Preferential growth of Pt on rutileTiO2

Abstract

The characterization of Pt/TiO2 (Degussa P25) catalyst system using atomic resolution Z-contrast images and electron energy loss spectroscopy in the scanning transmission electron microscope has recently revealed that Pt particles have a strong tendency to nucleate on the rutile phase of TiO2 rather than anatase. Comparative ab initio pseudopotential calculations for Pt and Pt2 on the stoichiometric and reduced TiO2 surfaces, and oxygen vacancy (VO) formation energies are performed to address the microscopic origin of this finding. The results, which show that Pt actually binds more strongly to anatase surfaces, indicate that the selective growth of Pt on rutile must be controlled by the lower formation energy of VO on rutile, and possibly by the stronger tendency of VO sites on rutile to trap large Pt clusters compared to anatase.The fundamental and technological importance of TiO 2 , stemming to a large extent from its wide spread use as a catalyst and catalyst support, has made it the subject of many experimental and theoretical studies over the last decade.[1] As one of the most active catalysts for CO oxidation reactions and photocatalysis, in addition to being the prototype system for the strong-metalsupport-interaction (SMSI) phenomenon, [2] Pt/TiO 2 has recently received particular attention. The catalytic properties of Pt/TiO 2 and the occurrence of SMSI has a strong dependence on the phase of TiO 2 (rutile versus anatase). For example, it was recently shown that anatase titania palladium supported catalyst presents SMSI at low H 2 pre-reduction temperatures, while rutile does not.[3] It is also well known that anatase is more efficient than rutile as an oxidative photocatalyst.[4] The presence of a small amount of rutile, however, such as in commercial mixed-phase titania samples results in an unusually high activity.[5] A fundamental comparative study of the interaction of Pt with both rutile and anatase TiO 2 surfaces will, therefore, contribute to our understanding of the catalytic properties of this system and the occurrence of SMSI.Recently, using a combination of Z-contrast imaging and electron energy loss spectroscopy (EELS) in the scanning transmission electron microscope (STEM), we examined the atomic and electronic structure of the Pt/TiO 2 interface.[6] The experiments were performed on a commercial mixed-phase titania sample, known as Degussa P25, which is composed of about 80 % anatase and 20 % rutile. We observed rather unexpectedly that Pt particles were not uniformly distributed over the titania particles, but showed a selective distribution, as shown in Fig. 1(a). The oxygen−K edges of these specific particles [ Fig. 1 Oxygen K−edge EEL spectra taken at the locations specified in (a). Note the difference in the shape of the secondary peaks (from 538 eV to 548 eV) for particles 1 and 2 in comparison to particle 3. (c) O K−edge EEL spectra of bulk rutile and anatase shown for comparison with the spectra in (b), showing that particles 1 and 2 with few Pt clusters are of anatase and the d...

Modeling the noble metal/TiO2 (110) interface with hybrid DFT functionals: A periodic electrostatic embedded cluster model study

“…The calculated adsorption energies for the periodic slab and PEEC models are listed in Table I. Pt adsorption energies for the hollow site ͑H͒, obtained from the periodic slab models, agree well with the previously reported values by Iddir et al 51,52 These authors predicted, using the PW91 functional, 36 that Pt adsorption on the hollow site ͑H͒ is more stable than Pt adsorption on top of a surface oxygen atom ͑T͒. Although our periodic slab calculations with PBE functional predict the adsorption of Pt at the T site to be more favorable, the adsorption energy difference for the H and T sites is less than 0.1 eV.…”

“…Iddir et al 51 studied the adsorption and diffusion of a single Pt atom on stoichiometric and reduced TiO 2 ͑110͒ surfaces and later discussed the interaction of Pt 2 with the reduced TiO 2 ͑110͒ surface. 52 A few other reports were also made on the interaction of small Pt clusters with the anatase TiO 2 ͑101͒ surface. 69,70 All of these computational studies were done using periodic slab models with the GAA-PW91 or PBE functional.…”

“…The calculated adsorption energies for the Au 2 and Au 3 clusters on the periodic slab models agree well with values previously reported by Chrétien and Metiu using the PW91 functional. 60,67 In the case of adsorbed Pt complexes, Iddir et al 52 computed a slightly stronger Pt 2 adsorption energy on the reduced TiO 2 surface ͑Ϫ3.62 eV versus Ϫ3.33 eV͒, which is likely the result of a different computational setup and the use of a different DFT functional. Adsorption energies for the metal clusters on the stoichiometric surface calculated with the PEECM methodology and PBE functional are, except for the Au 3 cluster, within 0.3 eV to results from periodic slab calculations.…”

Epitaxial growth of CeO2(111) film on Ru(0001): Scanning tunneling microscopy (STM) and x-ray photoemission spectroscopy (XPS) study

“…It has been considered that metal particles are likely to nucleate at oxygen vacancy sites which are argued for TiO 2 surface [42][43][44] and MgO 45 the number of cluster is proportional to the number of oxygen defect sites. At the same time Galhenage et al reported a larger diffusion coefficient on the reduced TiO 2 surface than that on non-reduced one.…”

EELS Study of Co-Based Fischer-Tropsch Catalysts on TiO2 and SiO2 Supports

“…In summary, we will give a detailed theoretical explanation and experimental evidence for the mechanism of Mn migration in Co/TiO 2 and Co/SiO 2 catalysts after calcination and reduction treatment. [3,4] Figu ure. 4…”