2-Propanol reactivity on in situ prepared Au(1 1 1)-supported TiO 2 nanocrystals Denis V. Potapenko a , Zhisheng Li a , Yang Lou b , Yun Guo b , Richard M. Osgood Jr. a,⇑ a Department of Applied Physics and Applied Mathematics, Columbia University, New York, NY 10027, USA b Laboratory for Advanced Materials, Research Institute of Industrial Catalysis, East China University of Science and Technology, Shanghai 200237, China article info Article history: Received 3 August 2012 Revised 17 October 2012 Accepted 18 October 2012 Available online 27 November 2012 Keywords: TiO 2 Nanocrystal Au(1 1 1) 2-Propanol TPD STM Rutile(1 1 0) Nanoparticle abstract The reactivity of 2-propanol with TiO 2 nanocrystals supported on Au(1 1 1) was studied by temperature- programmed desorption (TPD) and scanning tunneling microscopy (STM). The nanocrystals, which are grown through oxidation of a TiAAu surface alloy, had an average height of 1 nm and width of 15 nm with a dominantly hexagonal morphology. The desorption of propanol and propanol-derived products from the TiO 2 nanocrystal surfaces was observed in the 270–570 K temperature range and could be dis- tinguished from desorption of propanol from the Au(1 1 1) surface below 270 K. With increasing propanol coverage, the TiO 2 -related TPD peaks were occupied before the appearance of any Au(1 1 1)-related peaks. Our calculations showed that the TiO 2 nanocrystals were saturated at 0.4 ML of local propanol surface concentration, where 1 ML  5.2  10 14 cm 2 refers to surface density of five-coordinated Ti atoms on rutile(1 1 0). Our TPD measurements showed that 61% of this adsorbed propanol desorbed molecularly at 310 K, while 23% dehydrated into propene and 6% dehydrogenated to form acetone, both products desorbing in the 370–570 K temperature range. The desorption temperatures of products from supported TiO 2 nanocrystals were shown to depend strongly on the morphology of the nanocrystals. Ó 2012 Elsevier Inc. All rights reserved. 1. Introduction Nanometer-scale forms of catalytically important materials have become an increasingly significant research area due to the prospects of tailoring the properties of catalysts through nano- scale size effects. Titanium dioxide has attracted particular atten- tion due to its photocatalytic properties that enable many possible applications including water and air purification from organic pol- lutants, cathode material for dye-sensitized solar cells, and poten- tially light-driven water splitting [1–5]. In situ UHV preparation of nanoparticles on chemically inert single-crystal substrates, such as in this work, is a convenient approach for the exploration of mech- anistic details of catalytic reactions since it allows application of surface science tools for atomic-scale characterization of the nano- particles and their chemical properties [6–12]. Several methods for in situ preparation of TiO 2 nanocrystals on Au(1 1 1) surface have been demonstrated including oxidation of titanium during or after deposition on a gold surface with O 2 [13,14] and reactive H 2 O and NO 2 layer-assisted deposition [15,16]. Thus, recently we have shown that TiO 2 growth by TiAAu surface-alloy-assisted method offers a significant degree of struc- tural homogeneity and a narrow size distribution of the nanocrys- tals on Au(1 1 1) surface [17]. This approach is used in the present study to prepare nano-TiO 2 /Au(1 1 1) surfaces. Alcohol [18–20], and particularly 2-propanol [21,22], chemistry on single-crystal TiO 2 surfaces have been extensively studied to ac- quire a fundamental understanding of the catalytic properties of titania. These studies have shown that, on a rutile(1 1 0) surface, 2-propanol can undergo dehydration to form propene. Two reac- tion channels were identified using thermal programmed desorp- tion (TPD) experiments: a minor low-temperature path at 450 K, which is attributed to a 2-propanol reaction with the five-coordi- nated titanium rows at the surface and a more prominent high temperature path at 580 K, which is associated with bridge- bonded oxygen vacancies (BBOv) [21,22]. Methanol reactivity on nano-TiO 2 /Au(1 1 1) has been explored previously and it was shown in that work that a fraction of methanol undergoes deoxy- genation into methane [23]. As a probe molecule, 2-propanol offers the important additional possibility of a dehydration reaction, thus enabling testing of a broader range of chemical reactions. Additional interest in alcohol chemistry on the TiO 2 AAu system stems from a series of recent reports on hydrogen production from ethanol over a nano-Au/TiO 2 catalyst [24,25]. These reports showed that there is a strong dependence of the catalyst’s proper- ties on both the size of Au clusters and the phase of TiO 2 support [24]. Given this interest, the reactivity of an alcohol with the re- verse nano-TiO 2 /Au(1 1 1) system can bring a deeper understand- ing of the involved chemistry. In this paper, we report preparing nanometer-size single-crystal TiO 2 crystallites on a Au(1 1 1) substrate by surface-alloy-assisted synthesis. In addition, STM is used to characterize the geometry 0021-9517/$ - see front matter Ó 2012 Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.jcat.2012.10.020 ⇑ Corresponding author. E-mail address: osgood@columbia.edu (R.M. Osgood Jr.). Journal of Catalysis 297 (2013) 281–288 Contents lists available at SciVerse ScienceDirect Journal of Catalysis journal homepage: www.elsevier.com/locate/jcat