Browsing by Author "Wu, Jeffrey C. S."

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Direct gas-phase photocatalytic epoxidation of propylene with molecular oxygen by photocatalysts
(2012-01-01)
Van-Huy Nguyen
;
Chan, Hsiang-Yu
;
Wu, Jeffrey C. S.
;
Bai, Hsunling
;
環境工程研究所
The photocatalytic epoxidation of propylene by molecular oxygen is one of the best methods to produce propylene oxide (PO) from the environmental viewpoints. The key is using photo-energy to achieve high PO selectivity and yield at mild conditions. A series of photocatalysts including SiO2, TiO2, V-Ti/MCM-41, V2O5/SiO2, Au/TiO2 and TS-1, were used to evaluate their performance in the photo-epoxidation. The photocatalytic epoxidation of propylene was carried out in the gas mixture of C3H6:O-2:N-2 = 1:1:18 at atmospheric pressure. In addition to PO, other products, such as propionaldehyde, acetone, acetaldehyde, ethanol and methanol, were detected. The results indicated that the most favorable photocatalysts for photocatalytic epoxidation were silicates supported group. The highest PO formation rate of 114 mu mol g cat(-1) h(-1) with selectivity of 47% was obtained over V-Ti/MCM-41 on stream after 4 h at 50 degrees C and atmospheric pressure under UVA irradiation of 0.2 mW/cm(2). In addition, the selectivity of products was very stable on stream. A possible reaction mechanism was proposed based on the knowledge of species presented during the photocatalytic reaction. (C) 2011 Elsevier B.V. All rights reserved.
Influence of co-feeds additive on the photo-epoxidation of propylene over V-Ti/MCM-41 photocatalyst
(2015-05-01)
Nguyen, Van-Huy
;
Lin, Shawn D.
;
Wu, Jeffrey C. S.
;
Bai, Hsunling
;
環境工程研究所
In this work, the effects of co-feed species, namely, H2O or H-2, on the photocatalytic epoxidation of propylene over V-Ti/MCM-41 are examined. A promoting effect on the C3H6 consumption rate is found under 0.6 kPa H2O co-feed when the PO (propylene oxide) formation rate is not proportionally promoted, resulting a slightly decreased PO selectivity. With increasing H2O concentration, the reaction activity decreases and this can be attributed to surface site blocking by excess H2O. The presence of H2O also increases the stability of photocatalyst during reaction. Similar observation of the enhanced C3H6 consumption rate and the improved stability is found when 5.6 kPa H-2 is used as co-feed. We found that the catalyst stability is improved when the AA (acetaldehyde) is increased. This suggests that AA accumulation on the catalyst surface may lead to surface fouling and the observed deactivation. The presence of H2O or H-2 co-feed, which can lead to hydroxyl radical (OH.), may impose a shift in the production formation of photocatalytic reaction. (C) 2014 Elsevier B.V. All rights reserved.
Metal-doped Photocatalysts to Reduce Carbon Dioxide in Ethanolamine Solution for Methane Production
(2012)
Wu, Hung-Yu
;
Bai, Hsunling
;
Wu, Jeffrey C. S.
;
環境工程研究所
;
Institute of Environmental Engineering
Photocatalytic reduction of carbon dioxide (CO2) to form valuable energy source of methane (CH4) in the ethanolamine (MEA) solution is investigated in this study. The TiO2 photocatalysts were prepared by doping with nano-sized metals (Fe, Zn, Mn, Ce) via the co-precipitation method. The photocatalytic reduction process was performed in the MEA solution because the MEA absorption is one of the most popular methods for CO2 greenhouse gas capture from flue gas streams. And it is intended to integrate the CO2 capture and utilization into one process. The tests were performed with the UV light source of 9W and 365 nm. The light intensity of 6.3 mW/cm(2) was measured at the center point between the UV light source and the outer glass of the reactor. The 5 hours test results showed the methane yield followed the order of Ce-TiO2 > Mn-TiO2> Zn-TiO2 > Fe-TiO2. Tests were also evaluated with a solar light concentrator, and it has been proved that it is possible to produce CH4 under solar light without the addition of any external energy source.
Photocatalytic reduction of CO2 using molybdenum-doped titanate nanotubes in a MEA solution
(2015-01-01)
Wu, Hung-Yu
;
Nhat Huy Nguyen
;
Bai, Hsunling
;
Chang, Sue-min
;
Wu, Jeffrey C. S.
In this study, the photocatalytic reduction of CO2 in a monoethanolamine solution to form valuable energy sources was investigated using Mo-doped TNTs photocatalysts for the first time. The results revealed that the structure of Mo-doped TNTs changed with the increase of calcination temperature. For Mo-doped TNTs calcined at 500 degrees C, the partial corruption of titanate nanotubes into anatase particles caused the reduction of Mo species from Mo6+ to Mo5+ and produced oxygen vacancies, which resulted in the highest CO2 reduction ability. The yield rates of CH4, CO and total combustible organic compounds were 0.52, 10.41 and 13.53 mu mol g(cat)(-1), respectively, under UVA (8 W, 63 mu W cm(-2)) irradiation. The photoreduction quantum efficiencies of CH4 and CO were achieved at 0.036% and 0.180%, respectively. It was found that the molybdenum structure and oxygen vacancies could be the key factors controlling the photocatalytic reduction efficiency of CO2. A possible structure transformation of Mo-doped TNTs at different calcination temperatures was inferred and the reaction mechanism for photocatalytic CO2 reduction with oxygen vacancy sites of Mo-doped TNTs was proposed.
Photocatalytic Reduction of CO2 Using Ti-MCM-41 Photocatalysts in Monoethanolamine Solution for Methane Production
(2014-07-16)
Wu, Hung-Yu
;
Bai, Hsunling
;
Wu, Jeffrey C. S.
;
環境工程研究所
;
Institute of Environmental Engineering
Photocatalytic reduction of carbon dioxide (CO2) to form a valuable energy source of methane (CH4) in monoethanolamine (MEA) solution is first investigated by mesoporous photocatalysts of Ti-MCM-41 in this study. The MEA solution was chosen as the absorbent and reductant because amine absorption is one of the most popular methods for CO2 capture from flue gas streams. Also, it is intended to integrate the CO2 capture and utilization into one process. The photocatalytic results of methane yields indicated that MEA served as a better reductant than water and NaOH which have been commonly used for CO2 reduction. For the best photocatalyst of Ti-MCM-41(50) manufactured at a Si/Ti molar ratio of 50, its methane yield (62.42 mu mol/g of cat.) was much higher than that of commercial P25 photocatalyst after 8 h of UV illumination. A photoreduction quantum efficiency (PQE) of 9.18% was achieved.
Photocatalytic Reduction of CO2 Using Ti-MCM-41 Photocatalysts in Monoethanolamine Solution for Methane Production
(2014-07-16)
Wu, Hung-Yu
;
Bai, Hsunling
;
Wu, Jeffrey C. S.
;
環境工程研究所
;
Institute of Environmental Engineering
Photocatalytic reduction of carbon dioxide (CO2) to form a valuable energy source of methane (CH4) in monoethanolamine (MEA) solution is first investigated by mesoporous photocatalysts of Ti-MCM-41 in this study. The MEA solution was chosen as the absorbent and reductant because amine absorption is one of the most popular methods for CO2 capture from flue gas streams. Also, it is intended to integrate the CO2 capture and utilization into one process. The photocatalytic results of methane yields indicated that MEA served as a better reductant than water and NaOH which have been commonly used for CO2 reduction. For the best photocatalyst of Ti-MCM-41(50) manufactured at a Si/Ti molar ratio of 50, its methane yield (62.42 mu mol/g of cat.) was much higher than that of commercial P25 photocatalyst after 8 h of UV illumination. A photoreduction quantum efficiency (PQE) of 9.18% was achieved.
Real-Time Raman Monitoring during Photocatalytic Epoxidation of Cyclohexene over V-Ti/MCM-41 Catalysts
(2015-06-01)
Chan, Hsiang-Yu
;
Van-Huy Nguyen
;
Wu, Jeffrey C. S.
;
Calvino-Casilda, Vanesa
;
Banares, Miguel A.
A series of V- and/or Ti-loading MCM-41 catalysts are successfully synthesized with a hydrothermal method. The photocatalytic and thermal epoxidations of cyclohexene in the presence of tert-butyl hydroperoxide (t-BuOOH) were investigated with real-time monitored by NIR-Raman spectroscopy. It suggests that both V- and Ti-loading can be responsible for the cyclohexene epoxidation. Moreover, the complementary behavior of V- and Ti-loading may be related to a similar role of activation. Interestingly, the progress of the photo-epoxidation on V0.25Ti2/MCM-41 photocatalyst was monitored by changes in intensity of the characteristic Raman bands without interference from the UV-light irradiation. The result, for the first time, reveals that cyclohexene was directly photo-epoxidized to 1,2-epoxycyclohexane by t-BuOOH during the reaction. A possible mechanism of cyclohexene photo-epoxidation is also proposed for this study.
Temperature effect on the photo-epoxidation of propylene over V-Ti/MCM-41 photocatalyst
(2013-03-05)
Nguyen, Van-Huy
;
Wu, Jeffrey C. S.
;
Bai, Hsunling
;
環境工程研究所
;
Institute of Environmental Engineering
The effect of reaction temperature on the gas-phase photocatalytic epoxidation of propylene was systematically studied over V-Ti/MCM-41 photocatalyst at different temperatures (298-393 K). Temperature significantly influences the product distribution of photo-epoxidation. Raising temperature is favorable towards the formation of propionaldehyde (PA) due to inhibition of PA transformation to propionic acid (C2H5COOH), the intermediate product of acetaldehyde (AA). Results indicated that the reaction temperature has a dual-action to the reaction rate: (1) improving the desorption of reaction products, which provides more active sites for reaction and (2) reducing the adsorption of propylene on the photocatalyst, which declines the reaction efficiency. (C) 2012 Elsevier B.V. All rights reserved.
Vitalizing fuel cells with vitamins: pyrolyzed vitamin B12 as a non-precious catalyst for enhanced oxygen reduction reaction of polymer electrolyte fuel cells
(2012-01-01)
Chang, Sun-Tang
;
Wang, Chen-Hao
;
Du, He-Yun
;
Hsu, Hsin-Cheng
;
Kang, Chih-Ming
The limited natural abundance and high cost of Pt has been a major barrier in its applications for hydrogen or methanol fuel cells. In this work, based on the pyrolyzed corrin structure of vitamin B12 (py-B12/C), it is reported to produce superior catalytic activity in the oxygen reduction reaction (ORR) with an electron transfer number of 3.90, which is very close to the ideal case of 4. The H-2-O-2 fuel cell using py-B12/C provides a maximum power density of 370 mW cm(-2) and a current density of 0.720 A cm(-2) at 0.5 V at 70 degrees C. Calculations based on density functional theory suggests that the corrin complex with a low-symmetric structure offers a much preferable path for the ORR, which is not applicable to the porphyrin with a high-symmetric structure. The long-term stability and high ORR activity of py-B12/C make it a viable candidate as a Pt-substitute in the ORR.