The interaction of size-selected Ru3 clusters with TiO2: depth-profiling of encapsulated clusters.

Ru is a metal of interest in catalysis. Monodisperse Ru3 clusters as catalytic sites are relevant for the development of catalysts because clusters use significantly lower amounts of precious materials for forming active sites due to the small size of the cluster. However, retaining the mono-dispersity of the cluster size after deposition is a challenge because surface energy could drive both agglomeration and encapsulation of the clusters. In the present work Ru3 clusters are deposited by chemical vapor deposition (CVD) of Ru3(CO)12 and cluster source depositions of bare Ru3 onto radio frequency sputter-deposited TiO2 (RF-TiO2) substrates, TiO2(100), and SiO2. When supported on RF-TiO2, bare Ru3 is encapsulated by a layer of titania substrate material during deposition with a cluster source. Ligated Ru3(CO)12 is also encapsulated by a layer of titania when deposited onto sputter-treated RF-TiO2, but only through heat treatment which is required to remove most of the ligands. The titania overlayer thickness was determined to be 1-2 monolayers for Ru3(CO)12 clusters on RF-TiO2, which is thin enough for catalytic or photocatalytic reactions to potentially occur even without clusters being part of the very outermost layer. The implication for catalysis of the encapsulation of Ru3 into the RF-TiO2 is discussed. Temperature-dependent X-ray photoelectron spectroscopy (XPS), angle-resolved XPS, and temperature-dependent low energy ion scattering (TD-LEIS) are used to probe how the cluster-surface interaction changes due to heat treatment and scanning transmission electron microscopy (STEM) was used to image the depth of the surface from side-on.

Electrocatalytic Hydrogen Evolution at Full Atomic Utilization over ITO-Supported Sub-nano-Ptn Clusters: High, Size-Dependent Activity Controlled by Fluxional Pt Hydride Species.

A combination of density functional theory (DFT) and experiments with atomically size-selected Ptn clusters deposited on indium-tin oxide (ITO) electrodes was used to examine the effects of applied potential and Ptn size on the electrocatalytic activity of Ptn (n = 1, 4, 7, and 8) for the hydrogen evolution reaction (HER). Activity is found to be negligible for isolated Pt atoms on ITO, increasing rapidly with Ptn size such that Pt7/ITO and Pt8/ITO have roughly double the activity per Pt atom compared to atoms in the surface layer of polycrystalline Pt. Both the DFT and experiment find that hydrogen under-potential deposition (Hupd) results in Ptn/ITO (n = 4, 7, and 8) adsorbing ∼2H atoms/Pt atom at the HER threshold potential, equal to ca. double the Hupd observed for Pt bulk or nanoparticles. The cluster catalysts under electrocatalytic conditions are hence best described as a Pt hydride compound, significantly departing from a metallic Pt cluster. The exception is Pt1/ITO, where H adsorption at the HER threshold potential is energetically unfavorable. The theory combines global optimization with grand canonical approaches for the influence of potential, uncovering the fact that several metastable structures contribute to the HER, changing with the applied potential. It is hence critical to include reactions of the ensemble of energetically accessible PtnHx/ITO structures to correctly predict the activity vs Ptn size and applied potential. For the small clusters, spillover of Hads from the clusters to the ITO support is significant, resulting in a competing channel for loss of Hads, particularly at slow potential scan rates.

Growth and passivation of individual carbon nanoparticles by C2H2 addition at high temperatures: Dependence of growth rate and evolution on material and size.

Absolute kinetics for reactions of C2H2 with a series of ∼60 individual carbon nanoparticles (NPs) from graphite, graphene, graphene oxide, carbon black, diamond, and nano-onion feedstocks were measured for temperatures (TNP) ranging from 1200 to 1700 K. All the NPs were observed to gain mass by carbon addition under conditions that varied with feedstock but with large variations in initial growth rate. Long reaction periods were studied to allow the evolution of growth rates over time to be observed. Diamond NPs were found to passivate against C2H2 addition if heated above ∼1400 K, and the highly variable initial reactivity for carbon nano-onions was found to depend on the presence of non-onion-structure surface carbon. For graphitic and carbon black NPs, three distinct growth modes were observed, correlated with the initial NP mass (Minitial). Smallest graphitic and carbon black NPs, with masses <∼25 MDa, initially grew rapidly but also passivated quickly after adding <4% of Minitial. NPs in the 20-50 MDa range also passivated but only after multiple waves of fast growth separated by periods of low reactivity, with up to ∼11% total mass gain before passivation. The largest carbon black and graphitic NPs, with Minitial >50 MDa, grew rapidly and continuously, adding up to ∼300% of Minitial with no sign of rate slowing as long as C2H2 was present. The efficiencies for C2H2 addition and etching by O2 are strongly correlated, but the correlation changes as the NPs passivate. Growth and passivation mechanisms are discussed.

Hydrogen Evolution on Electrode-Supported Ptn Clusters: Ensemble of Hydride States Governs the Size Dependent Reactivity.

We report the size-dependent activity and stability of supported Pt1,4,7,8 for electrocatalytic hydrogen evolution reaction, and show that clusters outperform polycrystalline Pt in activity, with size-dependent stability. To understand the size effects, we use DFT calculations to study the structural fluxionality under varying potentials. We show that the clusters can reshape under H coverage and populate an ensemble of states with diverse stoichiometry, structure, and thus reactivity. Both experiment and theory suggest that electrocatalytic species are hydridic states of the clusters (≈2 H/Pt). An ensemble-based kinetic model reproduces the experimental activity trend and reveals the role of metastable states. The stability trend is rationalized by chemical bonding analysis. Our joint study demonstrates the potential- and adsorbate-coverage-dependent fluxionality of subnano clusters of different sizes and offers a systematic modeling strategy to tackle the complexities.

High-Temperature Oxidation of Single Carbon Nanoparticles: Dependence on the Surface Structure and Probing Real-Time Structural Evolution via Kinetics.

O2 oxidation and sublimation kinetics for >30 individual nanoparticles (NPs) of five different feedstocks (graphite, graphene oxide, carbon black, diamond, and nano-onion) were measured using single-NP mass spectrometry at temperatures (TNP) in the 1100-2900 K range. It was found that oxidation, studied in the 1200-1600 K range, is highly sensitive to the NP surface structure, with etching efficiencies (EEO2) varying by up to 4 orders of magnitude, whereas sublimation rates, significant only for TNP ≥ ∼1700 K, varied by only a factor of ∼3. Its sensitivity to the NP surface structure makes O2 etching a good real-time structure probe, which was used to follow the evolution of the NP surface structures over time as they were either etched or annealed at high TNP. All types of carbon NPs were found to have initial EEO2 values in the range near 10-3 Da/O2 collision, and all eventually evolved to become essentially inert to O2 (EEO2 < 10-6 Da/O2 collision); however, the dependence of EEO2 on time and mass loss was very different for NPs from different feedstocks. For example, diamond NPs evolved rapidly and monotonically toward inertness, and evolution occurred in both oxidizing and inert atmospheres. In contrast, graphite NPs evolved only under oxidizing conditions and were etched with complex time dependence, with multiple waves of fast but non-monotonic etching separated by periods of near-inertness. Possible mechanisms to account for the complex etching behavior are proposed.

Sublimation Kinetics for Individual Graphite and Graphene Nanoparticles (NPs): NP-to-NP Variations and Evolving Structure-Kinetics and Structure-Emissivity Relationships.

A single nanoparticle (NP) mass spectrometry method was used to measure sublimation rates as a function of nanoparticle temperature (TNP) for sets of individual graphite and graphene NPs. Initially, the NP sublimation rates were ∼400 times faster than those for bulk graphite, and there were large NP-to-NP variations. Over time, the rates slowed substantially, though they remained well above the bulk rate. The initial activation energies (Ea values) were correspondingly low and doubled, as a few monolayers worth of material was sublimed from the surfaces. The high initial rates and low Ea values are attributed to large numbers of edge, defect, and other low coordination sites on the NP surfaces, and the changes are attributed to atomic-scale "smoothing" of the surface by preferential sublimation of the less stable sites. The emissivity of the NPs also changed after heating, more frequently increasing. The emissivity and sublimation rates were anticorrelated, leading to the conclusion that high densities of low-coordination sites on the NP surfaces enhance sublimation but suppress emissivity.

Sn-modification of Pt7/alumina model catalysts: Suppression of carbon deposition and enhanced thermal stability.

An atomic layer deposition process is used to modify size-selected Pt7/alumina model catalysts by Sn addition, both before and after Pt7 cluster deposition. Surface science methods are used to probe the effects of Sn-modification on the electronic properties, reactivity, and morphology of the clusters. Sn addition, either before or after cluster deposition, is found to strongly affect the binding properties of a model alkene, ethylene, changing the number and type of binding sites, and suppressing decomposition leading to carbon deposition and poisoning of the catalyst. Density functional theory on a model system, Pt4Sn3/alumina, shows that the Sn and Pt atoms are mixed, forming alloy clusters with substantial electron transfer from Sn to Pt. The presence of Sn also makes all the thermally accessible structures closed shell, such that ethylene binds only by π-bonding to a single Pt atom. The Sn-modified catalysts are quite stable in repeated ethylene temperature programmed reaction experiments, suggesting that the presence of Sn also reduces the tendency of the sub-nano-clusters to undergo thermal sintering.

Oxidation of a Levitated Droplet of 1-Allyl-3-methylimidazolium Dicyanamide by Nitrogen Dioxide.

Understanding the reaction mechanisms of ionic liquids and their oxidizers is necessary to develop the next generation of hypergolic, ionic-liquid-based fuels. We studied reactions between a levitated droplet of 1-allyl-3-methylimidazolium dicyanamide ([AMIM][DCA]), with and without hydrogen-capped boron nanoparticles, and nitrogen dioxide (NO2). The reactions were monitored with Fourier-transform infrared (FTIR) and Raman spectroscopy. The emergence of new structures in the FTIR and Raman spectra is consistent with the formation of functional groups including organic nitrites (RONO), nitroamines (R1R2NNO2), and carbonitrates (R1R2C=NO2-). Possible reaction mechanisms based on these new functional groups are discussed. The reaction rates were deduced at various temperatures by heating the levitated droplets with a carbon dioxide laser. We thereby determined an overall activation energy of 38.5 ± 2.3 kJ mol-1 for the oxidation of [AMIM][DCA] for the first time.

Thermal emission spectroscopy for single nanoparticle temperature measurement: optical system design and calibration.

We discuss the design of an optical system that allows measurement of 600-1650 nm emission spectra for individual nanoparticles (NPs), laser-heated in an electrodynamic trap in controlled atmospheres. An approach to calibration of absolute intensity versus wavelength for very low emission intensities is discussed, and examples of NP graphite and carbon black spectra are used to illustrate the methodology.

Spectroscopic Study on the Intermediates and Reaction Rates in the Oxidation of Levitated Droplets of Energetic Ionic Liquids by Nitrogen Dioxide.

To optimize the performance of hypergolic, ionic-liquid-based fuels, it is critical to understand the fundamental reaction mechanisms of ionic liquids (ILs) with the oxidizers. We consequently explored the reactions between a single levitated droplet of 1-butyl-3-methylimidazolium dicyanamide ([BMIM][DCA]), with and without hydrogen-capped boron nanoparticles, and the oxidizer nitrogen dioxide (NO2). The apparatus consists of an ultrasonic levitator enclosed within a pressure-compatible process chamber interfaced to complementary Fourier-transform infrared (FTIR), Raman, and ultraviolet-visible spectroscopic probes. First, the vibrational modes for the Raman and FTIR spectra of unreacted [BMIM][DCA] are assigned. We subsequently investigated the new structure in the infrared and Raman spectra produced by the reaction of the IL with the oxidizer. The newly produced peaks are consistent with the formation of the functional groups of organic nitro-compounds including the organic nitrites (RONO), nitroamines (RR'NNO2), aromatic nitro-compounds (ArNO2), and carbonitrates (RR'C═NO2-), which suggests that the nitrogen or oxygen atom of the nitrogen dioxide reactant bonds to a carbon or nitrogen atom of [BMIM][DCA]. Comparison of the rate constants for the oxidation of pure and boron-doped [BMIM][DCA] at 300 K shows that the boron-doping reduces the reaction rate by a factor of approximately 2. These results are compared to the oxidation processes of 1-methyl-4-amino-1,2,4-triazolium dicyanamide ([MAT][DCA]) with nitrogen dioxide (NO2) studied previously in our laboratory revealing that [BMIM][DCA] oxidizes faster than [MAT][DCA] by a factor of about 20. The present measurements are the first studies on the reaction rates for the oxidation of levitated ionic-liquid droplets.

Boron Switch for Selectivity of Catalytic Dehydrogenation on Size-Selected Pt Clusters on Al2O3.

Size-selected supported clusters of transition metals can be remarkable and highly tunable catalysts. A particular example is Pt clusters deposited on alumina, which have been shown to dehydrogenate hydrocarbons in a size-specific manner. Pt7, of the three sizes studied, is the most active and, therefore, like many other catalysts, deactivates by coking during reactions in hydrocarbon-rich environments. Using a combination of experiment and theory, we show that nanoalloying Pt7 with boron modifies the alkene-binding affinity to reduce coking. From a fundamental perspective, the comparison of experimental and theoretical results shows the importance of considering not simply the most stable cluster isomer, but rather the ensemble of accessible structures as it changes in response to temperature and reagent coverage.

Electrocatalysis by Mass-Selected Ptn Clusters.

Mass-selected Ptn+ ion deposition in ultrahigh vacuum (UHV) was used to prepare a series of size-selected electrodes with Ptn (n ≤ 14) clusters supported on either glassy carbon (GC) or indium tin oxide (ITO). After characterization of the physical properties of the electrodes in UHV, an in situ method was used to study electrocatalytic activity for the oxygen reduction and ethanol oxidation reactions, without significant air exposure. For each reaction studied, there are similarities between the catalytic properties of Ptn-containing electrodes and those of nanoparticulate or bulk Pt electrodes, but there are also important differences that provide mechanistic insights. For all systems, strong cluster size effects were observed. For comparison, select experiments were done under identical conditions but with the Ptn electrodes exposed to air prior to electrochemical studies, resulting in strong modification/suppression of catalytic activity due to adventitious contaminants. For ethanol oxidation at Ptn/ITO, activity varies with size nonmonotonically, by more than an order of magnitude. The sharp size dependence persists during at least 30 to 40 cycles through the Pt redox potential, indicating that processes that would tend to broaden the size distribution are not efficient. All but the least active sizes are substantially more active per mass of Pt, than Pt nanoparticles under the same conditions. The oscillatory dependence of activity on size is anticorrelated with the binding energy of the Pt 4d core level, demonstrating that activity is controlled by the electronic structure of the supported clusters. For oxygen reduction at Ptn/ITO, the branching between water and hydrogen peroxide production is strongly dependent on cluster size, with small clusters selectively producing peroxide with high activity. The selectivity appears to be related to the size of the active site, with no obvious correlation to Pt electronic properties. The most unusual effect seen was for Ptn/GC, studied under acid conditions appropriate to oxygen reduction. Pt7 and a few other cluster sizes show "normal" oxygen reduction activity, similar to what is measured for Pt nanoparticles on GC under the same conditions. Many of the small clusters, however, are found to catalyze highly efficient oxidation, by water, of the glassy carbon support, with essentially no overpotential. The high activity for carbon oxidation for many Ptn/GC electrodes and the absence of significant carbon oxidation for a GC electrode with Pt nanoparticles raise the question of whether small Pt clusters may be responsible for much of the corrosion observed in Pt/carbon electrodes. This system provides another example where activity for oxidation catalysis is anticorrelated with the Pt core level binding energies, indicating that it is electronic, rather than geometric, structure that limits activity.

Size-dependent electronic structure controls activity for ethanol electro-oxidation at Ptn/indium tin oxide (n = 1 to 14).

Understanding the factors that control electrochemical catalysis is essential to improving performance. We report a study of electrocatalytic ethanol oxidation - a process important for direct ethanol fuel cells - over size-selected Pt centers ranging from single atoms to Pt14. Model electrodes were prepared by soft-landing of mass-selected Ptn(+) on indium tin oxide (ITO) supports in ultrahigh vacuum, and transferred to an in situ electrochemical cell without exposure to air. Each electrode had identical Pt coverage, and differed only in the size of Pt clusters deposited. The small Ptn have activities that vary strongly, and non-monotonically with deposited size. Activity per gram Pt ranges up to ten times higher than that of 5 to 10 nm Pt particles dispersed on ITO. Activity is anti-correlated with the Pt 4d core orbital binding energy, indicating that electron rich clusters are essential for high activity.

Single Nanoparticle Mass Spectrometry as a High Temperature Kinetics Tool: Sublimation, Oxidation, and Emission Spectra of Hot Carbon Nanoparticles.

In single nanoparticle mass spectrometry, individual charged nanoparticles (NPs) are trapped in a quadrupole ion trap and detected optically, allowing their mass, charge, and optical properties to be monitored continuously. Previous experiments of this type probed NPs that were either fluorescent or large enough to detect by light scattering. Alternatively, small NPs can be heated to temperatures where thermally excited emission is strong enough to allow detection, and this approach should provide a new tool for measurements of sublimation and surface reaction kinetics of materials at high temperatures. As an initial test, we report a study of carbon NPs in the 20-50 nm range, heated by 10.6 µm, 532 nm, or 445 nm lasers. The kinetics for sublimation and oxidation of individual carbon NPs were studied, and a model is presented for the factors that control the NP temperature, including laser heating, and cooling by sublimation, buffer gas collisions, and radiation. The estimated NP temperatures were in the 1700-2000 K range, and the NP absorption cross sections ranged from ∼0.8 to 0.2% of the geometric cross sections for 532 nm and 10.6 µm excitation, respectively. Emission spectra of single NPs and small NP ensembles show a feature in the IR that appears to be the high energy tail of the thermal (blackbody-like) emission expected from hot particles but also a discrete feature peaking around 750 nm. Both the IR tail and 750 nm peak are observed for all particles and for both IR and visible laser excitation. No significant difference was observed between graphite and amorphous carbon NPs.

Oxygen activation and CO oxidation over size-selected Pt(n)/alumina/Re(0001) model catalysts: correlations with valence electronic structure, physical structure, and binding sites.

Oxidation of CO over size-selected Ptn clusters (n = 1, 2, 4, 7, 10, 14, 18) supported on alumina thin films grown on Re(0001) was studied using temperature-programmed reaction/desorption (TPR/TPD), X-ray and ultraviolet photoelectron spectroscopy (XPS/UPS), and low energy ion scattering spectroscopy (ISS). The activity of the model catalysts was found to vary by a factor of five with deposited Ptn size during the first reaction cycle (TPR) and by a factor of two during subsequent cycles, with Pt2 being the least active and Pt14 the most active. The limiting step in the reaction appears to be the binding of oxygen; however, this does not appear to be an activated process as reaction is equally efficient for 300 K and 180 K oxidation temperatures. Size-dependent shifts in the valence band onset energy correlate strongly with CO oxidation activity, and there is also an apparent correlation with the availability of a particular binding site, as probed by CO TPD. The morphology of the clusters also becomes more three dimensional over the same size range, but with a distinctly different size-dependence. The results suggest that both electronic structure and the availability of particular binding sites control activity.

Effects of translational and vibrational excitation on the reaction of HOD+ with C2H2 and C2D2: mode- and bond-specific effects in exoergic proton transfer.

Reactions of mode-selectively excited HOD(+) with C2H2 and C2D2 were studied over the center-of-mass collision energy (Ecol) range from 0.15 to 2.9 eV. HOD(+) was prepared in each of its fundamental vibrational states: ground state (000), bend (010), OD stretch (100), and the OH stretch (001). Charge transfer is the dominant reaction at all energies, although it is inhibited by increasing Ecol, and is accompanied by hydrogen exchange. The total charge transfer cross section is similar for C2H2 and C2D2, however, the tendency toward charge transfer with hydrogen exchange (CTHE) is significantly greater for C2D2 compared to C2H2. Charge transfer shows no significant effects of HOD(+) vibrational excitation, however, CTHE is significantly enhanced by vibration at Ecol < 0.62 eV. Both H(+) and D(+) transfer reactions (HT, and DT, respectively) are observed for both C2H2 and C2D2, with little dependence on collision energy, but with mode- and bond-specific enhancements from excitation of the OH and OD stretches. Recoil velocity measurements show that all channels are direct, except perhaps at the lowest collision energies. Mode-specific effects on the recoil velocity distributions are also observed, revealing how vibrational excitation affects reaction at different collision impact parameters.

Strong effects of cluster size and air exposure on oxygen reduction and carbon oxidation electrocatalysis by size-selected Pt(n) (n ≤ 11) on glassy carbon electrodes.

Model Pt(n)/glassy carbon electrodes (Pt(n)/GCE) were prepared by deposition of mass-selected Pt(n)(+) (n ≤ 11) on GCE substrates in ultrahigh vacuum. Electrocatalysis under conditions appropriate for the oxygen reduction reaction (ORR) was studied, for samples both in situ with no exposure to laboratory air and with air exposure prior to electrochemical measurements. Of the small clusters, only a few cluster sizes show the expected ORR activity, and in those cases, the activity per Pt atom is similar to that seen under identical conditions with a conventionally prepared electrode with Pt nanoparticles grown on a GCE. For other small Pt(n) on GCE, any ORR signal is overwhelmed by large oxidative currents attributed to catalysis of carbon oxidation by water. If the samples are exposed to air prior to electrochemistry, both ORR and carbon oxidation signals are absent, and instead only small capacitive currents or currents attributed to redox chemistry of adventitious organic adsorbates are observed, indicating that air exposure results in passivation of the small Pt clusters.

Effects of collisional and vibrational velocity on proton and deuteron transfer in the reaction of HOD+ with CO.

Reaction of HOD(+) with CO was studied over the collision energy (E(col)) range between 0.18 and 2.87 eV, for HOD(+) in its ground state and with one quantum in each of its vibrational modes: (001)--predominantly OH stretch; (010)--bend, and (100)--predominately OD stretch. In addition to integral cross sections, product recoil velocity distributions were also measured for each initial condition. The dominant reactions are near-thermoneutral proton and deuteron transfer, generating HCO(+) and DCO(+) product ions by a predominantly direct mechanism. The HCO(+) and DCO(+) channels occur with a combined efficiency of 76% for ground state HOD(+) at our lowest E(col), increasing to 94% for E(col) around 0.33 eV, then falling at high E(col) to ~40%. The HCO(+) and DCO(+) channels have a complicated dependence on the HOD(+) vibrational state. Excitation of the OH or OD stretch modes enhances H(+) or D(+) transfer, respectively, and inhibits D(+) or H(+) transfer. Bend excitation preferentially enhances H(+) transfer, with no effect on D(+) transfer. There is no coupling of energy initially in any HOD(+) vibrational mode to recoil velocity of either of the product ions, even at low E(col) where vibrational excitation doubles or triples the energy available to products. The results suggest that transfer of H or D atoms is enhanced if the atom in question has a high vibrational velocity, and that this effect offsets what is otherwise a general inhibition of reactivity by added energy. HOCO(+) + D and DOCO(+) + H products are also observed, but as minor channels despite being barrierless and exoergic. These channels appear to be complex mediated at low E(col), essentially vanish at intermediate E(col), then reappear with a direct reaction mechanism at high E(col).

Vibrationally enhanced charge transfer and mode/bond-specific H+ and D+ transfer in the reaction of HOD+ with N2O.

The reaction of HOD(+) with N2O was studied over the collision energy (E(col)) range from 0.20 eV to 2.88 eV, for HOD(+) in its ground state and in each of its fundamental vibrational states: bend (010), OD stretch (100), and OH stretch (001). The dominant reaction at low E(col) is H(+) and D(+) transfer, but charge transfer becomes dominant for E(col) > 0.5 eV. Increasing E(col) enhances charge transfer only in the threshold region (E(col) < 1 eV), but all modes of HOD(+) vibrational excitation enhance this channel over the entire energy range, by up to a factor of three. For reaction of ground state HOD(+), the H(+) and D(+) transfer channels have similar cross sections, enhanced by increasing collision energy for E(col) < 0.3 eV, but suppressed by E(col) at higher energies. OD stretch excitation enhances D(+) transfer by over a factor of 2, but has little effect on H(+) transfer, except at low E(col) where a modest enhancement is observed. Excitation of the OH stretch enhances H(+) transfer by up to a factor of 2.5, but actually suppresses D(+) transfer over most of the E(col) range. Excitation of the bend mode results in ~60% enhancement of both H(+) and D(+) transfer at low E(col) but has little effect at higher energies. Recoil velocity distributions at high E(col) are strongly backscattered in the center-of-mass frame, indicating direct reaction dominated by large impact parameter collisions. At low E(col) the distributions are compatible with mediation by a short-lived collision complex. Ab initio calculations find several complexes that may be important in this context, and RRKM calculations predict lifetimes and decay branching that is consistent with observations. The recoil velocity distributions show that HOD(+) vibrational excitation enhances reactivity in all collisions at low E(col), while for high E(col) with enhancement comes entirely from the subset of collisions that generate strongly back-scattered product ions.

Tuning azolium azolate ionic liquids to promote surface interactions with titanium nanoparticles leading to increased passivation and colloidal stability.

The passivation and stability of suspensions of titanium nanoparticles in azolium azolate ionic liquids can be tuned by introducing metal specific binding sites in the azolate anion.