Propiolic Acid on Cu(100) and Oxygen-Precovered Cu(100): Multiple Adsorption States and Diversified Reaction Routes

Abstract

Multiple adsorption geometries and diversified reaction pathways of the bifunctional propiolic acid (HC�C−COOH) on Cu(100) and oxygen-covered Cu(100) (O/Cu(100)) have been investigated, using the surface analytical techniques of X-ray photoelectron spectroscopy, reflection−absorption infrared spectroscopy, and temperatureprogrammed reaction/desorption, with the assistance of density functional theory calculations. Upon adsorption on O/Cu(100) at 105 K, the deprotonation occurs promptly to form perpendicular HC�C−COO (propiolate) with the COO attaching to the surface. Decomposition of this intermediate results in the loss of CO and CO 2 at ∼230 K and formation of the plausible surface intermediates of CCCOOH, tilted HCCCOO, and CCH. The first two are derived from rearrangement or geometric transformation of the perpendicular HC�C−COO. CCH is the precursor for the C 2 H 2 desorption at ∼335 K. C 2 (acetylide) and >C�C�O (ketenylidene) exist on the surface at higher temperatures and are responsible for the desorption of CO and CO 2 at 580 K. On Cu(100), adsorption of propiolic acid at 105 K generates tilted HCCCOOH and HCCCOO, via the HCC group bonding to the surface. Perpendicular HC�C−COO is an additional species found at a higher coverage. Hydrogenation of the HCCCOO occurs, possibly involving the surface species of CHCHCOO and CH 2 CCOO. H 2 , H 2 O, CO, and CO 2 evolve from decomposition of these carboxylates at ∼315 K, also forming perpendicular CH 2 �CHCOO and >C�C�O. Adsorbed CH 3 CH 2 COO can be produced at a higher coverage. In addition, C 2 H 2 and C 2 H 4 desorb at ∼360 K. Decomposition of the perpendicular CH 2 �CHCOO, >C�C�O, and CH 3 CH 2 COO is responsible for the products of H 2 , CO, CO 2 , and C 6 H 6 found at ∼550 K.

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“…The π‐stacking peak at 292.2 eV disappeared, which could be explained by the destructive effect of carboxyl groups on π‐stacking. [ 41 ] Therefore, clear fluorescence could be observed in the PDA NPs, while the large amount of π‐stacking in PDA led to fluorescence quenching (Figure S5, Supporting Information). [ 41 ] This was confirmed by the O 1s spectra, in which a new peak of the PDA NPs at 535.1 eV appeared (Figure 2h) and the integral area ratio was 11.3% (Table S1, Supporting Information), demonstrating the existence of COOH.…”

“…[ 41 ] Therefore, clear fluorescence could be observed in the PDA NPs, while the large amount of π‐stacking in PDA led to fluorescence quenching (Figure S5, Supporting Information). [ 41 ] This was confirmed by the O 1s spectra, in which a new peak of the PDA NPs at 535.1 eV appeared (Figure 2h) and the integral area ratio was 11.3% (Table S1, Supporting Information), demonstrating the existence of COOH. [ 42 ] Next, matrix‐assisted laser desorption/ionization‐time of flight mass spectrometry was carried out to obtain more structural information about the PDA NPs.…”