TPD and HREELS reinvestigation of ethylene oxide adsorption on Pt()

Studies of Ethylene Oxide Adsorption on Pt−Sn Alloys with TPD, HREELS, UPS, and DFT Calculations

“…These values are good estimates for the adsorption energy since there is no appreciable activation barrier for adsorption. TPD results and AES measurements taken after TPD experiments place an upper limit on the extent of decomposition at 0.02 ML . Introduction of step sites on the surface does not strongly alter this chemistry, and similar results were found in previous studies of EO adsorption on the Pt(110)-(1 × 2) surface …”

“…This red shift with decreasing lower coverage can be attributed to stronger binding of EO to the surface due to reduction of lateral repulsions from neighboring adsorbed EO molecules. Such a red shift of the ring deformation mode was also observed for EO on Pt(111), where the peak position was red-shifted by 24 cm −1 from its value in thick multilayer EO films . Red-shifts of 15 and 10 cm −1 were also observed for the loss peaks from CH 2 wagging (1160 cm −1 ) and ring stretching (1270 cm −1 ) modes, respectively, at submonolayer coverages.…”

“…Although most EO adsorbed at 90 K desorbs reversibly below 210 K, a combination of HREELS, TPD, and DFT also allows us to analyze a small fraction of EO that remains on the surface, transforms, and then decomposes at higher temperatures. As mentioned above, the upper limit on the remaining EO amount is 0.02 ML for Pt(111) and 0.006 ML for the alloys. The evolution of the HREELS spectra after heating in Figures b and b is consistent with the onset of the transformation of EO bonded with the ring intact (Figure ) into a metallacycle configuration (Figure ) at 120−160 K. By ∼200 K, EO remaining on the surface completes the transformation to the metallacycle configuration and begins to decompose, as evidenced by CO formation.…”

“…Decomposition reactions were reported to be predominant over molecular desorption at low coverages, evolving H 2 and CO into the gas phase and leaving adsorbed carbon as the residual decomposition product. Our reinvestigation of this chemistry, however, has shown that EO has only a minor decomposition channel (<0.015 ML) on Pt(111) and evolves at 158−207 K with a desorption energy of 9.3 to 12.8 kcal/mol . EO adsorbed at low temperatures was similarly reported to be unreactive on Pt(110)-(1 × 2) with EO desorbing molecularly at 140−230 K and undergoing only minor decomposition (≤0.02 ML) …”

Adsorption and decomposition of γ-butyrolactone on Pd(111) and Pt(111)

“…cyclic ethers) show qualitatively similar shifts between the multilayer and monolayer spectra. Only minor changes in the vibrational frequencies of ethylene oxide on Pd(110) [16] and Pt(1 1 1) [17] and of propylene oxide on Pd(1 1 1) [18] were observed, with most shifts being <20 cm À1 . Fig.…”