The Case of Formic Acid on Anatase TiO₂(101): Where is the Acid Proton?

Abstract

Carboxylic‐acid adsorption on anatase TiO2 is a relevant process in many technological applications. Yet, despite several decades of investigations, the acid‐proton localization—either on the molecule or on the surface—is still an open issue. By modeling the adsorption of formic acid on top of anatase(101) surfaces, we highlight the formation of a short strong hydrogen bond. In the 0 K limit, the acid‐proton behavior is ruled by quantum delocalization effects in a single potential well, while at ambient conditions, the proton undergoes a rapid classical shuttling in a shallow two‐well free‐energy profile. This picture, supported by agreement with available experiments, shows that the anatase surface acts like a protecting group for the carboxylic acid functionality. Such a new conceptual insight might help rationalize chemical processes involving carboxylic acids on oxide surfaces.

Redox‐Mediated Ambient Electrolytic Nitrogen Reduction for Hydrazine and Ammonia Generation

“…Hence, to better represent the actual conditions, a protonated Fe‐TiO 2 model is applied in the DFT calculations in which the surface Ti III atoms are saturated with −OH. This is also in line with the literature that TiO 2 surface has a strong tendency to form hydrogen bond with proton in acidic environment [40] . DFT calculations of the charge distribution was first conducted on the traditional TiO 2 and protonated Fe‐TiO 2 models to provide detailed information of the TiO 2 electrode electronic structure changes.…”

Redox‐Mediated Ambient Electrolytic Nitrogen Reduction for Hydrazine and Ammonia Generation

“…This is also in line with the literature that TiO 2 surface has as trong tendencyt o form hydrogen bond with proton in acidic environment. [40] DFT calculations of the charge distribution was first conducted on the traditional TiO 2 and protonated Fe-TiO 2 models to provide detailed information of the TiO 2 electrode electronic structure changes.F or traditional TiO 2 model, the surface Ti atoms host 61.51 e À (a 4 4T iO 2 (101) model), which is increased to 64.44 e À after Fe doping and protonation. The5%increase in the total electron of the surface Ti atoms is broadly consistent with XANES and XPS results (Figure 2a It is noted that NH 2 NH 2 has been reported as the final product catalyzed by as ingle Fe-oxygen vacancy (V O ) pair and only with multiple oxygen vacancies (i.e.2V O next to Fe atom) could ammonium be obtained.…”

The Early Steps of Molecule-to-Material Conversion in Chemical Vapor Deposition (CVD): A Case Study

“…In addition, in the Pyr@SiO2 structure, the distances of both O2' and O2 atoms from the metal center are higher than in the isolated precursor (see Table 4). These differences can be attributed to the presence of a very strong hydrogen bond, characterized by a distance (1.586 Å) close to those typical of proton-sharing moieties on oxide surfaces [17,66,[69][70][71][72]. Moreover, the complex pyramidal geometry also favors the formation of a hydrogen bond between a surface -OH proton and a F atom of the hfa ligand (F-H distance = 2.002 Å).…”

“…Overall, these results could be taken as a validation of our modeling strategy for the finite temperature reactivity of Zn(hfa)2TMEDA on the CVD growth surface. As a matter of fact, due to the high computational overhead of statistical sampling approaches on oxide material surfaces [11,51,[66][67][68], the simulation of the Zn-ligand bond dissociation process is currently viable at reasonable time scales only through (dispersion-corrected) Generalized Gradient Approximation DFT approaches such as the PBE-D2/PW one. Figure 3.…”