Ethylene hydrogenation mechanism on the platinum(111) surface: theoretical determination

Abstract

Figure 2. The error sum as a function of 8: (*) 1; ( ) 2; (O) 3.were recorded on a Varían VXR-500 (500 MHz) instrument at 30 ± 1 °C. A normal NOESY pulse sequence was employed. The mixing time was 0.1 s. Additional experimental details have been reported previously.7Computational Procedures. Equation 2 contains three unknown parameters (rs, t(, S), but rs is equal for all protons in the surfactant. When s is chosen, the experimental 7, values can be fitted to eq 2. Variation of ts produces a shallow minimum in the error sum (Figure 2). The error sum is defined20 as the sum over all squares of the differences between the observed and calculated Tf^s, divided by the square of the observed value. The ts values obtained in this way are of moderate accuracy (±1 ns).The errors in rf and 5 were estimated from a data set of 100 7,'s.These 7,'s were calculated from the experimental 7,'s and the experimental errors in 7, using an inverse Gaussian function and a confidence interval of 80%.eter), 200 (Nicolet NT-200 spectrometer), and 300 MHz (Varían VXR-300 spectrometer). Typical parameters in the experiments were 10 pulse interval times from 0.005 to 15 s. The delay time between the pulse sequences was at least 5 times the longest 7,.Good experimental fits were obtained. Using a series of different samples, the 7, values were found to be accurate to within 4% at 200 and 300 MHz, and to within 6% at 90 MHz. All experiments were performed at 35 ± 1 °C. The 2D NOE spectra Acknowledgment. The investigations were supported by the Netherlands Foundation for Chemical Research (SON) with financial aid from the Netherlands Foundation for Scientific Research (NWO). We thank Dr. R. M. Scheek and K. Dijkstra for expert assistance with the Varían VXR-500 spectrometer and with the data analysis of the NOESY experiments. Stimulating discussions with these scientists and with Professor H. J. C. Berendsen are also gratefully acknowledged.

An Investigation of the Reaction Pathway for Ethylene Hydrogenation on Pd(111)

“…This conclusion is in accord with theoretical work on Pt(111). 40 The surface properties of adsorbed ethyl iodide on Pd(111) are summarized in Figures 4 and 5. The infrared data of Figure 4 indicate that a condensed layer of ethyl iodide forms after an exposure of 10 L and the assignments for the multilayer are displayed in Table 1, showing good agreement with the spectrum of liquid ethyl iodide.…”

Germanium as key dopant to boost the catalytic performance of small platinum clusters for alkane dehydrogenation

“…The reason is that, as mentioned above, the di-σ binding mode of ethylene on Pt is considered precursor of further dehydrogenation, whereas the π bonded species is more likely to desorb. [34][35][36][37] Therefore, the dehydrogenation of ethylene on Pt is expected to occur from the di-σ geometry. In the most favorable case, the reaction needs to overcome a barrier of 0.53 eV.…”

The importance of hydrogen’s potential-energy surface and the strength of the forming R–H bond in surface hydrogenation reactions

“…[11][12][13][14][15][16][17] In addition, they are crucial to the removal of reaction products which would otherwise poison the catalyst surface, and an efficient means of multiple carbon bond reduction in alkynes, alkenes, and long chain fatty acids. [18][19][20][21] In spite of the importance of hydrogenations and other association reactions ͑bond forming reactions͒, many aspects of their reactivity are still unclear. This is largely due to the fact that most association reactions occur by the Langmuir-Hinshelwood ͑L-H͒ mechanism, and that there are experimental difficulties in monitoring surface reactions at the atomic level.…”