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Various forms of cobalt catalysts have been studied extensively for selective aerobic oxidation of hydrocarbons. However, it remains unclear whether cobalt can directly activate molecular oxygen under mild reaction conditions. Here we investigated the catalytic roles of cobalt in ethylbenzene oxidation with and without a hydroperoxide initiator. The contribution of different cobalt species was studied by varying the metal loading on Co-impregnated ZSM-5 samples. Quantitative EPR was used to determine the impact of cobalt catalysts on the free radical concentrations. This work provided strong evidence that cobalt, in several different forms, catalyzes hydrocarbon oxidation by facilitating peroxy bond cleavage, instead of direct oxygen activation.

Vapor phase catalytic hydrogen peroxide production by oxidation of water is possible by coupling the reaction with oxidation of an organic sacrificial reductant. It is potentially a safer process than direct synthesis from H2 and O2. Based on mechanistic information available mostly for liquid phase catalytic processes, feasible reaction mechanisms for such coupled reactions are proposed based on which desirable catalyst properties are identified. It is found that the surface-adsorbed oxygen bond is an important parameter for identifying desirable catalysts. Thermodynamics can be used to identify the types of organic oxidation reactions that can couple with water oxidation such that H2O2 formation becomes thermodynamically favorable. Reactions such as epoxidation of alkenes and selective oxidation of alkanes to alcohols cannot provide sufficient thermodynamic driving force, whereas oxidation of alcohols to aldehydes and to acids can. Finally, further research is suggested to identify catalytic properties important for H2O2 decomposition and for coupling selective oxidation of organic compounds to oxidation of H2O in order to facilitate development of H2O2 production coupled with selective organic oxidation.

Catalytic oxidation of organic pollutants is an attractive and sustainable method of water purification. This paper focuses on discussion of catalytic activity, selectivity, and stability in cataly...

Aerobic oxidation of α-C H bond of organic compounds to valuable chemicals is widely investigated in both fundamental research and industry. Due to the good stability of molecular oxygen, severe reaction conditions are generally required. Herein, by in situ synthesis we used molecular oxygen to induce cobalt nanoclusters with the sensitive catalysis in mild selective oxidation. The cobalt containing clusters with an average diameter around 0.9 nm are in situ prepared in the presence of cis-cyclooctene epoxidation and cyclooctene dimer oxide is formed at the interface to stabilize Co clusters with electron donation as an oil-soluble surfactant. The soluble clusters exhibit high activity in selective oxidation of α-C H bond of ethylbenzene into acetophenone and turnover number (TON) reaches about 7 × 104 during 50 h’ reaction at 373 K, which is around 960 times more active than the one using CoCl2 salt as the catalyst, resulting from efficient mass transportation, π bond interaction and oxygen gas activation. Extended work based on this understanding demonstrates that cobalt nanoclusters also effectively catalyze aerobic oxidation of cyclohexene.

The catalytic properties of physical mixtures of Ni particles (100–200 nm) with nanoparticles of anatase TiO2 (TiO2-A), ZrO2, Al2O3, rutile TiO2 (TiO2-R), and CeO2 were investigated for the hydrode...

Interfacial perimeter sites between metal and support are often important for catalysis. A mononuclear titanium siloxy complex III, Ti(acac)2[OSiC6H5N(OCH3)2]2 was synthesized to generate TiOx units of different degrees of clustering to decorate Au nanoparticles. Two different methods of preparation were examined; one was to deposit III onto Au/SiO2 and the other was to form III-covered Au nanoparticle first before deposition onto SiO2. The former method generated more highly dispersed TiOx units, while larger domains of TiO2 were formed with the latter method, as deduced by UV–vis and XAS characterization. A model was proposed to explain how TiOx dispersity could be related to the preparative procedures. These samples were further tested as catalysts in selective oxidation of propane in a stream of O2 and H2. They exhibited different product selectivities. The sample with more dispersed TiOx units were more selective for acetone formation versus propene formation. The results confirmed the important role of both the Au–TiOx interface at the perimeter and the extent of Ti isolation in the TiOx phase in the reaction.

Ternary metal fluoride Fe x Mn 1−x F 2 (x = 0.00, 0.25, 0.50, 0.75, and 1.00), which is a potential cathode material for next-generation Li-ion batteries, were synthesized via a convenient, low-temperature, bottom-up solution-phase method. The lattice dimensions deduced from X-ray diffraction suggested formation of homogeneous solid solutions. With increasing Fe content, the morphology of the solid changed from cubic particles to dendritic, with an average particle size of 20–40 nm. The results suggested that this synthetic method constitutes a translatable route to large-scale production of ternary metal fluoride nanoparticles.

Inverse gas chromatography (IGC) was employed in evaluating the catalytic surface of meso-microporous KIT-6 impregnated Ni (0.5–2.0 wt%) in methane dry reforming reaction. The free energy of adsorption did not changed significantly for the sample modified with highly dispersed Ni species (0.5 wt%). At higher Ni loadings, higher free energy of adsorption and enthalpy of adsorption of the probes were observed, together with high dispersive interaction and specific interaction of aromatics. The results indicated that during the impregnation, Ni species preferably penetrated into the microporous region to form Ni particles and became ‘unaccessible’. This feature was used to understand the dependence of activity on Ni loading for the gas phase catalytic methane reforming with carbon dioxide on Ni/KIT-6. The lower TOF at low metal loadings was attributed to Ni particles located in the micropores which result in diffusional constraint of reactants and products.

Electrically conducting, 3D elastomeric composite foams are fabricated successfully using multiple cycles of infusing polyurethane foams with graphene oxide sheets followed by reduction, to form coatings of reduced graphene oxide up to ∼1260 nm thick. The reduced graphene oxide coating increases the compression modulus of the composite and lowers the electrical resistance significantly compared with polyurethane foam, the extents of which increase with increasing coating thickness. The electrical resistance of the coated foams varies by as much as three orders of magnitude for coating thickness between ∼150 and ∼1200 nm, whereas the capacitance varies by one order of magnitude. Both the stress-strain and the resistance-strain behavior are highly repeatable with compression cycles performed up to 70% strain. Both SEM and X-ray tomography characterization show that deformation is mostly through bending of the pore walls up to about 20% strain, collapse of pore openings to about 60% strain, and densification beyond that. Micro-fractures also develop on the coating during the first few cycles of compression, but no obvious structural changes can be detected afterwards.

Cu-modified Au/TiO2 (anatase, 200 m2/g) has been prepared by the incipient-wetness technique with introduction of the modifier either before or after Au loading. Such catalysts gave higher catalytic activities for the water–gas shift (WGS) reaction when compared to the unmodified catalysts mainly because of the existence of a synergetic interaction between Cu and Au, as the activities of both Cu/TiO2 and Au/TiO2 are lower than that of the bimetallic system. The WGS activities of both the as-prepared Au/TiO2 and a Au–Cuc/TiO2 catalyst were found to be high and stable. The presence of nitrates on Cuc–Au/TiO2 was found to be detrimental to the activity of Au on TiO2, as a result of the poisoning of Au and enhanced Au agglomeration by NO2 formed during reaction. The activities of Au/TiO2 catalysts modified with Cu-containing acetate counterions were found to decrease during the first 30 min on stream, reaching a constant value of (45 ± 2)%. However, when the poisoning by the acetate anion was eliminated throu...

In a noncontact catalytic system, intermediaries derived from Au-catalyzed cyclooctene epoxidation effects ethylbenzene oxidation., Traditionally, a catalyst functions by direct interaction with reactants. In a new noncontact catalytic system (NCCS), an intermediate produced by one catalytic reaction serves as an intermediary to enable an independent reaction to proceed. An example is the selective oxidation of ethylbenzene, which could not occur in the presence of either solubilized Au nanoclusters or cyclooctene, but proceeded readily when both were present simultaneously. The Au-initiated selective epoxidation of cyclooctene generated cyclooctenyl peroxy and oxy radicals that served as intermediaries to initiate the ethylbenzene oxidation. This combined system effectively extended the catalytic effect of Au. The reaction mechanism was supported by reaction kinetics and spin trap experiments. NCCS enables parallel reactions to proceed without the constraints of stoichiometric relationships, offering new degrees of freedom in industrial hydrocarbon co-oxidation processes.

Grafting of pairs of functional groups onto a silica surface was demonstrated by tethering both terminals of an organochlorosilane precursor molecule, Cl2(CH3)Si(CH2)4(CO)(OSi(i-Pr)2)(CH2)2Si(CH3)Cl2, that possess a cleavable silyl ester bond, onto a silica surface. Hydrolytic cleavage of the silyl ester bond of the grafted molecule resulted in the generation of organized pairs of carboxylic acid and organosilanol groups. This organosilanol moiety was easily transformed into other functional groups through condensation reactions to form, together with the neighboring acid group, pairs such as carboxylic acid/secondary amine, carboxylic acid/pyridine, and carboxylic acid/phosphine. In the case of carboxylic acid/amine pairing, there was evidence of the formation of amide. A sample grafted with amine–carboxylic acid pairs was three times more active (per free amine) than a sample without such pairs for the nitroaldol condensation of 4-nitrobenzaldehyde and nitromethane.

The efficiency of H2O2 formation during Au/C-catalyzed aerobic oxidation of 1,2-propanediol (diol) at 35 °C increased with increasing concentrations of diol and NaOH. Diol conversion and H2O2 accumulation data collected at different concentrations of diol and NaOH could be fitted to a Langmuir–Hinshelwood kinetics model using the diolate as the reactant, indicating that the primary role of hydroxide ions is to deprotonate the diol and not as a reactant in the rate limiting step. Using the model to extrapolate the data to full surface coverage of diolate, it was found that one molecule of diol oxidized would produce one molecule of H2O2 and one molecule of lactate. At lower diolate coverages, unoccupied active sites adjacent to adsorbed hydroperoxy/peroxy enabled O O bond cleavage and lowered the H2O2 production efficiency. Catalytic degradation of H2O2 decreased its production efficiency, and accumulation of trace amounts of heavy products likely caused the slow catalyst deactivation.

There is an urgent need to provide adequate and sustainable supplies of water and food to satisfy the demand of an increasing population. Catalysis plays important roles in meeting these needs by facilitating the synthesis of hydrogen peroxide that is used in water decontamination and chemicals production, and ammonia that is used as fertilizer. However, these chemicals are currently produced with processes that are either very energy-intensive or environmentally unfriendly. This article offers the perspectives of the challenges and opportunities in the production of these chemicals, focusing on the roles of catalysis in more sustainable, alternative production methods that minimize energy consumption and environmental impact. While not intended to be a comprehensive review, the article provides a critical review of selected literature relevant to its objectives, discusses areas needed for further research, and potential new directions inspired by new developments in related fields. For each chemical, production by thermal, electro-, and photo-excited processes are discussed. Problems that are common to these approaches and their differences are identified and possible solutions suggested.

The ability of Au catalysts to effect the challenging task of utilizing molecular oxygen for the selective epoxidation of cyclooctene is fascinating. Although supported nanometre-size Au particles are poorly active, here we show that solubilized atomic Au clusters, present in ng ml−1 concentrations and stabilized by ligands derived from the oxidized hydrocarbon products, are active. They can be formed from various Au sources. They generate initiators and propagators to trigger the onset of the auto-oxidation reaction with an apparent turnover frequency of 440 s−1, and continue to generate additional initiators throughout the auto-oxidation cycle without direct participation in the cycle. Spectroscopic characterization suggests that 7–8 atom clusters are effective catalytically. Extension of work based on these understandings leads to the demonstration that these Au clusters are also effective in selective oxidation of cyclohexene, and that solubilized Pt clusters are also capable of generating initiators for cyclooctene epoxidation., Gold catalysts have previously been reported for the epoxidation of alkenes with molecular oxygen. Here the authors show that, rather than the gold nanoparticles, the active species for this reaction are actually small, soluble gold species stabilized by the oxidised organic products.

Mild calcination in ozone of a (POSS)-Sn-(POSS) complex grafted on silica generated a heterogenized catalyst that mostly retained the tetrahedral coordination of its homogeneous precursor, as evidenced by spectroscopic characterizations using EXAFS, NMR, UV–vis, and DRIFT. The Sn centers are accessible and uniform and can be quantified by stoichiometric pyridine poisoning. This Sn-catalyst is active in hydride transfer reactions as a typical solid Lewis acid. However, the Sn centers can also create Bronsted acidity with alcohol by binding the alcohol strongly as alkoxide and transferring the hydroxyl H to the neighboring Sn–O–Si bond. The resulting acidic silanol is active in epoxide ring opening and acetalization reactions.

An example of unusual addition of a main-group-metal alkoxide across an alkene C═C bond was demonstrated with a dimethylvinylsilyl-substituted Sn-POSS complex (POSS = incompletely condensed polyhedral oligomeric silsesquioxane). The structure of the pentacoordinated Sn chelate product was confirmed by 1H, 13C, and 119Sn NMR and ESI-MS.