L. N. Belonogova

Formation of a hydrogenation catalyst in the cobalt acetylacetonate-triethylaluminum system

Based on the results obtained using chemical, kinetic, and physical techniques (EPR, IR, and UV spectroscopy; transmission electron microscopy; and XRD analysis), the formation of active species in the triethylaluminum-bis(tris)(acetylacetonato)cobalt system, which is known to be a hydrogenation catalyst, has been considered. It has been found that nanosized particles are formed in this system; the core of these particles consists of Co0 atoms stabilized by a shell containing Et2Al(acac), AlEt3, and their reaction products. The extremal dependence of the hydrogenation activity of the system on the Al/Co ratio is primarily due to changes in the composition of the protective shell of nanosized particles.

Effect of the nature of the acido ligand in the precursor on the properties of nanosized palladium-based hydrogenation catalysts modified with elemental phosphorus

The effect of the nature of the acido ligand in the precursor and the modifying action of elemental phosphorus on palladium catalysts for hydrogenation are reported. The large turnover frequency (TOF) and turnover number (TON) values observed for styrene hydrogenation on the Pd blacks prepared in situ by PdCl2 reduction with hydrogen in DMF are due to the formation of fine-particle catalyst with a base particle size of 6–10 nm. This is explained by the high PdCl2 reduction rate and by the formation of a palladium cluster stabilizer—dimethylammonium chloride—in the reaction system via the catalytic hydrolysis of the solvent (DMF). The modifying action of elemental phosphorus on the properties of the palladium catalysts depends on the nature of the acido ligand in the precursor. In the case of oxygen-containing precursors at small P/Pd ratios, elemental phosphorus exerts a promoting effect, raising the TON and TOF values by a factor of about 9. In the case of palladium dichloride as the precursor, white phosphorus exerts an inhibiting effect. At the same time, it enhances the stability of the catalyst, raising the TON value at P/Pd = 0.3. The causes of these distinctions are considered.

Synthesis, Properties, and Activity of Nanosized Palladium Catalysts Modified with Elemental Phosphorus for Hydrogenation

The applicability of elemental phosphorus as a modifier of palladium catalysts for hydrogenation was demonstrated, and the conditions for the synthesis of nanoparticles that are highly efficient in hydrogenation catalysis were optimized. The modifying effect of elemental phosphorus depends on the P/Pd ratio; it is associated with changes in the catalyst dispersity and the nature of the formed nanoparticles containing various palladium phosphides (PdP2, Pd5P2, and Pd6P) and Pd(0) clusters. The main stages of the formation of palladium catalysts for hydrogenation were determined, and a model of an active catalyst, in which the Pd6P phosphide is the core of a nanoparticle and Pd(0) clusters form a shell, was proposed.

Nature of the modifying action of white phosphorus on the properties of nanosized hydrogenation catalysts based on bis(dibenzylideneacetone)palladium(0)

The catalytic properties and nature of the nanoparticles forming in the system based on Pd(dba)2 and white phosphorus are reported. A schematic mechanism is suggested for the formation of nanosized palladium-based hydrogenation catalysts. The mechanism includes the formation of palladium nanoclusters via the interaction of Pd(dba)2 with the solvent (N,N-dimethylformamide) and substrate and the formation of palladium phosphide nanoparticles. The inhibiting effect exerted by elemental phosphorus on the catalytic process is due to the conversion of part of the Pd(0) into palladium phosphides, which are inactive in hydrogenation under mild conditions, and the formation of mainly segregated palladium nanoclusters and palladium phosphide nanoparticles. By investigating the interaction between Pd(dba)2 and white phosphorus in benzene, it has been established that the formation of palladium phosphides under mild conditions consists of the following consecutive steps: Pd(0) → PdP2 → Pd5P2 → Pd3P. It is explained why white phosphorus can produce diametrically opposite effects of on the catalytic properties of nanosized palladium-based hydrogenation catalysts, depending on the nature of the palladium precursor.

Hydrogenation catalysts based on polynuclear palladium complexes with organophosphorus ligands

A new procedure is proposed for the preparation of hydrogenation catalysts. This procedure includes the synthesis of cyclic tetranuclear palladium complexes with bridging diphenylphosphide ligands followed by a reaction with Pd(CH3COO)2 in the presence of hydrogen to form nanosized particles. In the test catalysts, the ensembles of palladium atoms (or palladium hydrides) immobilized on supramolecular structures formed by the association of phosphinidene and phosphide complexes of palladium are responsible for the catalytic activity.

Nanosized hydrogenation catalyst based on palladium bisacetylacetonate and phosphine: Formation, the origin of activity, and properties

The nature and catalytic properties of a hydrogenation catalyst based on Pd(acac)2 and PH3 are considered. As demonstrated by a variety of physicochemical methods (IR and UV spectroscopy, 31P and 1H NMR, electron microscopy, and X-ray powder diffraction), nanoparticles consisting of various palladium phosphides (Pd6P, Pd4.8P, and Pd5P2) and Pd(0) clusters form under the action of dihydrogen during catalyst preparation. The promoting effect of phosphine at low PH3: Pd(acac)2 ratios is mainly due to the ability of phosphine to increase the extent of dispersion of the catalyst.

Reaction of palladium bisacetylacetonate with elemental phosphorus. Effect of water on the composition of palladium phosphides

Reaction of palladium bisacetylacetonate with elemental phosphorus in an inert atmosphere is shown to proceed as a redox process forming palladium phosphides of different compositions: PdP2, Pd5P2, Pd4,8P, and Pd12P3,2. The conversion of Pd(acac)2 and the composition of palladium phosphides formed in benzene is established to be affected by water. A tentative scheme of the formation of palladium phosphides is suggested.

Formation of palladium phosphides in the reaction of bis(dibenzylideneacetone)palladium(0) with white phosphorus

The reaction of bis(dibenzylideneacetone)palladium(0) with white phosphorus was studied using the methods of NMR, UV spectroscopy, and X-ray powder diffraction. The products of the reaction are shown to be palladium phosphides, their composition depending on the ratio of the reagents. The mechanism of the formation of the palladium-enriched phosphides is suggested, which includes the formation of palladium diphosphide PdP2 that subsequently reacts with the excess of bis(dibenzylideneacetone)palladium(0) leading to palladium phosphides Pd5P2, Pd3P0.8, Pd4.8P, and free dibenzylideneacetone.

Preparation of high-performance nanosized palladium hydrogenation catalysts using white phosphorus and phosphine

The nature and properties of nanosized palladium hydrogenation catalysts modified with elemental phosphorus and phosphine (PH3) were studied.

Hydrogenation catalysts based on palladium bisacetylacetonate and lithium tetrahydroaluminate: Formation mechanism and reasons for modified effect of water

Mechanism of formation, nature of activity, and properties of species active in hydrogenation catalysis in systems based on Pd(acac)2 and LiAlH4 were studied. The effect consisting in activation of catalytic systems was observed and reasons for the modifying action of water were considered.