In this paper, the kinetics of polyphenols extraction from spruce bark (Picea abies) under ultrasounds action was investigated. Studies were performed in order to express the effect of some specific parameters (as: ultrasounds, surface contact between solvent and solid, extraction time and temperature) on the total phenolic content (TPC). Experiments were performed in the presence and absence of ultrasounds, using different contact surfaces between solvent and solid, for times from 5 to 75min and temperatures of 318, 323 and 333K. All these factors have a positive influence on the process, enhancing the extraction rate by recovering higher amounts of polyphenols. The process takes place in two stages: a fast one in the first 20-30min (first stage), followed by a slow one approaching to an equilibrium concentration after 40min (second stage). In these conditions, the second-order kinetic model was successfully developed for describing the mechanism of ultrasound-assisted extraction of polyphenols from P. abies bark. Based on this model, values of second-order extraction rate constant (k), initial extraction rate (h), saturation concentration (Cs) and activation energy (Ea) could be predicted. Model validation was done by plotting experimental and predicted values of TPC's, revealing a very good correlation between the obtained data (R(2)>0.98).

The removal of mercury from flue gases in scrubbers is greatly facilitated if the mercury is present as water-soluble oxidized species. Therefore, increased mercury oxidation upstream of scrubber devices will improve overall mercury removal. For this purpose heterogeneous catalysts have recently attracted a great deal of interest. Selective catalytic reduction (SCR), noble metal and transition metal oxide based catalysts have been investigated at both the laboratory and plant scale with this objective. A review article published in 2006 covers the progress in the elemental mercury (Hg^el) catalytic oxidation area. This paper brings the review in this area up to date. To this end, 110 papers including several reports and patents are reviewed. For each type of catalyst the possible mechanisms as well as the effect of flue gas components on activity and stability are examined. Advantages and main problems are analyzed. The possible future directions of catalyst development in this environmental research area are outlined.

Methane, discovered in 1766 by Alessandro Volta, is an attractive energy source because of its high heat of combustion per mole of carbon dioxide. However, methane is the most abundant hydrocarbon in the atmosphere and is an important greenhouse gas, with a 21-fold greater relative radiative effectiveness than CO₂ on a per-molecule basis. To avoid or limit the formation of pollutants that are dangerous for both human health and the atmospheric environment, the catalytic combustion of methane appears to be one of the most promising alternatives to thermal combustion. Total oxidation of methane, which is environmentally friendly at much lower temperatures, is believed to be an efficient and economically feasible way to eliminate pollutants. This work presents a literature review, a statu quo, on catalytic methane oxidation on transition metal oxide-modified ceria catalysts (MO_x/CeO₂). Methane was used for this study since it is of great interest as a model compound for understanding the mechanisms of oxidation and catalytic combustion on metal oxides. The objective was to evaluate the conceptual ideas of oxygen vacancy formation through doping to increase the catalytic activity for methane oxidation over CeO₂. Oxygen vacancies were created through the formation of solid solutions, and their catalytic activities were compared to the catalytic activity of an undoped CeO₂ sample. The reaction conditions, the type of catalysts, the morphology and crystallographic facets exposing the role of oxygen vacancies, the deactivation mechanism, the stability of the catalysts, the reaction mechanism and kinetic characteristics are summarized.

Direct hydrothermal synthesis (HT), template ion-exchange (TIE) and molecular dispersion (MD) approaches were used to introduce manganese species into MCM-48-type mesoporous materials. The tungsten was highly dispersed within the channels of mesoporous MnMCM-48 samples by chemical grafting (CG) via a liquid–solid reaction. The prepared manganesosilicate and tungstenomanganesosilicate MCM-48-type mesoporous materials were characterized by physico-chemical techniques, including TEM, N₂ sorption, XRD, XPS, UV-Vis and elemental analysis. The physico-chemical characterization revealed that all of the samples retained a high surface area, a regular cubic mesoporosity and that the Mn and W were highly dispersed. The higher unit cell parameter/pore wall thickness values of the MnMCM-48 and WMnMCM-48 samples relative to that of pure MCM-48 indicate the incorporation of Mn and W into the framework/channels of MCM-48. The Mn and W species existed as isolated sites in the framework/extra-framework or as monomolecular species. No bulk manganese or tungsten was observed outside the MCM-48-type mesoporous materials. The coexistence of Mn²⁺, Mn³⁺ or/and W⁶⁺ was evidenced by XPS and UV-Vis spectroscopic measurements. The catalytic activities of these samples were studied with respect to the conversion of methylcyclopentane (MCP) in reductive media as a function of Mn loading and reaction temperature (200–500 °C). Whatever the manganese content and irrespective of the temperature of reaction, the MnMCM-48 mesoporous samples did not exhibit catalytic activity, which suggests that the electrophilic manganese oxygen species, operative over all the samples, were inactive sites for the conversion of MCP. The addition of tungsten favored catalytic activity. When the WMnMCM-48 was not calcined, only the methane (C₁) cracking product was observed to be formed by successive rupture of C–C bonds starting at 400 °C. When the WMnMCM-48 was calcined, ring-opening products formed by the C–C rupture, at substituted and unsubstituted carbon atoms, were observed starting at 400 °C. This behavior is associated with a symbiotic process between the MnMCM-48 support and the W nanoparticles.