Identification of surface intermediates during ethylidyne formation on Pt(111) by calculation of infrared intensities and deuterium isotope shifts

Abstract

a b s t r a c tThe conversion of ethylene to ethylidyne on Pt(111) is a well-studied model reaction related to conversion of hydrocarbons over noble metal catalysts. For this chemistry, a two step mechanism that proceeds via an ethylidene intermediate has been generally accepted since the mid-1990s. However, recent DFT calculations (J. Phys Chem. C 2010, 114, 12190) have suggested that this intermediate may, in fact, be short-lived and should not be observed. Experimental verification of this prediction, though, is not straightforward, and to provide further theoretical results by which the prediction could be more easily evaluated, we present a set of benchmark calculations of infrared frequencies and intensities of candidate intermediates adsorbed on the Pt(111) surface at realistic coadsorbate coverages. The results show that only modest differences in frequencies and intensities exist between these intermediates, rendering direct spectroscopic differentiation difficult. However, by substituting the C 2 species and intermediates with deuterium, it is shown that one characteristic vibrational band of vinylidene and ethylidene can be separated by well over 100 cm −1 . This result provides a clear prediction that, if coupled with measured vibrational spectra of deuterium-labeled C 2 species, could definitively differentiate between the most likely intermediates in this reaction network.

Nature of the Active Sites of VOx/Al2O3 Catalysts for Propane Dehydrogenation

“…In addition, DFT calculation showed that η-vinyl over the Pt(111), which preserves double bond nature, exhibited C=C vibration at 1547 cm -1 , much close to our experimental result, further supporting our proposal 45. Although the first step of propane dehydrogenation over metal oxides catalyst is commonly considered to be the dissociative adsorption of propane, forming metal alkyl and bridging hydroxyl, 28, 46-49 saturated alkyl (such as propyl) would not lead to the IR vibration as high as 1555 cm -1 50. Therefore, we propose that vanadium propyl would form at the first step of PDH, which instantly transforms to propenyl-vanadium due to instability, containing one C=C double bond and five H atoms.…”

An experimental and theoretical study of glycerol oxidation to 1,3‐dihydroxyacetone over bimetallic Pt‐Bi catalysts

“…The DFT‐determined lattice constant for Pt was found to be 3.98 Å, which agrees well with the experimental bulk lattice constant (3.92 Å); this lattice value is also consistent with other lattice constants reported in the literature for Pt . Four‐layer slab models were employed to model the Pt(111) surfaces in a super‐cell geometry with 1.2 nm vacuum spacing between them.…”

Catalytic behavior of metal catalysts in high-temperature RWGS reaction: In-situ FT-IR experiments and first-principles calculations

“…Additionally, methane (CH 4 ), adsorbed methyl (CH 3 ), and carbonate (CO 3 2− ) groups were observed in small quantities on the catalyst surface. Gaseous CH 4 and adsorbed CH 3 were only found on the Pd and Ni/Al 2 O 3 catalysts at 600 °C, as indicated by the peaks at 3000 and 2890 cm −1  262728, respectively. This result is in agreement with the suppressed CO selectivity observed at 600 °C due to CH 4 formation.…”