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Abstract: In the present work, two different methods of catalyst promotion, the electrochemical promotion (EP) and the conventional promotion (CP), were comparatively applied on a catalytic system of significant environmental and practical importance: the N2O reduction by hydrocarbons (alkanes and alkenes), in the presence or absence of O2, over Pd catalysts. A galvanic cell of the type Pd/K + -conducting β″-Al 2 O 3 /Au was constructed for the application of the EP concept whereas the CP concept was investigated via a series of highly dispersed Pd/γ-Al2O3 catalysts, conventionally promoted (by impregnation) with K modifier. Given that EP is a straightforward, efficient and in situ way for investigating the effect of a promoter on a catalytic system, the present study is dealing with its prior use as a rapid “research tool” for exploring the effect of K promoter on the catalytic system under consideration. Subsequently, the insight obtained from EP studies is applied to the design of conventional catalysts'' composites, i.e. Pd/γ-Al2O3 catalysts conventionally promoted by K at loadings indicated from EP studies. For the system investigated, the optimal promoter loading was in the range of ∼0.45–0.55, in terms of K-coverage. In this range of K-loadings significant enhancement on de-N2O activity was obtained under reducing conditions using both methods of K-promotion. However, in the presence of excess oxygen in the reaction mixture the effect of K-promotion was less pronounced, independently of the reducing agent used. [Copyright &y& Elsevier]

Abstract: The effect of hydrogen partial pressure (1.3–5.8 kPa) and cell temperature (600–800 °C) on the kinetics and mechanism of the charge transfer electrode reaction taking place at the three phase boundary H2–Fe–SCY (SCY=SrCe0.95Yb0.05O2.975), was thoroughly examined by performing electrode polarization measurements. A three electrode single chamber proton conducting solid electrolyte cell of the type Fe–SCY–Au, was used in order to conduct the electrode kinetic studies. The steady-state current–overpotential characteristics were analysed with the high field approximations of the Butler–Volmer equation, by taking into account the presence of limiting currents. Both, apparent exchange current density, I o, and anodic/cathodic charge transfer coefficients (α a / α c), were calculated. Limiting currents, I l, were observed in all reaction conditions. The apparent reaction order, q, was found in most cases, within experimental error, close to 0.5 suggesting a possible reaction model, where a competition exists between charge transfer and mass transport of hydrogen ad-atoms or protons along the electrode/solid electrolyte interface. [Copyright &y& Elsevier]

Abstract: The catalytic abatement of nitrous oxide (N2O), a powerful greenhouse and ozone depletion gas, is an efficient end-of-pipe technology for N2O emissions control. However, de-N2O performance is notably suppressed by SO2 and H2O presence on the flue gases, whereas little is known about their influence on catalyst surface chemistry. In the present study, the impact of sulfur dioxide and water vapor on the catalytic performance of Pd/Al2O3 catalysts during the N2O decomposition in the presence of CH4 and O2 excess is investigated, with particular emphasis on the corresponding surface chemistry modifications. Catalytic activity and stability measurements, in conjunction with a kinetic study, were carried out to elucidate the individual effect of each molecule on de-N2O performance. X-ray photoelectron spectroscopy (XPS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and Fourier transform infrared spectroscopy (FTIR) of pyridine adsorption are employed to evaluate the impact of SO2 and H2O molecules on catalyst surface chemistry, which is appropriately correlated with the achieved catalytic performance. The results revealed that the de-N2O efficiency can be substantially improved by CH4 under reducing (absence of O2) conditions, due to the scavenging of strongly adsorbed Oads species by the hydrocarbon; however, under O2 excess conditions the beneficial effect of CH4 is marginal. Water vapor in the feed has a detrimental influence on both N2O and CH4 conversions, which, however, is totally reversible; the latter is mainly ascribed to the competitive adsorption of H2O molecules on catalyst surface. In contrast, SO2 addition in feed stream results in a severe, irreversible deactivation; SO2 leads to the creation of Brönsted acid sites on Al2O3 support, which in turn results in highly oxidized Pd entities, inactive for N2O decomposition. [Copyright &y& Elsevier]

Water reservoirs are used for many purposes, such as water supply, irrigation, flood mitigation, and hydroelectric energy generation. Although hydroelectric energy is considered "green," many studies show that the construction of a reservoir enhances greenhouse gas (GHG) emissions at the transformed area. These emissions, mainly of CO 2 , CH 4 , and N 2 O gases, depend on the age of the reservoir, landscape and soil composition, fauna and flora remnants of the impounded area, climatic conditions, and basin runoffs. Consequently, GHG emissions significantly vary between reservoirs and depending on local specificities. Several studies have investigated GHG emissions from reservoirs around the world, focusing mainly on reservoirs located in cold regions, temperate regions, and tropical regions. Research is lacking for reservoirs in Mediterranean countries, like Greece, and similar regions. This work initially assesses the net GHG emissions of a newly created reservoir (Ilarion est. 2012) in Western Macedonia, Greece. The methodology for net GHG emission calculation was based on the use of literature data concerning pre-impoundment emission factors and local specificities of the reservoir (terrain type, canopy cover), as well as on the 2-year measurement data that were collected using a "static floating chamber." Furthermore, in this work, the gross GHG emissions of an older, in-line reservoir (Polyfytos est. 1974) were also calculated, based on 2-year measurement data. The results show that the global warming potential (GWP) of the reservoirs is dictated by methane emissions; it minimizes during winter and spring and maximizes during summer and autumn. Hydroelectric energy production at Ilarion Reservoir results in 32 to 97 times less total CO 2 equivalent emissions in comparison to fossil fuels, while at Polyfytos Reservoir only 8 to 24 times less (based on gross emissions). It appears that the impact of a reservoir's morphology on GHG emissions is more significant than that of a reservoir's age.