The role of promoters in metallic nickel catalysts used for green diesel production: A critical review

The most important contributions were reviewed relevant to the promoting action of metals (Cu, Zn, Fe, Pd, Pt, Sn, Ga, Re) and metal oxides (Mo, W, Nb, Ca-Mg oxides) concerning reduced nickel catalysts used for green diesel production. The promoting effect concerns not only the acceleration of the green diesel production but, in addition, the shift of the reaction network to the dehydration pathway, the decrease of the extent of C-C hydrogenolysis (and thus the extent of fragmentation of the side chains of triglycerides and coke diminution) and the decrease in the extent of methanation. The promoting action is manifested through different effects: the increase in the nickel active surface, the formation of alloys, intermetallic compounds and/or mixed oxides and the synergy between nickel or Ni-Me hydrogenation sites and oxygen vacancies of the second metal oxide. The relative contribution of each effect depends mainly on the kind of the promoter.

Automated summary

This paper reviews the important contributions of metals and metal oxides as promoters in the production of green diesel using reduced nickel catalysts. The promotion effect includes accelerating green diesel production, shifting the reaction network to the dehydration pathway, reducing C-C hydrogenolysis and fragmentation of triglyceride side chains, and decreasing methanation. The promoting action is achieved through various mechanisms such as increasing the active surface of nickel, forming alloys, intermetallic compounds, and mixed oxides, as well as the synergy between nickel or Ni-Me hydrogenation sites and oxygen vacancies of the second metal oxide. The contribution of each mechanism depends on the type of promoter used.