Laminar Flow Tube Reactor Research Articles

Dehydrogenation of diborane on small Nbn+ clusters.

The reactivity of Nbn+ (1 ≤ n ≤ 21) clusters with B2H6 is studied by using a self-developed multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). The Nbn+ clusters were generated by a magnetron sputtering source and reacted with the B2H6 gas under fully thermalized conditions in the downstream flow tube where the reaction time was accurately controlled and adjustable. The complete and partial dehydrogenation products NbnB1-4+ and NbnB1-4H1,2,4+ were detected, indicative of the removal of H2 and likely BHx moieties. Interestingly, these NbnB1-4+ and NbnB1-4H1,2,4+ products are limited to 3 ≤ n ≤ 6, suggesting that the small Nbn+ clusters are relatively more reactive than the larger Nbn>6+ clusters under the same conditions. By varying the B2H6 gas concentrations and the reactant doses introduced into the flow tube, and by changing the reaction time, we performed a detailed analysis of the reaction dynamics in combination with the DFT-calculated thermodynamics. It is demonstrated that the lack of cooperative active sites on the Nb1+ cations accounts for the weakened dehydrogenation efficiency. Nb2+ forms partial dehydrogenation products at a faster rate. In contrast, the Nbn>6+ clusters are subject to more flexible vibrational relaxation which disperse the energy gain of B2H6-adsorption and thus are unable to overcome the energy barriers for subsequent hydrogen atom transfer and H2 release.

Weak Interactions Initiate C-H and C-C Bond Dissociation of Ethane on Nbn + Clusters.

The conversion of ethane into value-added chemicals under ambient conditions has attracted much attention but the mechanisms remain not fully understood. Here we report a study on the reaction of ethane with thermalized Nbn + clusters based on a multiple-ion laminar flow tube reactor combined with a triple quadrupole mass spectrometer (MIFT-TQMS). It is found that ethane reacts with Nbn + clusters to form both products of dehydrogenation and methane-removal (odd-carbon products). Combined with density functional theory (DFT) calculations, we studied the reaction mechanisms of the C-C bond activation and C-H bond cleavage on the Nbn + clusters. It is unveiled that hydrogen atom transfer (HAT) initiates the reaction process, giving rise to the formation of Nb-C bonds and an elongated C-C distance in the HNbn + CH2 CH3 motif. Subsequent reactions allow for C-C bond activation and a competitive HAT process which is associated with CH4 removal or H2 release, resulting in the production of the observed carbides.

An integrated instrument of a tandem quadrupole mass spectrometer for cluster reaction and soft-landing deposition.

We have developed an integrated instrument system of a multiple-ion laminar flow tube (MIFT) reactor combined with a tandem quadrupole mass spectrometer (TQMS) and soft-landing deposition (SD) apparatus. A customized water-cooling magnetron sputtering (MagS) source is designed, by which we are able to attain a highly efficient preparation of metal clusters of 1-30 atoms with tunable size distributions. Following the MagS source, a laminar flow tube reactor is designed, allowing for sufficient gas-collision reactions of the as-prepared metal clusters, which is advantageous for probing magic clusters and minimizing wall effects when probing the reaction dynamics of such clusters. The customized TQMS analyzer involves a conical octupole, two linear octupoles, a quadruple ion deflector, and a 19mm quadruple mass analyzer, allowing to decrease the pressure stepwise (from ∼5 to ∼10-9 Torr), thus ensuring high sensitivity and high resolution of the mass spectrometry analysis. In addition, we have designed a dual SDapparatus for the mass-selected deposition of clusters and their reaction products. For the whole system, abbreviated as MagS-MIFT-TQMS-SD, we have performed a detailed ions-fly simulation and quantitatively estimated the ions transfer efficiency under vacuum conditions determined by real experiments. Taking these advantages, well-resolved Pbn +, Agn +, and Nbn + clusters have been produced, allowing for meticulous studies of cluster reactions under sufficient gas-phase collisions free of electric field trapping. Also, we have tested the efficiency of the dual SD.

What Determines the Drastic Reactivity of Nbn+ Clusters with Nitric Oxide under Thermalized Conditions?

We report an in-depth study of the adsorption and reaction of NO with cationic Nbn+ (n = 1-20) clusters under thermalized conditions in a laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer (FT-TQMS). It is found that the small-sized Nbn+ clusters (2 ≤ n ≤ 7) readily react with NO giving rise to dominant fragmentation products pertaining to the loss of a stable diatomic molecule NbO or NbN. In contrast, the reaction products of larger-sized clusters (n ≥ 10) proceed through diverse channels, including NO adsorption, N2/N2O release, and even NO2 formation. These experimental observations provided the incentive for us to dig deep into the reaction mechanism with the help of DFT calculations. In contrast to the NO-donation coordination in transition metal complexes, here the cationic Nbn+ clusters exhibit dominant electronic donation in initiating the reactions with NO molecules. We fully demonstrated the reaction rate constants, compared the reaction energy diagram of typical Nbn+ clusters, and unveiled the distinct interaction mechanism of niobium clusters available for NO activation and conversion.

A comparative study on the reactivity of cationic niobium clusters with nitrogen and oxygen

We have prepared well-resolved Nbn+ (n = 1–10) clusters and report here an in-depth study on the essentially different reactivity with N2 and O2, by utilizing a multiple-ion laminar flow tube reactor in tandem with a customized triple quadrupole mass spectrometer (MIFT-TQMS). As results, the Nbn+ clusters are found to readily react with N2 and form adsorption products NbnN2m+; in contrast, the reactions with O2 give rise to NbnO1−4+products, and the odd-oxygen products indicate O-O bond dissociation, as well as increased mass abundance of NbO+ pertaining to oxygen-etching reactions. We illustrate how N2 prefers a physical adsorption on Nbn+clusters with an end-on orientation for all the products, and allow for size-selective Nbn+clusters to act as electron donor or acceptor in forming NbnN2m+. In contrast to these nitrides, the dioxides NbnO2+display much larger binding energies, with O2 always as an electron acceptor, corresponding to superoxide or peroxide states in the initial reactions. Density-of-states and orbital analyses show that the interactions between Nbn+ and O2 are dominated by strong π-backdonation indicative of incidental electron transfer; whereas weak π-backdonation and simultaneous σ donation interactions exist in NbnN2+. Further, reaction dynamics analysis illustrates the different interactions for N2 and O2 in approaching the Nbn+ clusters, showing the energy diagrams for N2 adsorption and O-O bond dissociation in producing odd-oxygen products. Fragment analyses with orbital correlation and donor-acceptor charge transfer are also performed, giving rise to full insights into the reactivities and interactions of such transition metal clusters with typical diatomic molecules.

Iodization Threshold in Size-Dependent Reactions of Lead Clusters Pbn+ with Iodomethane.

Utilizing a magnetron-sputtering (MagS) source in tandem with a multiple-ion laminar flow tube (MIFT) reactor and a customized triple quadrupole mass spectrometer (TQMS), we have prepared clean Pbn+ (n = 1-13) clusters and measured their reactivity with iodomethane under high carrier gas pressures. Strong size dependences are found for the reactivity of these cationic Pbn+ clusters with CH3I. For the Pbn+ with n ≤ 4, iodinated clusters PbnI+ were found to be the dominant products, in strong contrast to n > 4 where no such products were seen. Quantum chemical studies show that with an increasing number of Pb atoms, the Pb-Pb interatomic interactions become stronger compared with the Pb-I bonding in PbnI+ clusters. Furthermore, the reactions of Pb1-4+ with CH3I have fairly small transition state energy barriers, in contrast to those for Pbn>4+ clusters which have magnitudes that will prevent reactions under the ambient conditions.

Cluster-π Interactions Cause Size-Selective Reactivity of Cationic Silver Clusters with Acetylene: The Distinctive Ag7+[C2H2

Utilizing a customized multiple-ion laminar flow tube reactor in tandem with a triple quadrupole mass spectrometer, we report a study of the gas-phase reactivity of Agn+ clusters with acetylene. Well-resolved Agn+ clusters (n = 1-20) are produced by a self-designed magnetron sputtering source (MagS); however, on their reactions with acetylene under sufficient collisional conditions, only Ag7+[C2H2] is produced with a reasonable intensity. DFT calculations reveal that Agn+ clusters do not form strong Ag-C bonds with C2H2 and Ag7+[C2H2] bears larger binding energy than the other Agn+[C2H2] although within similar cluster-π interactions. Besides gas-phase reaction rate estimation, the relatively large noncovalent cluster-π interaction in Ag7+[C2H2] is fully demonstrated via topological analysis and natural bonding orbital analysis. Also, we illustrate both thermodynamically and kinetically favored channels in producing the Ag7+[C2H2]. This study helps in understanding metal-involved noncovalent bonds and how such weak interactions are able to tune the material function and biological activity.

The Caltech Photooxidation Flow Tube reactor: design, fluid dynamics and characterization

Abstract. Flow tube reactors are widely employed to study gas-phase atmospheric chemistry and secondary organic aerosol (SOA) formation. The development of a new laminar-flow tube reactor, the Caltech Photooxidation Flow Tube (CPOT), intended for the study of gas-phase atmospheric chemistry and SOA formation, is reported here. The present work addresses the reactor design based on fluid dynamical characterization and the fundamental behavior of vapor molecules and particles in the reactor. The design of the inlet to the reactor, based on computational fluid dynamics (CFD) simulations, comprises a static mixer and a conical diffuser to facilitate development of a characteristic laminar flow profile. To assess the extent to which the actual performance adheres to the theoretical CFD model, residence time distribution (RTD) experiments are reported with vapor molecules (O3) and submicrometer ammonium sulfate particles. As confirmed by the CFD prediction, the presence of a slight deviation from strictly isothermal conditions leads to secondary flows in the reactor that produce deviations from the ideal parabolic laminar flow. The characterization experiments, in conjunction with theory, provide a basis for interpretation of atmospheric chemistry and SOA studies to follow. A 1-D photochemical model within an axially dispersed plug flow reactor (AD-PFR) framework is formulated to evaluate the oxidation level in the reactor. The simulation indicates that the OH concentration is uniform along the reactor, and an OH exposure (OHexp) ranging from ∼ 109 to ∼ 1012 molecules cm−3 s can be achieved from photolysis of H2O2. A method to calculate OHexp with a consideration for the axial dispersion in the present photochemical system is developed.

Heterogeneous Reactions of Limonene on Mineral Dust: Impacts of Adsorbed Water and Nitric Acid.

Biogenic volatile organic compounds (BVOCs), including the monoterpene limonene, are a major source of secondary organic aerosol (SOA). While gas-phase oxidation initiates the dominant pathway for BVOC conversion to SOA, recent studies have demonstrated that biogenic hydrocarbons can also directly react with acidic droplets. To investigate whether mineral dust may facilitate similar reactive uptake of biogenic hydrocarbons, we studied the heterogeneous reaction of limonene with mineral substrates using condensed-phase infrared spectroscopy and identified the formation of irreversibly adsorbed organic products. For kaolinite, Arizona Test Dust, and silica at 30% relative humidity, GC-MS identified limonene-1,2-diol as the dominant product with total organic surface concentrations on the order of (3-5) × 1018 molecules m-2. Experiments with 18O-labeled water support a mechanism initiated by oxidation of limonene by surface redox sites forming limonene oxide followed by water addition to the epoxide to form limonenediol. Limonene uptake on α-alumina, γ-alumina, and montmorillonite formed additional products in high yield, including carveol, carvone, limonene oxide, and α-terpineol. To model tropospheric processing of mineral aerosol, we also exposed each mineral substrate to gaseous nitric acid prior to limonene uptake and identified similar surface adsorbed products that were formed at rates 2 to 5 times faster than without nitrate coatings. The initial rate of reaction was linearly dependent on gaseous limonene concentration between 5 × 1012 and 5 × 1014 molecules cm-3 (0.22-20.5 ppm) consistent with an Eley-Rideal-type mechanism in which gaseous limonene reacts directly with reactive surface sites. Increasing relative humidity decreased the amount of surface adsorbed products indicating competitive adsorption of surface adsorbed water. Using a laminar flow tube reactor we measured the uptake coefficient for limonene on kaolinite at 25% RH to range from γ = 5.1 × 10-6 to 9.7 × 10-7. After adjusting for reactive surface areas, we estimate uptake coefficients for limonene on HNO3-processed mineral aerosol on the order of (1-6) × 10-6. Although this heterogeneous reaction will not impact the atmospheric lifetime of gaseous limonene, it does provide a new pathway for mineral aerosol to acquire secondary organic matter from biogenic hydrocarbons, which in turn will alter the physical properties of mineral dust.

An investigation into the conversion of specific carbon atoms in oleic acid and methyl oleate to particulate matter in a diesel engine and tube reactor

The paper is concerned with particulate formation from the fuels oleic acid and methyl oleate. In particular the paper reports, quantitatively, the propensity of individual carbon atoms in these two molecules in being converted to particulate. The conversion of individual carbon atoms to particulate was traced by ‘labelling’ individual carbon atoms in those two fuel molecules with isotopic carbon-13 (13C) and then measuring how many of the labelled atoms was found in the particulate. This allowed the measuring of the conversion rates of individual fuel carbon atoms to particulate. In the case of oleic acid, three carbon atoms were selected as being particularly relevant to particulate formation, and 13C labelled. One of the carbon atoms was double bonded to the oxygen atom on the carboxylic acid group; and the other two were part of the oleic acid molecule alkyl chain and double bonded to each other. In the case of the methyl oleate, one carbon atom was 13C labelled. This was the carbon atom that was double bonded to one of the oxygen atoms of the ester group. Experimental results are presented for particulate matter (PM) formed in a laminar flow tube reactor, and also in a direct injection compression ignition engine. The tube reactor has been used for the pyrolysis of oleic acid and methyl oleate at 1300 °C, under oxygen-free conditions and at air–fuel equivalence ratios (λ) of 0.1, and 0.2. Samples of PM were also collected from the compression ignition engine at an intermediate engine load. Isotope ratio mass spectrometry (IRMS) has been used to determine the relative abundance of 13C in the initial fuel and in the resulting PM. Significant differences in the relative conversion rates of individual carbon atoms are reported; a negligible contribution to PM from the carbon atom directly bonded to two oxygen atoms was found in both the engine and reactor. The labelling technique used in this paper requires low quantities of 13C labelled molecules to enrich otherwise unlabelled oleic acid; enrichment is at volumetric concentrations typically less than 0.7% (v/v). In addition, emissions data from the engine and tube reactor, including unburned hydrocarbons, CO, CO2, NOx, and PM size and number distributions measured by differential mobility spectrometer, are also presented.

Reactive Uptake of N2O5 by Aerosols Containing Dicarboxylic Acids. Effect of Particle Phase, Composition, and Nitrate Content

Reactive uptake coefficients for loss of N(2)O(5) to micron-size aerosols containing oxalic malonic, succinic, and glutaric acids, and mixtures with ammonium hydrogen sulfate and ammonium sulfate, are presented. The uptake measurements were made using two different systems: atmospheric pressure laminar flow tube reactor (Cambridge) and the Large Indoor Aerosol Chamber at Forschungszentrum Juelich. Generally good agreement is observed for the data recorded using the two techniques. Measured uptake coefficients lie in the range 5 x 10(-4)-3 x 10(-2), dependent on relative humidity, on particle phase, and on particle composition. Uptake to solid particles is generally slow, with observed uptake coefficients less than 1 x 10(-3), while uptake to liquid particles is around an order of magnitude more efficient. These results are rationalized using a numerical model employing explicit treatment of both transport and chemistry. Our results indicate a modest effect of the dicarboxylic acids on uptake and confirm the strong effect of particle phase, liquid water content, and particulate nitrate concentrations.

Reactive Uptake of Nitric Acid onto Sodium Chloride Aerosols Across a Wide Range of Relative Humidities

Reactive uptake coefficients for nitric acid onto size-selected (d(ve) = 102 and 233 nm) sodium chloride aerosols are determined for relative humidities (RH) between 85% and 10%. Both pure sodium chloride and sodium chloride mixed with magnesium chloride (X(Mg/Na) = 0.114, typical of sea salt) are studied. The aerosol is equilibrated with a carrier gas stream at the desired RH and then mixed with nitric acid vapor at a concentration of 60 ppb in a laminar flow tube reactor. At the end of the reactor, the particle composition is determined in real time with a laser ablation single particle mass spectrometer. For relative humidities above the efflorescence relative humidity (ERH), the particles exist as liquid droplets and the uptake coefficient ranges from 0.05 at 85% RH to >0.1 near the ERH. The droplet sizes, relative humidity and composition dependencies, are readily predicted by thermodynamics. For relative humidities below the ERH, the particles are nominally "solid" and uptake depends on the amount of surface adsorbed water (SAW). The addition of magnesium chloride to the particle phase (0.114 mole ratio of magnesium to sodium) facilitates uptake by increasing the amount of SAW. In the presence of magnesium chloride, the uptake coefficient remains high (>0.1) down to 10% RH, suggesting that the displacement of chloride by nitrate in fine sea salt particles is efficient over the entire range of conditions in the ambient marine environment. In the marine boundary layer, displacement of chloride by nitrate in fine sea salt particles should be nearly complete within a few hours (faster in polluted areas)-a time scale much shorter than the particle residence time in the atmosphere.

Laboratory measurement of water nucleation using a laminar flow tube reactor

A Laminar Flow Tube Reactor (LFTR) was used to study the nucleation of water vapor. Computational analysis was carried out to define the operating conditions of the LFTR suitable for water nucleation measurements. An interface between the LFTR and a mass spectrometer was developed to analyze the chemical content of the freshly nucleated water particles. Contaminants were detected in the initial configuration of the LFTR. As a result, improvements were made to the LFTR to achieve ultrahigh purity conditions in the system. The nucleation rate of water vapor as a function of supersaturation was measured over the temperature range 210–250 K. The first measurement of the nucleation rate of water at a temperature of 210 K was obtained. Reasonable agreement with the classical theory predictions is observed for temperatures in the range 230–250 K. However, below 220 K, classical theory begins to overestimate nucleation rates compared to experimental data and the disagreement grows with decreasing temperature. The experimental data obtained provide an excellent benchmark for further nucleation studies of binary, ternary, and more complex systems.

Combustion Generated Nickel Species Aerosols: Role of Chemical and Physical Properties on Lung Injury

Systematic manipulation of furnace temperature, residence time, and dilution air was used to study the formation of submicrometer nickel oxide (NiO) or nickel sulfate hexahydrate (NiSO 4 ) particles in a horizontal, laminar flow tube reactor. Chemical speciation, morphological changes, and aerosol size distributions were measured using x-ray diffraction, transmission electron microscopy, and diffusion mobility analysis, respectively. A technique was developed to use these submicrometer nickel species aerosols in animal inhalation studies. Representative aerosols were administered to C57BL/6J mice by intratracheal instillation or whole-body inhalation to study the effect of submicrometer particles on pulmonary injury. For instillation, NiO particles having a geometric mass mean diameter ( d pg ) of 40, 300, and 1000 nm were generated by pyrolysis of nickel nitrate hexahydrate aerosol suspended in physiological saline and administered at a dose corresponding to 3, 30, 300, or 3000 w g Ni/kg body weight. Bro...

The laminar flow tube reactor as a quantitative tool for nucleation studies: Experimental results and theoretical analysis of homogeneous nucleation of dibutylphthalate

A laminar flow tube reactor was designed and constructed to provide an accurate, quantitative measurement of a nucleation rate as a function of supersaturation and temperature. Measurements of nucleation of a supersaturated vapor of dibutylphthalate have been made for the temperature range from −30.3 to +19.1 °C. A thorough analysis of the possible sources of experimental uncertainties (such as defining the correct value of the initial vapor concentration, temperature boundary conditions on the reactor walls, accuracy of the calculations of the thermodynamic parameters of the nucleation zone, and particle concentration measurement) is given. Both isothermal and the isobaric nucleation rates were measured. The experimental data obtained were compared with the measurements of other experimental groups and with theoretical predictions made on the basis of the self-consistency correction nucleation theory. Theoretical analysis, based on the first and the second nucleation theorems, is also presented. The critical cluster size and the excess of internal energy of the critical cluster are obtained.

Laminar flow tube reactor. Analysis of the experimental accuracy of the measurement of nucleation of dibutylphthalate. Theoretical analysis of teh experimental data

Laminar flow tube reactor. Analysis of the experimental accuracy of the measurement of nucleation of dibutylphthalate. Theoretical analysis of teh experimental data

Growth characteristics of aerosols in a laminar flow tube reactor

Growth characteristics of aerosols in a laminar flow tube reactor

Nucleation study using the laminar flow tube reactor. Detecting the influence of trace contaminants on nucleation

Nucleation study using the laminar flow tube reactor. Detecting the influence of trace contaminants on nucleation

Nucleation studies using a laminar flow tube reactor and a mass-spectrometer with atmospheric pressure ionization.

Nucleation studies using a laminar flow tube reactor and a mass-spectrometer with atmospheric pressure ionization.

Homogeneous nucleation of dibuthylphthalate the comparison of the experimental data obtained using the laminar flow tube reactor technique and SCC theory

Homogeneous nucleation of dibuthylphthalate the comparison of the experimental data obtained using the laminar flow tube reactor technique and SCC theory