title: Transformation of Cerium Oxide Nanoparticles from a Diesel Fuel Additive during Combustion in a Diesel Engine.
abstract: Nanoscale cerium oxide is used as a diesel fuel additive to reduce particulate matter emissions and increase fuel economy, but its fate in the environment has not been established. Cerium oxide released as a result of the combustion of diesel fuel containing the additive Envirox, which utilizes suspended nanoscale cerium oxide to reduce particulate matter emissions and increase fuel economy, was captured from the exhaust stream of a diesel engine and was characterized using a combination of bulk analytical techniques and high resolution transmission electron microscopy. The combustion process induced significant changes in the size and morphology of the particles; ∼15 nm aggregates consisting of 5-7 nm faceted crystals in the fuel additive became 50-300 nm, near-spherical, single crystals in the exhaust. Electron diffraction identified the original cerium oxide particles as cerium(IV) oxide (CeO2, standard FCC structure) with no detectable quantities of Ce(III), whereas in the exhaust the ceria particles had additional electron diffraction reflections indicative of a CeO2superstructure containing ordered oxygen vacancies. The surfactant coating present on the cerium oxide particles in the additive was lost during combustion, but in roughly 30% of the observed particles in the exhaust, a new surface coating formed, approximately 2-5 nm thick. The results of this study suggest that pristine, laboratory-produced, nanoscale cerium oxide is not a good substitute for the cerium oxide released from fuel-borne catalyst applications and that future toxicity experiments and modeling will require the use/consideration of more realistic materials.
authors.affiliation: The Center for NanoBioEarth, Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: James G
authors.identifier: 0000-0001-6564-1077
authors.initials: JG
authors.lastname: Dale
authors.affiliation: Department of Civil and Environmental Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Steven S
authors.initials: SS
authors.lastname: Cox
authors.affiliation: Department of Civil and Environmental Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Marina E
authors.initials: ME
authors.lastname: Vance
authors.affiliation: Department of Civil and Environmental Engineering, Virginia Tech , Blacksburg, Virginia 24061, United States.
authors.forename: Linsey C
authors.initials: LC
authors.lastname: Marr
authors.affiliation: The Center for NanoBioEarth, Department of Geosciences, Virginia Tech , Blacksburg, Virginia 24061, United States.|Geosciences Group, Energy and Environment Directorate, Pacific Northwest National Laboratory , Richland, Washington 99352, United States.
authors.forename: Michael F
authors.initials: MF
authors.lastname: Hochella
mesh_terms: D002563:Cerium / Q000737:chemistry; D005742:Gasoline; D053758:Nanoparticles / Q000737:chemistry; D010316:Particle Size; D052638:Particulate Matter; D001335:Vehicle Emissions
chemical_list: D005742:Gasoline; D052638:Particulate Matter; D001335:Vehicle Emissions; D002563:Cerium