Guanidinium Formate Decomposition on the (101) TiO₂-Anatase Surface: Combined Minimum Energy Reaction Pathway Calculations and Temperature-Programmed Decomposition Experiments

Abstract

Local minima, saddle points, and connecting intrinsic reaction paths for the decomposition of guanidinium formate (GuFo) on a (101) TiO2-anatase surface and in the gas phase have been studied on the basis of density functional theory (DFT) energy surfaces. We are aware of only one preceding electronic structure theory study of reaction barriers at a slab surface model. The formation of ammonia and carbon dioxide as final products of the GuFo decomposition is proposed to proceed in three principal stages: first, the decomposition of GuFo to guanidine and formic acid, then the hydrolysis or decomposition of guanidine to ammonia and carbon dioxide via urea and isocyanic acid intermediates, and, in parallel to the latter, the decomposition of formic acid to water and carbon monoxide or to hydrogen and carbon dioxide. The moment in which water enters the decomposition of guanidine is crucial and determines its course. Temperature-programmed decomposition experiments propose a decomposition of guanidine to urea and subsequent decomposition to isocyanic acid and its rapid hydrolysis to ammonia.

Free‐radical polymerization of urea, acrylic acid, and glycerol in aqueous solutions

“…1 . Bernhard et al (2012) and Todorova et al (2010) showed that ammonia could also be formed by the hydrolysis of urea in the presence of TiO 2 . The ammonia concentrations (and, therefore, the urea concentrations) were obtained at room temperature with help of a calibration model, using a UV–Visible spectrophotometer (Model Lambda 35, manufactured by Perkin Elmer) in the wavelength range of 570 to 720 nm.…”

Studies on the reaction pathway of arsenate adsorption at water–TiO2 interfaces using density functional theory

“…According to the optimized geometries of the adsorbed intermediate species, reactant and product, the tentative geometry of transition state was prepared by gradually adjusting the cluster structures along the minimum energy path on the PES [35]. The initial guess structure is crucial to making the subsequent optimization of transition states be successfully converged.…”

Catalytic urea hydrolysis in the selective catalytic reduction of NOx: catalyst screening and kinetics on anatase TiO2and ZrO2

“…Only recently, we have reported about catalytic urea thermolysis (1) under steady state conditions over different metal oxides. 26 Also, a theoretical study of Todorova et al (2011) proposes catalytic urea thermolysis. These authors calculated the reaction energy barriers for the hydrolysis of guanidine on anatase TiO 2 (101) using density functional theory (DFT) and found adsorbed urea as an intermediate on the TiO 2 surface.…”

“…These authors calculated the reaction energy barriers for the hydrolysis of guanidine on anatase TiO 2 (101) using density functional theory (DFT) and found adsorbed urea as an intermediate on the TiO 2 surface. 27 From the adsorbed urea NH 3 can be eliminated, leaving HNCO on the catalyst surface. HNCO then hydrolyzes via carbamic acid as another intermediate.…”