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The Control of Selectivity through a New Hydrogen-Transfer Mechanism in Photocatalytic Reduction Reactions: ElectronicallyRelaxed Neutral H and the Role of Electron-Phonon Coupling Samiksha Poudyal, Morghan Parker, and Siris Laursen J. Phys. Chem. Lett., Just Accepted Manuscript • DOI: 10.1021/acs.jpclett.9b01614 • Publication Date (Web): 29 Jul 2019 Downloaded from pubs.acs.org on July 30, 2019

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The Journal of Physical Chemistry Letters

The Control of Selectivity through a New Hydrogen-Transfer Mechanism in Photocatalytic Reduction Reactions: Electronically-Relaxed Neutral H and the Role of Electron-Phonon Coupling Samiksha Poudyal, Morghan Parker, and Siris Laursen∗ Department of Chemical and Biomolecular Engineering, University of Tennessee, Knoxville, TN, 37996 E-mail: [email protected] Abstract Controlling the fate of hydrogen in photocatalytic synthesis reactions has been an ongoing challenge in CO2 reduction by H2 O and nitrogen fixation efforts. Our studies have identified catalysts (SiC) that exhibit dramatically improved selectivity towards hydrogenation and a photocatalytically-active ground-state neutral H that is transferred via vibrational excitation through electronic-vibrational coupling with excited states. This new species and mechanism have been directly connected to the fate of H by comparing GaN and SiC and purposefully manipulated over a single catalyst (SiC) to illustrate generality. Studies included surface reaction modeling using density functional theory (DFT), experimental performance, H-NMR spectroscopy, and deuterium kinetic isotope effect. The discovery of this mechanism may have considerable impact on the

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direction of photocatalytic synthesis, the understanding of the coupling of thermal and photoelectrochemical reaction steps, and electronic-vibrational spectrum coupling in energy sequestration.

Progress in the photocatalytic synthesis of increasingly complex molecules from CO2 or N2 and H2 O has been limited due to a lack of a mechanistic understanding of the surface reaction, viable design rules for catalyst discovery and optimization, and reliable experimental results not affected by organic contamination. Focusing on the photocatalytic reduction of CO2 by H2 O and light only, design of catalysts using a purely electrochemical view of the reaction, e.g., band gap, band edge alignment, and electrochemical CO2 reduction potentials for various products, has otherwise failed to yield a path that allows for systematic activity improvements or control over product selectivity (hydrogenation vs. H2 evolution). Our prior investigations have shown that photocatalyst surface chemistry towards C, O, and H plays a significant role in dictating catalytic activity and the degree of CO2 reduction. 1,2 These studies also suggested that catalyst surface reactivity and electronic properties can produce unique surface-bound atomic H that dramatically shifts selectivity away from H2 evolution to hydrogenation. Herein, we focus upon understanding how the nature of atomic H from H2 O dissociation dictates the fate of H in the reaction. This study highlights the discovery of photocatalytically-active neutral H, a new H-transfer mechanism in photocatalysis, and how the transfer mechanism and stability of atomic H correlate well with the ability of the catalyst to achieve hydrogenation and limit unselective H2 evolution. 2


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Photocatalytic CO2 reduction by H2 O has been demonstrated in many studies, yet control of catalyst selectivity towards hydrogenation vs. H2 evolution has not, nor have the catalytic properties that dictate this selectivity been fundamentally determined. 1,3–6 The inherent bias induced by investigating catalytic activity at or near room temperature has focused the community on oxides and nitrides that greatly favor H2 evolution over hydrogenation and remove oxygen from CO2 to a limited degree. 1,7–9 Recent studies by ourselves and others have demonstrated that catalytic activity could be significantly improved by utilizing a concentrated-solar photocatalytic reaction (CSPR) approach that can combine photon and thermal energy inputs within one photocatalytic reaction. Elevated temperatures are achieved in CSPR via autogenous heating through light absorption or via ancillary electrical heating. 1,6,10,11 Our studies show that these new reaction environments clearly enhance the activity of alternative non-oxide/nitride photocatalysts, e.g., SiC. In fact, under CSPR conditions, SiC exhibited one of the highest rates for CH4 production from CO2 and H2 O only in comparison to other verifiably-organic-free reaction systems. 1 Our studies further indicate that the elevated surface reactivity available over SiC may stabilize reaction intermediates, facilitate C–O bond cleavage, and dramatically shift selectivity from H2 evolution to hydrogenation. 1,2 These studies also suggested that different types of surface-bound atomic H and their transfer mechanisms may dictate product selectivity. For example, SiC under CSPR conditions demonstrated an unprecedented selectivity towards hydrogenation vs. H2 evolution, e.g., CH4 :H2 of 1:9. Whereas, GaN exhibited high activity and a significant selectivity preference for H2 production, e.g., CH4 :H2 of 1:1000+. The elevated reactivity of SiC appeared to be one source of these differences, but could not fully explain the selectivity trends. Therefore, we focus further on understanding the dynamics of H in the reaction. In this study, we have connected the the electronic nature and stability of surface-bound atomic H to a new H-transfer mechanism that may be responsible for significant changes in photocatalyst selectivity towards hydrogenation vs. H2 evolution. Kinetic isotope effect (KIE) experiments under CSPR conditions, solid-state 1 H-NMR spectroscopy, and computa3



tional surface science calculations were utilized to scrutinize the electronic nature of atomic H and understand its transfer mechanism over SiC and GaN. The extreme difference in performance of SiC and GaN and the greatly elevated activity of SiC towards CH4 production in the reaction made these materials ideal for the study. Results suggest that the effective electronegativity of the photocatalyst can be selected to produce photocatalytically-active, ground-state neutral atomic H0 from H2 O dissociation that is orders of magnitude more selective towards hydrogenation. Elevated surface reactivity of the catalyst was also determined to contribute to promoting hydrogenation by stabilizing H and carbonaceous intermediates in a highly energetic environment. The effect of H+ vs H0 in determining catalyst selectivity was also demonstrated using the same catalytic material (SiC) to illustrate the effect was not catalyst specific. Kinetic isotope effect (KIE) studies were utilized to access the vibrational aspect of the reaction mechanism and the rate-determining step, specifically to understand whether reaction mechanisms exhibited a vibrational barrier. To shed light on the nature of the hydrogen transfer over SiC and GaN, we employed D2 O as a reactant in CO2 photocatalytic reduction under CSPR conditions (Figure 1). A clear suppression in hydrogenation activity was encountered over SiC towards CH4 production. Presence of KIE (∼1.7 at steady state) towards hydrogenation (CH4 production) suggested a significant vibrational component to the H-transfer mechanism. Strong KIE also indicated hydrogenation is the rate-determining step in the production of CH4 . CO production showed no KIE suggesting a direct CO2 dissociation (redox mechanism) involving no H-transfer steps may be active towards first C–O cleavage, as predicted by our prior computational studies. 2 D2 evolution, on the other hand, showed a reverse KIE in H2 production. Enhanced D2 production may be reasonable when taking into account the decrease in the rate of hydrogenation. However, it could also result from a combined effect of photoelectrochemical and non-electrochemical H-transfer mechanisms active over SiC since SiC also exhibits appropriate electronic structure towards photoelectrochemical H-transfer. On the contrary, no KIE effect was observed over GaN to4


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wards CH4 , CO, or H2 production suggesting that H-transfer steps are photoelectrochemical in nature, i.e., vibrational barriers do not play a role since atomic H are highly destabilized upon reduction by an excited electron. These results suggest that two different H-transfer mechanisms are active over SiC and GaN that likely result in the selectivity differences encountered in experiments.

Figure 1: Gas-phase concentrated-solar photocatalytic activity of SiC and GaN using H2 O or D2 O. SiC exhibited strong KIE of ∼1.7 towards hydrogenation to CH4 at steady state. No KIE was observed in case of CO production. D2 evolution was slightly higher compared to H2 evolution over SiC. GaN did not exhibit KIE towards any products. The differences encountered in KIE and selectivity towards hydrogenation versus H2 evolution over SiC (1:9) vs. GaN (∼1:1000) suggest a unique atomic H on the surface of SiC. To probe the electronic nature of surface-bound atomic H, solid-state H-NMR was utilized (Figure 2). An adsorbate-free SiC was achieved by heating the catalysts at 400◦ C under active turbo pump vacuum (1E-6 Torr) for 30 minutes. H-NMR showed that H0 and H+ (from OH) persisted to a minor extent on the cleaned SiC (black spectra). In the case 5



of GaN, the synthesis procedure involved NH3 as a reducing agent thus it was more difficult producing a clean GaN surface. An already hydrogenated GaN surface with a low signal of protonic H+ (shift ∼3.6 ppm) was all that could be achieved. A similar effect has been reported previously over GaN produced by ammonolysis by others. 12 After dosing 1.0 ML of H2 O, ready dissociation at room temperature over SiC was encountered. H-NMR captured two major species of hydrogens - a neutral H0 (shift at ∼0 ppm) and a protonic H+ with a shift similar to that of H+ in H2 O (shift at ∼4.3 ppm). Ready dissociation of H2 O was also encountered over GaN with two distinct protons produced: N–H+ (shift ∼3.7 ppm) and OH+ (shift at ∼4.4 ppm) close to that of H+ in H2 O (green spectra). Higher loading of H2 O (∼2 ML) was utilized to further track the different H oxidation states produced via dissociative and molecular H2 O adsorption. Addition of more H2 O resulted in a deshielding effect and greater averaging of the nuclear excitation, hence a sharper, solution-like signal dominated in both cases (red spectra). Both H-NMR and KIE studies collectively suggest a connection between the oxidation state of surface-bound atomic H and photocatalytic selectivity towards hydrogenation versus H2 evolution.

Figure 2: Solid state 1 H-NMR of H2 O dissociation over SiC (left) and GaN (right). More significantly shielded neutral H over SiC correlated with improved hydrogenation. H-NMR results directly agree with the oxidation state of surface-bound atomic H and 6


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binding sites encountered in DFT calculations (neutral H0 adsorption atop C site of SiC and protonic H+ adsorption atop N site of GaN). Results are in direct agreement with electronegativity of constituent atoms of both SiC and GaN (Table 1). DFT energetics further suggest highly stabilized surface-bound atomic H over SiC (∆Ediss−ads,H 2 = –2.51 eV), while comparatively less stable atomic H over GaN (∆Ediss−ads,H 2 = –0.66 eV). Results collectively suggest that the transfer of surface-bound H to coadsorbed carbonaceous intermediates towards hydrocarbon synthesis may be directly connected to the production and stability of neutrally charged atomic H. Understanding this new H-transfer mechanism that involves the production and transfer of highly stabilized neutrally charged atomic H for hydrogenation (CH4 production) may be necessary to allow successful tuning of photocatalyst selectivity towards C2+ hydrocarbons and oxygenates.

Figure 3: (a-c) Comparison of the selectivity difference induced by hydrogen oxidation state and transfer mechanism using a single material, SiC. (d) Schema to illustrate the effect of the partial oxidation of SiC on the oxidation state of atomic H. To ascertain whether the effect of oxidation state of atomic H on catalyst product selectivity towards hydrogenation versus H2 evolution is general or catalyst specific, i.e., simply a feature of SiC vs. GaN, we investigated the activity of partially oxidized SiC to capture 7



the H0 vs. H+ effect keeping the catalytic material constant (Figure 3). Incorporation of O atoms on the surface of pristine SiC was expected to result in less stable and more positively charged surface-bound atomic H, which would promote H2 evolution. As expected, CO2 photocatalytic reduction experiments under CSPR conditions resulted in a drastic selectivity change from CH4 to H2 evolution upon partial oxidation of pristine SiC (oxidized at 400◦ C under air for 4 hours). TEM analysis of particle morphology after oxidation indicated no particle size change. DFT investigation of atomic H adsorbed to an O atom of partially oxidized SiC surface (1/3rd ML O coverage) revealed it was protonic in nature and far less stable than H0 adsorbed on stoichiometric SiC (∆∆Ediss−ads,H 2 = +2.78 eV). Solid-state H-NMR further revealed the presence of both protonic H+ and neutral H0 (at ∼2.53 ppm and ∼0.56 ppm, respectively) on the surface of partially oxidized SiC (Figure S9 in the SI). Results revealed an interesting phenomena—the presence of two different reaction sites (C and O) that produced two different nature of atomic H (H0 on C and H+ on O). Again, more stable neutral H0 over pristine SiC correlated with selectivity towards hydrogenation and less stable H+ over partially oxidized SiC correlated with selectivity towards H2 evolution. This selectivity trend observed over the same material further solidifies the effect of stability of atomic H and its oxidation state in dictating the product selectivity. To understand the observed phenomenon at the mechanistic level, we highlight the current understanding of the photocatalytic H-transfer mechanism and the aspects of this understanding that are challenged by our results. It is generally accepted that the mechanism involves the production of protonic H from H2 O dissociation, electrochemical reduction of the proton by excited e− to produce destabilized H0 , and transfer of the destabilized H0 with little to no vibrational barrier (Figure 4(a)). This mechanistic view is consistent with what Table 1: Dissociative H2 adsorption and Bader charge analysis of atomic H adsorbed on SiC and GaN surfaces with the electronegativity of the semiconductor constituent elements. Catalyst Eads−H (eV) Charge on H (e-) SiC –2.51 +0.04 GaN –0.66 +1.00 8


EN of atoms Si(1.9), C(2.5) Ga(1.8), N (3.0)

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is observed in our studies of GaN where protonic H was observed in H-NMR and no KIE was observed in either H2 or CH4 production. The absence of a kinetically important vibrational barrier in the transfer of H in the classically understood mechanism illustrates that H must be significantly destabilized through its reduction and catalyst surface reactivity must be low enough to enable H-transfer at the commonly low reaction temperature employed in most studies. This mechanistic feature suggests that the surface chemistry of room-temperatureactive photocatalysts can be tuned only to a minor extent before the materials cease to exhibit activity further limiting control of the fate of H to electronic factors of reaction intermediates. Moreover, entropic effects that promote small molecule production may also be prevalent and promoted because of degree of H0 destabilization required for H-transfer at low-T. The absence of a selectivity change in GaN when utilized in CSPR conditions further supports this view. 1,2 The lack of success of the community to demonstrate the required control using common oxide or nitride catalysts tested near ambient temperatures in condensed H2 O illustrate the difficulty in controlling electronic features of the intermediates to control selectivity. The presence and photocatalytic activity of neutrally charged atomic H over SiC surface suggests a new H-transfer mechanism may be accessed over more reactive photocatalysts with lower effective electronegativity under CSPR conditions. We postulate H-transfer of H0 over SiC may occur via a nonradiative decay of excited electrons that results in significant vibrational excitation of the adsorbate (Figure 4(b)). A similar mechanism has been widely reported in the electron or photon-mediated desorption of similar neutral species from metal surfaces. 13–16 This phenomenon promotes markedly higher desorption rates in comparison to purely thermal desorption and changes in reaction pathways that affect selectivity. It is also thermal-like, but operates at a much higher energy scale due to energy available in the excited state. Moreover, the H-transfer via this mechanism also exhibits a strong KIE. The exact mechanism of this effect is still unclear, but it is postulated that it operates via nonradiative energy dissipation through a coupling of electronic and vibrational states which 9



leads to significant vibrational excitation of the adsorbate that drives coupling or associative desorption. 14–17 The effect has also been demonstrated over semiconductor surfaces of oxides and nitrides. 18–24 It has also been unknowingly demonstrated over materials that contain a metal co-catalyst in KIE studies in water-splitting. 25–27 The presence of this phenomenon and its connection to vibrational energy and selectivity changes suggests that many new routes may be available for photocatalyst tuning and new roles for catalyst surface chemistry (Figure 4(c)).

Figure 4: (a) Classical view of the photoelectrochemical reaction potential energy surface (b) Proposed vibrational-excitation H-transfer mechanism of neutral H over SiC. (c) PES illustrating electrochemical and electronic-vibrational coupling mechanisms. At a greater level, these studies have begun to clarify the interface between purely electrochemical and vibrational reaction steps in photocatalytic reactions and present the possibility of using enhanced catalyst surface chemical reactivity to promote electronic-vibrational coupling for even greater photon energy sequestration and control surface reactions like hydrogenation or C–C coupling. Isolating an electronic-vibrational coupling mechanism that dramatically affects catalyst performance also promotes reconsideration of the catalysts and reaction conditions that are most ideal for the reaction. Allowing the use of catalysts that exhibit higher surface reactivity may help to limit reverse-reaction driving forces and entropic effects that likely promote small molecule production from highly unstable reaction intermediates. Entertaining concentrated illumination reaction conditions in the gas phase 10


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may allow for more significant coupling and excitation of H and other intermediates such that more energetically demanding reactions like CO2 reduction or NH3 synthesis can be promoted, as already shown in our prior studies. 1,6,10,11,28 This effect may also provide energy needed to perform other non-electrochemical steps like C-C coupling or N-N cleavage where no oxidation state change occurs. It may also provide far higher energy than purely thermal heating and allow large energy barriers to be surmounted due to high electronic temperatures. 2,13,14,17 Beyond photon-driven vibrational excitation, the phenomenon may allow for ancillary heating to improve photocatalytic activity, which has been already demonstrated in our prior work. 1 It is also critical to note that high Debye temperature catalysts would be most promising for these new approaches (SiC, Debye T = 927◦ C 29 ). In summary, we have isolated a new H-transfer mechanism for neutral atomic H in photocatalytic reactions that is enabled by the electronic relaxation of protonic H over semiconductors with lower effective electronegativity. The transfer mechanism is photon-driven, vibrational in nature, and clearly connected to the ability of the photocatalyst to effectively hydrogenate carbonaceous intermediates and limit unselective H2 evolution in CO2 reduction by H2 O and light only. The vibrational nature of the mechanism and the more significant energy available through nonradiative excited electron relaxation allowed the elevated surface reactivity of SiC to stabilize intermediates and facilitate hydrogenation. Whereas, the classical electrochemical H-transfer mechanism and lower surface reactivity of GaN led to less stable reaction intermediates and entropically favored CO and H2 production and limited hydrogenation for CH4 production. The greater implications of the study are that: i) photoelectrochemical reaction steps may be combined with high energy vibrational excitation to achieve new catalytic chemistry that is otherwise inaccessible via purely photoelectrochemical or thermochemical routes; ii) photocatalyst surface reactivity can be employed to tune photocatalytic reactions; and iii) photocatalytic transfer of ground-state neutral H is of significant interest in artificial photosynthesis.

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Experimental Method Catalyst synthesis: Beta-SiC (nanoparticles with diameter 240 nm). The catalyst bed heated autogenously to 350◦ C, hence no external heating was necessary. The reactor system was specifically designed to be free of plastic and polymer seals and any other organic contaminants that would otherwise produce questionable results. The reactor body was constructed from ultra-high vacuum conflat flange and quartz window, sealed with copper gaskets, and baked under flowing ultra-high 12


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pure air at 600◦ C for 12 hours before assembly. The reactor bed assembly was constructed with nickel-free grade 420 stainless steel to circumvent the formation of Ni carbonyls that would otherwise affect the quantification of CO production. The optically pure quartz viewport above the catalyst bed allowed irradiation of catalyst. Catalyst bed depth of 2 mm was employed, which limited channeling through the planer (25.4 mm diameter)catalyst bed. Ultrapure SFC grade CO2 and doubly distilled Milli-Q water were used as reactants to produce a hydrocarbon-free reactant flow. The H2 O to CO2 concentration ratio of 10:1 was employed for the study. The incident illumination at the surface of catalyst bed (∼5.1 cm2 ) was approximately 100 Watts or 200 suns. Products were analyzed using an SRI gas chromatograph with flame ionization and thermal conductivity detectors. A high degree of reproducibility was ensured by testing the photocatalytic reactions multiple times. Error bars in plots represent the standard deviation of the data sets. Only CH4 , CO, and H2 were detected as products throughout experiments. Heavy water (D2 O) was employed in CO2 photocatalytic reduction studies in place of H2 O as a reactant for kinetic isotope effect study.

Acknowledgement This work was supported by the National Science Foundation (NSF) under the award CHE1465137. This work used the Extreme Science and Engineering Discovery Environment (XSEDE), which is supported by National Science Foundation grant number ACI-1548562. TEM and XRD analysis were conducted at the Center for Nanophase Materials Sciences (CNMS project number CNMS2016-322) at Oak Ridge National Lab (ORNL), which is a US Department of Energy Office of Science User Facility.

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Supporting Information Available Computational methods, detailed experimental methods and reactor design, characterization results, and computational results are provided in the supporting information document. This material is available free of charge via the Internet at http://pubs.acs.org/.

References (1) Poudyal, S.; Laursen, S. Insights into Elevated-Temperature Photocatalytic Reduction of CO2 by H2 O. The Journal of Physical Chemistry C 2018, 122, 8045–8057. (2) Poudyal, S.; Laursen, S. Photocatalytic CO2 Reduction by H2 O: Insights from Modeling Electronically Relaxed Mechanisms. Catalysis Science & Technology 2019, 9, 1048– 1059. (3) Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K. Photoelectrocatalytic Reduction of Carbon Dioxide in Aqueous Suspensions of Semiconductor Powders. Nature 1979, 277, 637–638. (4) White, J. L.; Baruch, M. F.; Pander III, J. E.; Hu, Y.; Fortmeyer, I. C.; Park, J. E.; Zhang, T.; Liao, K.; Gu, J.; Yan, Y.; Shaw, T. W.; Abelev, E.; Bocarsly, A. B. LightDriven Heterogeneous Reduction of Carbon Dioxide: Photocatalysts and Photoelectrodes. Chemical Reviews 2015, 115, 12888–12935. (5) Li, X.; Yu, J.; Jaroniec, M. Hierarchical Photocatalysts. Chem. Soc. Rev. 2016, 45, 2603–2636. (6) Kho, E. T.; Tan, T. H.; Lovell, E.; Wong, R. J.; Scott, J.; Amal, R. A Review on Photo-thermal Catalytic Conversion of Carbon Dioxide. Green Energy & Environment 2017, 2, 204 – 217.

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Page 14 of 22

Page 15 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(7) AlOtaibi, B.; Fan, S.; Wang, D.; Ye, J.; Mi, Z. Wafer-Level Artificial Photosynthesis for CO2 Reduction into CH4 and CO using GaN Nanowires. ACS Catalysis 2015, 5, 5342–5348. (8) Kuriki, R.; Sekizawa, K.; Ishitani, O.; Maeda, K. Visible-Light-Driven CO2 Reduction with Carbon Nitride: Enhancing the Activity of Ruthenium Catalysts. Angewandte Chemie International Edition 2015, 54, 2406–2409. (9) Diwald, O.; Thompson, T.; Zubkov, T.; Goralski, E.; Walck, S.; Yates, J. Photochemical Activity of Nitrogen-doped Rutile TiO2 (111) in Visible Light. Journal of Physical Chemistry B 2004, 108, 6004–6008. (10) Hoch, L. B.; O’Brien, P. G.; Jelle, A.; Sandhel, A.; Perovic, D. D.; Mims, C. A.; Ozin, G. A. Nanostructured Indium Oxide Coated Silicon Nanowire Arrays: A Hybrid Photothermal/Photochemical Approach to Solar Fuels. ACS Nano 2016, 10, 9017– 9025. (11) Guan, G.; Kida, T.; Harada, T.; Isayama, M.; Yoshida, A. Photoreduction of Carbon Dioxide with Water over K2 Ti6 O13 Photocatalyst Combined with Cu/ZnO Catalyst under Concentrated Sunlight. Applied Catalysis A: General 2003, 249, 11–18. (12) Schwenzer, B.; Hu, J.; Seshadri, R.; Keller, S.; DenBaars, S. P.; Mishra, U. K. Gallium Nitride Powders from Ammonolysis: Influence of Reaction Parameters on Structure and Properties. Chemistry of Materials 2004, 16, 5088–5095. (13) Denzler, D. N.; Frischkorn, C.; Hess, C.; Wolf, M.; Ertl, G. Electronic Excitation and Dynamic Promotion of a Surface Reaction. Physical Review Letters 2003, 91 . (14) Bonn, M. Phonon- Versus Electron-Mediated Desorption and Oxidation of CO on Ru(0001). Science 1999, 285, 1042–1045.

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(15) LaRue, J. L.; Katayama, T.; Lindenberg, A.; Fisher, A. S.; Öström, H.; Nilsson, A.; Ogasawara, H. THz-Pulse-Induced Selective Catalytic CO Oxidation on Ru. Phys. Rev. Lett. 2015, 115, 036103. (16) Kao, F.-J.; Busch, D. G.; Gomes da Costa, D.; Ho, W. Femtosecond versus Nanosecond Surface Photochemistry: O2 +CO on Pt(111) at 80 K. Phys. Rev. Lett. 1993, 70, 4098– 4101. (17) Denzler, D. N.; Frischkorn, C.; Wolf, M.; Ertl, G. Surface Femtochemistry: Associative Desorption of Hydrogen from Ru(001) Induced by Electronic Excitations. J. Phys. Chem. B 2004, 108, 14503–14510. (18) Zhu, X.-Y.; Wolf, M.; Huett, T.; White, J. M. Dynamics of Ammonia Photodesorption from GaAs(100): A Vibration-Mediated Mechanism. Desorption Induced by Electronic Transitions DIET V. Berlin, Heidelberg, 1993; pp 63–66. (19) Petrik, N. G.; Kimmel, G. A. Electron-Stimulated Reactions in Nanoscale Water Films Adsorbed on α-Al2 O3 (0001). Physical Chemistry Chemical Physics 2018, 20, 11634– 11642. (20) Petrik, N. G.; Mu, R.; Dahal, A.; Wang, Z.; Lyubinetsky, I.; Kimmel, G. A. Diffusion and Photon-Stimulated Desorption of CO on TiO2 (110). The Journal of Physical Chemistry C 2018, 122, 15382–15389. (21) Kollmannsberger, S. L.; Walenta, C. A.; Winnerl, A.; Weiszer, S.; Pereira, R. N.; Tschurl, M.; Stutzmann, M.; Heiz, U. Doping-Dependent Adsorption and PhotonStimulated Desorption of CO on GaN(0001). The Journal of Physical Chemistry C 2017, 121, 8473–8479. (22) Diebold, U.; Madey, T. E. Electron Stimulated Desorption (ESD) of Ammonia on TiO2 (110): The Influence of Substrate Defect Structure. Desorption Induced by Electronic Transitions DIET V. Berlin, Heidelberg, 1993; pp 284–288. 16


Page 16 of 22

Page 17 of 22 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


(23) Yoshinobu, J.; Ballinger, T.; Xu, Z.; Jänsch, H.; Zaki, M.; Xu, J.; Yates, J. Ultraviolet Photodesorption of CO from NiO as Measured by Infrared Spectroscopy. Surface Science 1991, 255, 295 – 302. (24) Rosenberg, R. A.; Wen, C.-R.; Mancini, D. C. Temperature-Dependent PSD of H+ from H2 O/Si(111) (7×7). Desorption Induced by Electronic Transitions DIET III. Berlin, Heidelberg, 1988; pp 220–224. (25) Hisatomi, T.; Maeda, K.; Takanabe, K.; Kubota, J.; Domen, K. Aspects of the Water Splitting Mechanism on (Ga1−x Znx )(N1−x Ox ) Photocatalyst Modified with Rh2−y Cry O3 Cocatalyst. The Journal of Physical Chemistry C 2009, 113, 21458–21466. (26) Hisatomi, T.; Miyazaki, K.; Takanabe, K.; Maeda, K.; Kubota, J.; Sakata, Y.; Domen, K. Isotopic and Kinetic Assessment of Photocatalytic Water Splitting on ZnAdded Ga2 O3 Photocatalyst Loaded with Rh2y Cry O3 Cocatalyst. Chemical Physics Letters 2010, 486, 144–146. (27) Hisatomi, T.; Takanabe, K.; Domen, K. Photocatalytic Water-Splitting Reaction from Catalytic and Kinetic Perspectives. Catalysis Letters 2015, 145, 95–108. (28) Westrich, T. A.; Dahlberg, K. A.; Kaviany, M.; Schwank, J. W. High-Temperature Photocatalytic Ethylene Oxidation over TiO2 . Journal of Physical Chemistry C 2011, 115, 16537–16543. (29) Madelung, O., Rössler, U., Schulz, M., Eds. Group IV Elements, IV-IV and III-V Compounds. Part b - Electronic, Transport, Optical and Other Properties; Springer Berlin Heidelberg: Berlin, Heidelberg, 2002; pp 1–4.

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311x432mm (300 x 300 DPI)




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310x310mm (300 x 300 DPI)




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Control of Selectivity through a New Hydrogen ... - ACS Publications

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