The surface defects of graphite play a key role in its catalytic activity towards the oxygen reduction reaction.

Environmentally persistent free radicals (EPFRs), are toxic products deriving from incomplete combustion and are able to generate DNA damage and pulmonary dysfunction. They are formed on particulate matter through interaction with aromatic hydrocarbons, catalyzed by transition metal oxides, and produce reactive oxygen species (ROS) in aquatic media. The processes are already described, for substituted aromatic molecules, for example, phenol, but not for unsubstituted aromatic systems, such as benzene. This Article reports on the reaction of benzene with molecular oxygen in the presence of CuxO/SiO2, suggesting a mechanism based on cluster and periodic computational models. The activation of O-2 by,interaction with silica coordinated Cu(I) centers leads to a peroxy species that yields the phenoxy radical upon reaction with benzene. Dissociation of OH center dot radical eventually allows for the recovery of the catalyst. The experimental characterization of the CuxO/SiO2 catalyst regarded morphology, crystal structure; copper electronic state, and crystal field around Cu(II). Electron paramagnetic resonance (EPR) spectroscopy revealed the formation of phenoxy radical entrapped in the catalyst upon reaction between benzene and CuxO/SiO2. Moreover, EPR investigation of ROS in aqueous solution evidenced the generation of OW radicals by benzene-coritacted CuxO/SiO2. All,of the experimental results nicely fit the outcomes of the computational models.

The adduct between Tris[3-(trifluoromethylhydroxymethilene)-d-camphorate]europium(III) and 4,4’-Bis(N,N-dimethylamino)benzophenone (EABP) presents an absorption band in the visible region that the neat reagents do not display, making this system interesting as an antenna system devoted to an efficient absorption in the visible region. The UV–Vis spectroscopic properties of the reagents and the adduct have been determined by a combined experimental and theoretical investigation. The equilibrium constant of the adduct formation has been determined. The theoretical investigation, carried out in the framework of density functional theory and its time-dependent extension by using the PBE1PBE and B3-LYP hybrid functionals, allowed to nicely reproduce the features of the experimental spectra of the neat reagents and of the mixture and to propose an interpretation at the molecular level of the observed appearance of the absorption band for the adduct in the visible region: It originates from the redshift of the S 0 → S 1 transition observed in EABP—essentially deriving from the πHOMO → π*LUMO excitation—due to the energy stabilization of the LUMO of EABP consequent to the electrostatic interaction between the Eu3+ ion and EABP in the adduct.

A 13-years study shows that a careful design of the flue gas cleaning system of a full scale secondary aluminium refining plant results in a minimized and very stable emission of Polychlorinated Dibenzo-p-Dioxins (PCDD), Polychlorinated Dibenzo Furans (PCDF) and dioxin-like Polychlorinated Biphenyls (PCB). The value of equivalent toxicity of PCDD/F in the emission was definitely of an order of magnitude less than the regulation limit. In the initial flue gas cleaning system, the PCB mean fingerprint after the slow cooling of the flue gas was typical of de novo synthesis. Instead, in the presence of quenching, there was evidence that the fast cooling of flue gas prevented the PCB de novo synthesis. In fact, the PCB profile was similar to that in the air collected from the aspiration hoods for the quenching. The gas-phase and solid-phase partitioning of PCBs, before and after the fabric filters, highlights the predominant role of the vapor phase with respect to the total removal efficiency. The polycyclic aromatic hydrocarbons breakdown could be an additional de novo formation pathway even in industrial plants.

DFT calculations were used to investigate the cycloaddition reaction of CO2 to styrene oxide for the formation of styrene carbonate. The uncatalyzed process alongside the reactions assisted by tetrabutylammonium bromide (TBAB), the novel nonsymmetrical single-center aluminum(III) salen-acac hybrid complex (salenac) (Al1cat) and the binary Al1cat/TBAB system were all investigated and for all of them the optimized structures, rate-determining steps, and lowest energy barrier reaction pathways were intercepted for both gas-phase and solvent environments. For the catalyzed systems, the reaction mechanism consists of three key elementary steps: 1)epoxy ring opening; 2)CO2 electrophilic attack and 3)intramolecular cyclization. In the presence of Al1cat, the central metal of the catalyst coordinates with an oxygen atom of the epoxide, activating it towards a nucleophilic attack by the halide. An oxyanion species is formed that affords the corresponding cyclic carbonate after reaction with CO2. Our results provide important hints on the cycloaddition of CO2 and epoxides promoted by nonsymmetrical aluminum complex containing a single metal center, and can satisfactorily explain the previous experimental observations allowing the development of more efficient catalysts for organic carbonate production.

E stata studiata la possibile correlazione tra la velocita di ossidazione del carbone nativo nelle fly ash da processi termici, misurata come diminuzione del contenuto di carbonio organico totale, TOC, e la formazione per sintesi de novo di PCDD/F. I risultati delle prove sperimentali su scala di laboratorio sono riportati e discussi come ossidazione del reagente carbone nativo nelle fly ash e come formazione dei prodotti primari, CO e CO 2 , e dei sottoprodotti in tracce, PCDD e PCDF, della reazione di ossidazione. Considerando l’andamento dei dati sperimentali relativi alla scomparsa del carbone nativo, e stato ipotizzato che la diminuzione del TOC sia il risultato di due processi che avvengono simultaneamente sulla superficie delle fly ash: il chemisorbimento dissociativo di ossigeno seguito dalla formazione di CO 2 a partire dai complessi ossigenati C(O) e l’ossidazione diretta del carbone nativo. L'ossidazione dei complessi ossigenati e lo stadio determinante del processo di ossidazione. Di conseguenza, e stato ipotizzato che una piccola frazione di C(O) sia coinvolta nella formazione di PCDD/F. L’elaborazione dei dati mediante due modelli cinetici, uno per la diminuzione del TOC e uno per la formazione di PCDD/F, ha permesso di dimostrare che la formazione dei complessi ossigenati, C(O), costituisce lo stadio cinetico determinante per la sintesi de novo di PCDD/F. La conoscenza del meccanismo di formazione di PCDD/F ha suggerito gli interventi mirati di prevenzione della formazione di questi microinquinanti alla scala industriale.

We developed a phenomenological approach to explain the kinetic experimental data of PCDD/F formation/destruction based on a reaction mechanism model at the congener group level. In the present work, we investigated the formation and destruction of PCDD/F on fly ash as a function of time at 280 °C, chlorine mass balance, evolution of the total equivalent toxicity and kinetic modelling. We determined that the volatilization process is negligible and that the reactive processes at short reaction times only become important above 300 °C. The results provide a substantial improvement on existing studies. We experimentally demonstrated, for the first time, that there is a correlation between the oxidative breakdown of native carbon and PCDD/F de novo synthesis. Data processing by our kinetic model showed that the formation of oxygen complexes C(O) was the determining step for de novo synthesis of PCDD/F. Indeed, the calculated reaction time at which the PCDD/F concentration was at a maximum (850 min) was greater than that calculated for the oxygen complexes C(O) (435 min). Moreover, the experimental carbon conversion efficiency for PCDD/F production (0.0032% at 600 min maximum) was in a very good agreement with the theoretical conversion (0.0041%).

In this study a 2(4) factorial design was employed to investigate the supercritical CO2 devulcanization process of ground tire rubber from end of life tires performed using diphenyl disulfide (DD) as devulcanizing reagent.The aim of the experimental design was to investigate the influence on the process of temperature, pressure, amount of devulcanizing reagent, treatment time and their interactions.The crosslink density, sol fraction, gel fraction and sulfur content were chosen as experimental responses. Multiple linear regression was used for modeling the relationship between each response and the process variables. Reduced regression models were obtained for each response, considering only the significant variables and interactions. The predicted results from these reduced models showed good agreement with the experimental values.Temperature, amount of DD and DD-temperature interaction resulted the relevant parameters for the process. On the contrary, the influence of treatment time, pressure and all other interactions proved to be negligible.These results have an important outcome since this devulcanization process can be carried out in a short time and at relatively low pressure, with subsequent energy saving. (C) 2014 Elsevier B.V. All rights reserved.

Ground truck-tire rubber (GTR) was characterized and subsequently devulcanized in supercritical CO2 (scCO(2)) in the presence of Diphenyl Disulfide (DD) as devulcanizing agent.Temperature and pressure were kept respectively at 180 degrees C and 15 MPa and the ratio between rubber and DD was 10 wt %.The treatment effect on the properties of GTR was widely studied. The reached degree of devulcanization was about 50% with a low amount of sol fraction.The results display that the treatment with the DD in presence of scCO(2) reduces the crosslink density of the GTR, increasing the property of the gel fraction and the compatibility of this material with the raw rubber.The suitability of the devulcanized GTR to be reemployed in new tire blends was investigated through the final mechanical properties.The unreacted DD can strongly affect the revulcanization process and the mechanical properties of the blends containing devulcanized rubber, resulting the only limiting factor for the application of this devulcanization process. (C) 2014 Elsevier Ltd. All rights reserved.

The use of residential wood combustion represents an important renewable energy source, but it contributes in a considerable way to atmospheric particulate matter (PM) concentration in urban as well as in rural sites. Moreover, recent studies pointed out wood burning as an important source of PAH.In the present work, the influence of wood combustion on PM was studied, investigating its contribution to the carbonaceous PM fraction and to benzo(a)pyrene (B[a]P) and polychlorodibenzo-p-dioxins and polychlorodibenzofurans (PCDD/F) concentrations, using levoglucosan as a marker. PM10 samples were collected daily for six months in two sites located in Piemonte (Northern Italy): Torino and Susa. Composite monthly samples were chemically characterized, analyzing the concentrations of levoglucosan, B[a]P, PCDD/Fs, organic carbon (OC), elemental carbon, major anions and cations, and metals.PM and OC concentrations were almost twice in Torino with respect to Susa, while levoglucosan and B[a]P concentrations were almost comparable at the two sites. Therefore, wood combustion affects more Susa than Torino. Concentrations of B[a]P and levoglucosan were highly correlated in both sites. Using the macro tracer method and the emission factors reported in literature, the wood combustion percentage contribution to B[a]P concentration was estimated and resulted as the main source in both sites. The levoglucosan to soluble potassium ratio was higher in Torino with respect to Susa, indicating that combustion plants with different efficiency are used at the two sites. PCDD/F concentrations were higher in Torino than in Susa. (C) 2012 Elsevier Ltd. All rights reserved.

The aim of this study was to investigate the effect on the induction of interleukin-8 of particulate matter (PM) from fir and beech pellets burnt in domestic appliances on two human cells lines, namely the lung epithelial cell line A549 and the promyelocytic cell line THP-1. The effects of PM2.5 obtained from combustion of beech and fir pellets were compared to reference diesel exhaust particulates (DEP). In parallel, wood smoke PM-induced genotoxicity and oxidative stress were also investigated in A549 cells. Cells were treated for different times (3–72 h) with increasing concentrations of PM2.5 obtained from sequential combustions of fir and beech pellets or reference DEP. Cell viability was assessed by lactate dehydrogenase leakage, and the release of interleukin-8 or CXCL8 (IL-8) was measured to evaluate the pro-inflammatory effect. Oxidative stress was evaluated by the 5(6)-carboxy-2′,7′dichlorofluorescein diacetate (DCFH-DA) assay and DNA damage by the alkaline comet assay and micronucleus frequency by flow cytometry. Both A549 and THP-1 cells responded in a dose- and time-related manner to wood smoke PM2.5 with IL-8 release, particles obtained from late combustions being the most active. THP-1 cells were more sensitive than A549 cells. On a mass base, similar effects were observed for both fir and beech PM2.5. However, the combustion of beech pellets generated approximately three times more PM2.5 than fir pellets. Regarding the mechanism of PM2.5 uptake, in both THP-1 and A549 cells, cytochalasin D prevented PM2.5-induced IL-8 mRNA expression and cytokine release, indicating a key role for actin polymerization in particles uptake and that the production of IL-8 correlated with particle phagocytosis. As signal transduction pathway involvement, in both THP-1 and A549 cells, PM2.5-induced IL-8 release could be completely blocked by the selective inhibitor SB203580, indicating a role of p38 MAPK activation. PM2.5 from both fir and beech pellets also induced modest DNA lesions dose related, measured as strand breaks, whereas no increase in the number of micronucleus was observed. Similar effects were observed with DEP, arguing against less dangerous effects of wood smoke particles than other categories of combustion-derived particles in the same size range. Overall, results suggest that combustion conditions can significantly affect the characteristics of particles and the consequent toxicity, and that different woods can generate different amounts of PM2.5.

The kinetics for the oxidative breakdown of native carbon in raw fly ash samples (RFA) and for the formation and destruction of polychlorinated dibenzo-p-dioxins (PCDD) and polychlorinated dibenzofurans (PCDF), abbreviated PCDD/F, were investigated using a flow-over solid system in which the RFA samples were thermally treated at 300 °C under synthetic air. This study investigated the correlation between the disappearance of the reagent and the formation of the products to gain insight into the underlying mechanisms that govern these reactions at congener groups level. The detailed analyses of the experimental concentration-time data revealed significant differences in the behavior between the 2,3,7,8-substituted PCDD and the 2,3,7,8-substituted PCDF, non-2,3,7,8-substituted PCDD and PCDF. The chlorine balance for the former was always negative, that is, chlorine was released regardless of reaction time and primarily resulted from the dechlorination of the hepta- and octa-homologues. However, for the others, the balance was substantially positive up to approximately 240 min and became negative at longer intervals when the dechlorination reactions took over. The processes involving PCDD and PCDF in which the thermal destruction was only partial were found to increase the total equivalent toxicity (TEQ) levels rather than reduce them.

The dominating route to polychlorinated Dibenzo-p-dioxin and Dibenzofuran formation in the “cold zones” of flue gas cleaning systems of municipal solid waste incinerators is the so-called de novo synthesis, that is, carbonaceous matrix burnoff with simultaneous oxidation and chlorination reactions. Pyrene (1) and Benzodibenzofuran (2) were chosen as the model compounds of carbonaceous material present in fly ash. Possible routes of Dibenzofuran formation by oxidative pathways of compounds (1) and (2) were investigated by theoretical calculations at the density functional theory level. The key intermediate peroxy radical, formed by reaction with molecular oxygen, can follow three main paths leading to Dibenzofuran. In the kinetically favourite path, the highest energetic barriers (25–30 kcal mol−1) are encountered in the steps where CO molecules are released from ketene-like structures. These findings agree with previously reported temperature-programmed desorption results on CO desorption. Moreover, along this path, phenanthrene and biphenyl intermediates are formed, in agreement with the detection of these products in previously reported experimental Pyrene oxidation. Along the preferred path, different steric constraints in compounds (1) and (2) play a role in determining the relative stability of the intermediates, while they have less influence on the energetic barriers. As a consequence, compounds (1) and (2) should present similar kinetic behaviour as they present similar energetic barriers.