Shi Yin, Ph. D. Bernstein Group Colorado State University Chemistry Department 1872 Campus Delivery Fort Collins, CO 80523-1872 E-mail: syin@lamar.colostate.edu Tel: 970-491-5741 (office), 970-491-5787 (lab)

Education and Academic Experience

- 07. 2010 ~ now

          Postdoc and Research Scientist in the group of Prof. Elliot R. Bernsteinn at Colorado State University.

- 09. 2005 ~ 06. 2010

          Ph.D. of Physical Chemistry, Supervised by Prof. Maofa Ge at ICCASS, Beijing, China.

- 09. 2001 ~ 07. 2005

          B.S. of Science (Chemistry), Department of Chemistry, Jilin University, China.

Researchh Interests

1. Heterogeneous Catalytic Reactions through Transition Metal and Transition Metal Oxide/Sulfide Clusters

♦ Catalytic reactions have been developed over about 150 years, however, most of commercial catalysts are still evaluated and optimized through trial-and-error processes. To date, existing theory cannot direct modern catalyst design due to the complex nature of the real catalyst reaction system: most of the important industrial catalytic reaction mechanisms are still not well understood at the fundamental level. Thus, the development of gas phase model systems to simulate the condensed phase catalyst surface is an urgent and compelling need.

♦ Neutral transition metal (TM) and transition metal oxide/sulfide clusters, which are accessible by time of flight mass spectrometry (TOF-MS) coupled with single photon ionization (SPI) in the gas phase and theoretical calculations, serve as model systems for local site, catalytic surfaces. These clusters can enhance the reaction rate for small gas phase molecule reactions through changing reaction mechanisms and lowering reaction barriers, and thus, these clusters can act as real catalysts in the gas phase.

♦ My research focuses on the marriage of gas phase and condensed phase catalytic reactions, so that we can understand heterogeneous catalytic reaction mechanisms at an electronic, atomic, and molecular level. Small metal and metal compound clusters (< 50 atoms), can be generated, reacted, and detected experimentally. Moreover, reactants, products, and even experimentally undetectable reaction intermediates, can be explored by both DFT and ab initio calculations.

2. Experimental Setup

(1) Laser ablation source - fast flow reactor system - TOFMS

♦ Gas phase neutral transition metal containing clusters are generated through laser ablation of metal and/or metal compounds or through laser ablation of metals and their subsequent reaction with various gases (e.g., H₂, C_xH_y, CO, H₂O, N_xO_y, etc.). These clusters are cooled in a supersonic expansion with He or He/O₂, H₂, CH₄, etc. mixed gases and are then available for reaction and photochemistry reaction in a fast flow reactor (high pressure, cluster T ~350 K). Reactant gas (e.g., C_xH_y, CO, H₂O, N_xO_y) is then added to the cell for the study of neutral cluster (e.g., Ti_mO_n, Mn_mO_n, V_mS_n, Fe_mS_n) reactivity. Reactants and products are ionized by SPI employing UV (193 nm, 6.4 eV), VUV (118 nm, 10.5 eV), or EUV (46.9 nm, 26.5 eV) low intensity laser radiation. The ions generated in the ionization region are detected and characterized by TOF-MS. To obtain reaction mechanisms, electronic and geometric structures, and potential energy surfaces (PESs) for this heterogeneous chemistry both density functional theory (DFT) in by Gaussian and ADF softwares and ab initio calculations are employed. A complete and detailed potential energy surface for the reaction is thereby generated, and thus the reaction barriers and dynamics are established. Based on these experimental and theoretical total results, condensed phase catalytic cycles and suggest ways to prove, improve, and enhance existing catalytic processes are proposed.

(2) Magnetic-bottle TOF - PES equipped with a laser vaporization supersonic cluster source

♦ A magnetic-bottle time-of-flight (MTOF) photoelectron spectroscopy (PES) apparatus is constructed in our lab. It consists of a laser vaporization cluster/molecular source, an orthogonal acceleration/extraction reflectron time of flight (oaRETOF) mass spectrometer, a mass gate, a momentum decelerator, and a MBTOF electron analyzer. Negative ions are generated in a laser ablation source, and carried by helium expansion gas, which is pulsed into the vacuum by a supersonic nozzle (R. M. Jordan, Co.) with a backing pressure of typically 75 psi. The negative ions are extracted perpendicularly from the beam by a -250 V high voltage pulse and are subjected to an oaRETOF mass analysis with +750 V on the liner. A three-grid mass gate is used for mass selection. The first and third grids are at the liner voltage (+750 V), and the middle grid is at negative high voltage -250 V, so that no ions are able to pass. Once the desired ion arrives at the first grid, the high voltage on the middle grid is pulsed to the liner voltage (+750 V) for a short period allowing the ion to pass unaffected. Following the mass gate, the selected ion beam enters a momentum decelerator. Once the ion packet passes the third grid of the mass gate, a positive square high voltage pulse (+1750 V) is applied to this grid for the momentum deceleration. The high voltage is pulsed back to the liner voltage before the ion packet leaves the deceleration stack. The interesting ion is mass selected by the mass gate and subsequently decelerated by a momentum decelerator before interacting with the detachment laser. Different photon energies laser (532nm, 355nm, 266nm, 193nm, 118nm, and 46.9nm) is used for the photo detachment. The photoelectrons are collected by the magnetic bottle and parallelized down to a ~1 m long TOF tube for electron kinetic energy analysis.

(3) Recent Research of Heterogeneous Catalytic Systems

♦ Ethylene hydrogenation on on neutral vanadium sulfide clusters

The hydrogenation reactions of C₂H₄ on neutral vanadium sulfide clusters are investigated by TOFMS employing 118 nm single photon ionization and DFT calculations. We find that the hydrogenation reactions of C₂H₄ are thermodynamically available on V_mS_n (m = 1, n = 1-3; m = 2, n = 1-5) clusters. The V atoms are the active sites for these V_mS_n clusters to attach a C₂H₄ molecule. Two types of association products for ethylene on active V sites of catalytic V_mS_n clusters are determined by DFT calculations. The C₂H₄ can connect with the active V atom through its π orbital or form a σ bond with active V atoms. Both π and σ associated ethylene can be hydrogenated with H₂ on catalytic V_mS_n clusters. PESs are calculated for hydrogenation reactions of C₂H₄ on the VS_1-3, V₂S₂ clusters. The H₂ molecule is predicted to be adsorbed on the V sites of VS_1,2C₂H₄ and V₂S₂C₂H₄ clusters, and dissociate to form -VH and/or -SH groups. On the VS₃C₂H₄ cluster, the H-H bond of the H₂ molecule ruptures directly on two adjacent S sites and forms -SH groups. Theoretical calculations suggest that the reaction of the H₂ molecule on the V_mS_nC₂H₄ cluster is associated with electron density localized on different active sites. Sufficient electron spin density on V or S atoms is responsible for the adsorption or dissociation of H₂. The H atoms of -VH and -SH groups transfer to C₂H₄ step by step. The ethane molecule can be formed through an ethyl intermediate species which bonds to an active V site, and desorbs to the gas phase with the catalytic V_mS_n cluster unchanged. Additionally, all reactions are estimated as overall barrierless or with a small barrier (~0.1 eV), in thermodynamically favorable processes. A catalytic cycle for the hydrogenation reaction of C₂H₄ on a condensed phase vanadium sulfide catalyst surface is proposed based on the present gas phase cluster experimental and theoretical studies. The exposed V sites on a vanadium sulfide catalyst surface are suggested to be important for holding the C₂H₄ and H₂ molecules; S sites near an active V site are responsible for breaking the H-H bond of the adsorbed H₂ molecule.

♦ Ammonia generation from reaction of H₂ with neutral cobalt nitride clusters

Mass peaks Co_mNH₃ (m = 7, 8, 9) are observed for reactions of hydrogen with the Co_mN_n clusters. Theoretical DFT calculations are performed to explore the potential energy surface for the reaction Co₇N + 3/2H₂ → Co₇NH₃, and a barrierless, thermodynamically favorable pathway is obtained. The odd number of hydrogen atoms in Co_mNH₃ (m = 7, 8, 9) clusters probably arise from the hydrogen molecule dissociation reaction on two active cobalt nitride clusters based on the DFT calculations: for example, 2Co₇N + H₂ → 2Co₇NH. Both experimental observations and theoretical calculations suggest that the reaction of ammonia generation requires two active clusters, and hydrogen dissociation on these two active clusters is the key step to form NH₃ in the gas phase reaction. Clusters Co_mN (m = 7, 8, 9) have high reactivity with H₂ for ammonia generation. A catalytic cycle for ammonia generation from N₂ and H₂ on a cobalt catalyst surface is proposed based on the present gas phase cluster experimental and theoretical studies. Dissociation of N₂ is a very difficult step due to the high bond energy for N≡N. Efficient N₂ activation requires more investigation, and should be considered in practical catalysis. H₂ molecules can attach to Co sites, and the activation of the H-H bond is a barrierless process. The dissociated hydrogen atom is attached to two cobalt sites, one of which is connected to a nitrogen atom. Then, the dissociated H atoms can transfer stepwise to the active nitrogen, and the ammonia molecule can be formed and desorbed to the gas phase. Two adjacent active sites may promote hydrogen dissociation, and we suggest that sites, whose structures are like Co_7-9N, have high reactivity with H₂ for ammonia generation.

♦ Methanol and Formaldehyde formation from reaction of CO and H₂ on neutral Fe₂S₂ clusters

A strong size dependent reactivity of (FeS)_m clusters toward CO is characterized: an association reaction is observed for the Fe₂S₂ cluster; the reaction FeS + CO → Fe + OCS is found for the FeS cluster; and no association products are observed on (FeS)_3,4 clusters due in part to their weaker interaction with CO molecules. Products Fe₂S₂¹³COH₂ and Fe₂S₂¹³COH₄ are identified for reactions of ¹³CO with H₂ on Fe_mS_n clusters; this chemistry suggests that Fe₂S₂ clusters have high catalytic activity for hydrogenation reactions of CO to form formaldehyde and methanol. DFT calculations are additionally performed and the following conclusions can be drawn from the theoretical studies: (1) neutral carbonyl sulfide (OCS) is suggested to be generated from the reactions of FeS with CO at room temperature; (2) reaction of Fe₂S₂ + CO + 2H₂ → Fe₂S₂ + CH₃OH is barrierless and thermodynamically favorable, and the formaldehyde formed on the reaction potential energy surface is a very important intermediate for the methanol formation ; and (3) the Fe atoms are active sites for (FeS)_1,2 clusters to attach CO molecules. The H₂ molecule is also predicted to be adsorbed on Fe sites of Fe₂S₂ clusters. The attached H₂ molecule dissociates on the active Fe site, and one H atom transfers to the adjacent S site to form -FeH and -SH moieties. Electron spin density on Fe and S atoms is correlated with the adsorption of CO and H₂, and also with dissociation of adsorbed H₂. The various reaction mechanisms explored by DFT are in good agreement with the experimental results. The exposed Fe₂S₂ units on an iron sulfide catalyst surface are suggested to be active sites for methanol synthesis through reaction of carbon monoxide and hydrogen.

♦ O-Atom transport catalysis by neutral manganese oxide clusters

Strong cluster size dependent behavior is observed for the oxidation reactions of CO by Mn_mO_n clusters (m = 2-13, n = 1-21). PESs are calculated for CO oxidation reactions on Mn₂O₄,₅ and Mn₃O₇ clusters: CO molecules are predicted to be adsorbed on the Mn_I(IV) site. Reactions for CO to form CO₂ on Mn₂O₅ and Mn₃O₇ clusters are estimated as overall barrierless and thermodynamically favorable processes. Theoretical calculations suggest that activity of Mn₂O₅ and Mn₃O₇ clusters is related to: (1) a Mn_I(IV)-O_t moiety, (2) the HSOMO distribution on the O_t atom, and (3) the bond length of the Mn_I(IV)-O_t bond. Two essential steps are present in the oxidation of CO by Mn_mO_n clusters: (1) the initial intermediate formation that involves a carbon-manganese interaction; and (2) the Mn_I(IV)-O_t bond activation that determines the overall reaction barrier. The Mn-O bond activation energy at room temperature varies from -0.11 (Mn₂O₅) to 0.60 eV (Mn₂O₄). For reactions with C₂H₄, only association products, such as, Mn₂O₅(C₂H₄) and Mn₃O₇(C₂H₄), are observed, which suggests that Mn₂O₅ and Mn₃O₇ clusters, which have high activity for the oxidation of CO, adsorb, but do not oxidize small hydrocarbon compounds. In order to generate a whole catalytic reaction cycle for CO oxidation through commonly used oxidants, reactions of Mn_mO_n clusters with NO₂ and O₂ are also investigated. Small Mn₂O_n clusters are easily oxidized by NO₂, which suggests that the catalytically reactive Mn₂O₅ clusters can be regenerated by NO₂ after reaction with CO: Mn₂O₅ + CO + NO₂ → Mn₂O₄ + CO₂ + NO₂ →Mn₂O₅ + CO₂ + NO. A condensed phase surface catalytic cycle for CO oxidation by NO₂ is proposed based on the present gas phase cluster experimental and theoretical studies. The various reaction mechanisms explored by DFT calculations are in good agreement with the experimental results. The exposed Mn_I(IV) species with only one terminal oxygen on a manganese oxide surface are predicted to be the active catalytic sites for low temperature catalytic oxidation of CO by oxidants like NO₂.

♦ H₂O oxidation by neutral Ti₂O_4,5 clusters under visible light irradiation

A new photo excited fast flow reactor system is constructed and used to investigate reactions of neutral Ti_mO_n clusters with H₂O under visible (532 nm) light irradiation. Association products Ti₂O₄(H₂O) and Ti₂O₅(H₂O) are observed for reactions of H₂O without irradiation. Under 532 nm light irradiation on the fast flow reactor, only the Ti₂O₅(H₂O) feature disappears. This light activated reaction suggests that visible (532 nm) radiation can induce chemistry for Ti₂O₅(H₂O), but not for Ti₂O₄(H₂O). DFT and TDDFT calculations are performed to explore the ground and first excited state PESs for the reactions Ti₂O₅ + H₂O → Ti₂O₄ + H₂O₂. A high barrier (1.33 eV) and a thermodynamically unfavorable (1.14 eV) pathway are obtained on the ground state PES for the Ti₂O₅ + H₂O reaction; the reaction is also thermodynamically unfavorable (1.54 eV) on the first excited state PES. Both the reaction of excited Ti₂O₅ (absorbing a 532 nm photon) with H₂O and the reaction of excited association product Ti₂O₅H₂O (absorbing a 532 nm photon) are able to generate products Ti₂O₄ and H₂O₂ on the ground state PES through a conical intersection between the first excited and ground state potential energy surfaces. The conical intersection is an essential component of the reaction coordinate and mechanism for the water oxidation by Ti₂O₅ under light irradiation. Theoretical studies suggest that electronic excitation of Ti₂O_4,5 clusters is from an O-2p orbital (HOMO) to a Ti-3d orbital (LUMO). The S₀ - S₁ vertical excitation energy of Ti₂O₅ (2.48 eV) is smaller than that of Ti₂O₄ (3.66 eV), possibly because the Ti₂O₅ HOMO is composed mostly of 2p orbitals from single bonded terminal oxygens O_t, while the 2p orbitals for Ti₂O₄ comprising the HOMO are from the double bonded O_t and O_b atoms. The reaction mechanisms explored by calculations are in good agreement with the experimental results. The TDDFT calculated optical absorption spectra of Ti₂O₄ and Ti₂O₅ suggest that the Ti₂O₅ like structures on a titanium oxide surface are better active catalytic sites than Ti2O4 structures for visible light photo-catalysis of water oxidation.

Publicationss

[22]   Shi Yin and Elliot. R. Bernstein, CH bond activation of ethylene by a gas phase neutral Mn₂O₅ cluster under visible light irradiation, J. Phys. Chem. Lett. 2016, 7, 1709-1716. PDF

[21]    Shi Yin and Elliot. R. Bernstein*, Experimental and theoretical studies of H₂O oxidation by neutral Ti₂O_4,5 clusters under visible light irradiation in gas phase, Phys. Chem. Chem. Phys., 2014, 16, 13900-13908. PDF

[20]    Shi Yin, Zhechen Wang and Elliot. R. Bernstein*, O-Atom Transport Catalysis by Neutral Manganese Oxide Clusters in the Gas Phase: Reactions with CO, C₂H₄, NO₂, and O₂, J. Chem. Phys., 2013, 139, 084307. PDF

[19]    Shi Yin, Zhechen Wang, and Elliot. R. Bernstein*, Formaldehyde and methanol formation from reaction of carbon monoxide and hydrogen on neutral Fe₂S₂ clusters in the gas phase. Phys. Chem. Chem. Phys. 2013, 15(13), 4699-4706. PDF

[18]    Shi Yin, and Elliot. R. Bernstein*, Gas phase chemistry of neutral metal clusters: Distribution, reactivity and catalysis. Int. J. Mass Spectrom. 2012, 321, 49-65. PDF

[17]    Shi Yin, Yan Xie and Elliot. R. Bernstein*, Experimental and theoretical studies of ammonia generation: Reactions of H₂ with neutral cobalt nitride clusters. J. Chem. Phys. 2012, 137(12). PDF

[16]    Shi Yin, Yan Xie and Elliot. R. Bernstein*, Hydrogenation Reactions of Ethylene on Neutral Vanadium Sulfide Clusters: Experimental and Theoretical Studies. J. Phys. Chem. A 2011, 115(37), 10266-10275. PDF

[15]    Shi Yin, Shenggui He*, Maofa Ge*, Reaction between sulfur dioxide and iron oxide cationic clusters. Chinese Sci. Bull., 2009, 54, 4017-40200. PDF

[14]    Shi Yin, Wei Xue, Xunlei Ding, Weigang Wang, Shenggui He*, Maofa Ge*, Formation, distribution, and structures of oxygen-rich iron and cobalt oxide clusters in the gas phase. Inter. J. Mass Spectros., 2009, 281, 72-788. PDF

[13]    Shi Yin, Li Yao, Xiaoqing Zeng, Manyu Li, Maofa Ge*, A HeI Photoelectron Spectroscopy and Theoretical Study of 2,6-dichloropyrazine, 2,3-dichloropyrazine, 4,6-dichloropyrimidine and 3,6-dichloropyridazine. J. Mol. Struct., 2008, 872, 24-299. PDF

[12]    Shi Yin, Yanping Ma, Lin Du, Shenggui He, Maofa Ge*, Experimental and theoretical study of the reaction between cationic vanadium oxide clusters and acetylene. Chinese Sci. Bull., 2008, 53(24) 3829-38388. PDF

[11]   Shi Yin, Weigang Wang, Maofa Ge*, The uptake of ethyl iodide on Black Carbon Surface. Chinese Sci. Bull., 2008, 53(5), 733-7388. PDF

[10]   Shi Yin, Weigang Wang, Maofa Ge*, The uptake of isopropyl iodide on black carbon surface. Acta Meteorologica Sinica, 2007, 65(5), 753-7599. PDF

[9]  Zhechen Wang, Shi Yin and Elliot. R. Bernstein, Catalytic oxidation of CO by N₂O conducted by a neutral oxide cluster couple VO₂/VO₃, Phys Chem Chem Phys., 2013, 15, 10429. PDF

[8]  Zhechen Wang, Shi Yin and Elliot. R. Bernstein, Generation and reactivity of putative support systems, Ce-Al neutral binary oxide nanoclusters: CO oxidation and C-H bond activation, J. Chem. Phys., 2013, 139, 194313. PDF

[7]   Zhechen Wang, Shi Yin, and Elliot. R. Bernstein*, Double C-H Bond Activation of Hydrocarbons by a Gas Phase Neutral Oxide Cluster: The Importance of Spin State. J. Phys. Chem. A 2013, 117(11), 2294-2301. PDF

[6]   Zhechen Wang, Shi Yin, and Elliot. R. Bernstein*, Gas-Phase Neutral Binary Oxide Clusters: Distribution, Structure, and Reactivity toward CO. J. Phys. Chem. Lett. 2012, 3(17), 2415-2419. PDF

[5]   Wei Xue, Shi Yin, Xunlei Ding, Shenggui He*, Maofa Ge*, Ground State Structures of Fe₂O_4-6⁺ clusters probed by reactions with N₂. J. Phys. Chem. A, 2009, 113(18), 5302-53099. PDF

[4]   Maofa Ge*, Weigang Wang, Shi Yin, Heterogeneous Chemistry of Dimethyl Sulfide on Soot Surfaces. Chem. Phys. Letters, 2008, 453, 296-3000. PDF

[3]   Maofa Ge*, Weigang Wang, Shi Yin, Carlos Omar Della Vedova, Gas-Phase Generation and Electronic Structure Investigation of Vanadyl Triisocyanate, OV(NCO)₃. Eur. J. Inorg. Chem., 2008，1518-15222. PDF

[2]   Li Yao, Lin Du, Shi Yin, Maofa Ge*, Study on the Atmospheric Photochemical Reaction of CF₃ radical Using Ultraviolet Photoelectron and Photoionization Mass Spectrometer. Sci China Ser B-Chem, 2008, 51(4),316-3211. PDF

[1]    Maofa Ge*, Shengrui Tong, Weigang Wang, Shi Yin, Kinetics and mechanism of SO₂ oxidation by O₃ on the surface of aluminum oxide particles, 《Aerosols: Chemistry, Environmental Impact and Health Effects》, Nova Science Publishers, 2009，Pub. Date: 2009, 2nd Quarter，  ISBN: 978-1-60692-925-44.

Conferencess

[5]     Shi Yin, Z. Wang and E. R. Bernstein, -- Presentation: "Formation, stability, and reactivity studies of neutral iron sulfide clusters" American Physics Society March Meeting, Denver, CO, USA, March 3 - 7, 2014.

[4]]      Shi Yin and E. R. Bernstein, -- Poster: "Experimental and theoretical studies of H₂O oxidation by neutral Ti₂O_4,5 clusters under visible light irradiation in gas phasee" Outstanding Poster Award, 247th American Chemical Society National Meeting, Dallas, TX, USA, March 16 - 20, 2014.

[3]]      Shi Yin , Z. Wang and E. R. Bernstein, -- Presentation: "Gas Phase Neutral Metal Oxide Clusters: Distribution, Reactivity, and Catalyssis." 247th American Chemical Society National Meeting, Dallas, TX, USA, March 16 - 20, 2014.

[2]]      Shi Yin and M. Ge -- Presentation: "Heterogeneous Chemistry of Atmospheric Organic Amine." International Symposium on Ambient Air Particulate Matter - Techniques and Policies for Pollution Prevention and Control Meeting, Tianjin, China, 2009.

[1]]      Shi Yin and M. Ge -- Presentation: "Atmospheric Chemistry: Reactive species & Heterogeneous Processes." International Symposium on Gasification and Application Meeting, Shanghai, China, 2008.