Deoxygenations of palm oil-derived methyl esters over mono- and bimetallic NiCo catalysts

Abstract

Abstract In this work, series of SAPO-11-supported monometallic Ni, Co and bimetallic NiCo catalysts were prepared and tested for their activities toward the deoxygenation of palm oil-derived fatty acid methyl esters (FAMEs). Effects of metal introduction methods, i.e., co-impregnation (NiCo/SAPO-11) and sequential-impregnation (Ni/Co/SAPO-11 and Co/Ni/SAPO-11) for bimetallic catalysts on their catalytic performance were also investigated. It was confirmed by X-ray diffraction and transmission electron microscopy with elemental mapping that bimetallic Ni–Co alloy phase was formed. X-ray photoelectron spectroscopy results revealed that different metal loading steps caused different Ni:Co ratios on catalyst surfaces. Those values corresponded to the sequence of metal loading from which the outer shell possessed higher concentration than the co-impregnated NiCo/SAPO-11 with a comparable Ni and Co atomic concentration. H2 temperature programmed reduction investigation showed that the incorporation of Co species could improve the reducibility of bimetallic catalysts. Among all synthesized catalysts, the deoxygenation of palm-oil derived FAMEs over Co/Ni/SAPO-11 catalyst, with Co surface enrichment, exhibited the highest yield of diesel range fuel (i.e., ~ 89% at 330\xa0°C). It was revealed that Co active sites play an important role to promote the deoxygenation due to the strong Co–O interaction. The synergy through Ni–Co alloying would be an efficient approach to enhance the deoxygenation of palm-oil derived FAMEs to diesel-like hydrocarbon fuels.