Partial Hydrogenation of Palm Oil-Derived Biodiesel over Ni/Electrospun Silica Fiber Catalysts

Given the high accessibility of reactants to the active metal sites of fibrous catalysts, in this research, an electrospun silica fiber was applied as a support of nickel catalysts (Ni/SF) for the partial hydrogenation of palm oil fatty acid methyl ester (FAME) in a fixed-bed reactor. The textural properties, reducibility Ni dispersion and morphology of Ni/SF catalysts were characterized and compared to those of a Ni/porous silica ball (Ni/SB). Under 1 bar [H.sup.2] pressure at 140 [degrees]C, the 30 wt% Ni/SF catalyst exhibited a high turnover frequency (TOF) of 1396 [h.sup.-1] to convert methyl linoleate (C18:2) to more saturated structures. On the other hand, the system using Ni/SB catalysts showed a TOF of only 141 [h.sup.-1]. This result was due to the effect of the higher acidity of the silica fiber, which promoted the higher adsorption of polyunsaturated portions in FAME. The non-porous characteristics and open morphology of the Ni/SF catalysts also allowed FAME and [H.sup.2] molecules to easily access the Ni active sites deposited on the surface of the silica fiber and suppressed the selectivity to cis-trans isomerization. Stability testing of the Ni/SF catalyst showed that the C18:2 conversion decreased from 71% to 60% after long-term operation for 16 h possibly due to the weak metal-support interaction that facilitated Ni particle loss from the catalyst surface.