Short-Lived Reactive Intermediate in the Decomposition of Formate on NiO(111) Surface Observed by Picosecond Temperature Jump

Abstract

Unstable intermediates are indispensable ingredients of chemical reactions, but their identification at solid surfaces has been hampered by the lack of techniques to detect short-lived and fractionally generated species. We succeeded in identifying the intermediate in a thermal decomposition reaction by utilizing the picosecond temperature jump induced by the irradiation of laser pulses and the observation by sum-frequency generation spectroscopy. We verified that the decomposition of formate on the NiO(111) surface is preceded by the transformation of stable bidentate formate to unstable monodentate formate, which is the reactive intermediate, and two species are found to be in equilibrium before decomposition.

Femtosecond Surface Vibrational Spectroscopy of CO Adsorbed on Ru(001) during Desorption

“…Using picosecond (ps) techniques, information about the dynamics of energy exchange between adsorbed carbon monoxide (CO) and metal substrates has been obtained [4], by monitoring transient band shifts of the C-O vibration after optical excitation. The technique has further been used to observe vibrational energy relaxation [5] and reversible transient chemical transformations [6] at surfaces. These experiments were limited to temperatures below those at which desorption of the adsorbate occurs.…”

“…PACS numbers: 68.35.Ja, 33.70.Jg, 78.47. + p, 82.20.Rp The dynamics of the interaction between molecules and metal surfaces is of fundamental importance in surface science, since these determine key physical and chemical properties-essential in, e.g., catalysis-such as energy transfer and molecular reactivity [1] [6] at surfaces. These experiments were limited to temperatures below those at which desorption of the adsorbate occurs.…”

Density Functional Study of Formate Decomposition on NiO(111) Surface

“…These results are in good agreement with our recent experimental results. 21 The temperature jump of ca. 300 K caused by the irradiation of picosecond near-infrared (1.06 µm) laser pulses revealed the irradiation induced transformation between the bidentate and monodentate configurations.…”

“…The calculated small energy difference between the bidentate and monodentate and the relatively low barrier (not estimated by our measurements) are consistent with our current understanding that the two configurations must coexist and can be converted mutually. 21 The optimized structures for HCOO and H groups with the (NiO) 4 cluster are reproduced with the (NiO) 19 cluster shown in Figure 1, and the energies are estimated by single-point calculations. (The H atom is bonded to the bottom layer O atom on the right side with the same local geometry.)…”

“…14- 21 The reaction mechanism is rather complicated. The dehydrogenation and dehydration compete with each other and the relative ratio depends on various reaction conditions, such as catalyst materials, surface conditions, temperature, gas pressure, and so on.…”