1,721,090 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Novel insights on the Pd speciation in Pd/SSZ-13 and on the role of H2O in the pd reduction by CO
No full textHigh reactive mixed LNT/CeZr catalytic systems for the simultaneous removal of NOx and soot from Diesel exhausts
No full textPathways for N 2 O Formation/Reduction During Operation of Commercial LNT Catalysts
No full textIn this study the pathways involved in N2O formation over a commercial LNT catalyst are addressed, when using H-2 as a reductant. For this purpose, flow microreactor experiments coupled with FT-IR under operando conditions are used. The results indicate that N2O formation occurs both at the lean-to-rich (primary N2O) and rich-to-lean (secondary N2O) transitions. Primary N2O originates at the reduction front due to the presence of partially reduced PGM sites that do not readily dissociates NO released from the stored NOx. Undissociated NO couples with N-adatoms leading to the formation of N2O. At variance, secondary N2O originates upon oxidation with NO/O-2 of reducing species left adsorbed on the catalyst surface (adsorbed CO, isocyanates and possibly NH3) during the rich phase, as pointed out by FT-IR spectroscopy. The concentration of such adsorbed species is however limited and hence the formation of secondary N2O is much smaller than that of primary N2O, when using H-2 as reducing agent. The emissions of N2O reduce upon increasing the temperature, and above 250 degrees C N2O formation is negligible. Finally the reactivity of N2O with adsorbed NOx species (nitrites) and with the actual reductants (H-2 and NH3) is also investigated, to provide further indications concerning the pathways leading to N2O emissions. It is found that N2O does not react with NOx species stored downstream the reduction front; at variance both H-2 and NH3 may reduce N2O to N-2 and water at rather low temperatures. The role of this reaction on N2O emission is herein discussed
Low-temperature Pd/FER NOx adsorbers: Operando FT-IR spectroscopy and performance analysis
Full text linkA Pd-doped FER zeolite sample is synthesized and investigated for potential use in the low-temperature NOx adsorption. The catalyst is characterized by BET, XRD, TEM, NaCl titration and by in-situ FT-IR spectroscopy following adsorption of CO, NH3 and NO for the characterization of the Pd sites. Over the calcined sample, Pd is present mainly as PdOx clusters/particles; near 13 % of Pd is present in the form of isolated ions. The NOx adsorption / desorption performances at low temperature are investigated by microreactor studies and operando FT-IR upon NO/O2 adsorption followed by TPD under relevant operating conditions, i.e. in the presence of water and carbon dioxide. It is found that NO adsorbs in the form of Pd nitrosyls (hydrated and anhydrous) and nitrates; near 59 μmol/gcat of NOx could be adsorbed, corresponding to a NO/Pd ratio near 0.6. Upon heating, nitrosyls decompose and transform into anhydrous species leading to NO desorption in the low-T region (below 200 °C) and at higher temperature, with maximum near 370 °C. The presence of CO negatively affects the NOx storage capacity, due to a competition of CO and NO over the Pd storage sites
Chlorophyll-a concentration measure in coastal waters using MERIS and MODIS data
No full textUnderstanding the temporal dynamic of the biophysical properties of the coastal/shallow waters is a challenging and important task. In the present work Chlorophyll-a concentration in coastal zone shallow waters is obtained by inversion of the MERIS and MODIS level 1 calibrated, geo-located reflectance data. For this purpose, we have used both sensors 1:0 retrieve the chlorophyll concentration, in a scheme of multisensor data assimilation. In fact, the new generation sensor MERIS, on ESA's ENVISAT, with its spatial resolution of 300 meters and 3 days revisitation time, offers a high number of narrow spectral bands in the visible and in the IR. At the same time, MODIS, on NASA's Terra and Aqua Satellites, has a lower space resolution but an higher number of bands in the IR portion of the electromagnetic spectrum and can improve our atmospheric correction algorithms. Due to the high variability of the aerosol (type and concentration) and the water type, an accurate atmospheric correction method based on the 6S radiative transfer code has been performed. The atmospheric data required as input to the 6S code have been retrieved from the MODIS data. The estimated chlorophyll-a concentration has been computed from MERIS and MODIS data using a semi-analytic model, based on the optical properties of water and its components. To validate the inversion procedure, ground measurements have been collected monthly during the year 2003 and have been compared with the values derived from the inversion model
Investigation of DFMs for CO2 Capture and Methanation by Coupled Microreactor Experiments and FT-IR Spectroscopy
Full text linkIn this work, we discuss the role of different atmospheres and process conditions on the catalytic performances of Ru- and K/Ba-based dual-function materials (DFMs) for CO2 capture and methanation. By a combination of microreactor experiments and Fourier transform infrared (FT-IR) spectroscopy, we clarify the effect of temperature and H2 partial pressure during the hydrogenation step and the effect of water and oxygen during the CO2 adsorption step. In particular, we show that between 250 and 400 °C CO2 is rapidly adsorbed as bidentate carbonates on the basic sites (K or Ba) and as CO on Ru metal surfaces with decreasing storage capacity with increasing temperature. Increasing the operating temperature and the H2 partial pressure, the methanation rate of the bidentate carbonates increases. We also show that during the CO2 capture step, water not only reduces the amount of CO2 adsorbed by competitively adsorbing on basic sites but also changes the nature of the adsorbed carbonates, increasing their ionic character and hence their stability. This is observed in the case of both a K-based DFM and a Ba-based DFM, though in the case of the alkaline earth, the phenomenon is more evident. Finally, we point out that the presence of O2 during the CO2 capture step removes metallic Ru as CO adsorption site and reduces the amount of bidentate carbonates, possibly due to the additional presence of water formed upon Ru reduction in the methanation step. The information presented in this work is of interest to improve the design of DFMs to be used for flue gas, where the partial pressure of water and oxygen is relevant
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