Catalytic transformations of methyl oleate and biodiesel over mesoporous gallium–niobium oxides

The catalytic transformations of methyl oleate and a commercial sample of biodiesel over novel, mesoporous, gallium–niobium mixed oxides possessing both acidic and redox activities are compared with the corresponding results from acidic zeolites (H–Y, H–beta and H–ZSM-5) and SAPO-11. The products from the reaction included branched alkyl esters of FAMEs, and their double bond and cis/trans isomers. In the case of products from reactions over Ga–Nb oxides, dehydrogenated, diolefinic products (mainly, linoleates, and linolinates) were also observed. When traces of water were present (> 100 ppm) in the biodiesel, hydrolysis of the FAME to fatty acids was also observed. Dimerisation of the FAME molecules also occurred to some extent. Both the niobium content and the surface acidity of the mesoporous Ga–Nb mixed oxides influenced their catalytic activity and selectivity. The selectivity for skeletal isomerisation of the linear FAMEs over the mesoporous Ga–Nb oxides is comparable, if not better, than those observed over the aluminosilicate and silicoaluminophosphate molecular sieves.

Graphical AbstractThe catalytic transformations of methyl oleate and a commercial sample of biodiesel over novel, mesoporous, gallium–niobium mixed oxides possessing both acidic and redox activities are reported.Figure optionsDownload full-size imageDownload as PowerPoint slideResearch Highlights► Methyl oleate and biodiesel undergo a complex series of reactions in the presence of molecular sieves and mesoporous Ga-Nb oxides. ► Both acid–catalyzed reactions and redox reactions were observed over mesoporous Ga-Nb oxides. ► The selectivity for skeletal isomerisation of the linear FAMEs over the mesoporous Ga-Nb oxides is comparable than those observed over the molecular sieves.