Kinetics and mechanism of the production of higher olefins from stearic acid in the presence of an alumina-supported nickel sulfide catalyst

A nickel sulfide catalyst which efficient in the decarbonylation of fatty acids to olefins and dienes has been obtained for the first time by treating alumina-supported nickel sulfate with hydrogen, and its properties have been studied. In its presence, the olefin selectivity of the reaction can exceed 90%. The kinetics of stearic acid deoxygenation to heptadecenes has been investigated, a kinetic model has been constructed, and a mechanism has been proposed for the reaction over this catalyst. Olefin oligomerization is the dominant side reaction. Kinetic evidence for the catalytic inhibition of oligomerization by nickel hydrides formed on the catalyst has been obtained. The compositions of active site–reactant adsorption complexes have been discussed.     

The influence of the support on activity and selectivity of nickel sulfide catalysts in the decarbonylation of stearic acid to heptadecenes

The influence of the support nature on the performance of nickel sulfide catalyst in the decarbonylation of stearic acid to heptadecenes was investigated. The catalyst supported on silica demonstrated higher activity and selectivity in comparison with the catalyst on γ-Al₂O₃ used as a reference. The reaction schemes over these catalysts are nearly the same; however, the contributions from the side reactions of hydrogenation and oligomerization are reasonably different. Introduction of the products of decarbonylation (CO and water vapor) decreases the stearic acid conversion; and in the case of the catalyst supported on silica, the addition of CO strongly reduces the rate of hydrogenation of heptadecenes. The reasons for the observed differences were discussed. It was suggested that the dispersion of the nickel component as well as the nature of support acidity played a significant role.     

Mechanism of the formation of palladium complexes serving as catalysts in hydrogenation reactions : II. Reactivity of palladium phosphine halides towards molecular hydrogen

[(PPh₃)₃(PPh₂)₂Pd₃Cl] Cl, benzene and aniline hydrochloride were isolated as products of the reactions of (PPh₃)₂PdCl₂]₂ or [(PPh₃)PdCl₂]₂ with H₂ in organic amines (Am). Similar products were obtained when (Ph₃P)₂Pd(Ph)Br was treated with H2₃ Both in amines and aromatic solvents. The reaction between H₂ and [(PBu₃)PdCl₂]₂ resulted in the formation of [(PBu₃(PBu_2)PdCl2 ·. 2 Am The kinetic data for H₂ absorption by solutions of palladium(II) complexes are consistent with the heterolytic mechanism of cleavage fo hte HH bond in the coordination sphere of palladium(II); the function of the H⁺ acceptor being performed by the bases (e.g. Am or Ph). The reaction between the palladium complexes and H₂ is autocatalytic. Reduction of the initial Pd^II complexes leads to lower oxidation state palladium complexes, which catalyse the reduction of Pd^II complexes. In the coordination sphere of the lower oxidation state palladium complexes, the oxidative addition of PR₃ to Pd takes place with formation of compounds containing a Pd-R bond. It is the reaction between these complexes and H₂ that yields palladium compounds with PR₂ ligands.