Catalytic hydrodeoxygenation of waste cooking oil and stearic acid over reduced nickel-basded catalysts

Abstract

Waste cooking oil (WCO) and stearic acid (SA) were considered to be renewable and readily available bio-oil resources to produce bio-fuel via catalytic hydrodeoxygenation. The most often used catalysts for hydrodeoxygenation were the vulcanized NiMo catalysts, however, the vulcanized catalysts tend to deactivate due to the loss and oxidation of sulfur upon treating bio-oil with high oxygen content. Therefore, it is necessary to develop sulfur-free catalysts. In present study, the reduced NiMo catalysts were prepared by loading Ni and Mo on different supports (γ-Al2O3, HZSM-5, β-zeolite, activated carbon and bentonite) using incipient-wetness impregnation method, and followed by H2 reduction. The effects of the properties of supports (acidity, porosity) and H2 reduction on the dispersity and valence state of metal components were investigated. The hydrodeoxygenation activities of the reduced catalysts were evaluated by catalytic WCO and SA. It was found that when Ni2+ was loaded on a slightly acidic supports such as γ-Al2O3 and activated carbon, Ni2+ was easier to be reduced, and aggregate to form larger particles. When Ni2+ was loaded on a strongly acid supports e.g. HZSM-5, β-zeolite or bentonite, Ni2+ was more difficult to be reduced but could uniformly disperse on the supports. The aggregated Ni atoms could promote the formation of C17, while the dispersed Ni atoms could promote the formation of C18. γ-Al2O3 supported catalyst achieved the highest SA (97.9%) and WCO (80%) conversion under the mild reaction conditions of 300 °C and 2 MPa H2 for 3 h, exhibiting the superior catalytic activity.