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A combined DFT-Experimental study on FSP-made Ru/Ti-SiO2 catalysts for CO2 methanation
(2025-07-01)
Mekasuwandumrong, Okorn
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Saelee, Tinnakorn
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Noppakhun, Jakapob
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Rittiruam, Meena
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Khajondetchairit, Patcharaporn
Flame spray pyrolysis (FSP) was employed to synthesize Ti-modified SiO₂ in a single step, serving as the support for Ru-based catalysts in CO₂ methanation reactions. The addition of Ti led to the formation of anatase and rutile TiO₂ phases, enhancing the catalytic activity of Ru/Ti-SiO₂ catalysts. Benchmarking between Ru/Ti-SiO₂ catalysts of various Ti concentrations prepared using one-step FSP techniques indicated significantly higher catalytic activity for the impregnation-made catalysts compared to the FSP-made ones, where diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) revealed different CH₄ formation mechanisms between two techniques. For FSP-made catalysts, it predominantly occurred through the CO route, whereas the impregnation-made proceed via both the dissociative adsorption of CO₂ (CO route) and through surface formate species formation. To explain the effect of Ti loading on Ru/SiO₂ catalysts, a multiscale analysis combining density functional theory (DFT) and microkinetic modeling was performed to study the adsorption behavior of CO₂ on different catalysts. The results revealed that a high amount of Ti reduced the adsorption strength of CO₂ on Ru/SiO₂ catalysts, indicating a modified interaction between CO₂ and the catalyst surface.
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Tubular EVA copolymer/SiO2/PEG composite membrane for CO2 removal from household biogas
(2025-03-01)
Watasit, Prachya
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Ausavasukhi, Artit
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Rukchonlatee, Suparat
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Sooknoi, Tawan
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Ritvirulh, Chonlada
The fuel efficiency of household biogas is generally regulated by its CO<inf>2</inf> content (25%–50%). To improve its heating value, atmospheric CO<inf>2</inf> removal of household biogas using a polymeric membrane was attempted to avoid a complicated separation process. A tubular membrane of poly(ethylene-co-vinyl acetate), composed of 28% and 18% vinyl acetate (E28 and E18) modified with SiO<inf>2</inf> and polyethylene glycol (PEG), was fabricated by blown film extrusion. Model biogas containing CO<inf>2</inf>/CH<inf>4</inf> (40/60 v/v) was separated in an in-house continuous gas separation module, in which CO<inf>2</inf> was mainly permeated out of the tubular membrane at atmospheric pressure. Blending the E28 matrix with E18 (10 wt%) improves the membrane processability and inhibits the CH<inf>4</inf> permeation, leading to enhanced CO<inf>2</inf>/CH<inf>4</inf> selectivity (from ~2.3 to 2.9). Well-dispersed SiO<inf>2</inf> particles (0.5 wt%) increase the membrane modulus and suppress CH<inf>4</inf> loss. However, adding more SiO<inf>2</inf> (0.75–1.0 wt%) leads to higher total gas permeation flux with lower CO<inf>2</inf>/CH<inf>4</inf> selectivity due to particle agglomeration. Incorporation of PEG (0.5–1.5 wt%) increased the membrane polarity and CO<inf>2</inf> permeability. The CO<inf>2</inf>/CH<inf>4</inf> selectivity was also improved (~5.3), only up to 1.0 wt% PEG content. Highlights: Composite EVA/SiO2/PEG membrane separates CO<inf>2</inf>/CH<inf>4</inf> at atmospheric pressure. The concentration gradient across the membrane drives CO<inf>2</inf>/CH<inf>4</inf> permeation. Adding SiO<inf>2</inf> hinders CH<inf>4</inf> permeability and enhances CO<inf>2</inf>/CH<inf>4</inf> selectivity. Increasing PEG content enhances membrane polarity and interaction with CO<inf>2</inf>.
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Characterization of oxide films on wrought Co–Cr–Mo–xSi alloys exposed to high-temperature oxidation
(2021-10-01)
Tunthawiroon, Phacharaphon
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Kitiwan, Mettaya
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Srirussamee, Kasama
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Li, Yunping
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Yamanaka, Kenta
Co-based alloys are currently being used in a wide range of high temperature applications owing to their high resistance to oxidation and corrosion. However, their oxidation-induced degradation could still occur during the long-term exposure to high temperature. Thus, the continuous development of oxidation-resistant Co-based alloys is of crucial importance. In this research, the influence of Si addition on the oxidation behavior of Co–Cr–Mo–xSi alloys under the isothermal oxidation treatment at 700 °C in air was investigated. The Si concentration (x) was varied from 0.1 to 5.0 wt.%. Surface morphologies and chemical compositions of the oxide films formed were analyzed by using SEM-EDS and XPS. The chemical compositions obtained from the surface analysis revealed that Si has played a role in the stabilization of Cr oxides on the surface of Co–Cr–Mo–xSi alloys. With increasing Si concentration, Co-oxide formation on the alloy surface was suppressed by the presence of Cr-oxide due to the selective oxidation of Cr atoms. Furthermore, SiO<inf>2</inf> was both found along the grain boundaries and interfaces between the outmost oxide layer and matrix. It was also found that the oxide thickness was reduced with increasing Si concentration. This was a result of the formation of stable Cr-oxide and SiO<inf>2</inf> sub-layer that became a barrier inhibiting the inward and outward diffusion of O and Cr.
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Preparation of SiO2-diamond composites by spark plasma sintering
(2021-01-01)
Kitiwan, Mettaya
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Katsui, Hirokazu
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Goto, Takashi
SiO<inf>2</inf>-diamond composites with 65–85 mass% diamond were fabricated by spark plasma sintering at 1873 K under 130 MPa for 300 s using bimodal diamond particle size of 2 and 25 µm in diameter. The diamond particles were coated with a SiC layer by chemical vapor deposition. The effects of diamond content on relative density, microstructure, and Vickers hardness of the SiO<inf>2</inf>-diamond composites were investigated. The SiO<inf>2</inf>-diamond composites exhibited relative density of 96%, and Vickers hardness of 36.2 ± 3.6 GPa at 75 mass% diamond content.
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