Effect of Ni content in PdNi/C anode catalysts on power and methanol co-generation in alkaline direct methane fuel cell type.

PdNi electrocatalysts supported on carbon were used as anode materials for methane oxidation in alkaline direct methane fuel cells (ADMEFCs). The electrocatalysts were successfully synthesized by the NaBH4 reduction method. X-ray diffraction measurements showed the formation of non-alloyed Pd in the face- centered cubic (FCC) structure for all materials and formation of NiO and Ni(OH)2 species. TEM images showed that the metal particles are well dispersed on the support with small agglomeration regions. Information about the surface structure of the catalyst were obtained by Raman spectra, mainly confirming the presence of Ni(OH)2. The species observed by DEMS, that is, methanol (m/z = 32), CO2 (m/z = 44) and potassium formate (m/z = 84) were confirmed by FTIR, which also showed the presence of a high amount of carbonate in the methane oxidation products of the ADMEFC with Pd50Ni50/C as the anode catalyst. Tests in ADMEFCs showed that the dependence of the maximum power density on nickel content in the catalysts goes through a maximum value of 13.5 µW cm-2 at 50 at% Ni. Moreover, the amount of produced methanol decreases with increasing Ni content in the PdNi/C catalysts. Both these results can be explained by the enhanced methanol oxidation in the presence of nickel.

A model to evaluate half-lives of PAHs naturally occurring on airborne particulate.

Constant decay of polycyclic aromatic hydrocarbons (PAHs) adsorbed onto airborne particulate collected in glass fibre filters and exposed to sunlight ranged from 1.8 to 4.4 X 10(-3) (min-1), corresponding respectively to a half-life of 100 and 425 min. Half-life of PAHs appeared to be positively correlated with filter loading. Experimental results showed that decay of PAHs adsorbed on airborne particulate was induced by two concomitant reactions; a photochemical reaction involving the outer layers of collected particulate, and a "dark" reaction that may occur in the inner layers. The constant decays of these two reactions were calculated using a simplified mathematical model. The authors suggest the use of this model to compare chemical stability of airborne PAHs exposed, during their permanence in the atmosphere, to different physical (light intensity, temperature, humidity) as well as chemical conditions (oxidant concentration, chemical composition of particulate).