Hydrogenation of biodiesel catalysed by pyrazolyl nickel(ii) and palladium(ii) complexes

Biodiesel from renewable sources offers an attractive alternative to conventional diesel fuel and partial hydrogenation of free-fatty acid methyl esters (FAME) is one way to improve this renewable fuel. We have used the mononuclear pyrazolyl nickel(ii) and palladium(ii) complexes, [NiBr₂(L1)] (1), [NiBr₂(L2)] (2), [NiBr₂(L3)] (3), [PdCl₂(L1)] (4), [PdCl₂(L2)] (5) and [PdCl₂(L3)] (6) (where L1 = 3,5-dimethyl-1H-pyrazole, L2 = 3,5-di-tert-butyl-1H-pyr azole and L3 = 5-ferrocenyl-1H-pyrazole), as hydrogenation catalysts to improve the fuel properties of selected plant biodiesel. These nickel and palladium complexes exhibit significant catalytic activities in the selective and partial hydrogenation of biodiesel produced from Jatropha curcas, chinaberry (Melia azedarach), and tsamma melon (Citrullus ecirrhosus) seed oils. Depending on the catalyst and reaction time, a blend of un-hydrogenated, partially hydrogenated, and fully hydrogenated biodiesel was produced whose fuel properties meet the requirements of EN 14214 and ASTM D 6751 standards as fuels.