The feasibility of using ultrasonic mixing to obtain biodiesel from soybean oil was established. The alkaline transesterification reaction was studied at three levels of temperature and four alcohol-to-oil ratios. Excellent yields were obtained for all conditions. For example, at 40°C with ultrasonic agitation and a molar ratio of 6:1 methanol/oil, the conversion to FAME was greater than 99.4% after about 15 min. For a 6:1 methanol/oil ratio and a 25 to 60°C temperature range, a pseudo second-order kinetic model was confirmed for the hydrolysis of DG and TG. Reaction rate constants were three to five times higher than those reported in the literature for mechanical agitation. We suspect that the observed mass transfer and kinetic rate enhancements were due to the increase in interfacial area and activity of the microscopic and macroscopic bubbles formed when ultrasonic waves of 20 kHz were applied to a two-phase reaction system.

The electrochemical codeposition method has been used to prepare a series of Pt/MoO x /glassy carbon ͑GC͒ electrodes with different atomic ratios of Pt to Mo. The advantage of this method is the mixing of metal and support on a microscopic level ͑atomic or molecular scale͒. That is, to disperse the Pt microparticles into the molybdenum oxide on a GC substrate. The Pt/MoO x /GC electrode was prepared by scanning the electrode potential between 0.55 and Ϫ0.70 V vs. Hg͉Hg 2 SO 4 in potassium hexachloroplatinate, sodium molybdate, and 2.2 M sulfuric acid solution at a GC substrate using a scan rate of 20 mV/s. The scanning electron microscopy results show that the Pt and MoO x microparticles are uniformly dispersed on the GC electrode surfaces. In addition, the modified electrode exhibits electrocatalytic activity for the oxidation of methanol. Based on the catalytic properties, the optimal concentrations for the preparation of the composite electrode is 3.0 mM in K 2 PtCl 6 and 300 mM of Na 2 MoO 4 . X-ray photoelectron spectroscopy ͑XPS͒ analyses indicate that the best Pt to Mo atomic ratio is in the range between 1.5 and 2.0. In addition, the XPS spectra present a broad peak in the Mo ͑3d͒ binding energy region revealing the existence of Mo 6ϩ species as well as lower valence state Mo 5ϩ and Mo 4ϩ . Finally, a reaction mechanism is suggested for methanol oxidation at this composite Pt/MoO x GC electrode.Numerous research studies have been conducted on the development of a catalyst for the anode in direct methanol-air fuel cells ͑DMFCs͒ in the last ten years. As an example, we could mention PPy/Pt, 1 Pt/Ru/Os/Ir, 2 Pt/Ru/Os, 3 Pt/Re, 4 Pt/Ru, 5-12 Pt/Sn, 13-15 and Pt/Mo 16-18 composite systems. Nevertheless, the step toward the practical application has not been developed as fast as had been expected. Mainly, the poisoning of the anode catalysts hinders DMFC performance by the adsorbed carbonyl species derived from methanol oxidation. [19][20][21][22][23][24][25] Dispersed noble metal catalysts supported on high surface area inorganic oxides are of considerable interest for catalysis. 26,27 The support is used to separate the catalytic particles physically and decrease their agglomeration rate. The oxide support is believed to modify the electronic nature of the metal particles as well. Thus, affecting their chemisorptive and catalytic properties. The enhancement of surface catalytic activity by the metal-support interaction, as well as the large surface area achieved with the low loading levels, makes such systems attractive for the application in DMFCs. The requirement of these catalytic systems is that the intimate contact between metal and support should be as great as possible.Rolison and co-workers 10-12 have reported a thermogravimetric and X-ray photoelectron spectroscopy ͑XPS͒ analysis of as-received Pt-Ru electrocatalysts. These results indicate that DMFC materials contain substantial amount of hydrous ruthenium oxide (RuO x H y ). A potential misidentification of nanoscale Pt-Ru blacks arises because RuO...

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Biodiesel fuels have become more attractive recently because of their environmental benefits and cost competitiveness compared to diesel fuel. Many processing improvements have been proposed to increase the conversion rates and the yields of vegetable oil in order to lower production costs and improve biodiesel product quality. In conventional biodiesel production chemistries, alkaline transesterifications of alcohol/oil dispersions should occur primarily near the interface. Ultrasonic mixing has already been shown to increase overall conversion rates for alcohol/ vegetable oil mixtures. Our data show that ultrasonic mixing produced smaller droplet sizes than conventional agitation, leading to more interfacial area for the reaction to occur. Droplet size distributions have been measured for conventional impeller and ultrasonic mixing systems using methanol/soybean oil as a model system. The dispersions were stabilized by surfactant in order to obtain droplet size distribution for mixture samples. Ultrasonic mixing produced dispersions with average droplet sizes 42% smaller than those generated using standard impellers.