The dissociative chemisorption of CH4 on Pt(111) has been extensively studied as a basic activated adsorption. However, most of reports are concerning the flat Pt(111) surface. Although it is known that the defects on Pt(111) play an important role in the chemisorption of CH4 on practical catalyst, there is no systematic study on the influence of the defect. In this study, we have found that the defects on Pt(111) enhance the chemisorption of CH4, and that the initial sticking probability increases upon annealing, although the number of defects is expect to decrease upon annealing. This indicates that a specific step structure generated by annealing is effective for chemisorption of CH4.
In this work, we examine the influence of the defect by using thermal energy helium atom scattering (TEAS) method, which is extremely sensitive to the surface adsorbates and defects. The defects on Pt(111) was controlled by ion bombardment and subsequent annealing. The initial sticking probability on flat Pt(111) is 1.2×10-6 at the CH4 normal translation energy of 92 meV and at the surface temperature of 450 K. We have measured the initial sticking probability as a function of the annealing time after the 1 keV Ar+ spattering of the dose of 4.0×1014 cm-2. It is found that the initial sticking probability of 2.5×10-6 just after Ar+ spattering increases up to 2.6×10-5 after annealing for 30 min. at 450K. The STM observation on the anneal surface is in progress.
This peculiar result may be related to the "low energy pathway" 1) proposed by Walker and King. It is expected that the obtained results on the influence of the defect on the chemisorption of CH4 on Pt(111) contribute to the development of practical catalyst.
1) A.V. Walker, Phys. Rev. Lett. 82 (1999) 5156 |