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A combination of silicon carbide and zirconia open cell foams coated with 3% Pd/Co3O4 as structured catalysts for the lean combustion of methane
No full textDifferent combinations of ceramic open cell foams (OCF) made of silicon carbide (SiC) and zirconia (Zir) coated with 3 wt.% Pd/Co3O4 as the active phase, were studied as structured catalysts for the combustion of CH4 in lean conditions (inlet CH4 concentration: 0.5 and 1 vol.%). The catalytic activity of the structured catalysts was tested at different weight hourly space velocities, with an excess of oxygen. Among the various combinations tested, the reactor made of 1.5 cm SiC + 1.5 cm Zir (1.5SiC/1.5Zir) showed the best catalytic performance, thanks to the different thermal conductivity of the OFC used
Combined silicon carbide and zirconia open cell foams for the process intensification of catalytic methane combustion in lean conditions: impact on heat and mass transfer
Get PDFFor catalytic process intensification, a series of open cell foams (OCFs) made of silicon carbide (SiC) and zirconia (Zir) with pore density of 30 ppi coated with 3 wt.% PdO/Co3O4 as catalyst were combined together and tested toward methane oxidation in lean conditions. In each combination, the SiC OCF was positioned in the reactor on the inlet side of the reactant gases followed by the Zir OCF. The reactor was fed at different weight hourly space velocities (WHSV, 30 and 90 NL h−1 gcat−1) and inlet methane concentrations (0.5 and 1 vol.%). The best results are obtained with the combination where two supports of same length but with different thermal conductivity (higher at the inlet of the reactor, SiC, and lower at the outlet, Zir) are used in series. For all OCF combinations, mass transfer effects were evaluated using the characteristic resistances (kinetic, internal and external mass transfer). The external and internal heat transfer effects were analyzed using the Mears and Anderson criteria. Furthermore, a comparison in terms of volumetric heat transfer coefficient and heats of removal/reaction was performed
Steam reforming of methane on Pt/CeO2 catalyst: Effect of daily startup and shutdown on long term stability
No full textRobust Co3O4|α–Al2O3|cordierite structured catalyst for N2O abatement – Validation of the SCS method for active phase synthesis and deposition
No full textCo3O4|α-Al2O3|cordierite structured catalysts were developed, optimizing washcoating procedure, active phase loading, and its deposition method via impregnation and solution combustion synthesis (SCS). The catalysts were thoroughly characterized by XRD, μRS, SEM/EDS, and BET, revealing that the catalyst layer deposited over cordierite carrier, consists of a washcoated micrometric α-Al2O3 (0.1-0.3 μm grains), where spinel nanocrystals (30-50 nm) were uniformly dispersed. It was found out that the SCS method to synthesize and finely disperse spinel nanoparticles results in significant better catalytic performance in low-temperature N2O decomposition than the classic impregnation method. The effectiveness factor evaluated, based on catalyst morphological features and deN2O catalytic results, was found to be ≈1. The determined mass transfer coefficients and type of the catalyst working regime (purely kinetic in the whole temperature range) provides the useful platform for rational design of a real deN2O catalyst
Performance and Controlling Regimes Analysis of Methane Steam Reforming on Ru/γ-Al2O3 Cordierite Monoliths
Get PDFIn the frame of methane steam reforming (MSR) process intensification for H2 production, catalysts based on ruthenium (Ru) supported on alumina (Al2O3) on cordierite monolith have been studied in terms of catalytic performance, mass and heat transfer effects. Firstly, we compared the catalytic activity of Ru and
Rh supported catalysts. Secondly, we study the effect of catalyst loading by varying the amount of carrier and active metal phase corresponding to 3.20, 6.45 and 12.89 mg cm−2. Then, we evaluated the mass/heat transfer effects and controlling regimes for the best-selected catalyst. Finally, the best-selected catalyst was
characterized by means of Brunauer–Emmet–Teller (BET), X-ray diffraction analysis (XRD) and Fieldemission scanning electron microscopy (FESEM). The experiments were carried out in the temperature range of 550–850 °C, steam-to-carbon molar ratio (S/C) of 3.0 and different weight hourly space velocity
(WHSV = 750, 1500 and 3000 Nl h−1 gcat−1). The catalyst with 1.5% Ru on 10% Al (1.5Ru10Al) was found to be the most promising toward the MSR reaction in terms of CH4 conversion and H2 production. This catalyst operates in a mixed regime for all temperature range studied, in which both the kinetic and the
intraparticle diffusion co-exist. For the 1.5Ru10Al catalyst, the external thermal effects are important a temperature below 725 °C, while that intraparticle heat effects are absent for all the range of temperature studied. An excellent stability of the 1.5Ru10Al catalyst was observed over 70 h of time on stream (TOS)
for MSR process
Rh/CeO2 thin catalytic layer deposition on alumina foams: Catalytic performance and controlling regimes in biogas reforming processes
Get PDFThe application of ceramic foams as structured catalyst supports is clearly expanding due to faster mass/heat transfer and higher contact efficiency than honeycomb monoliths and, mainly, packed beds. In this paper, alumina open-cell foams (OCFs) with different pore density (20, 30 and 40 ppi) were coated with Rh/CeO2 catalyst via a two steps synthesis method involving: (i) the solution combustion synthesis (SCS) to in-situ deposit the CeO2 carrier and (ii) the wet
impregnation (WI) of the Rh active phase. The catalytic coatings were characterized in terms of morphology and adhesion properties by SEM/EDX analysis and ultrasounds test. Permeability and form coefficient were derived from pressure drop data. Catalytic performance was evaluated towards biogas Steam Reforming (SR) and Oxy-Steam Reforming (OSR) processes at atmospheric pressure by varying temperature (800–900 °C) and space velocity (35,000–140,000 mL·g−1·h−1). Characteristics time analysis and dimensionless numbers were calculated to identify the controlling regime. Stability tests were performed for both SR and OSR over 200 h of time-on-stream (TOS) through consecutive start-up and shut-down cycles. As a result, homogenous, thin and high-resistance catalytic layers were in situ deposited on foam struts. All structured catalysts showed high activity, following the order 20 ppi < 30 ppi ≈ 40 ppi. External interphase (gas-solid) and external diffusion can be improved by reducing the pore diameter of the OCF structures. Anderson criterion revealed the absence of internal heat transfer resistances, as well as Damköhler and Weisz-Prater numbers excluded any internal mass transfer controlling regime, mainly due to thin coating thickness provided by the SCS method. Good stability was observed over 200 h of TOS for both SR and OSR processes
Going Beyond Counting First Authors in Author Co-citation Analysis
Get PDFThe 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
Variations on the Author
Get PDF“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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