Fei Qi

Selective conversion of syngas to light olefins.

Small olefins from syngas The conversion of coal or natural gas to liquid fuels or chemicals often proceeds through the production of CO and H2. This mixture, known as syngas, is then converted to hydrocarbons with Fischer-Tropsch catalysts. For the light olefins (ethylene to butylenes) needed for chemical and polymer synthesis, conventional catalysts are mechanistically limited to <60% conversion and deactivate through carbon buildup. Jiao et al. developed a bifunctional catalyst that achieves higher conversions and avoids deactivation (see the Perspective by de Jong). A zinc-chromium oxide creates ketene intermediates that are then coupled over a zeolite. Science, this issue p. 1065, see also p. 1030 A composite catalyst circumvents conventional limitations on the Fischer-Tropsch synthesis of light olefins from syngas. [Also see Perspective by de Jong] Although considerable progress has been made in direct synthesis gas (syngas) conversion to light olefins (C2=–C4=) via Fischer-Tropsch synthesis (FTS), the wide product distribution remains a challenge, with a theoretical limit of only 58% for C2–C4 hydrocarbons. We present a process that reaches C2=–C4= selectivity as high as 80% and C2–C4 94% at carbon monoxide (CO) conversion of 17%. This is enabled by a bifunctional catalyst affording two types of active sites with complementary properties. The partially reduced oxide surface (ZnCrOx) activates CO and H2, and C−C coupling is subsequently manipulated within the confined acidic pores of zeolites. No obvious deactivation is observed within 110 hours. Furthermore, this composite catalyst and the process may allow use of coal- and biomass-derived syngas with a low H2/CO ratio.

The vacuum ultraviolet beamline/endstations at NSRL dedicated to combustion research

An undulator-based vacuum ultraviolet (VUV) beamline (BL03U), intended for combustion chemistry studies, has been constructed at the National Synchrotron Radiation Laboratory (NSRL) in Hefei, China. The beamline is connected to the newly upgraded Hefei Light Source (HLSu2005II), and could deliver photons in the 5-21u2005eV range, with a photon flux of 10(13)u2005photonsu2005s(-1) at 10u2005eV when the beam current is 300u2005mA. The monochromator of the beamline is equipped with two gratings (200u2005lines mm(-1) and 400u2005lines mm(-1)) and its resolving power is 3900 at 7.3u2005eV for the 200u2005lines mm(-1) grating and 4200 at 14.6u2005eV for the 400u2005lines mm(-1) grating. The beamline serves three endstations which are designed for respective studies of premixed flame, fuel pyrolysis in flow reactor, and oxidation in jet-stirred reactor. Each endstation contains a reactor chamber, an ionization chamber where the molecular beam intersects with the VUV light, and a home-made reflectron time-of-flight mass spectrometer. The performance of the beamline and endstations with some preliminary results is presented here. The ability to detect reactive intermediates (e.g. H, O, OH and hydroperoxides) is advantageous in combustion chemistry research.

Conformation-Specific Pathways of β-Alanine: A Vacuum Ultraviolet Photoionization and Theoretical Study

We report a photoionization and dissociative photoionization study of beta-alanine using IR laser desorption combined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry. Fragments at m/z = 45, 44, 43, and 30 yielded from photoionization are assigned to NH(3)CH(2)CH(2)(+), NH(2)CHCH(3)(+), NH(2)CHCH(2)(+), and NH(2)CH(2)(+), respectively. Some new conformation-specific dissociation channels and corresponding dissociation energies for the observed fragments are established and determined with the help of ab initio G3B3 calculations and measurements of photoionization efficiency (PIE) spectra. The theoretical values are in fair agreement with the experimental results. Three low-lying conformers of the beta-alanine cation, including two gauche conformers G1+, G2+ and one anti conformer A+ are investigated by G3B3 calculations. The conformer G1+ (intramolecular hydrogen bonding N-H...OC) is found to be another precursor in forming the NH(3)CH(2)CH(2)(+) ion, which is complementary to the previously reported formation pathway that only occurs with the conformer G2+ (intramolecular hydrogen bonding O-H...N). Species NH(2)CHCH(2)(+) may come from the contributions of G1+, G2+, and A+ via different dissociation pathways. The most abundant fragment ion, NH(2)CH(2)(+), is formed from a direct C-C bond cleavage. Intramolecular hydrogen transfer processes dominate most of the fragmentation pathways of the beta-alanine cation.

Intramolecular hydrogen transfer in the ionization process of α-alanine

Photoionization and dissociative photoionization of alpha-alanine have been studied with infrared laser desorption/tunable synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (IR LD/VUV PIMS) and theoretical calculations. By scanning photoionization efficiency (PIE) spectra, appearance energies (AEs) of the fragments CH(3)CHNH(3)(+) (m/z = 45, doublet state) and CH(3)CH = NH(2)(+) (m/z = 44, singlet state) are measured to be 9.53 and 9.21 +/- 0.05 eV, respectively, which are consistent with the theoretical values of 9.61 and 9.37 eV with ab initio G3B3 calculations. Formation of the CH(3)CHNH(3)(+) ion produced via intramolecular hydrogen transfer and subsequent decarboxylation processes is competitive to that of the CH(3)CH[double bond, length as m-dash]NH(2)(+) ion derived from a direct C-C(O) bond cleavage. The photoionization mass spectrum obtained at the photon energy of 10.0 eV shows that the intensity of CH(3)CH[double bond, length as m-dash]NH(2)(+) is much stronger than that of the CH(3)CHNH(3)(+) fragment. The formation of the CH(3)CHNH(3)(+) and CH(3)CH[double bond, length as m-dash]NH(2)(+) ions is thought to be thermodynamically and kinetically favorable, respectively. Detailed formation pathways for the two cations have been proposed by using ab initio calculations. The calculated results provide a clear picture of the photoionization and dissociative photoionization processes of the alpha-alanine cation.

Ultrasonic nebulization extraction/low pressure photoionization mass spectrometry for direct analysis of chemicals in matrices.

A novel ultrasonic nebulization extraction/low-pressure photoionization (UNE-LPPI) system has been designed and employed for the rapid mass spectrometric analysis of chemicals in matrices. An ultrasonic nebulizer was used to extract the chemicals in solid sample and nebulize the solvent in the nebulization cell. Aerosols formed by ultrasonic were evaporated by passing through a transferring tube, and desolvated chemicals were ionized by the emitted light (10.6xa0eV) from a Krypton discharge lamp at low pressure (∼68xa0Pa). First, a series of semi/non-volatile compounds with different polarities, such as polycyclic aromatic hydrocarbons (PAHs), amino acids, dipeptides, drugs, nucleic acids, alkaloids, and steroids were used to test the system. Then, the quantification capability of UNE-LPPI was checked with:xa01) pure chemicals, such as 9,10-phenanthrenequinone and 1,4-naphthoquinone dissolved in solvent; 2) soil powder spiked with different amounts of phenanthrene and pyrene. For pure chemicals, thexa0correlationxa0coefficient (R(2)) for the standard curve of 9,10-phenanthrenequinone in the range of 3xa0ng-20xa0μgxa0mL(-1) was 0.9922, and the measured limits of detection (LOD) was 1xa0ngxa0ml(-1). In the case of soil powder, linear relationships for phenanthrene and pyrene from 10 to 400xa0ngxa0mg(-1) were obtained with correlation coefficients of 0.9889 and 0.9893, respectively. At last, the feasibility of UNE-LPPI for the detection of chemicals in real matrices such as tablets and biological tissues (tea, Citrus aurantium peel and sage (Salvia officinalis) leaf) were successfully demonstrated.

Extractive Atmospheric Pressure Photoionization (EAPPI) Mass Spectrometry: Rapid Analysis of Chemicals in Complex Matrices.

AbstractExtractive atmospheric pressure photoionization (EAPPI) mass spectrometry was designed for rapid qualitative and quantitative analysis of chemicals in complex matrices. In this method, an ultrasonic nebulization system was applied to sample extraction, nebulization, and vaporization. Mixed with a gaseous dopant, vaporized analytes were ionized through ambient photon-induced ion–molecule reactions, and were mass-analyzed by a high resolution time-of-flight mass spectrometer (TOF-MS). After careful optimization and testing with pure sample solution, EAPPI was successfully applied to the fast screening of capsules, soil, natural products, and viscous compounds. Analysis was completed within a few seconds without the need for preseparation. Moreover, the quantification capability of EAPPI for matrices was evaluated by analyzing six polycyclic aromatic hydrocarbons (PAHs) in soil. The correlation coefficients (R2) for standard curves of all six PAHs were above 0.99, and the detection limits were in the range of 0.16–0.34 ng/mg. In addition, EAPPI could also be used to monitor organic chemical reactions in real time.n Graphical Abstractᅟ

Study of the Formation of the First Aromatic Rings in the Pyrolysis of Cyclopentene

The thermal decomposition of cyclopentene was studied in a jet-stirred reactor operated at constant pressure and temperature to provide new experimental information about the formation of the first aromatic rings from cyclic C5 species. Experiments were carried out at a residence time of 1 s, a pressure of 106.7 kPa, temperatures ranging from 773 to 1073 K and under diluted conditions (cyclopentene inlet mole fraction of 0.04). Species were quantified using three analytical methods: gas chromatography, synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS), and single photon laser ionization mass spectrometry (SPI-MS). Several species could be quantified using both methods allowing comparison of experimental data obtained with the three apparatuses. Discrepancies observed in mole fraction profiles of some large aromatics suggest that the direct sampling in the gas phase (with a molecular beam or a capillary tube) provide more reliable results. The main reaction products are 1,3-cyclopentadiene and hydrogen. The formation of many unsaturated C2-C6 olefins, diolefins and alkynes was also observed but in smaller amounts. Benzene, toluene, styrene, indene, and naphthalene were detected from 923 K. SVUV-PIMS data allowed the identification of another C6H6 isomer which is 1,5-hexadien-3-yne rather than fulvene. The quantification of the cyclopentadienyl radical was obtained from SVUV-PIMS and SPI-MS data with some uncertainty induced by the possible contribution to the signal for m/z 65 of a fragment from the decomposition of a larger ion. This is the first time that a radical is quantified in a jet-stirred reactor using non-optical techniques. SPI-MS analyses allowed the detection of species likely being combination products of allyl and cyclopentadienyl radicals. A model was developed for the pyrolysis of cyclopentene. This model includes routes of formation of aromatics from the cyclopentadienyl radical. The comparison of experimental and computed data is overall satisfactory for primary reaction products whereas discrepancies are still observed for aromatics.

Product Identification and Mass Spectrometric Analysis of n‐Butane and i‐Butane Pyrolysis at Low Pressure

The pyrolysis of n‐butane and i‐butane at low pressure was investigated from 823−1823 K in an electrically heated flow reactor using synchrotron vacuum ultraviolet photoionization mass spectrometry. More than 20 species, especially several radicals and isomers, were detected and identified from the measurements of photoionization efficiency (PIE) spectra. Based on the mass spectrometric analysis, the characteristics of n‐butane and i‐butane pyrolysis were discussed, which provided experimental evidences for the discussion of decomposition pathways of butane isomers. It is concluded that the isomeric structures of n‐butane and i‐butane have strong influence on their main decomposition pathways, and lead to dramatic differences in their mass spectra and PIE spectra such as the different dominant products and isomeric structures of butene products. Furthermore, compared with n‐butane, i‐butane can produce strong signals of benzene at low temperature in its pyrolysis due to the enhanced formation of benzene p...

Synchrotron vacuum ultraviolet (VUV) photo-induced fragmentation of cyclic dipeptides radical cations

Cyclic dipeptides, due to their chemical properties and various bioactivities, are very attractive for medicinal chemistry. Fragmentations of three simple cyclic dipeptides including cyclo(Gly–Gly), cyclo(Ala–Ala) and cyclo(Gly–Val) in the gas-phase are determined with synchrotron vacuum ultraviolet (VUV) photoionization mass spectrometry (VUV PIMS) and theoretical calculations. Cyclo(Gly-Gly) and cyclo(Ala-Ala) show the similar fragmentation pathways. The primary decomposition reactions of cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations are found to be HNCO loss and CO elimination. The appearance energies (AEs) of fragment ions [CH2NHCOCH2]+• and [CH3CHNHCOCHCH3]+• are measured to be 10.21 and 9.66xa0±xa00.05xa0eV, respectively, which are formed from cyclo(Gly-Gly) and cyclo(Ala-Ala) radical cations with HNCO elimination. Due to the stabilization of the radical cation of cyclo(Gly-Val) with isopropyl side group, the dominant fragment ion m/z 114 assigned as [C4H6N2O2]+• is produced by γ-H migration and i cleavage to lose propylene. The ionization energies (IEs) of three cyclic dipeptides decrease in the order cyclo(Gly-Gly) (9.33xa0±xa00.05xa0eV)xa0>xa0cyclo(Ala-Ala) (9.21xa0±xa00.05xa0eV)xa0>xa0cyclo(Gly-Val) (9.09xa0±xa00.05xa0eV) from measurements of photoionization efficiency spectra. It implies that IEs of cyclic dipeptides are affected by substituent groups and symmetrical characterization of molecular structures. These observations of the chemical properties of cyclic dipeptides radical ion (M+•) may be important for understanding gas-phase molecular reactivity of 2,5-diketopiperazines and guiding diketopiperazine-based drug design.

Studies of ion-molecule reactions within clusters (C2H3Cl)n☆

Abstract Intermolecular ion-molecule reactions within clusters (C2H3Cl)n, n=2, 3 have been studied at the photochemistry station of NSRL. In addition to the parent ions (C2H3Cl)n+, the intracluster reaction products (C4H5Cl)(C2H3Cl)n+ (n=0, 1) are detected in the mass spectra. The product ion C4H5Cl+ is most likely a stable molecular ion, not a weakly bound complex such as (C2H2…C2H3Cl)+.