Supporting Information:
Adsorption and reaction of SO2 on graphene-supported Pt nanoclusters
Karin Gotterbarm, Florian Späth, Udo Bauer, Hans-Peter Steinrück and Christian Papp*
Lehrstuhl für physikalische Chemie II, Universität Erlangen-Nürnberg, Egerlandstraße 3, 91058 Erlangen, Germany.
*: Author to whom correspondence should be addressed.
Figure S1:
Example fits of S2p spectra during adsorption of SO2 and a TP-XPS experiment are shown in FigureS1. The spectrum in Figure S1a was recorded after exposure to 0.14 L of SO2 at 150 K (thick black spectrum in Figure 1a and Figure 3d). During adsorption, we find four SO2 species due to different adsorption geometries (lying and standing) on both facets and steps of the nanoclusters. The signals of SO2 adsorbed on the facets, SO2st at 165.55 (166.74) eV and SO2ly at 164.70 (165.89) eV, are displayed in blue and red, respectively. And the signals of SO2 adsorbed at the steps, SO2step-st at 165.30 (166.49) eV and SO2step-ly at 164.55 (165.74) eV, are displayed in hatched blue and red, respectively. The spectrum displayed in Figure S1b was recorded during TP-XPS at 280K. At this temperature, the SO2 signals are shifted to lower binding energies due to diffusion of SO2 onto the steps of the clusters. The highest populated SO2 species is SO2step-st and the signal of SO2ly on the facets has completely vanished. From the disproportionation of SO2, atomic sulfur at 162.05 (163.24) eV (orange) and some SO3 at 166.10 (167.29) eV (green) are formed. We also observe a small amount of SO (black), which is formed due to beam damage. Upon further heating to 360 K (Figure S1c), the signals of sulfur and SO3 increase while the SO2 peaks decrease. At this temperature the SO3 signal is at its maximum coverage.
Figure S2:
Pt 4f7/2 spectra recorded before SO2 adsorption (black), after SO2 adsorption (blue) and after the TP-XPS experiment (red) are shown in Figure S2. The Pt4f spectra were recorded at 180eV photon energy and at a total energy resolution of 150meV. The black Pt 4f7/2 spectrum of the clean Pt nanoparticles at 150 K exhibits an asymmetric signal at 70.9 eV with a full width at half maximum (fwhm) of 1.1 eV. After adsorption of SO2 (blue), the peak is shifted to 70.6 eV and a shoulder at 71.8 eV has evolved due to interaction of Pt with SO2. The spectrum lost 16% of the intensity in comparison to the black spectrum, due to damping. The red spectrum was recorded after the TP-XPS experiment. In comparison to the black spectrum before SO2 adsorption the peak maximum is shifted to 71.0 eV, due to interaction with atomic sulfur remaining on the clusters. In comparison to the black spectrum before SO2 adsorption, the intensity is still damped by 6 %.
Table S1:
The S 2p fitting parameters and binding energies are listed in Table S1. The parameters are adapted from those of SOx on Pt single crystals.1,2 The relative binding energy shifts between SO2 species were kept constant in comparison to the single crystal data. The peak shape on the Pt nanoclusters is broader and more asymmetric than on Pt single crystals. Therefore, we adjusted the Lorentzian width and asymmetry of the SO2 signals accordingly. The ratio of all S 2p3/2 signals to corresponding S 2p1/2 signals is 2 and their binding energy difference is 1.19 ± 0.03 eV. This value falls well within the values used in previous studies.1,2
Figure S1: Example fits of selected S 2p spectra from Figures 1 and 4 in the paper. a) after adsorption of 0.14 L SO2 at 150 K (Figure 2d; thick black spectrum in Figure 1a); b) at 280 K (green spectrum in Figure 4a); c) at 360 K (orange spectrum in Figure 4a).
Figure S2: Pt 4f7/2 of 0.7 ML Pt/Gr/Rh(111); black spectra were recorded after deposition of Pt onto graphene at 150 K, blue spectra were recorded after exposure to 0.33 L SO2 at 150 K; and red spectra were recorded after TP-XPS until 500 K.
Table S1: Fitting parameters of the S 2p spectra. All S 2p contributions were fitted with an S 2p3/2 : S 2p1/2 ratio of 2 and a binding energy difference of 1.19 eV.
EB [eV] / Gaussian width [eV] / Lorentzian width [eV] / asymmetryS / 162.01 ± 0.06 / 0.55 / 0.171 / 0.173
SO / 163.32 ± 0.03 / 0.35 / 0.059 / 0.187
SO2step-ly / 164.55 / 0.21 / 0.17 / 0.22
SO2ly / 164.70 / 0.21 / 0.17 / 0.22
SO2step-st / 165.30 / 0.21 / 0.17 / 0.22
SO2st / 165.52 ± 0.03 / 0.21 / 0.17 / 0.22
SO3 / 166.10 / 0.339 / 0.133 / 0.141
multilayer / 167.54 / 1.00 / 0.17 / 0
1. Streber, R.; Papp, C.; Lorenz, M. P. A.; Höfert, O.; Darlatt, E.; Bayer, A.; Denecke, R.; Steinrück, H. P. SO2 Adsorption and Thermal Evolution on Clean and Oxygen Precovered Pt(111) Chem. Phys. Lett. 2010, 494, 188.
2. Streber, R.; Papp, C.; Lorenz, M. P. A.; Höfert, O.; Zhao, W.; Wickert, S.; Darlatt, E.; Bayer, A.; Denecke, R.; Steinrück, H.-P. Influence of Steps on the Adsorption and Thermal Evolution of SO2 on Clean and Oxygen Precovered Pt Surfaces J. Phys. Chem. C 2010, 114, 19734.