Carbon–Carbon Bond Scission Pathways in the Deoxygenation of Fatty Acids on Transition-Metal Sulfides

Abstract

The mechanism of the deoxygenation of fatty acids on transition-metal sulfides was determined on the basis of kinetic data obtained with fatty acids, their reaction intermediates (aldehyde and alcohol), and reactants of restricted reactivity (adamantanyl-substituted carboxylic acids). Deoxygenation on MoS2 proceeds exclusively via hydrogenolysis to aldehyde, followed by hydrogenation to the corresponding alcohol, consecutive dehydration to the olefin, and hydrogenation to the alkane. In contrast, the selectivity on Ni-MoS2 and on Ni3S2 substantially shifts toward carbon oxide elimination routes: i.e., direct production of C n–1 olefins and alkanes. The carbon losses occur by decarbonylation of a ketene intermediate, which forms only on sites associated with Ni. The rate determining steps are the cleavage of the C–C bond and the removal of oxygen from the surface below and above, respectively, 2.5 MPa of H2. The different reaction pathways catalyzed by MoS2 and Ni-MoS2 are attributed to a preferred deprotonation of a surface acyl intermediate formed upon the adsorption of the fatty acid on Ni-MoS2. The shift in mechanism is concluded to originate from the higher basicity of sulfur induced by nickel.

The Conversion of Jatropha Oil into Jet Fuel on NiMo/Al‐MCM‐41 Catalyst: Intrinsic Synergic Effects between Ni and Mo

“…These results suggested that the reduction at 360 °C increased the degree of electron transfer from Ni to Mo on bimetallic NiMo/A catalysts. The binding energy of O 1s on the monometallic 10% Mo/A catalyst in Figure c decreased from 531.0 to 530.6 e V, which might be caused by the formation of surface oxygen vacancy (SOV) or coordinatively unsaturated sites of Mo‐□‐Mo (□ represents SOV) . Indeed, in the case of oxide reduction using hydrogen, the oxygen vacancy generated from oxygen removal from the oxide lattice has been reported .…”

“…The binding energy of O 1s on the monometallic 10% Mo/A catalyst in Figure 9c decreased from 531.0 to 530.6 e V, which might be caused by the formation of surface oxygen vacancy (SOV) or coordinatively unsaturated sites of Mo-□-Mo (□ represents SOV). [69] Indeed, in the case of oxide reduction using hydrogen, the oxygen vacancy generated from oxygen removal from the oxide lattice has been reported. [70,71] There was no electron transfer on the SOV of Mo-□-Mo.…”

The Deoxygenation Pathways of Palmitic Acid into Hydrocarbons on Silica-Supported Ni12P5 and Ni2P Catalysts

“…Ni and Ni 3 S 2 catalysts resulted in DCO 2 hydrocarbon products, while HDO hydrocarbon products formed over Mo, MoS 2 catalysts [19,34,36,37]. Both CoMo and NiMo sulfide catalysts were efficient for deoxygenation by dehydration and DCO reactions [36,37].…”

“…Due to the high price of noble metal catalysts, many researchers have investigated bio-based oil deoxygenation using low-cost catalysts such as Ni, Mo, W, Co-based catalysts from an economic viewpoint [19,[30][31][32][33][34]. Peng et al [25,35] reported that the hydrogenation of the carboxylic group of fatty acid led to the formation of aldehyde catalyzed either solely by metallic Ni or synergistically by Ni and ZrO 2 via ketene as intermediate on Ni/ZrO 2 catalyst, and followed by DCO of octadecanal to the n-heptadecane and carbon monoxide.…”

“…DCO 2 and DCO pathways removed oxygen by the formation of carbon oxides, which would decrease the number of carbon atoms of the reactant. DCO 2 and DCO pathways were denoted as "carbon-loss reactions" (CLR) [19].…”