Structure and reactivity of Au–Rh bimetallic clusters on titanate nanowires, nanotubes and TiO2(110)

Abstract

a b s t r a c tAu and Rh clusters, as well as Au-Rh bimetallic nanoparticles were prepared on titanate nanowires, nanotubes and on TiO 2 (1 1 0). They were characterized by X-ray photoelectron spectroscopy (XPS), low energy ion scattering spectroscopy (LEIS) and Fourier transform infrared spectroscopy (FTIR). By performing careful LEIS experiments, it was found that for appropriate Au and Rh coverage, a thin Au layer almost completely covers the Rh nanoparticles, a Rh core-Au shell structure was detected. The formation of this structure was not affected by alkali (K) adatoms. LEIS and FTIR measurements disclosed that adsorbed CO at 300 K causes the segregation of Rh atoms to the surface of metal clusters in order to bind to CO. Upon CO adsorption on Rh/titanate nanostructures the IR stretching frequencies characteristic of the twin form were dominant, whereas bimetallic nanosystems featured a pronounced linear stretching vibration as well. In spite of this structure adsorbed CO is detectable during the ethanol adsorption on gold-rhodium bimetallic cluster and the ethanol decomposition rate is twice higher than on Au/TiO 2 .

The interaction of CO molecules on Au–Rh bimetallic nanoclusters supported on a thin film of Al2O3/NiAl(100)

“…For an altered surface composition, the adsorbed CO and increased temperature promoted the diffusion of Rh from the cluster interior to the surface during the annealing, which increased the surface Rh sites, as the CO-Rh bond is evidently stronger than the CO-Au bond. Similar structural changes were observed for Au-Pt bimetallic clusters on TiO 2 (100), 75 Au-Rh bimetallic clusters on titanate nanotubes and TiO 2 (110), 79 and Pd-Au bimetallic model catalysts synthesized either as thin lms on Mo(110) or as nanoparticles on a TiO 2 thin lm. 80 If this mechanism were responsible for the present observation, the increased absorption signals for CO Rh , corresponding to the increased Rh sites would be irreversible.…”

Metal loading determines the stabilization pathway for Co2+ in titanate nanowires: ion exchange vs. cluster formation

“…Very recently we observed the similar, unexpectedly high binding energy photoemission of gold stabilized in titanate nanowires and nanotubes in atomically dispersed states complexed with oxygen vacancies. [17][18][19] An atomically dispersed state was observed for Au atoms on TiO 2 (110) at low temperature. 59 In this case, Au deposited as Au + at 1 eV impact energy on rutile TiO 2 samples was studied over the temperature range between 115 K and 800 K, and both near-stoichiometric UHV-annealed TiO 2 and TiO 2 with high density of oxygen vacancies were created by He + bombardment.…”

Influence of gold additives on the stability and phase transformation of titanate nanostructures

“…particles of exactly the same diameter), in the past years significant progress was made in the preparation of gold particles with a narrow diameter distribution between ~2-10 nm. [23][24][25][26][27][28][29][30]34,40,41 In the present work we produced gold nanoparticles on titanate nanowires and nanotubes in two ways; (A) after deposition-precipitation the reduction step was done with molecular hydrogen at 473 K, or (B) NaBH 4 was used for reduction at 293 K (see Two different explanations can be offered for the appearance of this unusually high binding energy gold state. Core level shifts due to particle size must be considered first in the interpretation of the spectra of nanoparticles.…”