The mobility of an alkali promoter as probed in situ during a catalytic reaction: Li in the CO oxidation on Pt

Abstract

Fluctuations of the local ion rate of Li+ ions emitted during in situ monitoring of the catalytic CO oxidation on the nanofacets of a Pt field emitter tip with a lithium field desorption-microscope (Li-FDM) are utilized to study the Li surface diffusion. The 'virtual probe-hole' approach, which is based on the digitization of the Li-FDM video images, is used. This allows to analyze simultaneously the local fluctuations of ions originating from arbitrarily user-defined probed surface regions of nanometer size. The anisotropy of the Li diffusion on the spatially inhomogeneous Pt surface is directly proved and a slowing effect of the coadsorbed CO on the Li diffusion is observed.

Catalytic reactions on platinum nanofacets: bridging the size and complexity gap

“…This bimodal distribution evidences the fluctuation-induced transitions between the two possible states in the bistability region [7]. More detailed studies using the Haar-Wavelet-Analysis detected that such fluctuation-induced transitions occurs spatially correlated over the flat facet surface (the mentioned region in the vicinity of Pt(110) was identified as a small (331) facet) [45], and are confined by the first atomic step due to the disturbed diffusional coupling over the stepped surface [46,47]. We note that this effect cannot be predicted within the mean-field theory, the Monte Carlo simulations naturally incorporating the stochastic nature of the modelled processes can, in turn, predict such an effect provided the modelled system is sufficiently small and in close proximity to a bifurcation (critical) point where bistability vanishes and fluctuations diverge [48,49].…”

In situ investigation of Pt100−xAuxand Pt100−ySnynanoalloys

“…48 Tri-sodium citrate is effective at the solution boiling point developing a blue and then a red colour. 49 Now more intricate core-shell Au-Cu nanocomposites 50,51 and Au-Cu nanoparticles embedded in SiO 2 52 have been prepared. Here Pt 100Àx Au x (0 o x o 100, where x was 0 and 9 and also 25, 50 and 100 at% Au) was prepared in pre-cleaned glassware by reducing a mixed aqueous (HPLC grade water) solutions (30 mg dm À3 ) of H 2 PtCl 6 (Johnson Matthey) and HAuCl 4 (Johnson Matthey) with a 1% trisodium citrate solution and then stirring for 2-4 h at 373 K. 53 The product sol was purified by addition of Amberlite MBI ion-exchange resin with stirring until constant conductivity and pH were obtained.…”

Field Ion and Field Desorption Microscopy: Surface Chemistry Applications

“…[64] and applied to Li in CO oxidation on Pt. 72 Figure 15 shows the Li-FDM images taken at similar conditions as in Figure 14 and the corresponding locally measured intensity series. With the corresponding calibration, the intensity fluctuations can be related to the fluctuations of the number of Li adatoms N Li in the probed area.…”