ion from a primary OH group of glyc-erol. 223,231 A similar mechanism was proposed manyyears ago for alcohol oxidation on Pt/C, involving asecond step, the transfer of a hydride ion to the Ptsurface (Scheme 11). 8,87,237 We consider it more feasible that the rate-deter-mining step is the cleavage of the C-H bond at theR-carbon atom. A similar mechanism is now generallyaccepted for Au electrodes (Scheme 12). 238 Despite thestructural differences between Au nanoparticles andan extended Au electrode surface, there are alsosimilarities, such as the critical role of aqueousalkaline medium and the absence of deactivation dueto decomposition products (CO and C x H y frag-ments). 239,240 An important question is the nature of active siteson Au nanoparticles. Electrooxidation of ethanol onAu nanoparticles supported on glassy carbon re-quired the partial coverage of Au surface by oxides. 241 Another analogy might be the model proposed for COoxidation. 219,242,243 According to this suggestion, theactive site consists of an ensemble of metallic Auatoms and a cationic Au

Oxidation of Alcohols with Molecular Oxygen on Solid Catalysts

Cerium dioxide (CeO2, ceria) is becoming an ubiquitous constituent in catalytic systems for a variety of applications. 2016 sees the 40th anniversary since ceria was first employed by Ford Motor Company as an oxygen storage component in car converters, to become in the years since its inception an irreplaceable component in three-way catalysts (TWCs). Apart from this well-established use, ceria is looming as a catalyst component for a wide range of catalytic applications. For some of these, such as fuel cells, CeO2-based materials have almost reached the market stage, while for some other catalytic reactions, such as reforming processes, photocatalysis, water-gas shift reaction, thermochemical water splitting, and organic reactions, ceria is emerging as a unique material, holding great promise for future market breakthroughs. While much knowledge about the fundamental characteristics of CeO2-based materials has already been acquired, new characterization techniques and powerful theoretical methods are dee...

Fundamentals and Catalytic Applications of CeO2-Based Materials

Nanotechnology is being used to enhance conventional ceramic and polymeric water treatment membrane materials through various avenues. Among the numerous concepts proposed, the most promising to date include zeolitic and catalytic nanoparticle coated ceramic membranes, hybrid inorganic–organic nanocomposite membranes, and bio-inspired membranes such as hybrid protein–polymer biomimetic membranes, aligned nanotube membranes, and isoporous block copolymer membranes. A semi-quantitative ranking system was proposed considering projected performance enhancement (over state-of-the-art analogs) and state of commercial readiness. Performance enhancement was based on water permeability, solute selectivity, and operational robustness, while commercial readiness was based on known or anticipated material costs, scalability (for large scale water treatment applications), and compatibility with existing manufacturing infrastructure. Overall, bio-inspired membranes are farthest from commercial reality, but offer the most promise for performance enhancements; however, nanocomposite membranes offering significant performance enhancements are already commercially available. Zeolitic and catalytic membranes appear reasonably far from commercial reality and offer small to moderate performance enhancements. The ranking of each membrane nanotechnology is discussed along with the key commercialization hurdles for each membrane nanotechnology.

/pdf/a-review-of-water-treatment-membrane-nanotechnologies-1np07if946.pdf

A review of water treatment membrane nanotechnologies

Recent Advances in Polyoxometalate-Catalyzed Reactions

The global occurrence in water resources of organic micropollutants, such as pesticides and pharmaceuticals, has raised concerns about potential negative effects on aquatic ecosystems and human health. Activated carbons are the most widespread adsorbent materials used to remove organic pollutants from water but they have several deficiencies, including slow pollutant uptake (of the order of hours) and poor removal of many relatively hydrophilic micropollutants. Furthermore, regenerating spent activated carbon is energy intensive (requiring heating to 500-900 degrees Celsius) and does not fully restore performance. Insoluble polymers of β-cyclodextrin, an inexpensive, sustainably produced macrocycle of glucose, are likewise of interest for removing micropollutants from water by means of adsorption. β-cyclodextrin is known to encapsulate pollutants to form well-defined host-guest complexes, but until now cross-linked β-cyclodextrin polymers have had low surface areas and poor removal performance compared to conventional activated carbons. Here we crosslink β-cyclodextrin with rigid aromatic groups, providing a high-surface-area, mesoporous polymer of β-cyclodextrin. It rapidly sequesters a variety of organic micropollutants with adsorption rate constants 15 to 200 times greater than those of activated carbons and non-porous β-cyclodextrin adsorbent materials. In addition, the polymer can be regenerated several times using a mild washing procedure with no loss in performance. Finally, the polymer outperformed a leading activated carbon for the rapid removal of a complex mixture of organic micropollutants at environmentally relevant concentrations. These findings demonstrate the promise of porous cyclodextrin-based polymers for rapid, flow-through water treatment.

/pdf/rapid-removal-of-organic-micropollutants-from-water-by-a-1to1289nsk.pdf

Rapid removal of organic micropollutants from water by a porous β-cyclodextrin polymer

Volatile organic compounds (VOCs) are toxic and mainly contribute to the formation of photochemical smog with a consequent remarkable impact to the air quality. A few techniques are available to reduce VOC emission, among them catalytic oxidation is suitable especially for highly diluted VOCs. The development of noble metals and transition metal oxides as catalysts for VOCs oxidation has been widely reported in the literature and the research field continues to be very active. Selection of catalytic materials for the abatement of organic pollutants is not easy because the activity depends on the specific molecule, on the reactions conditions and many parameters can affect the catalyst activity and resistance. The present review focus on the most used noble metals catalysts for oxidation of not halogenated VOC. The effects of metal salt precursor, chlorine poisoning, water inhibition, particle size dependence, nature of the support are discussed. The calculated reaction order with respect to VOC and oxygen as well as the proposed reaction mechanisms are addressed. Examples of the most recent catalytic systems reported in literature are also included.

Catalytic oxidation of volatile organic compounds on supported noble metals

Co 3 O 4 /CeO 2 composite oxides with different cobalt loading (5, 15, 30, 50, 70 wt.% as Co 3 O 4 ) were prepared by co-precipitation method and investigated for the oxidation of methane under stoichiometric conditions. Pure oxides, Co 3 O 4 and CeO 2 were used as reference. Characterization studies by X-ray diffraction (XRD), BET, temperature programmed reduction/oxidation (TPR/TPO) and X-ray photoelectron spectroscopy (XPS) were carried out. An improvement of the catalytic activity and thermal stability of the composite oxides was observed with respect to pure Co 3 O 4 in correspondence of Co 3 O 4 –CeO 2 containing 30% by weight of Co 3 O 4 . The combined effect of cobalt oxide and ceria, at this composition, strongly influences the morphological and redox properties of the composite oxides, by dispersing the Co 3 O 4 phase and promoting the efficiency of the Co 3+ –Co 2+ redox couple. The presence in the sample Co 3 O 4 (30 wt.%)–CeO 2 of a high relative amount of Ce 3+ /(Ce 4+  + Ce 3+ ) as detected by XPS confirms the enhanced oxygen mobility. The catalysts stability under reaction conditions was investigated by XRD and XPS analysis of the used samples, paying particular attention to the Co 3 O 4 phase decomposition. Methane oxidation tests were performed over fresh (as prepared) and thermal aged samples (after ageing at 750 °C for 7 h, in furnace). The resistance to water vapour poisoning was evaluated for pure Co 3 O 4 and Co 3 O 4 (30 wt.%)–CeO 2 , performing the tests in the presence of 5 vol.% H 2 O. A methane oxidation test upon hydrothermal ageing (flowing at 600 °C for 16 h a mixture 5 vol.% H 2 O + 5 vol.%O 2 in He) of the Co 3 O 4 (30 wt.%)–CeO 2 sample was also performed. All the results confirm the superiority of this composite oxide.

Co3O4/CeO2 composite oxides for methane emissions abatement: Relationship between Co3O4–CeO2 interaction and catalytic activity

Heterogeneous catalytic degradation of phenolic substrates: catalysts activity.

Co3O4 nanocrystals and Co3O4–MOx binary oxides for CO, CH4 and VOC oxidation at low temperatures: a review

This review intends to describe and critically analyze the growing literature dealing with the use of supported gold catalysts in the catalytic deep oxidation of volatile organic compounds (VOC). Among the wide family of VOC, attention has been given to the oxidation of saturated (methane, ethane, propane, isobutane, n-hexane) and unsaturated (acetylene, ethylene, propene) aliphatic compounds, aromatic hydrocarbons (benzene, toluene, xylenes, naphthalene), alcohols (methanol, ethanol, n- and iso-propanol), aldehydes (formaldehyde), ketones (acetone), esters (ethylacetate). Moreover, the oxidation of chlorinated VOC (dichloromethane, o-dichlorobenzene, o-chlorobenzene), as well as of nitrogen- (trimethylamine) and sulphur-containing (dimethyldisulfide) compounds has been addressed. The reaction mechanism and the influence of different factors, such as the nature and the properties of the support, the Au particle size and shape, the electronic state of gold, the preparation method and the pretreatment conditions of catalysts, the nature and the concentration of the organic molecule, are discussed in detail.

Leonarda F. Liotta

Papers

Catalytic oxidation of volatile organic compounds on supported noble metals

Co3O4/CeO2 composite oxides for methane emissions abatement: Relationship between Co3O4–CeO2 interaction and catalytic activity

Heterogeneous catalytic degradation of phenolic substrates: catalysts activity.

Co3O4 nanocrystals and Co3O4–MOx binary oxides for CO, CH4 and VOC oxidation at low temperatures: a review

Supported gold catalysts for the total oxidation of volatile organic compounds