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Title: Methanol on Anatase TiO 2 (101): Mechanistic Insights into Photocatalysis

Authors:
ORCiD logo [1];  [2];  [1];  [1];  [1];  [1]; ORCiD logo [3]; ORCiD logo [2];  [1]
  1. Institute of Applied Physics, TU Wien, Wiedner Hauptstrasse 8-10/134, 1040 Vienna, Austria
  2. Department of Chemistry, Princeton University, Frick Laboratory, Princeton, New Jersey 08544, United States
  3. Dipartimento di Scienza dei Materiali, Università di Milano-Bicocca, Via Cozzi 55, 20125 Milano, Italy
Publication Date:
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1393722
Grant/Contract Number:
SC0007347
Resource Type:
Journal Article: Published Article
Journal Name:
ACS Catalysis
Additional Journal Information:
Journal Volume: 7; Journal Issue: 10; Related Information: CHORUS Timestamp: 2017-10-06 04:35:13; Journal ID: ISSN 2155-5435
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English

Citation Formats

Setvin, Martin, Shi, Xiao, Hulva, Jan, Simschitz, Thomas, Parkinson, Gareth S., Schmid, Michael, Di Valentin, Cristiana, Selloni, Annabella, and Diebold, Ulrike. Methanol on Anatase TiO 2 (101): Mechanistic Insights into Photocatalysis. United States: N. p., 2017. Web. doi:10.1021/acscatal.7b02003.
Setvin, Martin, Shi, Xiao, Hulva, Jan, Simschitz, Thomas, Parkinson, Gareth S., Schmid, Michael, Di Valentin, Cristiana, Selloni, Annabella, & Diebold, Ulrike. Methanol on Anatase TiO 2 (101): Mechanistic Insights into Photocatalysis. United States. doi:10.1021/acscatal.7b02003.
Setvin, Martin, Shi, Xiao, Hulva, Jan, Simschitz, Thomas, Parkinson, Gareth S., Schmid, Michael, Di Valentin, Cristiana, Selloni, Annabella, and Diebold, Ulrike. 2017. "Methanol on Anatase TiO 2 (101): Mechanistic Insights into Photocatalysis". United States. doi:10.1021/acscatal.7b02003.
@article{osti_1393722,
title = {Methanol on Anatase TiO 2 (101): Mechanistic Insights into Photocatalysis},
author = {Setvin, Martin and Shi, Xiao and Hulva, Jan and Simschitz, Thomas and Parkinson, Gareth S. and Schmid, Michael and Di Valentin, Cristiana and Selloni, Annabella and Diebold, Ulrike},
abstractNote = {},
doi = {10.1021/acscatal.7b02003},
journal = {ACS Catalysis},
number = 10,
volume = 7,
place = {United States},
year = 2017,
month = 9
}

Journal Article:
Free Publicly Available Full Text
Publisher's Version of Record at 10.1021/acscatal.7b02003

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  • The mechanism for methanol oxidation on both TiO{sub 2} and V/TiO{sub 2} was investigated using temperature-programmed experiments with in-situ infrared spectroscopy. Infrared and Raman spectroscopy, along with XANES, show that the V/TiO{sub 2} sample consists predominantly of isolated VO{sub 4} units after calcination. Methanol was found to adsorb on the catalyst in three ways at 323 K: (1) molecularly, (2) across Ti-O-Ti bonds to form Ti-OCH{sub 3}/Ti-OH pairs, and (3) across V-O-Ti bonds to form V-OCH{sub 3}/Ti-OH pairs. Upon heating, two desorption peaks for CH{sub 3}OH and H{sub 2}O were observed on all samples below 500 K. Although TiO{sub 2}more » produced small amounts of CH{sub 2}O, the addition of vanadium greatly enhanced the rate of formaldehyde formation. Also, on the V/TiO{sub 2} samples, it was noticed that the Ti-OCH{sub 3} groups disappear much more rapidly than on TiO{sub 2} alone. This is likely due to the reverse spillover of methoxide species from Ti to V, with the reaction occurring at lower temperatures at the vanadium center. Formate species were also detected during the experiments, and they are assumed to be intermediates in the decomposition of formaldehyde to CO, CO{sub 2}, and H{sub 2}O. The apparent activation energy of V/TiO{sub 2} for the formation of CH{sub 2}O is 16 kcal/mol.« less
  • A series of substituted pyridiniums were examined for their catalytic ability to electrochemically reduce carbon dioxide to methanol. It is found that in general increased basicity of the nitrogen of the amine and higher LUMO energy of the pyridinium correlate with enhanced carbon dioxide reduction. The highest faradaic yield for methanol production at a platinum electrode was 39 ± 4 % for 4-aminopyridine compared to 22 ± 2 % for pyridine. However, 4-tertbutyl and 4-dimethylamino pyridine showed decreased catalytic behavior, contrary to the enhanced activity associated with the increased basicity and LUMO energy, and suggesting that steric effects also playmore » a significant role in the behavior of pyridinium electrocatalysts. As a result, mechanistic models for the the reaction of the pyridinium with carbon dioxide are considered.« less
  • Graphical abstract: Anatase TiO{sub 2} nanocaps prepared by HF-assisted chemical etching method exhibit enhanced photocatalytic activity compared with commercial P25 because of HF served as an etching agent to remove doped impurities. - Highlights: • Anatase TiO{sub 2} nanocaps were synthesized by HF etching process. • The optimal conditions of experiment are 700 °C calcination and 0.2 mL HF solution. • The photocatalytic properties was studied upon UV and Visible irradiation. • The unique TiO{sub 2} nanocaps structure shows excellent photocatalytic activity. - Abstract: Anatase titanium dioxide (TiO{sub 2}) nanocaps were created via a four-step process including the preparation ofmore » SiO{sub 2} spheres, the deposition of a TiO{sub 2} layer to fabricate SiO{sub 2}@TiO{sub 2} composite spheres, the calcination for obtaining the crystal structure of anatase phase, and hydrofluoric acid (HF) etching to dissolve SiO{sub 2} cores. The SiO{sub 2}@TiO{sub 2} spheres calcined at 700 °C revealed fine photocatalytic activity. Interestingly, most of samples transformed into TiO{sub 2} nanocaps via HF etching, and TiO{sub 2} nanocaps prepared using optimal conditions exhibited quick degradation (k is 0.052 min{sup −1}) compared with commercial P25 (k is 0.030 min{sup −1}) and the TiO{sub 2} nanostructures etched by a NaOH solution. The excellent photocatalytic performance is attributed to its unique hollow hemispherical nanocaps structure, which is in favor of making full use of incident light. The photocatalysis phenomenon in visible light was also observed after depositing Au nanoparticles on anantase TiO{sub 2} nanocaps.« less
  • The photochemical water gas shift reaction (WGSR) catalyzed, under mild conditions (25[degrees]C, 1 atm CO, visible light, pH = 7), by [([eta][sup 5]-Me[sub 5]C[sub 5])Ir[sup III](bpy)X][sup +] (bpy = 2,2[prime]-bipyridine, X = H, Cl), [([eta][sup 5]-Me[sub 5]C[sub 5])Ir[sup III](phen)X][sup +] (phen = 1,10-phenanthroline, X = H, Cl), or [([eta][sup 5]-Me[sub 5]C[sub 5])Ir[sup III](bpyRR[prime])Cl][sup +] (R = R[prime] = COOH, COOiPr, Br, NO[sub 2], NMe[sub 2] in the 4,4[prime]-positions or R = R[prime] = COOH, R = H and R[prime] = SO[sub 3]H in the 5,5[prime]-positions of the bpy ligand) has been investigated. A turnover frequency for H[sub 2] formation ofmore » 32 h[sup [minus]1] was obtained in an aqueous phosphate buffer containing [([eta][sup 5]-Me[sub 5]C[sub 5])Ir[sup III](bpy-4,4[prime]-(COOH)[sub 2]Cl)][sup +] as catalyst, over a 7-h irradiation period at a constant CO pressure of 1 atm. An increase of 1 order of magnitude in catalytic activity was observed for the bpy ligand substituted with two carboxylate groups in the 4,4[prime]- or 5,5[prime]-positions or with one sulfonate group in the 5-position (over the nonsubstituted bpy equivalent). Conversely, catalytic activity was lost when the bpy was substituted with two dimethylamino groups. The presence of an electron withdrawing group on the bpy-chelate was shown to decrease the activation energy of the process (E[sub a] = 14.6 kJ mol[sup [minus]1] for R = COOH, E[sub a] = 22.2 kJ mol[sup [minus]1] for R = COOiPr), cf. the unsubstituted ligand (E[sub a] = 29.6 kJ mol[sup [minus]1] for R = H). 64 refs., 8 figs., 5 tabs.« less
  • The field of heterogeneous photocatalysis has grown considerably in the decades since Fujishima and Honda's ground-breaking publications of photoelectrochemistry on TiO2. Numerous review articles continue to point to both progress made in the use of heterogeneous materials (such as TiO2) to perform photoconversion processes, and the many opportunities and challenges in heterogeneous photocatalysis research such as solar energy conversion and environmental remediation. The past decade has also seen an increase in the use of molecular-level approaches applied to model single crystal surfaces in an effort to obtain new insights into photocatalytic phenomena. In particular, scanning probe techniques (SPM) have enabledmore » researchers to take a ‘nanoscale’ approach to photocatalysis that includes interrogation of the reactivities of specific sites and adsorbates on a model photocatalyst surface. The rutile TiO2(110) surface has become the prototypical oxide single crystal surface for fundamental studies of many interfacial phenomena. In particular, TiO2(110) has become an excellent model surface for probing photochemical and photocatalytic reactions at the molecular level. A variety of experimental approaches have emerged as being ideally suited for studying photochemical reactions on TiO2(110), including desorption-oriented approaches and electronic spectroscopies, but perhaps the most promising techniques for evaluating site-specific properties are those of SPM. In this review, we highlight the growing use of SPM techniques in providing molecular-level insights into surface photochemistry on the model photocatalyst surface of rutile TiO2(110). Our objective is to both illustrate the unique knowledge that scanning probe techniques have already provided the field of photocatalysis, and also to motivate a new generation of effort into the use of such approaches to obtain new insights into the molecular level details of photochemical events occurring at interfaces. Discussion will start with an examination of how scanning probe techniques are being used to characterize the TiO2(110) surface in ways that are relevant to photocatalysis. We will then discuss specific classes of photochemical reaction on TiO2(110) for which SPM has proven indispensible in providing unique molecular-level insights, and conclude with discussion of future areas in which SPM studies may prove valuable to photocatalysis on TiO2. This work was supported by the US Department of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. I.L. was partially supported by a Pacific Northwest National Laboratory (PNNL) Chemical Imaging Initiative project. PNNL is a multiprogram national laboratory operated for DOE by Battelle.« less