Environmental Molecular Sciences Laboratory

About: Environmental Molecular Sciences Laboratory is a facility organization based out in Richland, Washington, United States. It is known for research contribution in the topics: Mass spectrometry & Ion. The organization has 1471 authors who have published 3010 publications receiving 169961 citations.

Sub-micron Cu/SSZ-13: Synthesis and application as selective catalytic reduction (SCR) catalysts

Abstract: For the first time, sub-micron Cu/SSZ-13, obtained by modifying an existing synthesis procedure, was shown to be an effective and stable catalyst for selective catalytic reduction of NO. Characterization of the materials with X-ray diffraction, N2-physisorption and 27Al MAS NMR shows that hydrothermal aging, which simulates SCR reaction conditions, is more destructive for smaller particles in a sodium form. After Cu exchange, however, the catalytic performance and hydrothermal stability for Cu/SSZ-13 is independent of the particle size. In particular, a clear positive correlation is found between remaining tetrahedral framework Al and isolated Cu-ion concentrations in aged Cu/SSZ-13 catalysts of comparable Al and Cu contents. This indicates that (1) isolated Cu-ion and paired framework Al configurations display remarkable hydrothermal stabilities; and (2) paired-Al contents can be varied via modifying the synthesis procedures, which appear to have a more critical influence on stabilizing isolated Cu-ions during harsh hydrothermal aging than the particle size. This study is of high interest for applications in vehicular DeNOx technologies where high loadings of active species on wash coats can be achieved by using sub-micron Cu/SSZ-13.

A common intermediate for N2 formation in enzymes and zeolites: side-on Cu-nitrosyl complexes.

Abstract: Understanding the mechanisms of catalytic processes requires the identification of reaction centers and key intermediates, both of which are often achieved by the use of spectroscopic characterization tools. Due to the heterogeneity of active centers in heterogeneous catalysts, it is frequently difficult to identify the specific sites that are responsible for the overall activity. Furthermore, the simultaneous presence of a large number of surface species on the catalyst surface often poses a great challenge for the unambiguous determination of the relevant species in the reaction mechanism. In contrast, enzymes possess catalytically active centers with precisely defined coordination environments that are only able to accommodate intermediates relevant to the specific catalytic process. Here we show that side-on Cu+-NO+ complexes characterized by high magnetic field solid state magic angle spinning nuclear magnetic resonance (NMR) and Fourier transform infrared (FTIR) spectroscopies are the key intermediates in the selective catalytic reduction of NO over Cu-SSZ-13 zeolite catalysts. Analogous intermediates have been observed and characterized in nitrite reductase enzymes, and shown to be the critical intermediates in the formation of N2 for anaerobic ammonium oxidation reactions.[1] The identification of this key reaction intermediate, combined with the results of our prior kinetic studies, allows us tomore » propose a new reaction mechanism for the selective catalytic reduction of NO with NH3 under oxygen-rich environments over Cu-SSZ-13 zeolites, a key reaction in automotive emission control. The authors acknowledge the US Department of Energy (DOE), Office of Energy Efficiency and Renewable Energy/Vehicle Technologies Program for the support of this work. The research described in this paper was performed at the Environmental Molecular Sciences Laboratory (EMSL), a national scientific user facility sponsored by the DOE’s Office of Biological and Environmental Research and located at Pacific Northwest National Laboratory (PNNL). PNNL is operated for the US DOE by Battelle Memorial Institute.« less

Understanding and designing field asymmetric waveform ion mobility spectrometry separations in gas mixtures.

Abstract: Field asymmetric waveform ion mobility spectrometry (FAIMS) has significant potential for post-ionization separations in conjunction with MS analyses. FAIMS fractionates ion mixtures by exploiting the fact that ion mobilities in gases depend on the electric field in a manner specific to each ion. Nearly all previous work has used pure gases, for which FAIMS fundamentals are understood reasonably well; however, unexpected phenomena observed in some gas mixtures (e.g., N2/CO2) but not in others (N2/O2) remain unexplained. Here, we introduce and experimentally test a universal model for FAIMS separations in mixtures, derived from formalisms that determine high-field mobilities in heteromolecular gases. Overall, the theoretical findings are consistent with data for N2/CO2 (although quantitative discrepancies remain), while results for N2/O2 fit Blanc's law, in agreement with measurements. Calculations for He/N2 and He/CO2 are also consistent with observations and suggest why adding He to the working gas gener...

Nitrogen-Containing Organic Compounds and Oligomers in Secondary Organic Aerosol Formed by Photooxidation of Isoprene

Abstract: Electrospray ionization high-resolution mass spectrometry (ESI HR-MS) was used to probe molecular structures of oligomers in secondary organic aerosol (SOA) generated in laboratory experiments on isoprene photooxidation at low- and high-NOx conditions. Approximately 80–90% of the observed products are oligomers and up to 33% by number are nitrogen-containing organic compounds (NOC). We observe oligomers with maximum 8 monomer units in length. Tandem mass spectrometry (MSn) confirms NOC compounds are organic nitrates and elucidates plausible chemical building blocks contributing to oligomer formation. Most organic nitrates are comprised of methylglyceric acid units. Other important multifunctional C2–C5 monomer units are identified including methylglyoxal, hydroxyacetone, hydroxyacetic acid, and glycolaldehyde. Although the molar fraction of NOC in the high-NOx SOA is high, the majority of the NOC oligomers contain only one nitrate moiety resulting in a low average N:C ratio of 0.019. Average O:C ratios of...