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The nitrogen monoxide (NO) adsorption on platinum tetramer (Pt4) clusters supported on gamma alumina (gamma-Al2O3) with surface index (111) was investigated by using ab-initio calculation based on density functional theory. The Pt4 geometries used in this study are tetrahedron and planar rhombus. The adsorption of Pt4 on gamma-Al2O3 (111) surface in tetrahedron configuration is energetically more favorable as compared to that of the planar rhombus. However, it was found that NO molecule adheres strongly to Pt4 with planar configuration on gamma-Al2O3(111) surface. In addition, the NO adsorption calculation on the isolated Pt4 clusters also shows similar preference to planar configuration. The local density of states (LDOS) reveals that the difference in reactivity comes from the different hybridization strengths between the electronic states of nitrogen atom and those of platinum tetramers. The results are in good agreement with the experiments which show similar tendency for CO and N2O reactivity to gas-phase platinum clusters.

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Polycyclic aromatic hydrocarbons (PAHs) bound in particles from automobile emissions may cause adverse human health. In this study, a 3L heavy-duty diesel engine with and without the latest aftertreatment devices were characterized for PAH emissions and toxicity using European Transient Cycle (ETC) and the European Stationary Cycle (ESC). The latest combination of aftertreatment devices including a diesel oxidation catalyst (DOC) and a catalyzed diesel particulate filter (c-DPF) were used to remove diesel exhaust particles (DEP). Particle size distribution and number concentrations were measured using a TSI Engine Exhaust Particle Sizer. Eight PAHs [benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, benzo(a)pyrene, indeno(1,2,3-cd)pyrene, dibenz(a, h)anthracene, and benzo(ghi)perylene] within the DEP were analyzed by thermal desorptiongas chromatography/mass spectrometry (TD-GC/MS). Elemental carbon (EC) and organic carbon (OC) were also analyzed with a thermal/optical carbon analyzer. The results indicated that 4-ring PAH emissions are larger than 5 or 6-ring PAH emissions, with and without the aftertreatment devices in place. Number concentrations of particles, PAHs and EC mass emissions in diesel exhaust were dramatically decreased by the aftertreatment devices: > 99%, > 97% and > 99%, respectively. To evaluate the toxicity of PAHs in the DEP, we calculated benzo(a)pyrene equivalent (BaPeq) emissions using a toxic equivalency factor (TEF). Total BaPeq emissions of eight PAHs were also substantially decreased by the aftertreatment devices (> 95%). However, the decrease rate of OC was lower than EC (> 72%). We demonstrated that number concentrations of DEP, PAH emissions, EC and BaPeq emissions were similarly and substantially decreased by the latest aftertreatment devices.

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