Materials based on platinum metals with very good catalytic activity were tested in the reduction of p–nitrophenol (pNP) to p–aminophenol (pAP). The majority of presented catalytic materials are based on the adsorption of p–nitrophenol on the surface of the catalyst simultaneously with molecular hydrogen, coming from sodium borohydride in an aqueous medium, which reduces it. In the present paper, a catalytic material based on osmium dispersed in n–decanol or n–dodecanol is presented, which also works as an emulsion membrane, for the absorption of p–nitrophenol and molecular hydrogen at the n–alcohol aqueous solution interface. The hydrogenation of p–nitrophenol is carried out in a reaction and separation column in which the acid receiving phase emulsion is dispersed in the osmium nanodispersion, in n–alcohols. This emulsion circulates from the base of the column to its upper part in co-current or counter-current with the source phase consisting of p–nitrophenol and sodium borohydride. Experiments show that the circulation of counter-current phases is superior to that in co-current, and the emulsion based on n–decanol is more efficient than the one based on n–dodecanol. The increase in the pH difference between the source and receiving phases leads to the increase in the conversion of p–nitrophenol to p–aminophenol. The efficiency of separation of the reaction product in the receiving phase is lower than the conversion at the same operating time. The apparent catalytic rate constant (kapp) of the new catalytic material based on the emulsion membrane with nanodispersion of osmium nanoparticles (0.1×10−3 for n–dodecanol and 0.9×10−3 for n-decanol) is lower by an order of magnitude compared to those based on adsorption on catalysts from platinum metal group. The advantage of the tested membrane catalytic material is that it extracts p–aminophenol in the acid receiving phase. The paper proposes a mechanism of the studied reduction system.

The fixation and activation of the dinitrogen molecule, N2 by hexametallic clusters of the general formula {[(μ2-L)M)]6(μ-η1:η3-Ν2)}0/+6 (L = CH2-, NH2-, PH2-, OH-, SH-, BH2- and NH2-, M = Ru(II) or Os(II)) were scrutinized by means of density functional theory calculations. In these systems, the dinitrogen molecule, acts as a ligand that bridges the two opposite facing triangular metallic rings, cyclo-M3 of the {[(μ2-L)M)]6(μ-η1:η3-Ν2)}0/+6 clusters The hexametallic clusters, that mimick the six Fe cluster of nitrogenase, were found to strongly activate N2, converting it into a hydrazido-like group, N24-. This is substantiated by the calculated N-N bond lengths, Re(N-N) and the stretching frequencies of the N-N bond of dinitrogen, vs(N-N) found in the ranges 1.299 – 1.487 Å and 780 – 1270 cm-1 respectively. Based on the Re(N-N) and vs(N-N) values, the dinitrogen activation depends upon the nature of the hexametallic cluster. Accordingly, the Os(II) clusters were found to activate more strongly the dinitrogen molecule as compared to their Ru(II) counterparts. The nature of the ligand L also affects the extent of the N2 activation by the hexametallic clusters, which follows the order BH2- < NH2- < OH- < CH2- < NH2- < PH2-, SH- for M = Ru(II) and the order BH2- < NH2- < OH- < NH2- < CH2- < PH2- < SH- for M = Os(II). Thus, the strongest N2 activation is observed for the {[(μ2-SH)Os)]6(μ-η1:η3-Ν2)}+6 cluster and the weakest for the {[(μ2-BH)Ru)]6(μ-η1:η3-Ν2)}0 cluster. The calculated Nitrogen-15 NMR isotropic chemical shielding tensors, σiso(15N) exhibit shielding (upfield) upon N2 fixation to the metal centers of the hexametallic clusters, as a results of electron density transfer towards its constituent N nuclei. A multitude of electronic charge distribution partitioning schemes were applied to assist in delineating the bonding properties of the {[(μ2-L)M)]6(μ-η1:η3-Ν2)}0/+6 clusters. Accordingly, it is found that there is a donation/backdonation interaction between the bridging N2 ligand and the two opposing cyclo-M3 rings located on either side. The dinitrogen ligand forms six bonds of mixed covalent/electrostatic nature with the six metal centers of the {[(μ2-L)M)]6)}0/+6 clusters.