NCAFM2023 Programme Booklet

Tuesday 1140 - 1200

VISUALIZING THE PROMOTING ROLE OF INTERFACIAL WATER IN THE DEPROTONATION OF FORMIC ACID

Pu Yang 1‡ , Honggang Liu 2‡ , Qingwei Jin 1 , Chen Zhang 1 , Jia Dong 1 , Wenyu Sun 1 , Duanyun Cao 2* , Jing Guo 1* 1 College of Chemistry, Key Laboratory of Theoretical and Computational Photochemistry, Beijing Normal University, Beijing, 100875, China 2 Beijing Key Laboratory of Environmental Science and Engineering, School of Materials Science and Engineering, Beijing Institute of Technology, Beijing, 100081, China Email: dycao@bit.edu.cn; jguo1294@bnu.edu.cn

Water plays a crucial role in various heterogeneous catalytic reactions, but the atomic-scale characterization on how water participates in these chemical processes remains a significant challenge. Here we directly visualize the promoting role of interfacial water in the deprotonation of formic acid (FA) on metal surfaces, using combined scanning tunneling microscopy (STM) and qPlus based noncontact atomic force microscopy (nc-AFM). We find the dissociation of FA with the coadsorption of water on both Cu(111) and Au(111) surfaces and the formation of hydronium and formate ions. Interestingly, the hydrated proton and formate ions exhibit a phase-separated behavior on Cu(111), where Eigen and Zundel cations self-assemble into monolayer hexagonal hydrogen-bonding (H-bonding) network and bidentate formate ions are solvated with water and aggregate into one dimensional (1D) chains or two dimensional (2D) H-bonding networks. This phase-separated behavior is essential for preventing the proton transfer back from hydronium to formate and the reformation of FA, which is absent on Au(111). Density functional theory (DFT) calculations revealed that the participation of water significantly reduces the deprotonation barrier of FA on Cu(111), in which water catalyzes the decomposition of FA through the Grotthuss proton transfer mechanism and the solvent-separated ion pair of HCOO-…H 2 O…H 3 O + is energetically preferred. It is expected that the water-facilitated deprotonation mechanism and stabilization of transition states through solvation would be applicable to a broad range of organic acids.

Fig. Experimental characterization and DFT calculation on the proton transfer process in the water-promoted deprotonation of FA.

References [1] To be submitted.

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