Ordered SMSI Decoration Layer on Rh Nanoparticles Grown on TiO₂(110) Surface

Abstract

Supporting results on the activation of 1D growth by increasing the deposition temperatureWe have studied the effect of deposition temperature (in the range of 300-1100 K) on the particle formation of Rh deposited onto a TiO 2 (110) surface. Naturally, upon increasing the deposition temperature, we have received more and more agglomerated particles (i.e. increased average particle size). More surprisingly, a dramatic change appeared in the particle shape: below 950 K, the particles were basically of round or slightly elongated shape; above this temperature, they exhibited a strongly elongated form. Image A (50 nm x 50 nm) shows the surface morphology at room temperature after the deposition of app. 1 ML of Rh at 850 K. All the particles thus formed have a nearly same width and length. Deposition of 5 ML of Rh at 1050 K results in the formation of highly elongated particles (image B). This property changes only moderately after 10 min annealing at 1050 K in vacuum (image C). The size of the images B and C is 400 nm x 400 nm.

The formation and stability of Rh nanostructures on TiO2(110) surface and TiOx encapsulation layers

“…3 reveal that from 6 ML Rh coverage the TiO x overlayer is sampled by the electron beam without the contribution of TiO 2 (1 1 0) surface (as reflected by the constant Rh/Ti ratio, see also below), WF changes detected at the same coverage are stemming from the formation of the TiO x encapsulation layer and possibly from the smoothing of Rh particles during annealing. The smoothing of Rh clusters as a result of heat treatment was observed by STM [33]. It manifested in the formation of well-developed (1 1 1) crystal planes which -having the highest WF among all Rh planes -may result in WF enhancement.…”

“…of heavily reduced, O-deficient surface. Although annealing at 700 K is enough for the complete encapsulation of Rh by titania [11], the high temperature thermal treatment is necessary for the production of highly crystalline Rh and a well-ordered TiO x overlayer [33]. Encapsulation layers formed on titania supported Rh particles after a reduction treatment at 773 K was found to be amorphous and a few atomic layer thick by high resolution electron microscopy (HREM) [35].…”

Catalysis by gold: New insights into the support effect

“…It was originally reported by Tauster et al in 1978 over the Pt/TiO 2 system, which was characterized by a drastic change in the chemisorption properties of the catalysts before and after reduction in H 2 at high temperatures [159]. Since then, the SMSI has been intensively studied on PGMs by applying various characterizations and it has been found in many other supported catalysts including Rh/TiO 2 [160], Ru/TiO 2 [161], Pd/TiO 2 [162], Pd/Al 2 O 3 [163], and so on. Taking advantage of the SMSI, it is very easy to obtain highly dispersed nanoparticles, even single atom dispersion of Pt or Pd [164][165][166].…”

Pd deposition on TiO2(110) and nanoparticle encapsulation

“…Majzik et al 20 used Auger electron spectroscopy (AES) and scanning tunneling microscopy (STM) to show SMSI on Rh nanoparticles on TiO 2 (110). Scanning tunneling microscopy showed ordered decoration of TiO x on Rh, exhibiting a`wheel structure', which is very similar to that reported for other supported metal systems, such as Pt 14 and Pd islands, 21 and for thin films of oxidized titanium deposited on metal single crystals.…”

“…Scanning tunneling microscopy showed ordered decoration of TiO x on Rh, exhibiting a`wheel structure', which is very similar to that reported for other supported metal systems, such as Pt 14 and Pd islands, 21 and for thin films of oxidized titanium deposited on metal single crystals. 22 This decoration could be removed with a short sputtering procedure 20 (100 s, 0.5 keV). These pinwheel structures have also been observed by Castell on Pd clusters supported on reduced SrTiO 3 23 and in TiO x on Au(111) 24 using STM and Auger.…”