Gas-phase Reaction Products Research Articles

Selective CO2 electroreduction to C2H4 on porous Cu films synthesized by sacrificial support method

A series of copper-based electrocatalysts were prepared by the Sacrificial Support Method (SSM) with variation of synthesis parameters. Thin films of the materials were evaluated for their electrocatalytic activities towards CO2 electroreduction to short-chain (C1-C2) hydrocarbons by standard electrochemical methods. Gas-phase reaction products were quantified using an online gas chromatography system. At −0.98V vs reversible hydrogen electrode (RHE), copper oxide-derived catalysts were found to have selectivity toward C2H4 approximately one order of magnitude higher than to CH4. The highest selectivity towards C2H4 production at −0.98V was demonstrated by the catalyst with cube morphology, synthesized with 20wt% Cu: 80wt% SiO2 ratio in the precursor. Possible causes for this shift in selectivity are discussed in terms of the morphology and surface/core composition as determined by scanning electron microscopy (SEM), X-Ray diffraction (XRD), and X-Ray photoelectron spectroscopy (XPS).

Reaction path and product analysis of sodium-water chemical reactions using laser diagnostics

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a coolant because of its excellent heat transport capability and a large safety margin to the boiling point (1153K) at the atmospheric pressure. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow caused by a breach of heat transfer tubes. Therefore, the study on sodium-water chemical reactions is of importance for safety of SFR. The purpose of this study aims to clarify the gas phase sodium-water reaction path and reaction products quantitatively. The counter-flow diffusion experiment device was employed to analyze the reaction path and reaction products using laser diagnostics. sodium (Na), sodium dimer (Na2), water (H2O), sodium hydroxide (NaOH), sodium oxides (Na2O and NaO) and hydroxyl radical (OH) were measured using Raman spectroscopy, absorption spectroscopy, photo-fragmentation spectroscopy and laser induced fluorescence in the reaction field for the sodium-water vapor, sodium-oxygen and sodium-hydrogen reaction. Based on the measurement results by absorption spectroscopy, it was revealed that the sodium-oxygen reaction was faster than that of sodium-water. It was indicated that sodium-hydrogen reaction did not react noticeably with sodium from the measurement result as well. The main product of sodium-water reaction was determined to be NaOH and the sodium oxide was not notably measured compared with NaOH from the results by photo-fragmentation spectroscopy. The sodium oxide concentration ratio to NaOH was determined 2% with standard deviation of 3%. Its reaction path was also discussed using sodium-water, sodium-oxygen and sodium-hydrogen reaction analyses.

A Radical-Mediated Pathway for the Formation of [M + H](+) in Dielectric Barrier Discharge Ionization.

Active capillary plasma ionization is a highly efficient ambient ionization method. Its general principle of ion formation is closely related to atmospheric pressure chemical ionization (APCI). The method is based on dielectric barrier discharge ionization (DBDI), and can be constructed in the form of a direct flow-through interface to a mass spectrometer. Protonated species ([M + H](+)) are predominantly formed, although in some cases radical cations are also observed. We investigated the underlying ionization mechanisms and reaction pathways for the formation of protonated analyte ([M + H](+)). We found that ionization occurs in the presence and in the absence of water vapor. Therefore, the mechanism cannot exclusively rely on hydronium clusters, as generally accepted for APCI. Based on isotope labeling experiments, protons were shown to originate from various solvents (other than water) and, to a minor extent, from gaseous impurities and/or self-protonation. By using CO2 instead of air or N2 as plasma gas, additional species like [M + OH](+) and [M - H](+) were observed. These gas-phase reaction products of CO2 with the analyte (tertiary amines) indicate the presence of a radical-mediated ionization pathway, which proceeds by direct reaction of the ionized plasma gas with the analyte. The proposed reaction pathway is supported with density functional theory (DFT) calculations. These findings add a new ionization pathway leading to the protonated species to those currently known for APCI. Graphical Abstract ᅟ.

Limonene ozonolysis in the presence of nitric oxide: Gas-phase reaction products and yields

The reaction products from limonene ozonolysis were investigated using the new carbonyl derivatization agent, O-tert-butylhydroxylamine hydrochloride (TBOX). With ozone (O3) as the limiting reagent, five carbonyl compounds were detected. The yields of the carbonyl compounds are discussed with and without the presence of a hydroxyl radical (OH) scavenger, giving insight into the influence secondary OH radicals have on limonene ozonolysis products. The observed reaction product yields for limonaketone (LimaKet), 7-hydroxyl-6-oxo-3-(prop-1-en-2-yl)heptanal (7H6O), and 2-acetyl-5-oxohexanal (2A5O) were unchanged suggesting OH generated by the limonene + O3 reaction does not contribute to their formation. The molar yields of 3-isopropenyl-6-oxo-heptanal (IPOH) and 3-acetyl-6-oxoheptanal (3A6O) decreased by 68% and >95%; respectively, when OH was removed. This suggests that OH radicals significantly impact the formation of these products. Nitric oxide (NO) did not significantly affect the molar yields of limonaketone or IPOH. However, NO (20 ppb) considerably decreased the molar reaction product yields of 7H6O (62%), 2A5O (63%), and 3A6O (47%), suggesting NO reacted with peroxyl intermediates, generated during limonene ozonolysis, to form other carbonyls (not detected) or organic nitrates. These studies give insight into the transformation of limonene and its reaction products that can lead to indoor exposures.

Gas-phase reaction products and yields of terpinolene with ozone and nitric oxide using a new derivatization agent.

The new derivatization agent, O-tert-butylhydroxylamine hydrochloride (TBOX) was used to investigate the carbonyl reaction products from terpinolene ozonolysis. With ozone (O3) as the limiting reagent, four carbonyl compounds were detected: methylglyoxal (MG), 4-methylcyclohex-3-en-1-one, (4MCH), 6-oxo-3-(propan-2-ylidene) heptanal (6OPH), and 3,6-dioxoheptanal (36DOH). The tricarbonyl 36DOH has not been previously observed. Using cyclohexane as a hydroxyl radical (OH•) scavenger, the yields of 6OPH and 36DOH were reduced indicating the influence secondary OH• radicals have on terpinolene ozonolysis products. However, the MG yield increased and the 4MCH yield was unchanged when OH•radicals were scavenged suggesting they are only made by the terpinolene + O3 reaction. The detection of 36DOH using TBOX highlights the advantages of a smaller molecular weight derivatization agent for the detection of multi-carbonyl compounds. The product yields from terpinolene ozonolysis experiments conducted in the presence of 20 ppb nitric oxide (NO) remained unchanged except for MG which decreased. However, in experiments where O3 was kept constant at 50 ppb and NO was varied (20, 50, 100 ppb) MG, 6OPH, 36DOH decreased with increasing NO while 4MCH increased with increasing NO. The use of TBOX derivatization if combined with other derivatization agents may address a recurring need to simply and accurately detect multi-functional oxygenated species in air.

Gas phase click chemistry via ion/ion reactions

The 1,3-dipolar cycloaddition between azides and alkynes, i.e., ‘click’ chemistry, has been demonstrated in the gas phase via ion/ion reactions. Doubly protonated azide-modified peptide cations were reacted with singly deprotonated dibenzoazacyclooctyne DIBAC reagent anions to form a long-lived complex monocation. Similarly, ion/ion complex monoanions were generated in the negative mode via reactions between singly protonated azide-containing cations and doubly deprotonated DIBAC reagent anions. Activation of ion/ion complexes in either polarity resulted in the formation of a triazole, a covalent linkage that can be further probed via MSn. The click chemistry coupled species synthesized in solution and subsequently transferred into the gas phase yielded the same products as those synthesized in gas phase when activated in the mass spectrometer. Analogous click chemistry products were synthesized in the solution phase and activated via tandem mass spectrometry as a control for the dissociation of the novel gas-phase reaction products. Density functional theory (DFT) calculations were performed to provide estimates for key processes (e.g., reaction barriers and energies) that can occur in the overall reaction. The work herein demonstrates that it is possible to conjugate azide and alkyne functional groups in the gas-phase, and represents another example of the growing number of selective covalent reactions that can take place via gas-phase ion/ion reactions.

Effect of pressure on the gas-phase chemistry when using monomethylsilane and dimethylsilane in hot-wire chemical vapor deposition

The effect of source gas pressure on the gas-phase reaction chemistry of dimethylsilane (DMS) and monomethylsilane (MMS) in the hot-wire chemical vapor deposition process has been studied by examining the secondary gas-phase reaction products in a reactor using a soft laser ionization source coupled with mass spectrometry. For DMS, the increase in sample pressure has resulted in the formation of small hydrocarbons, including ethene, acetylene, propene, and propyne. This leads to a switch from silylene dominant chemistry to a free radical dominant one with the pressure increase at low filament temperatures of 1200 and 1300 °C. At the lower pressure of 0.12 Torr, the formation of 1,1,2,2-tetramethyldisilane by dimethylsilylene insertion reaction into the Si–H bond in DMS is favored over trimethylsilane produced from a free radical recombination reaction for a short reaction time. However, when the pressure is increased by 10 times, the gas-phase chemistry becomes dominated by the formation of trimethylsilane. We have demonstrated that trapping of the corresponding active intermediates by the small hydrocarbons produced in situ is responsible for the observed switch. In the study with MMS, the gas-phase chemistry is dominated by the formation of 1,2-dimethyldisilane and 1,3-disilacyclobutane at both pressures of 0.48 and 1.2 Torr. Unlike DMS, the gas-phase reaction chemistry with MMS does not involve free radicals, which are the precursors to produce small hydrocarbons. The absence of small hydrocarbons formed in situ with MMS explains the preservation in chemistry upon the increase in pressure when MMS is used as a source gas.

Formation of diatomic molecular radicals in reactive nitrogen-carbon plasma generated by electron cyclotron resonance discharge and pulsed laser ablation

The reactive nitrogen-carbon plasma generated by electron cyclotron resonance (ECR) microwave discharge of N2 gas and pulsed laser ablation of a graphite target was characterized spectroscopically by time-integrated and time-resolved optical emission spectroscopy with space resolution for a study of gas-phase reactions and molecular radical formation in the plasma. The plasma exhibits very high reactivity compared with the plasma generated solely by ECR discharge or by pulsed laser ablation and contains highly excited species originally present in the ambient gaseous environment and directly ablated from the target as well as formed as the products of gas-phase reactions occurring in the plasma. The space distribution and the time evolution of the plasma emission give an access to the gas-phase reactions for the formation of C2 and CN radicals, revealing that C2 radicals are formed mainly in the region near the target while CN radicals can be formed in a much larger region not only in the vicinity of the target, but especially in the region near a substrate far away from the target.

Effect of trimethylsilane pressure on hot-wire chemical vapor deposition chemistry using vacuum ultraviolet laser ionization mass spectrometry

In this study, the authors investigated the effect of sample pressure on the reaction chemistry of trimethylsilane (TriMS) in the hot-wire chemical vapor deposition (CVD) process. The secondary gas-phase reaction products were examined in a reactor with varying TriMS pressures. The reaction products were analyzed using a laser ionization source with a vacuum ultraviolet wavelength of 118 nm, coupled with mass spectrometry. By increasing TriMS pressure, methane formation was observed. To our knowledge, this is the first successful use of either open-chain alkylsilanes or four-membered-ring (di)silacyclobutane molecules as an independent precursor gas in the hot-wire CVD reactor to achieve methane formation. Our results showed that methane was formed mainly from the radical chain reactions with minor contributions from molecular elimination. The increase in the sample pressure also led to the formation of other small hydrocarbon molecules including acetylene, ethene, propyne, and propene. The formation of hydrogen molecules was enhanced when the sample pressure was increased. In addition, the change in the sample pressure had a direct effect on the radical recombination and disproportionation reactions. This is reflected in the different behavior assumed by the main products from these two types of reactions, i.e., tetramethylsilane, hexamethyldisilane from the former, and three methyl-substituted disilacyclobutanes from the latter. The trapping of free radicals resulting from the in-situ produced ethene and propene molecules is responsible for the observed difference.

Catalytic Combustion Reactions During Atomic Layer Deposition of Ru Studied Using18O2Isotope Labeling

The surface reaction products liberated during the atomic layer deposition (ALD) of Ru from (C5H5)Ru(CO)2(C2H5) and 18O2 were quantitatively analyzed using quadrupole mass spectrometry (QMS). The gas-phase reaction products during the Ru precursor pulse were CO2, CO, H2, and H2O, while during the O2 pulse primarily CO2 and CO were produced. Approximately 70% of the C atoms and ∼100% of the H atoms contained in the Ru precursor were released during the Ru pulse of the ALD process. From these observations, and on the basis of the surface science and catalysis literature, we conclude that the complex surface chemistry during Ru ALD can be described by catalytic combustion reactions. These reactions consist of the dissociative chemisorption of the Ru precursor’s ligands on the Ru surface during the metal pulse. These hydrocarbon ligands undergo dehydrogenation and combustion reactions on the catalytic metal surface in the presence of surface O formed due to the dissociation of O2 molecules in the previous O2 ...

Investigation of terpinolene + ozone or terpinolene + nitrate radical reaction products using denuder/filter apparatus

Terpinolene's (1-methyl-4-(propan-2-ylidene)cyclohexene) reaction with ozone or the nitrate radical was investigated using a denuder/filter apparatus in order to characterize gas-phase and particulate reaction products. Identification of the reaction products (i.e., aldehydes, ketones, dicarbonyls and carboxylic acids) was made using two derivatization methods; O-(2,3,4,5,6-pentafluorobenzyl)hydroxylamine (PFBHA) to derivatize the carbonyl products or 3-Ethyl-1-[3-(dimethylamino)propyl]carbodiimide hydrochloride (EDC) and 2,2,2-trifluoroethylamine hydrochloride (TFEA) to derivatize the carboxylic acid products. Proposed carbonyl products for ozonolysis of terpinolene are: 4-methylcyclohex-3-en-1-one, 2-hydroxy-4-methylcyclohex-3-en-1-one, glyoxal, methyl glyoxal, 3-oxobutanal, and 6-oxo-3-(propan-2-ylidene)heptanal. Proposed carbonyl products for nitrate radical reaction of terpinolene are: 2-hydroxy-4-methylcyclohex-3-en-1-one, glyoxal, methyl glyoxal, and 4-oxopentanal. No carboxylic acid products were detected with either oxidizing reactant.

E203 レーザ計測技術を用いたナトリウム-水化学反応場の反応経路解析(OS8 軽水路・新型炉・原子力安全(4))

In a sodium-cooled fast reactor (SFR), liquid sodium is used as a heat transfer fluid because of its excellent heat transport capability. On the other hand, it has strong chemical reactivity with water vapor. One of the design basis accidents of the SFR is the water leakage into the liquid sodium flow by a breach of heat transfer tubes. Therefore, the study on sodium-water chemical reactions is of importance for security reasons. This study aims to clarify the gas phase sodium-water reaction path and reaction products Na, Na_2, H_2O, and reaction products in the counter-flow sodium-water reaction field were measured using laser diagnostics such as Raman scattering and photo-fragmentation. The main product in the sodium-water reaction was determined to be NaOH and its reaction path was discussed using Na-H_2O elementally reaction analysis.

A statistical description of the evolution of cloud condensation nuclei activity during the heterogeneous oxidation of squalane and bis(2-ethylhexyl) sebacate aerosol by hydroxyl radicals

The heterogeneous reaction of hydroxyl radicals with chemically reduced organic aerosol comprised of either squalane or bis(2-ethylhexyl) sebacate are used as model systems to examine how cloud condensation nuclei (CCN) activity evolves with photochemical oxidation. Over the course of the reaction, the critical super-saturation evolves both by the formation of new oxygen functional groups and by changes in aerosol size through the formation of gas phase reaction products. A statistical model of the heterogeneous reaction reveals that it is the formation, volatilization, solubility, and surface activity of many generations of oxidation products that together control the average changes in aerosol hygroscopicity. The experimental observations and model demonstrate the importance of considering the underlying population or subpopulation of species within a particle and how they each uniquely contribute to the average hygroscopicity of a multi-component aerosol. To accurately predict changes in CCN activity upon oxidation requires a reduction in the surface tension of the activating droplet by a subpopulation of squalane reaction products. These results provide additional evidence that surface tension-concentration parameterizations based on macroscopic data should be modified for microscopic droplets.

Photocatalytic reactions of nanocomposite of ZnS nanoparticles and montmorillonite

ZnS nanoparticles stabilized by cetyltrimethylammonium bromide (CTAB) were deposited on montmorillonite (MMT) forming a ZnS–CTA–MMT nanocomposite. The nanocomposite was characterized by scanning electron microscopy (SEM), Fourier transformed infrared (FTIR) and UV diffuse reflectance spectra (DRS) spectrometry, X-ray powder diffraction (XRD) and specific surface area measurements. Thereafter, it was used for photocatalytic reactions under UV irradiation (Hg lamp) in three different reaction media with different pH: NaOH solution, HCl solution and water. Prior to the photocatalytic reactions the dispersions were saturated by carbon dioxide to buffer the systems. The main reaction products in gas phase determined by gas chromatography were hydrogen and methane. The reactions were monitored by measuring oxidation–reduction potentials. The highest yields of hydrogen were obtained in the dispersion acidified by HCl but the concentrations of methane were similar in all tested media. Hydrogen was supposed to be formed by the reaction of two hydrogen radicals. Methane was formed by the reduction of carbon dioxide and by the partial decomposition of CTAB.

Quantum Cascade Laser-Based Measurement of Metal Alkylamide Density during Atomic Layer Deposition

An in situ gas-phase diagnostic for the metal alkylamide compound tetrakis(ethylmethylamido) hafnium (TEMAH), Hf[N(C(2)H(5))(CH(3))](4), was demonstrated. This diagnostic is based on direct absorption measurement of TEMAH vapor using an external cavity quantum cascade laser emitting at 979 cm(-1), coinciding with the most intense TEMAH absorption in the mid-infrared spectral region, and employing 50 kHz amplitude modulation with synchronous detection. Measurements were performed in a single-pass configuration in a research-grade atomic layer deposition (ALD) chamber. To examine the detection limit of this technique for use as a TEMAH delivery monitor, this technique was demonstrated in the absence of any other deposition reactants or products, and to examine the selectivity of this technique in the presence of deposition products that potentially interfere with detection of TEMAH vapor, it was demonstrated during ALD of hafnium oxide using TEMAH and water. This technique successfully detected TEMAH at molecular densities present during simulated industrial ALD conditions. During hafnium oxide ALD using TEMAH and water, absorbance from gas-phase reaction products did not interfere with TEMAH measurements while absorption by reaction products deposited on the optical windows did interfere, although interfering absorption by deposited reaction products corresponded to only ≈4% of the total derived TEMAH density. With short measurement times and appropriate signal averaging, estimated TEMAH minimum detectable densities as low as ≈2 × 10(12) molecules/cm(3) could be obtained. While this technique was demonstrated specifically for TEMAH delivery and hafnium oxide ALD using TEMAH and water, it should be readily applicable to other metal alkylamide compounds and associated metal oxide and nitride deposition chemistries, assuming similar metal alkylamide molar absorptivity and molecular density in the measurement chamber.

The statistical evolution of multiple generations of oxidation products in the photochemical aging of chemically reduced organic aerosol

The heterogeneous reactions of hydroxyl radicals (OH) with squalane and bis(2-ethylhexyl) sebacate (BES) particles are used as model systems to examine how distributions of reaction products evolve during the oxidation of chemically reduced organic aerosol. A kinetic model of multigenerational chemistry, which is compared to previously measured (squalane) and new (BES) experimental data, reveals that it is the statistical mixtures of different generations of oxidation products that control the average particle mass and elemental composition during the reaction. The model suggests that more highly oxidized reaction products, although initially formed with low probability, play a large role in the production of gas phase reaction products. In general, these results highlight the importance of considering atmospheric oxidation as a statistical process, further suggesting that the underlying distribution of molecules could play important roles in aerosol formation as well as in the evolution of key physicochemical properties such as volatility and hygroscopicity.

Novel Products from C6H5 + C6H6/C6H5 Reactions

To date only one product, biphenyl, has been reported to be produced from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions. In this study, we have investigated some unique products of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via both experimental observation and theoretical modeling. In the experimental study, gas-phase reaction products produced from the pyrolysis of selected aromatics and aromatic/acetylene mixtures were detected by an in situ technique, vacuum ultraviolet (VUV) single photon ionization (SPI) time-of-flight mass spectrometry (TOFMS). The mass spectra revealed a remarkable correlation in mass peaks at m/z = 154 {C(12)H(10) (biphenyl)} and m/z = 152 {C(12)H(8) (?)}. It also demonstrated an unexpected correlation among the HACA (hydrogen abstraction and acetylene addition) products at m/z = 78, 102, 128, 152, and 176. The analysis of formation routes of products suggested the contribution of some other isomers in addition to a well-known candidate, acenaphthylene, in the mass peak at m/z = 152 (C(12)H(8)). Considering the difficulties of identifying the contributing isomers from an observed mass number peak, quantum chemical calculations for the above-mentioned reactions were performed. As a result, cyclopenta[a]indene, as-indacene, s-indacene, biphenylene, acenaphthylene, and naphthalene appeared as novel products, produced from the possible channels of C(6)H(5) + C(6)H(6)/C(6)H(5) reactions rather than from their previously reported formation pathways. The most notable point is the production of acenaphthylene and naphthalene from C(6)H(5) + C(6)H(6)/C(6)H(5) reactions via the PAC (phenyl addition-cyclization) mechanism because, until now, both of them have been thought to be formed via the HACA routes. In this way, this study has paved the way for exploring alternative paths for other inefficient HACA routes using the PAC mechanism.

Unimolecular rearrangements of ketene‐O,O‐acetals and fragmentations occurring in the gas phase

Gas phase skeletal rearrangements of regioisomeric 3-cyano-2-methoxy-3a-alkylfuro[2,3-b]- and [3,2-b]indoles were evidenced by product ions [M-32](+•), consistent with loss of methanol, on electron ionization in their mass spectra. The rearranged products occurring in gas phase were demonstrated to have elemental composition and fragmentation properties identical to those of authentic samples of 2-indolyl cyanomalonates. Isotopic labeling experiments support the formation mechanism of the [M-32](+•) ion. Additional thermal gas-phase reaction products were characterized by comparison with an authentic sample.

Silicidation and carburization of the tungsten filament in HWCVD with silacyclobutane precursor gases

Study of the tungsten filament alloying processes with different precursor molecules shows that silicidation occurs when using silacycobutane (SCB) and carburization with 1,1,3,3-tetramethyl-1,3-disilacyclobutane (TMDSCB). The difference in the decomposition chemistry with the two molecules is responsible for the observation. Comparison of the depth profile and temperature distribution of the Si or C content in the alloyed filament illustrates the interplay among the Si or C deposition onto, evaporation from, and diffusion into the filament. Examination of the time distribution of key products from secondary gas-phase reactions at various filament temperatures demonstrates that gas-phase reactions dominate only at low temperatures. Silicidation or carburization is the dominant process at high temperatures, which contributes to a large consumption rate of precursor gas and a reduction in formation rate of the gas-phase reaction products.

Gas-phase reaction chemistry of 1,1-dimethyl-1-silacyclobutane as a precursor gas in the hot-wire chemical vapor deposition process — Formation of tetramethylsilane and trimethylsilane

The secondary gas-phase reaction products of 1,1-dimethyl-1-silacyclobutane (DMSCB) and its isotopomer, 1,1-di(perdeuteratedmethyl)-1-silacyclobutane (DMSCB-d6), in a hot-wire chemical vapour deposition reactor were investigated using vacuum UV laser single photon ionization with time-of-flight mass spectrometry. Dimethylsilylene, one of the primary decomposition products, undergoes π-type addition across the double and triple C–C bond and an insertion reaction into the Si–H bond. A short-chain reaction mechanism, initiated by methyl radicals produced in the primary decomposition, is found to exist for both the source DMSCB molecule and its stable secondary products. The formation of tetramethylsilane and trimethylsilane via the reaction of 1,1-dimethylsilene with a methyl radical and an H2 molecule, respectively, has been demonstrated. These are two new reaction channels involving 1,1-dimethylsilene in secondary gas-phase reactions.