Molecular and physical composition of tar balls in wildfire smoke: an investigation with complementary ionisation methods and 15-Tesla FT-ICR mass spectrometry

Tar balls (TBs) are a major carbonaceous product of wildfires and other biomass-burning events that often exceed soot or other elemental forms of carbon in number and mass. Being a recalcitrant fraction of organic carbon, TBs are capable of long-range atmospheric transport, and thus, exert influence not only in the vicinity of wildfires but also in remote regions. Here, we characterised ambient atmospheric aerosol samples with varying TB number fractions collected downwind of Pacific Northwest wildfires using a 15-Tesla Fourier transform-ion cyclotron resonance mass spectrometer (15-T FT-ICR MS). Relative to non-TB aerosol, we found 2006 and 851 molecular formulae exclusively in TB-rich aerosol using laser desorption ionisation (LDI) of samples directly from an aerosol-loaded substrate and electrospray ionisation (ESI) of ACN-extracted aerosol, respectively. Elemental composition from LDI/15-T FT-ICR MS revealed TBs to be abundant in molecular species of low volatility and high viscosity, providing molecular detail that was consistent with key climate and air quality-related properties of TBs. Our findings demonstrate that the TB-specific molecular composition obtained from (−)LDI/15-T FT-ICR MS not only complements (−)ESI analyses, but provides a more apt reflection of the physical properties of TBs as well. We provide proof-of-concept evidence for the potential value of using LDI/15-T FT-ICR MS in routine OA analyses, specifically smoke samples rich in refractory OA, and improve the representation of OA in atmospheric and climate modelling studies that aim to fully understand its impact and occurrence

Ion irradiation of Fe-Fe oxide core-shell nanocluster films: Effect of interface on stability of magnetic properties

A cluster deposition method was used to produce films of loosely aggregated nanoclusters (NC) of Fe core-Fe3O4 shell or fully oxidized Fe3O4. Films of these NC on Si(100) or MgO(100)/Fe3O4(100) were irradiated to 10^16 Si2+/cm2 near room temperature using an ion accelerator. Ion irradiation creates structural change in the NC film with corresponding chemical and magnetic changes which depend on the initial oxidation state of the cluster. Films were characterized using magnetometry (hysteresis, first order reversal curves), microscopy (transmission electron, helium ion), and x-ray diffraction. In all cases, the particle sizes increased due to ion irradiation, and when a core of Fe is present, irradiation reduces the oxide shells to lower valent Fe species. These results show that ion irradiated behavior of the nanocluster films depends strongly on the initial nanostructure and chemistry, but in general saturation magnetization decreases slightly.Comment: 25 pages, 4 tables, 6 figure

Formation of zinc oxide films using submicron zinc particle dispersions

The thermal oxidation of submicron metallic Zn particles was studied as a method to form nanostructured ZnO films. The particles used for this work were characterized by electron microscopy, x ray diffraction, and thermal analysis to evaluate the Zn-ZnO core shell structure, surface morphology, and oxidation characteristics. Significant nanostructural changes were observed for films annealed to 400 °C or higher, where nanoflakes, nanoribbons, nanoneedles, and nanorods were formed as a result of stress induced fractures arising in the ZnO outer shell due to differential thermal expansion between the metallic Zn core and the ZnO shell. Mass transport occurs through these defects due to the high vapor pressure for metallic Zn at temperatures above 230 °C, whereupon the Zn vapor rapidly oxidizes in air to form the ZnO nanostructures. The Zn particles were also incorporated into zinc indium oxide precursor solutions to form thin film transistor test structures to evaluate the potential of forming nanostructured field effect sensors using simple solution processing

Energy-Economical Heuristically Based Control of Compass Gait Walking on Stochastically Varying Terrain

Investigation uses simulation to explore the inherent tradeoffs ofcontrolling high-speed and highly robust walking robots while minimizing energy consumption. Using a novel controller which optimizes robustness, energy economy, and speed of a simulated robot on rough terrain, the user can adjust their priorities between these three outcome measures and systematically generate a performance curveassessing the tradeoffs associated with these metrics

Heterogeneous catalysis on atomically dispersed supported metals: CO 2 reduction on multifunctional Pd catalysts

Because of their heterogeneous nature, supported metal catalysts always contain metal centers in a rather broad dispersion range, and the presence of even atomically dispersed metals has been reported on oxide supports. The role of the atomically dispersed metal centers in the overall catalytic performances of these supported metal catalysts, however, has not been addressed to date. In this study, temperature programmed reaction and scanning transmission electron microscopy experiments were applied to show the fundamentally different reactivity patterns exhibited by Pd metal in atomically dispersed and traditional 3D clusters in the demanding reaction of CO2 reduction. The requirement for two different catalyst functionalities in the reduction of CO2 with hydrogen on Pd/Al2O3 and Pd/MWCNT catalysts was also substantiated. The results obtained clearly show that the oxide support material, even when it is considered inert like Al 2O3, can function as a critical, active component of complex catalyst systems.close6

Dislocations in a Ni-based superalloy during low temperature creep

The nature and variety of the dislocations passing through the two-phase γγ′ microstructure of Ni-based superalloys is key to the properties of these materials. The chemistry, size and arrangement of the precipitates greatly affects the nature of these dislocations. We present High Angle Annular Dark Field (HAADF) TEM observations of the structure of dislocations entering, passing through the γ′ precipitates in the single-crystal superalloy CMSX-4®. The creep deformation of the sample was interrupted after 8 hours at 750 °C and 750 MPa, a critical stage just as secondary creep was being established, and shows a range of defects in both phases, not always those predicted by the Schmid factor for the deformation geometry. We show that dislocations lodged in the γγ′ interfaces have a significant effect on the structure of the interface and that they combine to produce stacking faults which cut through the γ′. The implications of these observations for secondary creep deformation are discussed. CMSX-4® is a registered Trade Mark of the Cannon Muskegon Company

Resolving the structural complexity of gamma-Al2O3: the nature of vacancy ordering and the structure of complex antiphase boundaries

The structure of gamma-Al2O3 remains largely undetermined despite decades of research. This is due to the high degree of disorder, which poses significant challenges for structural analysis using conventional crystallographic approaches. Herein, we study the structure of gamma-Al2O3 with Scanning Transmission Electron Microscopy (STEM) and ab-initio calculations to provide a complete structural description. We show that the microstructure can be understood in terms of two key structural features of nanoscale spinel domains and finite thickness segments termed as complex antiphase boundaries (cAPB) that provide the domain interconnectivity. The spinel domains have a distinctive preference for vacancy ordering, which can be rationalized in terms of a structure with a stacking disorder. Tetragonal P41212 or monoclinic P21 models, all based on the identical motif, can be considered as representative ordered forms. Individual spinel domains are interconnected via cAPBs, which adopt a distinct non-spinel bonding environment of gamma-Al2O3. The most common cAPB consists of a single delta motif with thickness of just 0.6 nm on (001), with the resulting displacement a/4 [101]. Remarkably, the cAPBs are shown to energetically stabilize the spinel domains of gamma-Al2O3 explaining their high abundance. We demonstrate how the tetragonal distortions naturally arise in this intricate microstructure and place the proposed model in the context of phase transformations to high temperature transition aluminas

Ultra-Low Amounts of Palladium (0.005-0.05 Wt% Pd) Supported on Titania: Remarkable Low-Temperature Activity for NO Reduction with CO and Structure-Function Property Relationships in Methane Oxidation

Atomically dispersed Pd +2 cations with ultra-dilute loading of palladium (0.005-0.05 wt%) were anchored on anatase titania and characterized with FTIR, microscopy and catalytic tests. CO infrared adsorption produces a sharp, narrow mono-carbonyl Pd(II)-CO band at ~2,130 cm-1 indicating formation of highly uniform and stable Pd+2 ions on anatase titania. The 0.05 wt% Pd/TiO2 sample was evaluated for methane combustion under dry and wet (industrially relevant) conditions in the presence and absence of carbon monoxide. Notably, we find the isolated palladium atoms respond dynamically upon oxygen concentration modulation (switching-on and switching off). When oxygen is removed from the wet methane stream, palladium ions are reduced to metallic state by methane and catalyze methane steam reforming instead of complete methane oxidation. Re-admission of oxygen restores Pd+2 cations and switches off methane steam reforming activity. Moreover, 0.05 wt% Pd/TiO2 is a competent CO oxidation catalyst in the presence of water steam with 90% CO conversion and TOF ~ 4,000 hr-1 at 260 ⁰C. More importantly, we find that diluting 0.05 wt% Pd/titania sample with titania to ultra-low 0.005 wt% palladium loading produces a remarkably active material for nitric oxide reduction with carbon monoxide under industrially relevant conditions with >90% conversion of nitric oxide at 180 ⁰C (~460 ppm NO and 150 L/g*hr flow rate in the presence of >2% water steam) and TOF ~6,000 hr-1. Pd thus outperforms state-of-the-art rhodium containing catalysts with (15-20 times higher rhodium loading; rhodium is ~ 3 times more expensive than palladium). Furthermore, palladium catalysts are more selective towards nitrogen and produce significantly less ammonia relative to the more traditional rhodium catalysts due to lower Pd amount nd lower water-gas-shift activity. Our study is the first example of utilizing ultra-low (0.05 wt% and less) noble metal (Pd) amounts to produce heterogeneous catalysts with extraordinary activity for nitric oxide reduction. This opens up a pathway to study other Pd, Pt and Rh containing materials with ultra-low loadings of expensive noble metals dispersed on titania or titania-coated oxides for industrially relevant nitric oxide abatement.</p

Achieving controllable distribution of metal cations (Pd, Pt, Ni, Cr, Cu) in a zeolite either as [M(II)-OH]/1Al or M(II)/2Al provides novel mechanistic insights for adsorptive and catalytic reactions

Utilizing H-BEA zeolites with similar Si/Al ratios but with different Al site distributions we show that the divalent metal cations (Ni, Pd, Pt, Cr, Cu) can be dispersed predominantly as either M(II)/2Al species (for conventional zeolite prepared in the hydroxide media) or as [M(II)-OH]/1Al species (for H-BEA prepared in HF). M(II) species are active in ethylene dimerization. However, Pd(II)-OH and Ni(II)-OH species, that were not previously prepared or evaluated for this reaction, are even more catalytically active. M(II)-OH species in zeolite can activate ethylene via formation of C2H4--M(II)-OC2H5 species which can eliminate butene restoring M(II)-OH species. We also reveal that Pt(II) and Pt(II)-OH in zeolite, not previously known to catalyze ethylene dimerization on solid materials, are in fact catalytically active. This synthetic realization further exemplifies the different NO adsorption aspects of these materials. Both Pd(II) and Pd(II)-OH are active for NO adsorption, the latter desorbing NO at higher temperature than isolated Pd(II). Notably, Pd(II)-OH is active for Wacker oxidation chemistry of ethylene into acetaldehyde, whereas Pd(II) is less active: this clarifies the missing mechanistic aspects of Wacker oxidation by homogeneous complexes. The presence of OH ligand in the Pd(II) first coordination sphere is important for reactivity. Further, we show that Cr/2Al in H-BEA is inactive for ethylene oligomerization, whereas Cr-OH has ethylene dimerization activity, illuminating a previously unknown possibility that Cr-OH species could be an active species for Cr/silica Phillips ethylene oligomerization catalysts