Pinsuda Viravathana

Fabrication of a micro-direct methanol fuel cell using microfluidics

A direct-methanol fuel cell containing three parts: microchannels, electrodes, and a proton exchange membrane (PEM), was investigated. Nafion resin (NR) and polystyrene-block-poly(ethylene-ran-butylene)-block-polystyrene (PS) were used as PEMs. Preparation of PEMs, including compositing with other polymers and their solubility, was performed and their proton conductivity was measured by a four point probe. The results showed that the 5 % Nafion resin has lower conductivity than the 5 % PS solution. The micro-fuel cell contained two acrylic channels, PEM, and two platinum catalyst electrodes on a silicon wafer. The assembled micro-fuel cells used 2 M methanol at the flow rate of 1.5 mL min−1 in the anode channel and 5 × 10−3 M KMnO4 at the flow rate of 1.5 mL min−1 in the cathode channel. The micro-fuel cell with the electrode distance of 300 μm provided the power density of 59.16 μW cm−2 and the current density of 125.60 μA cm−2 at 0.47 V.

Synthesis and Characterization of PdCoNi Nanocomposites Supported on Graphene as Anodic Electrocatalysts for Methanol Oxidation in Direct Methanol Fuel Cell

PdCoNi nanocomposites supported on graphene (PdCoNi/G) have been obtained from chemical reduction of metal catalysts and graphite oxide (GO) with a strong reducing agent, followed by calcination at high temperature under N2 condition, and used for electrooxidation of methanol in direct methanol fuel cell. The morphologies and structural properties of electrocatalysts were examined by scanning electron microscopy (SEM) and X-ray diffraction (XRD). X-ray spectroscopy techniques (X-ray photoelectron spectroscopy XPS) was used to investigate the chemical state of the synthesized catalysts. The results of Pd XPS spectra showed the metallic Pd and PdO phases for precalcined and calcined PdCoNi/G nanocomposite, respectively. The X-ray measurement of Co and Ni displayed the various metallic oxides in synthesized electrocatalysts. For electrochemical analysis, cyclic voltammetry (CV) and chronoamperometry (CA) indicated that the PdCoNi/G nanocomposites enhanced the methanol oxidation, compared to the lower activity in the calcined electrocatalysts.

Co-Promoted Cu/ZnO Catalysts for Fischer-Tropsch Synthesis

Co-promoted Cu/ZnO catalysts were studied for Fischer-Tropsch synthesis (FTS). All catalysts were prepared by the co-precipitation method, having the mass ratio of Co:Cu:Zn=0 (unpromoted), 0.05, 0.5:1:1, and characterized by X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), including X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). From XRD and XAS, the results confirmed the phase transformation of CuO to Cu foil and Co3O4 to Co foil in Co-promoted catalysts after reduction. After FTS reaction testing, the Co-promoted catalysts showed the decrease in methanol selectivity of 15 and 1.6% for 0.05Co-Cu/ZnO and 0.5Co-Cu/ZnO, respectively, and the increase in C5-C15 selectivity during 30 h of reaction.

Cu/ZnO Catalysts for Enhancing the Methanol Selectivity in Fischer-Tropsch Synthesis

Cu/ZnO catalysts were studied to enhance the methanol selectivity in Fischer-Tropsch synthesis (FTS). By knowing that the methanol production from syngas (CO/H2) accelerated the crystallization of Cu and ZnO and led to the deactivation of the catalysts, a small amount of iron added to the catalyst could improve the catalyst stability by suppressing the crystallization of Cu and ZnO. The promotional effects of iron on the textural properties, reduction behavior, and structural changes of the Cu-based FTS catalysts were investigated by X-ray diffraction (XRD), X-ray absorption near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS). Their catalytic activity was measured at 10 bar and 190°C with H2/CO ratio of 2 and the FTS products were analyzed by GC. The product distribution was presented in terms of methanol, C1, C2-C4, and C5+ selectivity.

La-ZrO2 and Ru-ZrO2 Promoted Co/SiO2 Catalysts for Fischer-Tropsch Synthesis

The performance of ZrO2-La promoted silica supported cobalt catalyst (100Co/15ZrO2/ 100Aerosil/0.66La) was compared to the ZrO2-Ru promoted one, 100Co/15ZrO2/100Aerosil/0.66Ru, in Fischer-Tropsch synthesis (FTS). These catalysts were prepared by co-precipitation and incipient wetness impregnation methods. The characterization by XRD confirmed the cobalt phase of Co3O4 in both catalysts. For their catalytic activity on FTS reaction, the results preliminarily showed the higher methane fraction (60-80%) and lower C2-C4 (10-20%) and C5+ (10-20%) fractions in ZrO2-La promoted catalyst compared to the fractions of methane (20-40%), C2-C4 (20-50%), and C5+(10-60%) from the ZrO2-Ru promoted catalyst. During reaction, the maximum n-paraffin selectivity of 40% was at C3 and the hydrocarbon chain was up to C6 for the ZrO2-La promoted catalyst. For the ZrO2-Ru promoted catalyst, the result showed the maximum n-paraffin of C3 at 30 min of reaction time. When the reaction time increased, the maximum n-paraffin selectivity shifted toward higher C number but levelled off (15%) and the hydrocarbon chain was up to C16.

XAS Study on Calcination Effect of Silica Supported Cobalt Catalysts for Fischer-Tropsch Synthesis

The precalcined and calcined silica supported cobalt catalysts at 15, 20, and 25%Co were investigated by X-ray Absorption Spectroscopy (XAS) including the X-ray absorption near edge structure (XANES) and the extended X-ray absorption fine structure (EXAFS). The results showed the phase of Co(NO3)2.6H2O in all precalcined catalysts, which corresponded to the XRD measurement. When increasing the amount of cobalt in the precalcined catalysts, there was the presence of ordered Co(NO3)2.6H2O phase. After calcination in Ar at 600°C for 6 h, the Co3O4 phase was presented in all calcined catalysts. For the catalytic performance testing, the selected 20%Co/Aerosil_wi_calcined catalyst was reduced at 450°C in H2 and operated at 190°C with a total pressure of 10 bar and H2/CO flow rate of 20:10 ml/min for Fischer-Tropsch synthesis. After reaction testing, the used 20%Co/Aerosil_wi catalyst showed the main phase of Co3O4. The result showed high methane selectivity at the beginning of reaction. By increasing of reaction time, the methane selectivity tended to decrease, whereas the C2-C4 and C5+ selectivity was increased.

Promoted and Un-Promoted Co/SiO2 Fischer-Tropsch Catalysts

Un-promoted and promoted Co/SiO2 catalysts with ZrO2 and Ru were prepared and the catalytic performances for Fischer-Tropsch synthesis were investigated. The prepared catalysts were characterized by XRD, N2 adsorption/desorption, and X-ray absorption techniques. XRD suggested that the cobalt species presence in all prepared catalysts was Co3O4. Promoted catalyst with ZrO2 and Ru showed high distribution of cobalt on silica surface resulted in smaller Co3O4 crystalline size than un-promoted ones. From the reaction testing, the obtained products of C1 to C9 from un-promoted and promoted Co/SiO2 were studied.

Na2WO4-Mn/mullite Catalysts for Oxidative Coupling of Methane

The catalysts, 5 wt% Na2WO4 -2 wt% Mn on mullites sintered at 1200°C, 1300°C, 1400°C, and 1500 °C, were prepared by incipient wetness impregnation method for the oxidative coupling of methane (OCM) reaction in a fixed-bed quartz tube reactor. These catalysts were characterized by XRD, XPS and BET method. The XRD pattern of Na2WO4-Mn/mullite indicated that the main crystal phase of metal oxide was MnWO4. From the XPS spectra, the results revealed the information on Na, W and Mn species distributed on the catalyst surface. For catalytic activity testing, Na2WO4-Mn/mullite sintered at 1300 °C showed the highest C2 selectivity of 11.4% and Na2WO4-Mn/mullite sintered at 1400 °C showed the highest CH4 conversion of 56.6%.