Role of Pt Loading in the Photocatalytic Chemistry of Methanol on

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Role of Pt Loading in the Photocatalytic Chemistry of Methanol on Rutile TiO2(110) Qunqing Hao, Zhiqiang Wang, Tianjun Wang, Zefeng Ren, Chuanyao Zhou, and Xueming Yang ACS Catal., Just Accepted Manuscript • DOI: 10.1021/acscatal.8b03359 • Publication Date (Web): 30 Nov 2018 Downloaded from http://pubs.acs.org on December 1, 2018

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Role of Pt Loading in the Photocatalytic Chemistry of Methanol on Rutile TiO2(110) Qunqing Hao,a, b, # ZhiqiangWang,a, c, # Tianjun Wang, a Zefeng Ren,a Chuanyao Zhou,a, *) Xueming Yang a, d, *) a. State Key Laboratory of Molecular Reaction Dynamics, Dalian Institute of Chemical Physics, Chinese Academy of Science, 457 Zhongshan Road, Dalian, 116023, Liaoning, P. R. China b. Science and Technology on Surface Physics and Chemistry Laboratory, P.O. Box No. 9-35, Huafengxincun, Jiangyou, Sichuan Province, 621908, P. R. China c. School of Physics and Optoelectronic Engineering, Xidian University, Xi’an, 710071, P.R. China d. Department of Chemistry, Southern University of Science and Technology, 1088 Xueyuan Road, Shenzhen, Guangdong, 518055, P. R. China

#)

*)

who made equal contribution to this work To whom all correspondence should be addressed: [email protected], [email protected] Tel: +86-411-84379701 Fax: +86-411-84675584

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Abstract As a cocatalyst, Pt is well-known for accepting photoexcited electrons and lowering the overpotential of hydrogen production in photocatalysis, being responsible for the enhanced photocatalytic efficiency. Despite the above existing knowledge, the adsorption of reactants on the Pt/photon-absorber (for example, Pt/TiO2) interface, a prerequisite to understand the photocatalytic chemistry, is extremely difficult to investigate mainly due to the complexity of the powdered material and solution environment. Combining ultrahigh vacuum and well-ordered single crystals, we study the photocatalytic chemistry of methanol on Pt loaded rutile TiO2(110) using temperature-programmed desorption (TPD) and ultraviolet photoelectron spectroscopy (UPS). Despite the same photocatalytic chemical products, i.e., formaldehyde and surface hydrogen species, as on Pt-free TiO2(110), the subsequent chemistry of surface hydrogen species and the photocatalytic reaction rate are much different. The bridging hydroxyls desorb as water molecules around 500 K on Pt-free TiO2(110) surface, by contrast, this desorption channel disappears completely and water and molecular hydrogen desorb at much lower temperature (200 K)

(8)

Molecular hydrogen evolves in two desorption features at 290 K and 550 K respectively (Figure 2F) on both clean and Pt loaded TiO2(110). On a methanol covered ideal clean TiO2(110), no H2 signal has been detected except the fragmentation of methanol.47 We thus tentatively attributed the molecular hydrogen signal to the decomposition of methanol on residual Pt on the TiO2(110) and/or Pt at the sample stage. Compared with Pt free TiO2(110), though low temperature methanol signal on Pt covered TiO2 surface is weaker (Figure 2A), the amount of molecular hydrogen at this temperature is higher. Fragmentation of methanol can not fully account for this part of H2, suggesting scission of CH on Pt also contributes. The high temperature H2 desorption feature at 550 K is consistent with methanol decomposition on Pt.37-39

2H a  heat(  300K )  H 2 g

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Photocatalytic Chemistry of Methanol on TiO2(110) and Pt/TiO2(110)

R: Pt/TiO2(110)

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Figure 3. TPD spectra from 0.5 ML methanol covered (L) clean and (R) 0.058 ML Pt loaded TiO2(110) respectively as a function of 380 nm light illumination. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1. Four masses (m/z=31, 30, 18 and 2) representing the main products and/or their fragmentation from the photocatalytic chemistry of methanol on clean and Pt loaded TiO2(110) are shown. The scales in all the figures are the same while the signal in each figure is multiplied by a value specified at the right bottom corner. Please note the representative illumination time in the left and right panel are different. 15


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The UV light irradiation dependent TPD spectra of possible products from 0.5 ML methanol covered clean and Pt loaded TiO2(110) are displayed in Figure S1. Methanol, formaldehyde, water and molecular hydrogen, which are most relevant to the photochemical reactions, are displayed in Figure 3. The left panel of Figure 3 shows the major photochemical products after the 0.5 ML methanol covered clean TiO2(110) has been exposed to 380 nm light for a few specific time durations. In accord with previous studies,16 the main reactions of methanol on clean TiO2(110) are Reaction 10 and Reaction 7.

CH 3OH Ti5 c  2Ob  hv  CH 2OTi5 c  2Ob H (120 K)

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Methanol (m/z=31, Figure 3A) has been slightly consumed at the high temperature side and formaldehyde (m/z=30, Figure 3B) develops at ～ 260 K and increases with UV light exposure. Resulting bridging hydroxyls reduce the TiO2 surface which is reflected by the increase of the band gap states in Figure 4A.33 The bridging hydroxyls mainly desorb as water (m/z=18, Figure 3C) through the abstraction of lattice bridging oxygen at ～480 K. It should be noted that there is a broad and UV light exposure independent water background ranging from 240 K to 350 K. This water signal corresponds to the adsorption at Ti5c sites and likely comes from residual (from UHV background and/or methanol reagent) water adsorption and also fragmentation of methanol. The H2 (m/z=2, Figure 3D) background remains unchanged with prolonged UV irradiation, suggesting there is no additional H2 production in the photo- and thermal-chemistry. Methyl (Figure S2A), methane (Figure S2B) and carbon monoxide (Figure S2C) shown little UV light irradiation dependence. The right panel of Figure 3 shows the major photochemical products of 0.5 ML methanol on 0.058 ML Pt covered TiO2(110) as a function of 380 nm light illumination. The main desorption feature of methanol at 300 K declines (Figure 3E), new feature develop at 235 K and signal in high temperature 16


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(A) Clean TiO2(110) Illumination (min) 0 3 40

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Figure 4. UPS spectra of the valence electronic structure in the photochemistry of methanol on (A) clean and (B) 0.058 ML Pt loaded TiO2(110). The band gap states, which is a fingerprint of the reduction extent of TiO2(110) due to the presence of ObH in the current work, is enlarged in the inset. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1.

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range increases. The total amount of methanol decreases slightly during the UV light illumination. The shoulder at 235 K resembles the fragmentation of methyl formate during the photochemistry of methanol on TiO2(110).52 However, no methyl formate has been detected at this temperature in the same TPD run. A plausible explanation for such downward shift of the methanol signal is the interaction with surface hydroxyls (which are produced by photocatalyzed dissociation of methanol and will be described later), which has been found on both rutile TiO2(110)16 and TiO2(011)22 surfaces. The signal around 510 K corresponds to recombinative desorption of methoxies and hydroxyls at the Pt/TiO2(110) interface. Enhanced methanol signal at high temperature region suggests the promotion of O-H scission, probably by thermal (UV light induced substrate heating) driven diffusion of Ti5c bounded methanol to Pt/TiO2 interface with a moderate barrier in the 0.5-0.7 eV range.21, 53 Apart from the cracking of methanol, a new feature of mass 30 develops at 265 K (Figure 3F). The identical desorption profiles of mass 30 and mass 29 at this temperature (Figure S3) suggest the chemical is formaldehyde. The desorption temperature of formaldehyde together with the similarity to the photochemistry of methanol on clean TiO2(110)16 suggests the photocatalyzed dissociation of methanol on Pt/TiO2(110) also takes place at the Ti5c sites, transferring the released hydroxyl and methyl hydrogen atoms to other surface sites, either Pt or bridging oxygen or both. UPS from the UV light irradiated methanol/Pt/TiO2(110) (Figure 4B) interface show increase of the band gap states at 1 eV binding energy, indicating the reduction of the surface by the formation of bridging hydroxyls as on clean TiO2(110). H2 (Figure 3H) and CO (Figure S2F) signals at high temperature region are also intensified, indicating more C-H bond cleavage events take place at Pt cluster with UV illumination. Variation of the methyl (Figure S2D) and methane (Figure S2E) signal are within the accuracy of repeated 18


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experiments. As discussed, Pt clusters change the subsequent thermal chemistry of surface hydroxyls dramatically. Instead of the recombinative desorption as water around 500 K, low temperature water signal (Figure 3G) continuously increases. Promoted dissociation of CH3O-H bonds during UV light illumination is responsible for the increasing of low water desorption according to Reaction 8. In addition to the two main hydrogen desorption features at 299 K and 538 K (Figure 3H), a new peak develops at 248 K. Drawing analogy to the desorption of molecular hydrogen from Pt surfaces,54 this low temperature H2 specie most likely originates from the recombinative desorption of atomic hydrogen. Although bridging hydroxyls are produced during the photocatalytic chemistry of methanol on Pt/TiO2(110), no water or hydrogen has been detected at around 500 K as on clean TiO2(110) surface.16, 23

A rough Redhead analysis of the TPD spectra23 shows the desorption energy of molecular hydrogen

and water from hydroxylated TiO2(110) is about 1.4 eV, whereas that for low temperature hydrogen desorption from Pt is 0.66 eV, suggesting the latter is thermodynamically favorable. Therefore, diffusion of bridging hydrogen to Pt cluster is crucial for the low temperature molecular hydrogen production. In fact previous STM study has demonstrated the facile migration of bridging hydrogen with the help of Ti5c bounded methanol molecules.55 Due to the easier desorption of the hydrogen species, their recombination with formaldehyde, the reverse reaction of methanol photodissociation on TiO2(110) surface,31 can be effectively prevented. Kinetics of Photocatalytic Chemistry of Methanol on TiO2(110) and Pt/TiO2(110) Besides altering the reaction channels of surface hydroxyls, Pt loading also enhance the photocatalytic yield and accelerate the photocatalytic chemistry on methanol/Pt/TiO2 interface. Since formaldehyde 19


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Time (min) Figure 5. Comparison of the kinetics of the photocatalyzed oxidation of methanol to formaldehyde on clean (red), 0.058 ML (green) and 0.12 ML (blue) Pt loaded TiO2(110). The red, green and blue lines show the multi-exponential fitting to the experimental data. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1. is the direct photochemical product of methanol on TiO2 and Pt/TiO2, its evolution reflects the kinetics of this reaction. Figure 5 shows the original and normalized (inset graph) formaldehyde production on clean and Pt loaded TiO2(110) respectively. A multi-exponential fitting is used to guide the eye. Compared with the Pt free TiO2(110), the absolute formaldehyde production after equilibrium increases by 30% and 53% respectively when 0.058 ML and 0.12 ML Pt are loaded. It takes 12 minutes, 3.5 minutes and 1.3 minutes for formaldehyde production to reach 90% of its maximum on clean, 0.058 ML Pt loaded and 0.12 ML Pt loaded TiO2(110) respectively. The photocatalytic reaction rate 20


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is accelerated by 9.2 times by 0.12 ML Pt decomposition. Abstraction of photoexcited electrons by Pt is well known in photocatalysis.5 By separating the charge carriers before recombination, the photocatalytic efficiency is then improved. In addition to the role in charge separation, this work suggests other effects of Pt on the photocatalytic chemistry of methanol on TiO2(110). Upon Pt deposition, methanol dissociates into the photocatalytically more reactive species, i.e., methoxy,15 at the Pt/TiO2 interface. Besides, Pt can substantially lower the desorption barrier of hydrogen species, which can effectively prevent their recombination with formaldehyde. As a result, through a cooperative effect of reactant conversion, charge separation and product desorption barrier lowering, the apparent efficiency of photocatalytic oxidation of methanol is enhanced by Pt deposition onto TiO2 surfaces. Future work using the imaging techniques such as scanning tunneling microscopy (STM) and/or atomic force microscopy (AFM) is needed to find the correlation between the photoactivity and the coverage and cluster size of Pt. In our most recent study, O-H cleavage is found to be the rate-determining step (RDS) in the photocatalyzed dissociation of methanol on TiO2(110).56 The molecular adsorption of methanol on this surface is slightly more stable than the dissociative form (methoxy and bridging hydroxyl) and the conversion barrier for both forward and reverse reactions are only several hundreds meV.57-58 The presence of noble metal clusters on TiO2(110) surface is able to change such energetics to build new chemical equilibrium, for example, by removing the dissociated hydrogen at relatively low temperature. Conversion of methanol to methoxy is likely a general reaction at the metal cluster/TiO2 interface. Methanol dissociates via O-H bond break to methoxy at the Au cluster/TiO2(110) interface and the reaction yield increase with interfacial sites.47 Promoting O-H cleavage is a strategy to enhance the photocatalytic chemistry of methanol on TiO2 and maybe other metal oxide semiconductors. 21


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Conclusion In summary, the photocatalytic chemistry of methanol on Pt/TiO2(110) has been investigated for the first time by TPD and UPS. Methanol adsorbs dissociatively at the Pt/TiO2(110) interface. Similar to the results on clean TiO2(110), methanol is finally converted into formaldehyde at the Ti5c sites. The resulting surface hydrogens, however, desorb as water and molecular hydrogen below 300 K in the presence of Pt, in sharp contrast to the recombinative desorption of water around 500 K on clean TiO2. The photocatalytic reaction rate is enhanced by 9.2 times when 0.12 ML Pt is loaded. We propose three effects of Pt loading on the photocatalytic chemistry of methanol on TiO2(110): promoting O-H dissociation, realizing charge separation and lowering the hydrogen desorption barrier. They can work cooperatively and enhance the photocatatlytic efficiency. Our work indicates the importance of cocatalysts in changing the surface structure and the interaction with both reactants and products which eventually affect the photocatalytic efficiency, in addition to the well-known role in charge separation. Acknowledgements We thank Professor Guoqing Zhang from University of Science and Technology of China for a critical reading of our manuscript. This work was supported by the National Natural Science Foundation of China (21573225, 21688102 and 21703164), the National Key Research and Development Program of China (2016YFA0200602 and 2018YFA0208703), the Strategic Pilot Science and Technology Project (XDB17000000) and the Youth Innovation Promotion Association of CAS (2017224). ASSOCIATED CONTENT Supporting Information The Supporting Information is available free of charge on the ACS Publications website at DOI: 22


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XX. TPD spectra from 0.5 ML methanol covered clean and 0.058 ML Pt loaded TiO2(110) respectively as a function of 380 nm light illumination; Corrected TPD spectra of mass 15, 16 and 28 on clean and 0.058 ML Pt loaded TiO2(110) as a function of illumination time; Original TPD spectra of mass 30 and mass 29 and those after correction for methanol fragmentation contribution from a UV light exposed, 0.5 ML methanol covered 0.058 ML Pt loaded TiO2(110).

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42. Thompson, T. L.; Diwald, O.; Yates, J. T., CO2 as a Probe for Monitoring the Surface Defects on TiO2(110) Temperature-Programmed Desorption, J Phys Chem B 2003, 107, 11700-11704. 43. Liu, Z. M.; Zhou, Y.; Solymosi, F.; White, J. M., Vibrational study of carbon dioxide(1-) on potassium-promoted platinum (111), The Journal of Physical Chemistry 1989, 93, 4383-4385. 44. Copperthwaite, R. G.; Davies, P. R.; Morris, M. A.; Roberts, M. W.; Ryder, R. A., The Reactive Chemisorption of Carbon Dioxide at Magnesium and Copper Surfaces at Low Temperature, Catal Lett 1988, 1, 11-19. 45. Linsebigler, A.; Lu, G. Q.; Yates, J. T., CO Chemisorption on TiO2(110) - Oxygen Vacancy Site Influence on CO Adsorption, J. Chem. Phys. 1995, 103, 9438-9443. 46. Szabo, A.; Kiskinova, M.; Yates, J. T., Carbon-Monoxide Oxygen Interaction on the Pt(111) Surface - an ElectronStimulated Desorption Ion Angular-Distribution (Esdiad) Study, J. Chem. Phys. 1989, 90, 4604-4612. 47. Tenney, S. A.; Cagg, B. A.; Levine, M. S.; He, W.; Manandhar, K.; Chen, D. A., Enhanced activity for supported Au clusters: Methanol oxidation on Au/TiO2(110), Surface Science 2012, 606, 1233-1243. 48. Wang, J. H.; Masel, R. I., C-O Bond Scission during Methanol Decomposition on (1x1)Pt(110), J Am Chem Soc 1991, 113, 5850-5856. 49. Oakes, D. J.; McCoustra, M. R. S.; Chesters, M. A., Dissociative adsorption of methane on Pt(111) induced by hyperthermal collisions, Faraday Discuss. 1993, 96, 325-336. 50. Chen, L.; Smith, R. S.; Kay, B. D.; Dohnálek, Z., Adsorption of small hydrocarbons on rutile TiO2(110), Surface Science 2016, 650, 83-92. 51. Picolin, A.; Busse, C.; Redinger, A.; Morgenstern, M.; Michely, T., Desorption of H2O from Flat and Stepped Pt(111), J Phys Chem C 2009, 113, 691-697. 52. Guo, Q.; Xu, C.; Yang, W.; Ren, Z.; Ma, Z.; Dai, D.; Minton, T. K.; Yang, X., Methyl Formate Production on TiO2(110), Initiated by Methanol Photocatalysis at 400 nm, The Journal of Physical Chemistry C 2013, 117, 5293-5300. 53. Shen, M.; Acharya, D. P.; Dohnalek, Z.; Henderson, M. A., Importance of Diffusion in Methanol Photochemistry on TiO2(110), J Phys Chem C 2012, 116, 25465-25469. 54. Xu, L.; Ma, Y.; Zhang, Y.; Teng, B.; Jiang, Z.; Huang, W., Revisiting H/Pt(111) by a combined experimental study of the H-D exchange reaction and first-principles calculations, Science China Chemistry 2011, 54, 745. 55. Zhang, Z. R.; Bondarchuk, O.; White, J. M.; Kay, B. D.; Dohnalek, Z., Imaging Adsorbate O-H Bond Cleavage: Methanol on TiO2(110), J Am Chem Soc 2006, 128, 4198-4199. 56. Wang, T.; Hao, Q.; Wang, Z.; Mao, X.; Ma, Z.; Ren, Z.; Dai, D.; Zhou, C.; Yang, X., Deuterium Kinetic Isotope Effect in the Photocatalyzed Dissociation of Methanol on TiO2(110), The Journal of Physical Chemistry C 2018, 122, 26512-26518. 57. de Armas, R. S.; Oviedo, J.; San Miguel, M. A.; Sanz, J. F., Methanol Adsorption and Dissociation on TiO2(110) from First Principles Calculations, J Phys Chem C 2007, 111, 10023-10028. 58. Lang, X.; Wen, B.; Zhou, C.; Ren, Z.; Liu, L.-M., First-Principles Study of Methanol Oxidation into Methyl Formate on Rutile TiO2(110), The Journal of Physical Chemistry C 2014, 118, 19859-19868.

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Figures and Captions:

15

4

UPS Intensity (10 a.u.)

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

ACS Catalysis

Pt Coverage (ML)

0 0.058 10 2.0

1.5

1.0

0.5

0.0

Binding Energy (eV)

5

0 10

8

6

4

2

0

Binding Energy (eV)

Figure 1. UPS spectra from clean and 0.058 ML Pt covered TiO2(110) surface. The inset graph shows the comparison in the band gap region. The band gap state is an indicator of surface reduction.

27


ACS Catalysis

(A)

Clean TiO2(110)

Clean TiO2(110) (D)

Pt/TiO2(110)

Pt/TiO2(110) +

m/z=16

m/z=31 (CH2OH ) +

(O )

(B)

x0.7

+

x1

(CH4 )

Clean TiO2(110)

Clean TiO2(110) (E)

Pt/TiO2(110)

Pt/TiO2(110)

TPD Signal (a.u.)

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

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+

+

m/z=15 (CH3 )

m/z=28 (CO )

x0.7

x0.2

(C)

Clean TiO2(110) (F)

Clean TiO2(110)

Pt/TiO2(110)

Pt/TiO2(110) +

m/z=2 (H2 )

+

m/z=18 (H2O )

x2

200

400

600

800 200

x0.1

400

600

800

Temperature (K)

Figure 2. TPD spectra of the main products from thermal chemistry of 0.5 ML methanol on clean (red lines) and 0.058 ML Pt loaded (blue lines) TiO2(110). To unify the scale, the signal in each graph is multiplied by a value specified at the right bottom corner. The dashed lines in Figure 2B and Figure 2D represent the pure CO and CH4 contribution by correcting for the CO2 & CH3OH and CO & CO2 cracking, respectively, while those in Figure 2E denoting the signal of CH3 by subtracting the fragmentation from CH4.

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R: Pt/TiO2(110)

L: Clean TiO2(110) (A)

Illumination (min) (E)

Illumination (min)

0 6 40

0 1 6

m/z=31

m/z=31

x1.0

x1.0 Illumination (min)

Illumination (min) (F)

(B)

0 1 6

0 6 40

m/z=30

m/z=30

TPD Signal (a.u.)

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

ACS Catalysis

x1.0

x1.0

Illumination (min) (G)

(C)

Illumination (min)

0 6 40

0 1 6

m/z=18

m/z=18

x1.4

x1.4 Illumination (min) (H)

(D)

0 6 40

Illumination (min) 0 1 6

m/z=2

m/z=2

x0.1

x0.1 200

400

600

800 200

400

600

800

Temperature (K)

Figure 3. TPD spectra from 0.5 ML methanol covered (L) Pt free and (R) 0.058 ML Pt loaded TiO2(110) respectively as a function of 380 nm light illumination. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1. Four masses (m/z=31, 30, 18 and 2) representing the main products and/or their fragmentation from the photocatalytic chemistry of methanol on clean and Pt loaded TiO2(110) are shown. The scales in all the figures are the same while the signal in each figure is multiplied by a value specified at the right bottom corner. Please note the representative illumination time in the left and right panel are different. 29


ACS Catalysis

(A) Clean TiO2(110) Illumination (min) 0 3 40

20

2

1

0

2

1

0

10

4

Intensity (10 a.u.)

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

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0

(B) Pt/TiO2(110) Illumination (min) 0 3 15

20

10

0 10

8

6

4

2

0

Binding energy (eV)

Figure 4. UPS spectra of the valence electronic structure in the photochemistry of methanol on (A) clean and (B) 0.058 ML Pt loaded TiO2(110). The band gap states, which is a fingerprint of the reduction extent of TiO2(110) due to the presence of ObH in the current work, is enlarged in the inset. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1.

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15 Normalized

1.3 min

12

-10

TPD Signal (10 a.u.)

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

ACS Catalysis

9

1.0

3.5 min

90%

12.0 min

0.5

0.0 0

10

20

30

40

6 Pt coverage (ML) 0 0.058 0.12

3

0 0

10

20

30

40

Time (min) Figure 5. Comparison of the kinetics of the photocatalyzed oxidation of methanol to formaldehyde on clean (red), 0.058 ML (green) and 0.12 ML (blue) Pt loaded TiO2(110). The red, green and blue lines show the multi-exponential fitting to the experimental data. The average flux of UV irradiation is 1.6×1018 photons cm-2 s-1.

31


ACS Catalysis 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

TOC Graphic

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Role of Pt Loading in the Photocatalytic Chemistry of Methanol on

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