RESUMEN
The role played by the metal - support (MSI) and metal - metal (MMI) interactions on two important processes in controlling the catalyst performance - nucleation and molecular adsorption - has been investigated using density functional theory (DFT), by means of B3LYP functional, combined with localized molecular orbital energy decomposition analysis (LMOEDA), and natural bond orbital (NBO) calculations, with aid of a Pd4/γ-alumina (110D) model (Pd4/Al13O23H7). Our results indicate the occurrence of an electronic metal - support interaction (EMSI) which induces a most intense charge transfer in the Pd4 â γ-alumina backdonation direction, most expressive in Pd â Al, promoting an electronic redistribution within the units and attenuating the MMI. Nevertheless, the MSI/MMI synergistic effect seems to favor slightly the nucleation of a fifth palladium atom, leading to a distorted square pyramidal arrangement for Pd5. The LMOEDA analysis points to a mostly covalent character in the Pd - Al bonds, whereas the Pd - O bonds are mainly electrostatic in nature. The palladium atoms deposited on oxygen anions are the acid centers, where both NO molecule and an additional palladium atom anchor more strongly. In addition, the MSI/MMI effect, through the electronic and geometric contributions, drives the adsorption of the NO molecule to the mode which most favors the Pd â NO (4dz2 â 2π*) backdonation (bridge mode). MSI and MMI effects on the nature of the Pd - O (electrostatic) and Pd - Al (covalent) bonds, charge transfer into Pd4/γ-Al2O3 (110D) interface (back donation) and preferential site for adsorption of a single NO molecule and an additional Pd atom (Pd - O).
RESUMEN
The formation of a polyelectrolyte complex through dimers of alginate and chitosan in the presence of sodium cations (SA/CS), and its interaction with the glyphosate herbicide, has been investigated at the DFT level (B3LYP/6â311+G(d,p)). The lowest energy structure for SA/CS presents one Na+ cation coordinated to both dimers and formation of two H-bonds involving COO- and NH3+. The coordination energy of Na+ contributes with about 40% of the total complex stabilization energy. LMOEDA method indicates important contribution of covalent nature to stabilization of SA/CS. This result is corroborated by NBO analysis which shows high contribution of lp(O)âσ*(NH) overlapping, with average energy of 30â¯kcalâ¯mol-1 for the formed H-bonds. Two water molecules neighboring the complex increases its stability and promotes an octahedral coordination arrangement around Na+. The glyphosate interacts with SA/CS coordinating to Na+ and bonding to the chitosan dimer by H-bond, in agreement to performed fluorescence microscopy measurements.