1:30 PM - 3:30 PM
▲ [19p-PA4-6] Investigation of characteristics of Pd nanoclusters adsorbed on Al2O3/NiAl (110) by AFM/KPFM
Keywords:catalytic mechanism, potential difference (CPD), AFM/KPFM
[Background] Oxide-supported metal nanoclusters as catalysts are widely used in catalytic oxidation reactions [1]. It still remains a challenge to clarify the mechanism of catalysis. In our previous research, the Al2O3/NiAl (110) surface have been obtained with atomic resolution by atomic force microscopy (AFM) at room temperature (RT) [2]. In this study, we clarify the active sites of Pd nanoclusters on this surface.
[Method] The experiments were performed by using the Kelvin probe force microscopy (KPFM) based on AFM. We use this powerful technology to quantify contact potential difference (CPD) between the tip and different sites on the surface with atomic resolution. In details, Pd nanoclusters were adsorbed on Al2O3/NiAl (110) surface and imaged by AFM/KPFM simultaneously at RT.
[Results and discussion] In topographic AFM image as shown in Figure 1(a), Pd nanoclusters are imaged as bright protrusions, which were mainly adsorbed on straight and zig-zag line defects. This result is summarized in Figure 1(b). We found that few Pd nanoclusters were adsorbed on the step, and hardly adsorbed on the terrace. Figure 1(c) shows the image of change of CPD for Pd nanoclusters on the surface. And the result of sites dependence as a function of CPD change is shown in Figure 1(d). Our result demonstrated that the work function of Pd nanoclusters adsorbed on straight and zig-zag line defects is higher than step site, which means that the straight and zig-zag line defects sites are more active than the step.
The more active site means more electrons transfer from substrate to nanoclusters. For proving the characteristics of active sites, the investigation of size dependence and charge state of Pd nanoclusters are necessary. This research is helpful to explain the catalytic mechanism of oxide-supported metal nanoclusters.
[Method] The experiments were performed by using the Kelvin probe force microscopy (KPFM) based on AFM. We use this powerful technology to quantify contact potential difference (CPD) between the tip and different sites on the surface with atomic resolution. In details, Pd nanoclusters were adsorbed on Al2O3/NiAl (110) surface and imaged by AFM/KPFM simultaneously at RT.
[Results and discussion] In topographic AFM image as shown in Figure 1(a), Pd nanoclusters are imaged as bright protrusions, which were mainly adsorbed on straight and zig-zag line defects. This result is summarized in Figure 1(b). We found that few Pd nanoclusters were adsorbed on the step, and hardly adsorbed on the terrace. Figure 1(c) shows the image of change of CPD for Pd nanoclusters on the surface. And the result of sites dependence as a function of CPD change is shown in Figure 1(d). Our result demonstrated that the work function of Pd nanoclusters adsorbed on straight and zig-zag line defects is higher than step site, which means that the straight and zig-zag line defects sites are more active than the step.
The more active site means more electrons transfer from substrate to nanoclusters. For proving the characteristics of active sites, the investigation of size dependence and charge state of Pd nanoclusters are necessary. This research is helpful to explain the catalytic mechanism of oxide-supported metal nanoclusters.