Molecular metal complexes such as MCl x react readily with hydroxyl-terminated surfaces to produce some of the “single-atom” catalysts used in important large-scale commercial reactions, including olefin metathesis, polymerization, and epoxidation. While the local oxide environment can vary at each metal site, the manner and degree to which these differences impact the catalytic activities of individual sites are poorly understood. In this work, we develop a computational framework to model the grafting of metal complexes onto amorphous supports and apply the framework to examine TiCl4 grafting onto amorphous silica. We use density functional theory (DFT) to calculate free energies for TiCl4 reactions at vicinal silanol sites. The kinetics and thermodynamics depend on the dihedral angle between the silanols. Vicinal silanol pairs with small dihedral angles are predicted to yield bipodal [(SiO)2TiCl2] sites initially, but they react further with TiCl4 vapor to give vicinal pairs of monopodal sites, [  SiOTiCl3]. In contrast, silanol pairs with large dihedral angles yield vicinal pairs of monopodal Ti sites directly. The DFT results were used to construct a population balance model to describe the kinetics of TiCl4 grafting onto nonuniform sites of an atomistic model for amorphous silica. The solution of the population balance model predicts that the majority of the vicinal pairs graft as bipodal [(SiO)2TiCl2] sites first and then slowly convert to monopodal [SiOTiCl3] sites. The predictions provide a plausible explanation for the variability in the populations of monopodal and bipodal sites previously reported for TiCl4 grafting.

We present a classical interatomic force field, silica-DDEC, to describe the interactions of amorphous and crystalline silica surfaces, parametrized using density functional theory-based charges. Charge schemes for silica surfaces were developed using the densityderived electrostatic and chemical (DDEC) method, which reproduces atomic charges of the periodic models as well as the electrostatic potential away from the atom sites. Lennard−Jones parameters were determined by requiring the correct description of (i) the amorphous silica density, coordination defects, and local coordination geometry, relative to experimental measurements, and (ii) water-silica interatomic distances compared with ab initio results. Deprotonated surface silanol sites are also described within the model based on DDEC charges. The result is a general electronic structure-derived model for describing fully flexible amorphous and crystalline silica surfaces and interactions of liquids with silica surfaces of varying structure and protonation state.

The adsorption of glycine on amorphous silica surface has been studied to demonstrate the catalytic activity of silica surfaces towards the formation of peptide bonds on prebiotic earth. Silica nanoparticles were synthesized using a microwave assisted method and the nanoparticles were characterized using SEM. Glycine was adsorbed from aqueous solution on the nanoparticles and the adsorption behavior was characterized using FTIR and TGA analyses. At a glycine concentration of 0.5M and at pH=7, favorable adsorption was observed which obeyed the Langmuir isotherm model. From the FTIR characterization, peptide bond formation was confirmed. It was concluded that the adsorption of glycine occurs via electrostatic interactions as well as hydrogen bonding between the silica surface and glycine molecules.