Insights on a methanation catalyst aging process: Aging characterization and kinetic study

Power to gas systems is one of the most interesting long-term energy storage solutions. As a result of the high exothermicity of the CO2 methanation reaction, the catalyst in the methanation subsystem is subjected to thermal stress. Therefore, the performance of a commercial Ni/Al2O3 catalyst was investigated over a series of 100 hour-long tests and in-process relevant conditions, i.e. 5 bar from 270 to 500 °C. Different characterization techniques were employed to determine the mechanism of the observed performance loss (N2 physisorption, XRD, TPO). The TPO analysis excluded carbon deposition as a possible cause of catalyst aging. The BET analysis evidenced a severe reduction in the total surface area for the catalyst samples tested at higher temperatures. Furthermore, a direct correlation was found between the catalyst activity decline and the drop of the catalyst specific surface. In order to correctly design a reliable methanation reactor, it is essential to have a kinetic model that includes also the aging kinetics. For this purpose, the second set of experiments was carried out, in order to determine the intrinsic kinetics of the catalyst. The kinetic parameters were identified by using nonlinear regression analysis. Finally, a power-law aging model was proposed to consider the performance loss in time

Photo-catalytic activity of BiVO4 thin film electrodes for solar-driven water splitting

There is an ever-increasing attention directed to the development of solar fuels by photo-electrochemical water splitting, given the inexhaustible availability of solar energy. The water oxidation half-reaction is a critical step for the overall water splitting reaction, and the development of suitable photoanodes is therefore required. The present research work focuses on bismuth vanadate thin films’ deposition on FTO glass electrodes, through the dip coating technique, and discusses the influence of the film preparation technique on the electrode's photo-electrochemical performance. The bismuth vanadate thin films were synthesized with thicknesses ranging from 60 to 210 nm, depending on a number of dip coatings from 2 to 15. The structural and optical characterization of the films showed that monoclinic scheelite-type phase was obtained in all samples, with crystal sizes ranging from 24 to 65 nm, at increasing film thicknesses, and corresponding band gaps between 2.55 and 2.35 eV. A maximum photo-current density of about 0.57 mA cm−2 at 1.23 V vs. RHE under sunlight illumination was obtained for an electrode thickness of 160 nm. The electrochemical impedance spectroscopy elucidated the transport mechanisms occurring at the electrolyte–electrode interface, as well as inside the film. The estimation of the equivalent circuit parameters showed that an increasing film thickness decreased the resistance associated to the charge transfer between the electrolyte and the electrode (from 1100 to 450 Ω, from 60 to 160 nm layer thickness, respectively), given the higher number of active sites involved in the reaction. However, excessive film thicknesses increase the probability of charge recombination within the film and, in the specific case here investigated, can also be associated to film imperfections arising from several deposition-calcination cycles, which further act as traps. These concurring phenomena are of high relevance to isolate the rate-determining step of the water oxidation half-reaction, in the perspective of an optimization of bismuth vanadate film coating on FTO to obtain photo anodes

400 ans d'exploration botanique en zone méditerranéenne algérienne Une histoire méconnue et inachevée

Cet article fait une mise au point quasi exhaustive de l'exploration botanique en Algérie. Exploration couronnée, en 1962, par la publication de la flore de Quézel et Santa, dont la révision reste toujours d'actualité

Transport and energy in India. Energy used by Indian transport systems and consequent emissions: the need for quantitative analyses (Well-to-Wheel, Lifecycle)

The purpose of this work is, at first, a general overview on the state-of-art of the transportation system in India outlining the related energy consumption, for the different transport modes, with consequent estimated emissions. These elements are essential for the preparation of a high-level strategic transport planning on the whole energy issue, to help India in the choices of most suitable transportation systems, according to the well-to-wheel analysis (WTW). Pursuing a WTW global index for India that takes into account both the energy and environmental aspects on a uniform basis is an important aim: it allows the best choices to be made as well as enabling the comparison between some of the most important powertrain and fuel options on the Indian market, the results are discussed from three different points of view: energy, environmental and economic impact

Impact of Power-to-Gas on distribution systems with large renewable energy penetration

The exploitation of the Power-to-Gas (PtG) technology can properly support the distribution system operation in case of large penetration of Renewable Energy Sources (RES). This paper addresses the impact of the PtG operation on the electrical distribution systems. A novel model of the PtG plant has been created to be representative of the entire process chain, as well as to be compatible with network calculations. The structure of the model with the corresponding parameters has been defined and validated on the basis of measurements gathered on a real plant. The PtG impact on the distribution systems has then been simulated on two network models representing a rural and a semi-urban environment, respectively. The testing has been carried out by defining a set of cases that contain critical situations for the distribution network, caused by RES plant placement. The objectives of the introduction of PtG are the reduction of the reverse power flow, as well as the reduction of the overcurrent and overvoltage issues in the distribution system. The results obtained from annual simulations lead to considerable reduction (from 78 to 100%) of the reverse power flow with respect to the base case, and to alleviating (or even solving) the overcurrent and overvoltage problems of the networks. These results indicate PtG as a possible solution for guaranteeing a smooth transition towards decarbonized energy systems. The capacity factors of the PtG plants largely vary depending on the network topology, the RES penetration, the number of the PtG plants and their sizes. From the test cases, the performance in a rural network (where the minimum capacity factor is about 50%) resulted better than in a semi-urban network (where the capacity factor values range between 21% and 60%)

Life cycle assessment of the biofuel production from lignocellulosic biomass in a hydrothermal liquefaction - aqueous phase reforming integrated biorefinery

The use of biofuels in the transport sector is one of the strategies for its decarbonization. Here, the LCA meth-odology was used for the first time to assess the environmental impacts of a biorefinery where hydrothermal liquefaction (HTL) and aqueous phase reforming (APR) were integrated. This novel coupling was proposed to valorize the carbon loss in the HTL-derived aqueous phase, while simultaneously reducing the external H2 de-mand during biocrude upgrading. Corn stover (residue) and lignin-rich stream (waste) were evaluated as possible lignocellulosic feedstocks. The global warming potential (GWP) was 56.1 and 58.4 g CO2 eq/MJbiofuel, respec-tively. Most of the GWP was attributable to the electrolysis step in the lignin-rich stream case and to the thermal duty and platinum use in the corn stover case. Other impact categories were investigated, and an uncertainty analysis was also carried out. A sensitivity analysis on biogenic carbon, electricity/thermal energy source and alternative hydrogen supply was conducted to estimate their influence on the GWP. Finally, the two scenarios were compared with the environmental impact of fossil-and other biomass-derived fuels, also considering fuel utilization. HTL-APR allowed a 37% reduction compared to fossil diesel, further reduced to 80% with the lignin -rich stream when green energy was used

Recycling CO2from flue gas for CaCO3nanoparticles production as cement filler: A Life Cycle Assessment

CaCO3 nanoparticles as filler have received considerable attention for the mechanical improvement that they provide to cements. However, their life-cycle impact on the environment remains almost unexplored, even if the cement industry is considered one of the largest CO2 emitters. In this perspective, this research work assessed a novel method for using CO2 from cement flue gases to produce nanoCaCO3 as cement filler within the cradle to cradle thinking. For this purpose, two routes of CO2 capture were assessed followed by the study of the synthesis of CaCO3 through a mineral carbonation. Three scenarios for the synthesis of CaCO3 nanoparticles were assessed targeting the use of waste or by-products as raw materials and recirculation of them to reduce any kind of emission. The three scenarios were evaluated by means of the Life Cycle Assessment methodology. Once the best considered route for nanoCaCO3 production was determined, this research work examined the environmental effect of including 2 wt% of CaCO3 nanoparticles into the cement. Closing the loop follows a circular economy approach since the CO2 is captured within the same cement factory. The results were compared with conventional Portland cement. Regarding nanoCaCO3 results, the scenario with simultaneous production of NH4Cl, and using as calcium source CaCl2 deriving from the soda ash Solvay process, proved to be the best option. Moreover, when cement was filled with 2 wt% of this nanoCaCO3, the benefit in terms of emission reductions in the Climate Change category was higher than 60 % compared to the conventional Portland cement.This project has received funding from the European Union's Horizon 2020 Research and Innovation Programme under Grant Agreement No. 768583- RECODE project (Recycling carbon dioxide in the cement industry to produce added-value additives: a step towards a CO2 circular economy, https://www.recodeh2020.eu/). This paper reflects only the author's view and the content is the sole responsibility of the authors. The European Commission or its services cannot be held responsible for any use that may be made of the information it contains.Publicad

Aqueous phase reforming of the residual waters derived from lignin-rich hydrothermal liquefaction: investigation of representative organic compounds and actual biorefinery streams

Secondary streams in biorefineries need to be valorized to improve the economic and environmental sustainability of the plants. Representative model compounds of the water fraction from the hydrothermal liquefaction (HTL) of biomass were subjected to aqueous phase reforming (APR) to produce hydrogen. Carboxylic and bicarboxylic acids, hydroxyacids, alcohols, cycloketones and aromatics were identified as model compounds and tested for APR. The tests were performed with a Pt/C catalyst and the influence of the carbon concentration (0.3–1.8 wt. C%) was investigated. Typically, the increase of the concentration negatively affected the conversion of the feed toward gaseous products, without influencing the selectivity toward hydrogen production. A synthetic ternary mixture (glycolic acid, acetic acid, lactic acid) was subjected to APR to evaluate any differences in performance compared to the tests with single compounds. Indeed, glycolic acid reacted faster in the mixture than in the corresponding single compound test, while acetic acid remained almost unconverted. The influence of the reaction time, temperature and carbon concentration was also evaluated. Finally, residual water resulting from the HTL of a lignin-rich stream originating from an industrial-scale lignocellulosic ethanol process was tested for the first time, after a thorough characterization. In this framework, the stability of the catalyst was studied and found to be correlated to the presence of aromatics in the aqueous feedstock. For this reason, the influence of an extraction procedure for the selective removal of these compounds was explored, leading to an improvement in the APR performance