Transition metal carbides and phosphides for the production of alkanes from fatty acids

Lately much attention has been given to the conversion of biomass into biofuel to decrease the crude oil dependency of countries and because of the sustainability of biomass. Vegetable oils have many similarities to fossil diesel however they present higher oxygen content, what induces corrosion of diesel engines. To overcome this problem, deoxygenation is needed to remove the oxygen atoms from vegetable oils.
The most used catalysts for deoxygenation reactions are based on noble metals. However, due to their limited availability, replacement by other good available metals is desirable. Transition metal carbides and phosphides have similar catalytic properties as noble metals and hold therefore great potential. The main goal of this project is investigate the role of the support, using different carbons, on the catalytic performance of metal-carbides (W2C and Mo2C) and phosphides (Ni2P) for the deoxygenation of fatty acids.

Highlight of the past year

Ni2P was synthesized on different carbon based supports i.e., activated carbon (AC), carbon covered alumina (CCA) and carbon nanofibers (CNF) and tested for deoxygenation of oleic acid at 350 oC and 30 bar of H2 in a continuous flow trickle bed reactor. All catalysts presented high conversion (> 90% under our conditions), however different product distributions (Figure 1) were obtained. The C17/C18 ratio increased in the order Ni2P/AC < Ni2P/CNF < Ni2P/CCA, which means that more C18 was obtained as product over Ni2P/AC compared to Ni2P/CCA. This difference can be attributed to the strength of the active site as visualized by CO binding strength (Figure 2) and to the density of the active sites. Active sites of Ni2P/CCA are stronger and are speculated to be responsible for the production of the higher C17/C18 ratio.  Besides, AC presents the highest surface area among the supports, leading to the lowest density of Ni sites and the lowest products C17/C18 ratio. We hypothize that the selectivity of C17 and C18 in deoxygenation of oleic acid over Ni2P catalyst is influenced by an electronic effect caused by the support and by the density of Ni sites.

Type of student projects envisioned

Lab work with use of some characterizations techniques to understand and make results clearer, e.g. transmission electron microscopy.