Key Engineering Materials Vol. 659

Abstract: The effect of gallium-promoted copper-based catalysts has been investigated in connection with the characteristic of the active copper phase. CuO-ZnO-Ga₂O₃ catalysts with different gallium loadings were prepared using oxalate co-precipitation method. The effects of gallium loading on the properties of catalysts were studied by means of X-ray diffraction (XRD), transmission electron microscopy (TEM) and temperature-programmed reduction (TPR). The dispersion and metal area of copper were also determined by dissociative nitrous (N₂O) adsorption technique conducted on a metal dispersion analyzer (BELCAT). The TPR profiles showed that the presence of two different reduction regions in the CuO-ZnO catalysts can be attributed to the reduction of highly dispersed copper oxide species (reduced at 246 °C) and bulk-like CuO (reduced at above 390 °C). By contrast, the only low-temperature reduction peak was presented in the TPR profiles after the Ga₂O₃ loading was higher than 4 wt%. With the same molar ratio (Cu/Zn = 2:1), the reducibility of CuO-ZnO-Ga₂O₃ was found to be more facile than CuO-ZnO due to the lower copper oxide crystallite sizes of gallium-promoted catalysts. Higher Ga₂O₃ loadings resulted in an increase in both copper dispersion and metal surface area of all the catalysts studied in good agreement with the reduction behaviors in the TPR profiles, although all the gallium-promoted catalysts were slightly different for the reducibility.

Abstract: The use of waste materials for producing biodiesel via transesterification has been of recent interest. In this study, the pork bone was used as the raw materials for natural hydroxyapatite (NHAp) catalyst. The calcination of animal bone was conducted at 900 °C for 2 h. The raw material and the resulting heterogeneous catalyst were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method. The effects of reaction time, microwave power, methanol/oil molar ratio, catalyst loading and reusability of catalyst were systematically investigated. The optimum conditions, which yielded a conversion of oil of nearly 94%, were reaction time 5 min and microwave power 800 W. The results indicated that the NHAp catalysts derived from pork bone showed good reusability and had high potential to be used as biodiesel production catalysts under microwave-assisted transesterification of Jatropha Curcas oil with methanol.

Abstract: The SiO₂-Al₂O₃ fiber composites had been successfully prepared by the combination technique of electrospinning and sol-gel method. The effects of Al₂O₃ contents (1, 2, 3, 4 and 5%wt) on fiber diameter and morphology were investigated by SEM. It was observed that alumina content significantly influenced the average diameter of fiber which increased by increasing the alumina content. The prepared fiber composites were used as a support for cobalt (Co)-based catalysts for Fischer–Tropsch synthesis (FTS). The FTS performances over the fiber and porous catalysts were carried out in a fixed bed reactor at 280°C, 1 atm, and H₂/CO of 2. The results showed that the fiber catalysts were easily reduced when comparing the porous catalyst. The fiber catalysts showed the activity at the same level of the porous catalyst, but their advantage was the lower water gas shift reaction which produced less CO₂ than the porous catalyst. The CO conversion was 59.62% with the fiber catalyst and 52.80% with the porous catalyst under the same experimental condition. The fiber catalyst gave the maximum methane selectivity of 96.08% compared to the porous catalyst (85.63%).

Abstract: In this study, we can fabricate Cu₂O on F-doped SnO₂ coated glass (FTO) substrates as photocathode for hydrogen evolution reaction by electro-deposition techniques. Cyclic voltammetry as a new deposition method was studied to fabricate Cu₂O photocathode in a mixed solution of Cu (NO₃)₂ and KNO₃ under a condition of low temperature and without pH value adjustment. Amperometry as a previous method was used to compare for Cu₂O electrode fabrication under the situation of pH adjustment and higher temperature condition. A photocurrent from hydrogen evolution reaction was performed by keep potential at-0.2 V in 0.1 M Na₂SO₄ under visible irradiation comparing with both fabricated method. The Cu₂O photocathode from cyclic voltammetry deposition method presents photoelectrocatalytic activity higher than that of amperometry deposition method with the optimum conditions. This electro-deposition technique represents the excellent method with simple, fast and low cost of Cu₂O photocathode fabrication for photoelectrochemical hydrogen evolution reaction.

Abstract: Lanthanum and carbon co-doped sodium tantalum oxide, La-C-NaTaO₃, are prepared by incorporating lanthanum and carbon into NaTaO₃ cluster via a sol-gel technique using a sucrose as carbon source. The La-C-NaTaO₃ prepared sample is calcined at a temperature of 700 °C. Effects of carbon contents on the crystal, shape, optical absorption response and activity of hydrogen production of the sample are evaluated. The crystal of La-C-NaTaO₃ is characterized by XRD analysis. The results show that the XRD pattern of the La C co-doped NaTaO₃ is found to be crystalline phase with monoclinic structure. From the analysis of SEM images, the particle size of the prepared powder is about 40-200 nm. The optical response is examined by diffuse reflectance spectra (DRS). It is depicted that the absorption edge of La-C-NaTaO₃ crystalline shift to higher wavelength. The extension to the visible light absorption edge became drastic with increasing carbon content in the sample. The photocatalytic activity of La-C-NaTaO₃ is examined from water-methanol aqueous solution under visible light irradiation. It is found that the photocatalytic activity of La-C-NaTaO₃ depend strongly on the doping content of C, and sample La-C-NaTaO₃ shows the highest photocatalytic activity for the water reduction. The optimum amounts of carbon to maximize the hydrogen evolution rate is to be 2.5 mol %. The La-C-NaTaO₃ catalyst has high activity of H₂ evolution of 40.0 [μmol h^-1] and long time stability under visible-light irradiation, suggesting a promising utilization of such photocatalyst. La C co-doped NaTaO₃ photocatalyst can be developed further in order to produce hydrogen as a green energy.

Abstract: Calcium oxide (CaO) is one of the most promising heterogeneous alkali catalysts since it is cheap, abundantly available in nature, and some of the sources of this compound are renewable (waste material consisting of calcium carbonate (CaCO₃)). In this study, the waste enamel venus shell was used as the raw material for CaO catalyst. The calcination of bio-waste was conducted at 900 °C for 2 h. The raw material and the resulting CaO catalyst were characterized using X-ray diffraction (XRD), X-ray fluorescence (XRF), scanning electron microscopy (SEM) and the Brunauer-Emmett-Teller (BET) method. The effects of reaction variables such as reaction time, microwave power, methanol/oil molar ratio, and catalyst loading on the yield of biodiesel were investigated by gas chromatograph-mass spectrometry (GC-MS). From the experimental results, it was found that the CaO catalysts derived from waste material showed good catalytic activity (the conversion of oil of nearly 93%, a very similar catalytic activity with laboratory CaO) and had high potential to be used as biodiesel production catalysts in transesterification of Jatropha Curcas oil with methanol.

Abstract: In a hydrogen production reactor, combustion of LPG was used as a heat source for ethanol steam reforming. For such purpose, the operating temperature was required to be around 700-900°C along the entire height of the reactor. Various types of porous media materials were used as a heat transfer media, i.e. 25mm ceramic saddles, random size bio-filter media from MTEC, ceramic foam, and ceramic balls. The objective of this study was to obtain the practical amount of total energy input, and compare with theoretical calculation which can achieve the required temperature of ethanol steam reforming for the hydrogen production. From our experiments, 13.20 kW of energy was needed to fulfill the requirement of the reactor, while only 2.49 kW was expected from theoretical calculation. Most energy loss was due mainly to: 1) heat loss at the top of the reactor where the metal part was directly exposed to the environment, 2) a large amount of energy loss at the furnace stack and, 3) insufficient mixing at the early stage of combustion at the bottom of the furnace as noticed by high CO concentration in flue gas. The porous media material has a significant effect on temperature distribution and energy consumption. The results show that the use of ceramic saddles as porous media consume more energy than the ceramic foam and the bio-filter media mixed with ceramic saddles during the start-up period of the reactor.

Abstract: The effect of the different metal atomic ratios deposited on Vulcan XC-72R on ethanol electrooxidation reaction were investigated by producing of the ternary catalysts (PtRuSn/C and PtRuNi/C) in various atomic ratios (75:20:5, 75:15:10, 75:10:15, 75:5:20). All catalysts were prepared via polyol process. The nominal atomic ratios of the metals on the support were confirmed by EDX-SEM. The cyclic voltammetry was used to investigate the electrocatalytic activity of the catalysts. It was found that PtRuSn/C (75:10:15) showed the highest maximum current density of 3.25 mA/cm² among all Sn containing catalysts. However, PtRuNi/C (75:5:20) also exhibited the high maximum current density of 2.66 mA/cm² which was the maximum current density for Ni containing catalysts. Moreover, PtRuNi/C (75:5:20) exhibited the best activity and stability for ethanol electrooxidation reaction as showed in chronoamperometry tests. The current density at 3000 s was 0.54 mA/cm². The size of the catalysts was about 1.9-3 nm measured by TEM. The catalyst also presented smaller particle size and better catalyst dispersion among all ternary catalysts. The addition of Sn facilitated the C-C bond breaking in molecule of ethanol while the addition of Ni facilitated better stability.

Abstract: Synthesis of nanoCu/ZnO catalyst for LPG production was prepared by ultrasonic spray pyrolysis (USP). Hollow spherical particles were obtained by USP technique using an aqueous solution of Cu (NO₃)₃.6H₂O and Zn (NO₃)₃.3H₂O with different concentration of 0.05, 0.1 and 0.5 molar under the pyrolysis temperatures of 600, 700 and 800°C. Mists of the solution were generated from the precursor solution by ultra sonic vibrators at frequency of ~1.7 MHz. The physicochemical properties of catalysts were characterized by X-ray diffraction, temperature-programmed reduction, scanning electron microscope, nitrogen adsorption-desorption, and energy dispersive X-ray spectrometer. The results showed that increasing in precursor concentration resulted in a large particle and particles size distributed in a range of 0.63-1.21 μm. Particles prepared at pyrolysis temperature 700°C exhibited homogeneous in size and shape compared to other temperature. The catalytic activity of nanoCu/ZnO-Pd-β catalysts was performed in a fixed-bed reactor for synthesizing LPG. The reaction took place at 260°C, 3.0 MPa, and the ratio of H₂/CO = 2/1. All the products from the reactor were in gaseous state, and analyzed by on-line gas chromatography. The results showed that %CO conversion was high but decreased rapidly with increasing reaction time. Cu/ZnO catalyst prepared by co-precipitation gave higher %CO conversion than that prepared by ultrasonic spray pyrolysis. Moreover, hydrocarbon product distribution for Cu/ZnO catalyst produced at concentration 0.1 M 700°C by ultrasonic spray pyrolysis gave the highest LPG selectivity.

Abstract: In the present work, vanadium pentoxide (V₂O₅) nanoparticles have been investigated for monitoring ethanol (C₂H₅OH) at ppm levels in air. A one-step flame spray pyrolysis (FSP) process has been applied for the synthesis of vanadium pentoxide (V₂O₅) and platinum-loaded vanadium pentoxide (Pt-V₂O₅) nanoparticles. The samples have been studied to characterize their morphological and microstructural properties by X-ray diffraction and transmission electron microscopy. Pt addition to V₂O₅ samples were verified by energy dispersive X-ray spectrometry mode. The specific surface area of the nanoparticles was measured by nitrogen adsorption method. The application of the produced nanoparticles as sensitive and selective ethanol resistive sensor has been demonstrated. The Pt-loaded V₂O₅ sensor has shown higher response towards ethanol at ppm-level concentrations compared to unloaded one.