Adsorption of ɳ2 (O, C)-tilted formaldehyde geometry on transition metal substituted p(2 × 1) SnO2 (1 1 0) surface: A first-principles analysis

Abstract

Density Functional Theory was used to study the adsorption mechanisms of bidentate η²(O, C)-tilted formaldehyde on SnO₂ (1 1 0) surfaces modeled with a p(2 × 1) periodicity and substituted with transition metals (Au, Cu, Ni, Pd). Formation energies identified suitable substitution sites between Sn_5c and Sn_6c for each of the selected dopant atoms. Except for Pd, the other dopants were found to be more stably substituted at the five-fold coordinated Sn site. Adsorption energy analysis showed that Ni and Pd substitutions enhanced adsorption compared to the pristine SnO₂ (1 1 0) surface by 0.038 eV and 0.077 eV, respectively. Pd substitution in the first two surface layers had the highest negative adsorption energy, showcasing a maximum increment by 0.101 eV, but its co-substitution with Ni did not yield improved adsorption. Bader charge analysis confirmed a two-fold charge transfer from the surface Sn_5c site to O_HCHO atom and from C_HCHO atom to the surface O_2c site, which is attributed to the diagonal-span bridged configuration of the η²(O, C) bidenate formaldehyde. The charge transfer from the surface to the gas molecule was found to be the highest for the Pd co-substituted SnO₂ surface (|1.332|e). The charge transfer is visually supported by charge density plots. Pd substitution was seen to introduce additional states at the Fermi energy. On the other hand, the introduction of the gas molecule predominantly injected additional states for the Ni-substituted surface, thereby improving the adsorption mechanism. Recovery times were calculated using the transition state equation, with values ranging from 7 to 11 s for the effectively substituted surfaces.