Conversion of Formic Acid on Single- and Nano-Crystalline Anatase TiO2(101)

Understanding thermochemical transformations of formic acid (FA) on metal oxide surfaces is important for many catalytical reactions. Here we study thermally induced reactions of FA on a single-crystalline and nanocrystalline anatase TiO2(101). We employ a combination of scanning tunneling microscopy (STM), temperature-programmed desorption (TPD), infrared reflection absorption spectroscopy (IRAS), diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and density functional theory (DFT) to follow the FA surface intermediates and reaction products above room temperature. We find that the primary reaction products desorbing at about 300, 480, and 515 K are molecular water, carbon monoxide, and formaldehyde, respectively. Bidentate (BD) formate and bridging hydroxyl (HOb) are identified as central intermediates in the FA transformations. Bridging oxygen vacancies (V-O) are also likely participants despite their low stability at the surface. Furthermore, the parallel studies on single crystals and faceted TiO2(101) nanoparticles reveal the spectroscopic commonalities of surface species and of the thermal conversion of molecular and deprotonated forms of FA.

Automated summary

The study investigates thermal-induced reactions of formic acid on metal oxide surfaces, particularly on single-crystalline and nanocrystalline anatase TiO2(101). Various techniques including STM, TPD, IRAS, DRIFTS, and DFT were used to analyze surface intermediates and reaction products. The primary reaction products were identified as molecular water, carbon monoxide, and formaldehyde, with bidentate formate and bridging hydroxyl as central intermediates. Bridging oxygen vacancies were also found to be potential participants despite their low stability.