2–3 h known as the induction period, the oxide catalyst precursors formed slowly by metal salt decomposition, which reveals that it is the rate-determining step. The sulfidation is rather fast based on high catalytic activity data on 2MN conversion retaining at 93–95% upon recycling.

Aroylhydrazone Schiff Base Derived Cu(II) and V(V) Complexes: Efficient Catalysts towards Neat Microwave-Assisted Oxidation of Alcohols.

A new hexa-nuclear Cu(II) complex [Cu3(μ2-1κNO2,2κNO2-L)(μ-Cl)2(Cl)(MeOH)(DMF)2]2 (1), where H4L = N′1,N′2-bis(2-hydroxybenzylidene)oxalohydrazide, was synthesized and fully characterized by IR spectroscopy, ESI-MS, elemental analysis, and single crystal X-ray diffraction. Complex 1 and the dinuclear oxidovanadium(V) one [{VO(OEt)(EtOH)}2(1κNO2,2κNO2-L)]·2H2O (2) were used as catalyst precursors for the neat oxidation of primary (cinnamyl alcohol) and secondary (1-phenyl ethanol, benzhydrol) benzyl alcohols and of the secondary aliphatic alcohol cyclohexanol, under microwave irradiation using tert-butyl hydroperoxide (TBHP) as oxidant. Oxidations proceed via radical mechanisms. The copper(II) compound 1 exhibited higher catalytic activity than the vanadium(V) complex 2 for all the tested alcohol substrates. The highest conversion was found for 1-phenylethanol, yielding 95.3% of acetophenone in the presence of 1 and in solvent and promoter-free conditions. This new Cu(II) complex was found to exhibit higher activity under milder reaction conditions than the reported aroylhydrazone Cu(II) analogues.

Copper–iron mixed oxide catalyst precursors prepared by glycine-nitrate combustion method for ammonia borane dehydrogenation processes

The influence of the properties of copper ferrite, prepared by the combustion method from glycine-nitrate precursor, on the kinetics of NH3BH3 hydrolysis, thermolysis and hydrothermolysis are presented. As-prepared and annealed samples were studied by X-ray diffraction, scanning electron microscopy, differential dissolution, and attenuated total reflection infrared spectroscopy. It has been shown that in the hydrolysis and hydrothermolysis of NH3BH3, the as-prepared combustion product, which mainly consisted of a cubic spinel Cu0.67Fe2.33O4 with Fe2+ higher content, had the highest activity, as compared with oxides of copper and iron and the annealed samples. According to transmission electron microscopy and X-ray diffraction, in the reaction medium copper ferrite is reduced to nanosized Cu0 and Fe0. This allowed the average rate of H2 evolution per 1 g of the composition to be increased from 30 to 76 ml⋅min−1, as compared with non-catalytic process. The high gravimetric hydrogen capacity (7.3 wt%) was observed at 90 °C.

An efficient and recyclable copper nano-catalyst for the selective oxidation of benzene to p-benzoquinone (p-BQ) using H2O2(aq) in CH3CN

The molecular copper complex tetrakis(acetonitrile)copper(I) perchlorate [Cu(CH3CN)4ClO4] (1) was shown to act as a catalyst precursor for the efficient oxidation of benzene to p-benzoquinone (p-BQ) with a percentage selectivity of 60–80% under mild conditions, and produces phenol (PhOH) as a minor product at room temperature. Here, we obtained evidences showing the formation of copper based nanoparticle catalyst (NC) (2) from 1 to be the vital step responsible for its ability to catalyze the conversion of benzene to p-BQ, presumably via double oxidation. Addition of a considerable amount of H2O to the reaction mixture improved the selectivity for forming p-BQ to 84% and/or the conversion efficiency to 98%. In addition, the copper NC easily formed in situ through the oxidation of substrate using H2O2 in CH3CN. After separating the NC from the reaction mixture and recycling them several times, it still maintained comparable catalytic efficiency and selectivity for the conversion of benzene to p-BQ.

Nanoclays as dispersing precursors of La and Ce oxide catalysts to produce high-valued derivatives of biodiesel by-product

Hydrotalcite-like compounds are valuable anionic nanoclays due to their functionalized capacity. Rare earth elements, La and Ce, were incorporated in those materials by co-precipitation and wet impregnation methods. The materials were calcined and used as mixed oxides in the selective production of monoglycerides at 220 °C and with a glycerol/methyl stearate molar ratio of 6:1. Catalysts were characterized by X-ray diffraction, surface area, scanning electron microscopy, inductively coupled plasma − optical emission spectroscopy, temperature-programmed desorption, and X-ray photoelectron spectroscopy. The product yield was determined by gas chromatography with flame ionization detector. The catalyst structural surface properties and basicity were determined by the composition of the mixed oxides, as was revealed by the catalytic behavior of the materials. The sample with Ce incorporated by the impregnation method exhibited the highest basicity, which is probably related to the highest monoglyceride yield of 77%.

Heteroleptic cobalt(iii) acetylacetonato complexes with N-heterocyclic carbine-donating scorpionate ligands: synthesis, structural characterization and catalysis.

Exposure of O2 to a reaction mixture containing bis(acac)cobalt(ii), a facially capping tris(N-heterocyclic carbene)borate ligand and 1-methylimidazole yields a heteroleptic cobalt(iii) complex with acac, 1-methylimidazole and tris(NHC)borate ligands. meta-Chloroperbenzoic acid is efficiently activated by this heteroleptic complex to catalytically oxidize cyclohexane at ambient temperature.

New Copper(II) Coordination Compounds Assembled from Multifunctional Pyridine-Carboxylate Blocks: Synthesis, Structures, and Catalytic Activity in Cycloalkane Oxidation.

Two new copper(II) coordination compounds, namely a 1D coordination polymer [Cu(µ-cpna)(phen)(H2O)]n (1) and a discrete tetracopper(II) derivative [Cu(phen)2(H2O)]2[Cu2(µ-Hdppa)2(Hdppa)2] (2), were hydrothermally synthesized from copper(II) chloride as a metal source, 5-(4-carboxyphenoxy)nicotinic acid (H2cpna) or 5-(3,4-dicarboxylphenyl)picolinic acid (H3dppa) as a principal building block, and 1,10-phenanthroline (phen) as a crystallization mediator. Compounds 1 and 2 were isolated as air-stable microcrystalline solids and fully characterized by elemental and thermogravimetric analyses, IR spectroscopy, powder and single-crystal X-ray diffraction. In the solid state, the structure of 1 discloses the linear interdigitated 1D coordination polymer chains with the 2C1 topology. The crystal structure of an ionic derivative 2 shows that the mono- and dicopper(II) units are extended into the intricate 1D hydrogen-bonded chains with the SP 1-periodic net (4,4)(0,2) topology. Thermal stability and catalytic properties of 1 and 2 were also investigated. In fact, both Cu derivatives act as efficient homogeneous catalysts (catalyst precursors) for the mild oxidation of cycloalkanes by hydrogen peroxide to give the corresponding alcohols and ketones; the substrate scope and the effects of type and amount of acid promoter as well as bond-, regio-, and stereo-selectivity features were investigated.

Effect of partial Mo substitution by W on HDS activity using sulfide CoMoW/Al2O3–TiO2 catalysts

A series of Al2O3–TiO2-supported trimetallic CoMoW catalysts were prepared with the aim to study the effect of Mo substitution by W on the catalyst performance in deep hydrodesulfurization (HDS) reaction. The oxide catalyst precursors were characterized by N2 physisorption, temperature-programmed desorption of NH3 (TPD-NH3), temperature-programmed reduction (TPR), diffuse reflectance spectroscopy (DRS UV–vis) and Raman spectroscopy. Sulfided catalysts were characterized by X-ray photoelectron spectroscopy (XPS) and high resolution transmission electron microscopy (HRTEM), and tested in the dibenzothiophene (DBT) hydrodesulfurization (HDS) reaction carried out in a batch reactor at T = 320 °C and total H2 pressure of 5.5 MPa. It was found that partial substitution of Mo by W leads to enhancement of catalyst metal and acid functions. The W-rich catalyst (W/Mo atomic ratio of 1.2) exhibited the best catalytic behavior and a larger selectivity toward HYD route products than W-free CoMo counterpart. The catalyst structure-activity correlation suggested that this is due to the combined effects of the best dispersion of metal oxides, the enhance of the catalyst acidity, a lower stacking of Mo(W)S2 layers and the formation of mixed “Co–Mo(W)–S” phase. In contrast, the less active phase (CoMo2S4) was formed on the surface of the conventional CoMo catalyst. For all catalysts, The HDS reaction proceeds via direct desulfurization (DDS) and hydrogenation (HYD) reaction routes, the former being the main reaction route.

New copper(II) salicylaldimine derivatives for mild oxidation of cyclohexane

Two new salicylaldiminato-copper(II) complexes, [ $$\hbox {Cu}(\mathbf{L}^{\mathbf{1}})_{2}$$ ] (1) and [ $$\hbox {Cu}(\mathbf{L}^{\mathbf{2}})_{2}$$ ] (2) (where $$\mathbf{HL}^{\mathbf{1}}=4$$ -tert-Butyl-2-[(thiophen-2-ylmethylimino)-methyl]-phenol and $$\mathbf{HL}^{2} = 2,4$$ -Di-tert-butyl-6-[(thiophen-2-ylmethylimino)-methyl]-phenol), endowed with a pendant thiophenyl moiety, were synthesized and characterized using standard spectroscopic techniques (FT-IR, UV-Vis, MS) and elemental analysis. Complexes 1 and 2 were unequivocally characterized by single crystal X-ray crystallography, which confirmed bidentate bis-chelation of the deprotonated - $$\mathbf{L}^{\mathbf{1}}$$ and - $$\mathbf{L}^{\mathbf{2}}$$ ligands to the copper (II) centres via the phenoxo and imine atoms forming square planar complexes. The copper(II)-hydroperoxo derivatives of 1 and 2 ([ $$(\mathbf{L}^{\mathbf{1}})_{2}\hbox {Cu}^\mathrm{II}\hbox {-OOH}$$ ] (3) and [ $$(\mathbf{L}^{\mathbf{2}})_{2}\hbox {Cu}^\mathrm{II}\hbox {-OOH}$$ ] (4)) were also synthesized and the formation of the active intermediate in solution studied. Complexes 1 and 2 were tested as catalyst precursors in cyclohexane oxidation under mild reaction conditions using hydrogen peroxide ( $$\hbox {H}_{2} \hbox {O}_{2}$$ ) as a terminal oxidant, and were found to catalyse oxidation of the substrate with yields comparable to similar mononuclear and even multinuclear copper complexes. Synopsis Synthesis, characterisation, and molecular structure of salicylaldiminato-copper(II) complexes, and their catalytic evaluation in the oxidation of cyclohexane employing hydrogen peroxide as a terminal oxidant have been studied. The complexes catalysed conversion of cyclohexane with appreciable yields.

Synthesis, structural characterization and catalytic potential of oxidovanadium(IV) and dioxidovanadium(V) complexes with thiazole-derived NNN-donor ligand

Reaction between the tridentate NNN donor ligand, (E)-2-(2-(1-(pyridin-2-yl)ethylidene)hydrazinyl)benzo[d]thiazole (HL), and V2O5 in ethanol gave a new vanadium(V) complex, [VO2L] (1), while the similar reaction by using [VIVO(acac)2] as the metal source gave two different types of crystals related to compounds [VO2L] (1) and [VIVO(acac)L] (2). The molecular structures of the complexes were determined by single-crystal X-ray diffraction and spectroscopic characterization was carried out by means of FT-IR, UV–vis and NMR experiments as well as elemental analysis. The oxidovanadium(IV) and dioxidovanadium(V) species were used as catalyst precursors for olefin oxidation in the presence of hydrogen peroxide (H2O2) as an oxidant. Under similar experimental conditions, the presence of 1 resulted in higher oxidation conversion than 2.

Pd-Catalyzed Aerobic Oxidation Reactions: Strategies To Increase Catalyst Lifetimes.

The palladium complex [(neocuproine)Pd(μ-OAc)]2[OTf]2 (1, neocuproine = 2,9-dimethyl-1,10-phenanthroline) is an effective catalyst precursor for the selective oxidation of primary and secondary alcohols, vicinal diols, polyols, and carbohydrates. Both air and benzoquinone can be used as terminal oxidants, but aerobic oxidations are accompanied by oxidative degradation of the neocuproine ligand, thus necessitating high Pd loadings. Several strategies to improve aerobic catalyst lifetimes were devised, guided by mechanistic studies of catalyst deactivation. These studies implicate a radical autoxidation mechanism initiated by H atom abstraction from the neocuproine ligand. Ligand modifications designed to retard H atom abstractions as well as the addition of sacrificial H atom donors increase catalyst lifetimes and lead to higher turnover numbers (TON) under aerobic conditions. Additional investigations revealed that the addition of benzylic hydroperoxides or styrene leads to significant increases in TON as well. Mechanistic studies suggest that benzylic hydroperoxides function as H atom donors and that styrene is effective at intercepting Pd hydrides. These strategies enabled the selective aerobic oxidation of polyols on preparative scales using as little as 0.25 mol % of Pd, a major improvement over previous work.

Perovskite as catalyst precursors in the partial oxidation of methane: The effect of cobalt, nickel and pretreatment

Perovskites with formula LaNi1-xCoxO3 (x=0.0, 0.2, 0.5 and 1.0) were investigated in the Partial Oxidation of Methane (POM) reaction. In situ XRD results suggest that the reduction of the perovskites under H2 lead to the formation of La2B2O5 (B=Ni and Co) which is further transformed to Ni1-xCox/La2O3. The phase structure evolution when increasing the temperature of LaNi0.8Co0.2O3 without pre-reduction with H2 but submitted to a mixture CH4+O2 allows the formation of a spinel phase La2BO4 (B=Ni and Co) before obtaining Ni and Co over La2O3. On the other hand LaNi0.8Co0.2O3 presented a different behavior after previous reduction with H2 and the spinel phase is not detected. The H2 pre-reduction favored lower mean crystallite size of Ni on La2O3. The catalytic tests suggest that H2 pretreatment promotes the production of the syngas with a H2/CO=2 close to the stoichiometry. Without pretreatment, the H2/CO ratio is lower (1.6) indicating the occurrence of parallel reactions such as RWGS. The sample Ni0.8Co0.2/La2O3 pretreated with H2 presented a higher molar rate H2/CO=2.2. Deactivation was not observed after 24h run test but graphitic carbon was detected on all samples. In the case of Ni0.8Co0.2/La2O3 less carbon formation was detected.

Effect of sulfidation process on catalytic performance over unsupported Ni-Mo-W hydrotreating catalysts

Oxidic unsupported Ni-Mo-W catalysts were chosen to elucidate the effect of sulfidation conditions on the catalytic performance. The catalysts were sulfided in situ by using dimethyl sulfide as sulfiding agent. The relationships between the time needed for sulfidation and the sulfiding conditions were studied by GC-analysis method. Straight-run gas oil with high sulfur and nitrogen content was used to evaluate the hydrotreating performance. The oxidic catalyst precursors and sulfided catalysts were characterized by X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and X-ray photoelectron spectroscopy (XPS). With increasing sulfiding liquid hourly space velocity (LHSV) of the sulfiding agent, the reaction time necessary for the sulfidation decreased, while the activity of the catalyst increased significantly. The higher catalytic activity might be due to the MoS2/WS2 slabs with shorter length and higher stacking number, which might contribute to the catalyst with more active sites. Sulfiding at 330 °C took the longest sulfidation time, while the catalytic activity was also the highest after sulfiding at this temperature. Furthermore, within a certain range, the sulfidation pressure had no evident effect on the catalytic behavior or activity. The purpose of this work was to provide a basis for actual production and a reference for further research.

Vanadium(V) Complexes with Substituted 1,5-bis(2-hydroxybenzaldehyde)carbohydrazones and Their Use As Catalyst Precursors in Oxidation of Cyclohexane.

Six dinuclear vanadium(V) complexes have been synthesized: NH4[(VO2)2((H)LH)] (NH4[1]), NH4[(VO2)2((t-Bu)LH)] (NH4[2]), NH4[(VO2)2((Cl)LH)] (NH4[3]), [(VO2)(VO)((H)LH)(CH3O)] (4), [(VO2)(VO)((t-Bu)LH)(C2H5O)] (5), and [(VO2)(VO)((Cl)LH)(CH3O)(CH3OH/H2O)] (6) (where (H)LH4 = 1,5-bis(2-hydroxybenzaldehyde)carbohydrazone, (t-Bu)LH4 = 1,5-bis(3,5-di-tert-butyl-2-hydroxybenzaldehyde)carbohydrazone, and (Cl)LH4 = 1,5-bis(3,5-dichloro-2-hydroxybenzaldehyde)carbohydrazone). The structures of NH4[1] and 4-6 have been determined by X-ray diffraction (XRD) analysis. In all complexes, the triply deprotonated ligand accommodates two V ions, using two different binding sites ONN and ONO separated by a diazine unit -N-N-. In two pockets of NH4[1], two identical VO2(+) entities are present, whereas, in those of 4-6, two different VO2(+) and VO(3+) are bound. The highest oxidation state of V ions was corroborated by X-ray data, indicating the presence of alkoxido ligand bound to VO(3+) in 4-6, charge density measurements on 4, magnetic susceptibility, NMR spectroscopy, spectroelectrochemistry, and density functional theory (DFT) calculations. All four complexes characterized by XRD form dimeric associates in the solid state, which, however, do not remain intact in solution. Compounds NH4[1], NH4[2], and 4-6 were applied as alternative selective homogeneous catalysts for the industrially significant oxidation of cyclohexane to cyclohexanol and cyclohexanone. The peroxidative (with tert-butyl hydroperoxide, TBHP) oxidation of cyclohexane was performed under solvent-free and additive-free conditions and under low-power microwave (MW) irradiation. Cyclohexanol and cyclohexanone were the only products obtained (high selectivity), after 1.5 h of MW irradiation. Theoretical calculations suggest a key mechanistic role played by the carbohydrazone ligand, which can undergo reduction, instead of the metal itself, to form an active reduced form of the catalyst.

Catalytic oxidation of olefins and sulfides in the presence of hydrazone-oxidovanadium(V) complex containing VOCl2+ core

A new oxidovanadium(V) complex, [VO(L)Cl2] (1), is synthesized by the reaction of VOCl3 with (E)-N′-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide (HL) in chloroform as a solvent. The complex is characterized by elemental analysis, spectroscopic methods (FT-IR, UV–vis), and its structure is determined by single crystal X-ray diffraction analysis. X-ray studies reveal a mononuclear complex of V(V) with the hydrazone ligand coordinated to the V(V) center as a tridentate mononegative ligand. This complex is used as a catalyst precursor for oxidation of olefins and sulfides in the presence of hydrogenperoxide (H2O2) as a green oxidant. The effect of various parameters is studied including the amount of the catalyst, temperature and solvent. The results show the system corresponds to an active and selective catalyst for oxidation of cyclooctene and thioanisole.

Dehydrogenation of methylcyclohexane to toluene over partially reduced silica-supported Pt-Mo catalysts

A series of bifunctional Pt/Mo(x)-SiO2 catalysts were investigated in the context of the hydrogen storage using the methylcyclohexane (MCH)-toluene-hydrogen cycle. The performance of partially reduced catalysts for hydrogen production was evaluated in the MCH dehydrogenation reaction carried out in a fixed-bed flow reactor at 673K and total hydrogen pressure of 2.2MPa. The catalysts with different acidity and Mo loading (4.1–12.7wt.%) were prepared by impregnation of the calcined Mo(x)-SiO2 samples with Pt precursor. The oxide catalyst precursors were characterized by chemical analysis (ICP-AES), N2 physisorption at 77K, X-ray diffraction (XRD), Raman spectroscopy and temperature-programmed reduction (H2-TPR) techniques whereas the partially reduced samples were characterized by temperature-programmed adsorption of ammonia (TPD-NH3), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS). The catalyst having optimized Mo loading (8.0wt.%) was the most active and its best catalytic performance was attributed to the high dispersion of MoO2 and Pt° phases and its lowest deactivation by coke formation. The activity drop of the catalysts having larger Mo loading (10.6 and 12.7wt.%) was linked with formation of MoOx-Pt core-shell nanoparticles, as confirmed by HRTEM.

Activated carbon surface chemistry: Changes upon impregnation with Al(III), Fe(III) and Zn(II)-metal oxide catalyst precursors from NO3− aqueous solutions

Because of the relevance in heterogeneous catalysis, the changes produced in the surface chemistry of activated carbon (AC) upon impregnation with the Al3+, Fe3+ and Zn2+ ions from aqueous solution of NO3− salts at pH 2.91 for Al3+, 1.54 for Fe3+ and 5.16 for Zn2+ in two successive soaking and oven-drying steps are studied. The samples (A120, F120 and Z120) were analyzed in terms of elemental composition and by energy dispersive X-ray analysis (EDX), FT-IR spectroscopy, X-ray photoelectron spectroscopy (XPS), and measurement of pH of the point of zero charge (pHpzc). The process yield was 102wt% for A120, 114wt% for F120, and 103wt% for Z120. Chromene, pyrone and ether type structures are by far predominant in AC. The hydrolysis of metal ions markedly influences the pH of the impregnation solution and thereby the oxidation of surface functional groups of AC by O2 and NO3− dissolved in such a solution. The degree of AC oxidation is larger with the Fe3+ solution than with the Al3+ and Zn2+ solutions. Carboxylic acid groups for F120 and phenolic hydroxyl groups for Z120 and especially for A120 are formed from reducing structures of AC. The nitrogen content is higher by Z120>A120>F120>AC. pHpzc is 10.50 for AC, 5.20 for A120, 4.00 for F120 and 6.30 for Z120.