Reduction of CO2 with Water on Pt-Loaded Rutile TiO

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Reduction of CO with Water on Pt Loaded Rutile TiO(110) Modeled with Density-functional Theory 2

Naoto Umezawa, Henrik Høgh Kristoffersen, Lasse B. Vilhelmsen, and Bjørk Hammer J. Phys. Chem. C, Just Accepted Manuscript • DOI: 10.1021/acs.jpcc.5b11625 • Publication Date (Web): 18 Apr 2016 Downloaded from http://pubs.acs.org on April 22, 2016

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The Journal of Physical Chemistry

Reduction of CO2 with Water on Pt Loaded Rutile TiO2(110) Modeled with Density-functional Theory Naoto Umezawa*,†,‡, Henrik H. Kristoffersen†, Lasse B. Vilhelmsen†, and Bjørk Hammer† †

Department of Physics and Astronomy and Interdisciplinary Nanoscience Center iNANO, Aarhus University, DK 8000 Aarhus C, Denmark ‡ International Center for Materials Nanoarchitectonics, National Institute for Materials Science (NIMS), 1-1 Namiki, Tsukuba, Ibaraki 305-0044, Japan AUTHOR INFORMATION Corresponding Author *Electric mail: [email protected] Present Addresses

ABSTRACT Photoreduction of CO2 for fuel production is considered to be an ultimate solution to today’s energy crisis. Platinum (Pt) particles are known to promote photocatalysis reactions when loaded on the surface of titanium dioxide (TiO2). In this study, we investigate the initial step of the reduction process of CO2 with water, i.e., the formation of formate, HCOO-, from surface bound CO2 and H2O on rutile TiO2(110) in terms of energetics of initial and final states using density-functional theory calculations. To understand the role of a Pt co-catalyst, chemisorption energies of HCOO and OH on TiO2(110) are investigated with and without a Pt cluster. It is revealed that free electrons provided by the Pt cluster dramatically decrease the chemisorption energy thanks to the electron transfer from high-lying Pt states to unoccupied

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valence states induced by the adsorbates, which facilitates ionization of HCOO- and OH- on the TiO2 surface near the Pt cluster. Direct adsorption of HCOO and OH on the surface of the Pt cluster is also energetically favored.

KEYWORDS CO2 reduction, TiO2, Pt co-catalyst, formate, density-functional theory Introduction Photosynthesis of methane or methanol from CO2 and water has drawn much attention due to a great potential for sustainable fuel production by solar energy conversion. Such attempts were initiated by the pioneering work of Inoue et al.,1 in which the production rate of methane from CO2 photoreduction was found to have a strong correlation with the energy level of the conduction band (CB) of heterogeneous photocatalysts. According to this work, semiconductors with a higher conduction band, such as CdS or SiC, exhibit higher production rates, and thus are considered to be suitable for the CO2 photoreduction. However, oxide photocatalysts such as TiO2 are still the major players in this field2 for several reasons such as the stability against photo corrosion and surface oxidation. Hence, many attempts have been conducted to improve the photocatalytic performance of TiO2 for CO2 reduction by controlling geometry3, optimizing particle size4, or loading metal co-catalysts.5-10 Recently, it was demonstrated that TiO2 surfaces coated with fine Pt nanoparticles (0.5 - 2nm) greatly enhance the photocatalytic activity for methane production from CO2 reduction.9 Similar effects were found for larger Pt particles (1.8 4.9 nm) which increased the production rate of methane fivefold compared to the case without Pt nanoparticles.10 These results clearly demonstrated that the Pt co-catalyst on TiO2 plays a significant role in the photoreduction of CO2.


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Theoretically, the reduction mechanism of CO2 has been extensively discussed both for anatase11-16 and rutile17 TiO2 surfaces. Lee et al. have pointed out the importance of four-fold coordinated titanium atoms for lowering the reaction barrier of the rate determining initial step of formate (HCOO-) formation.13 The reaction pathway from CO2 plus hydrogen to formate has been investigated by means of electron paramagnetic resonance measurements and firstprinciples calculations.14 He et al. have discussed the energetics of several reaction pathways for the production of HCOOH or CO on anatase TiO2(101) using density-functional theory calculations and suggested that cation doping into the subsurface of TiO2 can lower the reaction barriers.15 Sorescu et al. have studied adsorption and diffusion of CO2 on anatase TiO2(101) using dispersion-corrected density functional theory and found that surface defects such as oxygen vacancies and titanium interstitials promote dissociation as well as adsorption of CO216 in agreement with experimental information.18 Furthermore, an adsorbed formate was found to be much more stable than individual adsorption of CO2 + H2O or CO2+ OH on rutile TiO2(110).17 However, the role of Pt co-catalysts for CO2 reduction with water has never been discussed from theory. In this study, we investigate the effects of a Pt co-catalyst on the relative stability of HCOO and OH chemisorption over H2O and CO2 physisorption on rutile TiO2(110). Our computational results show that a Pt cluster on the surface of TiO2 acts as an electron reservoir providing free electrons that assist chemisorption of HCOO and OH. Although our research is motivated by the following chemical reaction: CO2 + H2O + 2e- HCOO- + OH-,

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we restrict our investigation to the energetics of initial and final states and any intermediate states and their reaction barriers are not discussed in this study. Computational details Our electronic structure calculations are based on density-functional theory (DFT). The exchange-correlation energy functional is represented by the generalized-gradient approximation proposed by Perdew, Burke, and Ernzerhof (PBE).19 Projector-augmented wave pseudopotentials are employed as implemented in the VASP code.20,21 The valence configurations of the pseudopotentials are 3p63d34s1 for Ti and 2s22p4 for O. We use an energy cutoff of 400 eV in the plane-wave basis set expansion. Monkhorst-Pack k-point sets of 6×6×6 are adopted for a 6atom unit cell of bulk rutile TiO2 (space group P42/mnm). The cell volume and atomic positions of the unit cell are relaxed until the total energy difference converged to less than 0.001 eV. The bulk lattice constants optimized by our DFT calculations are a= 4.60 Å and c= 2.96 Å in good agreement with experimental values (a= 4.58666 Å and c= 2.95407 Å).22 A (4×2) periodic slab model is used for rutile TiO2(110), which contains 2 layers of TiO2 and 16 Å of vacuum. The kpoint sets are sampled at 2×2×1 for the slab model. Atomic positions in the model structures are fully relaxed, but with a fixed Ti atom in the bottom layer. To investigate the effect of Pt cocatalyst, we introduce a Pt cluster consisting of ten platinum atoms (Pt10) on a trough of TiO2(110). The geometry of Pt10 has been individually optimized with a genetic algorithm method23,24 and further relaxed after the deposition on the TiO2(110) slab. The atomic coordinates of the model structure of Pt10/TiO2(110) are listed in Table S1. The adhesion energy of Pt10 on the surface of TiO2(110) was estimated to be 3.7 eV. The size of Pt10 is comparable to


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that of the Pt nanoparticles used in the experiment.9 The bond lengths and angles of CO2 and H2O were initially set at experimental values and fully relaxed on each surface model. Results and discussions The present work will proceed as a series of ground state density functional theory calculations for dissociation energies that are defined by energy differences of the chemisorbed HCOO + OH and physisorbed CO2 + H2O on TiO2 supports. We start by establishing the role of the presence or not of the Pt10 cluster on the surface for the overall stability of the adsorbates. Figure 1 presents the binding of CO2 + H2O or HCOO + OH to Ti-trough sites on a stoichiometric TiO2(110) surface. It is understood that there is no significant energy difference in the two molecular configurations of physisorbed CO2 + H2O (CO2 being parallel -0.66 eV or vertical -0.65 eV to a Ti-trough) on TiO2(110). Coming to the HCOO + OH chemisorption, the bidentate mode, where both of the oxygen atoms in HCOO coordinate to Ti atoms, is found to be more stable than the monodentate mode where only one oxygen atom coordinates to a Ti atom in the surface. However, HCOO + OH is 4.58 eV less stable than CO2 + H2O, and thus such dissociation is unlikely to occur on stoichiometric TiO2.


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Figure 1. Energy diagram for chemisorption energies of HCOO and OH with respect to a physisorption of CO2 and H2O on TiO2(110). Blue, red, black, and pink particles are Ti, O, C, and H atoms, respectively.

We now investigate the influence of a co-adsorbed Pt10 cluster on the overall stability of the chemisorption. The structure of the Pt10 cluster on the TiO2 (110) surface has been determined by a genetic algorithm search. We consider both the direct and the indirect interaction of adsorbates with Pt10. By direct, we mean the situation of adsorbates binding directly to the metal cluster, while by indirect we mean the perturbation of adsorbates in the Ti-trough neighboring that of the Pt10 cluster. The configurations considered are shown in Figure 2. The chemisorption becomes exothermic (-0.45 eV) with respect to physisorption when both HCOO and OH are adsorbed on a surface of Pt10. The chemisorption energy is much lower than the case in which adsorbates are adsorbed on a Ti-trough of TiO2(110) neighboring to Pt10 (+0.17 eV). The increased stabilization


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on the Pt10 cluster may be related to image charge effects,25 as both HCOO and OH are found to be negatively charged. In some models shown in Figure 2, two adsorbates are located at far distant sites. In those cases, we assume that protons are sufficiently mobile to have such chemisorption occur.

Figure 2. Energy diagram for chemisorption energies of HCOO and OH on various adsorption sites on Pt10/TiO2(110) with respect to a physisorption of CO2 and H2O on a trough of TiO2(110) in Pt10/TiO2(110). Blue, red, black, pink, and gray particles are Ti, O, C, H, and Pt atoms, respectively. In Figure 3, three cases are further compared to understand the dramatic decrease of the chemisorption energy with the presence of Pt10. In Figure 3a, a model structure of HCOO and OH formed on a Ti-trough of a clean TiO2 (110) surface (model A) is shown. In Figure 3b, the Pt10 cluster is included in the Ti-trough neighboring to the adsorption sites, i.e. leaving the


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adsorbates adsorbed without any direct interaction with the cluster (model B). In Figure 3c, adsorbates are directly placed on the surface of Pt10 instead of Ti-trough (model C). The role of the Pt10 cluster can be gauged from the chemisorption energetics reported in the figure, which are given relative to CO2 and H2O physisorbed on the same support. On the clean surface, model A, the dissociation is unfavored as its energy cost is as much as 4.58 eV suggesting the clean surface to be inert to any such reaction. Introduction of the Pt10 cluster, model B, leads to a sizable stabilization of the chemisorbed species. In fact, it is now almost thermoneutral (the energy cost is only 0.17 eV) for the dissociation. The further drop of the dissociation energy (0.45 eV) was observed in model C where both HCOO and OH are directly adsorbed on the surface of Pt10.

Figure 3: Relaxed geometries of HCOO and OH on a Ti-trough of (a) a clean TiO2(110) surface (model A), (b) Pt10 introduced TiO2(110) surface (model B), and (c) on the surface of Pt10 loaded on TiO2(110) (model C). Blue, red, grey, black, and pink particles represent the positions of Ti, O, Pt, C, and H atoms, respectively. Adsorption energy of each model with respect to CO2 and H2O co-adsorption on the same support is also shown on each panel. Total and local density of states (DOS) for the models A, B, and C are shown in (d), (e), and (f), respectively. The width of


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smearing was set at 0.1 eV. For the local DOS, we use spheres of radii 1.323 Å for Ti, 0.82 Å for O, 1.455 Å for Pt, 0.863 Å for C, and 0.37 Å for H. The zero energy is at the conduction-band minimum of a clean surface of TiO2(110), and is corrected for the surfaces with a Pt10 or adsorbates such that the averaged electro-static potential of a Ti atom located at the back side of the slab is aligned with that of the clean TiO2(110). The vertical broken line denotes the highest occupied state of each system. The dependence of the dissociation energy on the support can be rationalized by inspection of the electronic density of states of the three cases as done in Figure 3d, 3e, and 3f for model A, B, and C, respectively. First, Figure 3d shows how the clean surface with the adsorbates has the full energy gap of the TiO2, which in our calculation setup comes out as 1.8 eV owing to the usual DFT underestimation of semi-conductor band gaps. The highest occupied state, which is denoted as a vertical broken line, is pinned at 0.4 eV below the top of the valence band, with some states right at the top of the valence band being empty. The holes thus appearing reveal that the adsorbates are negatively charged in accord with the adsorbate projected DOSs (curves denoted “HCOO” and “OH” in the figure) having intensity at energies right below the valence band edge. The formal charge of both HCOO and OH is -1 and two holes are, therefore, induced at the top of the valence band. Moving to Figure 3e, the DOS is shown for the case with the Pt10 cluster coadsorbed with adsorbates (model B). Now, the gap region is filled with electronic states of the Pt cluster and the highest occupies state is shifted to the top of the gap/bottom of the conduction band. While, the adsorbate states remain at right below the valence band edge, and the comparison of DOSs for model A and B thus offers a simple explanation for the increased stability of the adsorbates in the presence of the Pt10 cluster: Two electrons are transferred from the HOMO of the Pt10 cluster to the empty states at the top of the valence band. Thus, each electron gains energy corresponding to the energy difference of the highest occupied states of the two models (1.95 eV) (see Fig. 3d and Fig. 3e). This explains the stabilization effect of HCOO and OH on the introduction of Pt10, i.e. the system with Pt10 gains energy from the two-electron


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transfers (1.95 eV × 2 electrons = 3.9 eV). This energy gain is somewhat consistent with the adsorption energy differences of the two models (4.4 eV). The rest of the energy gain should come from the local atomic relaxations near adsorbates. Coming to the case with both HCOO and OH directly adsorbed on Pt10 surface (Figure 3c, model C), which is the same model as the one giving the minimum dissociation energy in Figure 2, the adsorbate states are delocalized owing to the hybridization with Pt states (Figure 3f). As a result, the center of mass in the local DOS of the adsorbates is shifted downwards compared to those in model A or B, indicating the formation of strong covalent bonds. The Pt-O bond formation further stabilizes the system as understood from the significantly lower dissociation energy of model C. The above interpretation of the strengthened adsorption upon the introduction of Pt10 is further supported by our Bader charge analysis. In Table 1, Bader charges of adsorbate atoms and Pt10 are listed for the three models A, B, and C. It is clear that negative charge on HCOO and OH is increased in model B compared to that in model A due to the promoted electron transfer from Pt10 cluster to the adsorbates. While the ionization of HCOO and OH is limited in model C because of the competing effect of the formation of covalent bonds. The averaged Bader charge of Pt10 is more positive in model C than in model B, indicating that more electrons locate at Pt-O bond centers. Finally, we would like to comment on the effect of dispersion correction which is not included in the present study. The physisorption energy of a single CO2 molecule on a clean TiO2(110) surface was calculated to be -0.10 eV in the present work, while it is -0.45 eV when dispersion corrections are taken into account as reported in Ref. 17. The physisorption energy of CO2 and H2O should be mostly affected by the dispersion forces and the dissociation energies discussed in this work are rigidly shifted by applying the dispersion correction. Therefore, the relative


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stabilities of chemisorbed HCOO + OH on different sites are not affected by the dispersion correction and our conclusion should still hold. Conclusion In summary, we studied the effects of a Pt cluster on the formation of HCOO and OH on TiO2(110) using density-functional theory calculations. It was revealed that the HCOO and OH chemisorption is especially promoted directly on the surface of the Pt cluster or on TiO2(110) in the immediate vicinity of a Pt cluster. We attribute this effect to the presence of free electrons available on the metal surface, which facilitate the ionization of HCOO- + OH-. The direct chemisorption of HCOO and OH on a Pt cluster promotes the formation of Pt-O bonds and further stabilizes the system. The results clearly indicate that the surface of a Pt cluster is the reaction site for the first step of the CO2 reduction. The Pt cluster leads to the strongest adsorption of HCOO- + OH-. On such a surface, photoexcited electrons could be continuously supplied from TiO2 to the Pt cluster resulting in sustainable reduction of CO2 molecules. Our results are consistent with experimental observations that loading Pt nanoparticles on the surface of TiO2 can improve the production rate of methane from CO2 and water.9,10 Recently Yang et al. have reported effects of the morphology of supported Pt clusters on CO2 reduction without water for anatase TiO2(010) surface.26 They found that charge accumulation on a carbon site in CO2, which is largely influenced by the size or morphology of a loaded Pt cluster, exhibits a strong correlation with the O-C-O angle. Clarification of such geometrical effects of Pt clusters as well as intermediate states of the reduction process should be next steps for further understanding of the reduction reaction of CO2 with water on Pt/TiO2. Acknowledgement


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This work was supported by Japan Society for the Promotion of Science and University Denmark researchers exchange program, FY2013 and from the COST Action CM1104. Supporting Information Available: [Atomic coordinates for a model structure of a Pt10 cluster loaded on TiO2(110) are listed in the format of POSCAR file of VASP.] This material is available free of charge via the Internet at http://pubs.acs.org. REFERENCES (1) Inoue, T.; Fujishima, A.; Konishi, S.; Honda, K. Photoelectrocatalytic Reduction of Carbon Dioxide in Aqueous Suspensions of Semiconductor Powders. Nature 1979, 277, 637-638. (2) Izumi, Y. Recent Advances in the Photocatalytic Conversion of Carbon Dioxide to Fuels with Water and/or Hydrogen using Solar Energy and Beyond. Coord. Chem. Rev. 2013, 257, 171186. (3) Mori, K.; Yamashita, H.; Anpo, M. Photocatalytic Reduction of CO2 with H2O on Various Titanium Oxide Photocatalysts. RSC Adv. 2012, 2, 3165-3172. (4) Koci, K.; Obalova, L.; Matejova, L.; Placha, D.; Lacny, Z.; Jirkovsky, J.; Solcova, and O. Effect of TiO2 Particle Size on the Photocatalytic Reduction of CO2. Appl. Catal., B 2009, 89, 494-502. (5) Ishitani, O.; Inoue, C.; Suzuki, Y.; Ibusuki, T. Photocatalytic Reduction of Carbon Dioxide to Methane and Acetic Acid by an Aqueous Suspension of Metal-deposited TiO2. J. Photochem. Photobiol., A 1993, 72, 269-271.


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(6) Zhang, Q.-H.; Han, W.-D.; Hong, Y.-J; Yu, J.-G. Photocatalytic Reduction of CO2 with H2O on Pt-loaded TiO2Catalyst. Catal. Today 2009, 148, 335-340. (7) Uner, D.; Oymak, M. M. On the Mechanism of Photocatalytic CO2 Reduction with Water in the Gas Phase. Catal. Today 2012, 181, 82-88. (8) Feng, X.; Sloppy, J. D.; LaTempa, T. J.; Paulose, M.; Komarneni, S.; Bao, N.; Grimes, C. A. Synthesis and Deposition of Ultrafine Pt Nanoparticles within High Aspect Ratio TiO2 Nanotube Arrays: Application to the Photocatalytic Reduction of Carbon Dioxide. J. Mater. Chem. 2011, 21, 13429-13433. (9) Wang, W.-N.; An, W.-J.; Ramalingam, B.; Mukherjee, S.; Niedzwiedzki, D. M.; Gangopadhyay, S.; Biswas, P. Size and Structure Matter: Enhanced CO2 Photoreduction Efficiency by Size-Resolved Ultrafine Pt Nanoparticles on TiO2 Single Crystals. J. Am. Chem. Soc. 2012, 134, 11276-11281. (10) Xie, S.; Wang, Y.; Zhang, Q.; Fan, W.; Deng, W.; Wang, Y. Photocatalytic Reduction of CO2 with H2O: Significant Enhancement of the Activity of Pt–TiO2 in CH4 Formation by Addition of MgO. Chem. Comm. 2013, 49, 2451-2453. (11) Indrakani, V. P.; Kubicki, J. D.; Schobert, H. H. Quantum Chemical Modeling of Ground States of CO 2 Chemisorbed on Anatase (001), (101), and (010) TiO 2 Surfaces. Energy Fuels 2008, 22, 2611-2618. (12) Indrakanti, V. P.; Schobert, H. H.; Kubicki, J. D. Quantum Mechanical Modeling of CO2 Interactions with Irradiated Stoichiometric and Oxygen-Deficient Anatase TiO2 Surfaces: Implications for the Photocatalytic Reduction of CO2. Energy Fuels 2009, 23, 5247-5256.


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(13) Lee, D.; Kanai, Y. Role of Four-Fold Coordinated Titanium and Quantum Confinement in CO2 Reduction at Titania Surface. J. Am. Chem. Soc. 2012, 134, 20266-20269. (14) Dimitrijevic, N. M.; Vijayan, B. K.; Poluektov, O. G.; Rajh, T.; Gray, K. A.; He, H.; Zapol, P. Role of Water and Carbonates in Photocatalytic Transformation of CO2to CH4 on Titania. J. Am. Chem. Soc. 2011, 133, 3964-3971. (15) He, H.; Zapol, P.; Curtiss, L. A. Computational Screening of Dopants for Photocatalytic Two-electronreduction of CO2 on Anatase (101) Surfaces. Energy Environ. Sci., 2012, 5, 6196-6205. (16) Sorescu, D. C.; Al-Saidi, W. A.; Jordan, K. D. CO2 Adsorption on TiO2(101) Anatase: a Dispersion-corrected Density Functional Theory Study. J. Chem. Phys. 2011, 135, 124701 (117). (17) Sorescu, D. C.; Lee, J.; Al-Saidi, W. A.; Jordan, K. D. Coadsorption Properties of CO2 and H2O on TiO2 Rutile (110): a Dispersion-corrected DFT Study. J. Chem. Phys. 2012, 137, 074704 (1-16). (18) Henderson, M. A. Evidence for Bicarbonate Formation on Vacuum Annealed TiO2(110) Resulting from a Precursor-mediated Interaction between CO2 and H2O. Surf. Sci., 1998, 400, 203-219. (19) Perdew, J. P.; Burke, K.; Ernzerhof, M. Generalized Gradient Approximation Made Simple. Phys. Rev. Lett. 1996, 77, 3865-3868.


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(20) Kresse, G.; Hafner, J. Ab initio Molecular Dynamics for Liquid Metals. Phys. Rev. B 1993, 47, 558-561. (21) Kresse, G.; Furthmüller, J. Efficient Iterative Schemes for Ab Initio Total-energy Calculations Using a Plane-wave Basis Set. Phys. Rev. B 1996, 54, 11169-11186. (22) Burdett, J. K.; Hughbanks, T.; Miller, G. J.; Richardson Jr., J. W.; Smith, J. V. Structuralelectronic Relationships in Inorganic Solids: Powder Neutron Diffraction Studies of the Rutile and Anatase Polymorphs of Titanium Dioxide at 15 and 295 K. J. Am. Chem. Soc. 1987, 109, 3639-3646. (23) Martinez, U.; Vilhelmsen, L. B.; Kristoffersen, H. H.; Mørller, J. S.; Hammer, B. Steps on rutile TiO2(110): Active Sites for Water and Methanol Dissociation. Phys. Rev. B 2011, 84, 205434 (1-6). (24) Vilhelmsen, L. B.; Hammer, B. A Genetic Algorithm for First Principles Global Structure Optimization of Supported Nano Structures. J. Chem. Phys. 2014, 141, 044711 (1-11). (25) Lang, N. D.; Kohn, W. Theory of Metal Surfaces: Induced Surface Charge and Image Potential. Phys. Rev. B, 1973, 7, 3541-3550. (26) Yang, C.-T.; Wood, B. C.; Bhethanabotla, V. R.; Joseph, B. The Effect of the Morphology of Supported Subnanometer Pt Clusters on the First and Key Step of CO2 Photoreduction. Phys. Chem. Chem. Phys. 2015, 17, 25379-25392.


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Table 1. Calculated Bader charges for adsorbates and Pt10 for models A, B, and C in accord with the geometries shown in Figures 3a, 3b, and 3c. Atomic species

Model A

Model B

Model C

HCOO H

0.67

0.64

0.63

C

1.57

1.54

1.47

O

-1.06

-1.13

-1.04

O

-1.11

-1.15

-1.04

OH O

-1.05

-1.05

-1.02

H

0.10

0.06

0.12

-0.14

-0.18

-0.14

--

0.13

0.17

Adsorbates on average Pt10 on avarage


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Reduction of CO2 with Water on Pt-Loaded Rutile TiO

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