Abstract
Pure Ni12P5/SiO2 and pure Ni2P/SiO2 catalysts were obtained by adjusting the Ni and P molar ratios, while Ni/SiO2 catalyst was prepared as a reference against which the deoxygenation pathways of palmitic acid were investigated. The catalysts were characterized by N2 adsorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission election microscopy (TEM), infrared spectroscopy of pyridine adsorption (Py-IR), H2-adsorption and temperature-programmed desorption of hydrogen (H2-TPD). The crystallographic planes of Ni(111), Ni12P5(400), Ni2P(111) were found mainly exposed on the above three catalysts, respectively. It was found that the deoxygenation pathway of palmitic acid mainly proceeded via direct decarboxylation (DCO2) to form C15 on Ni/SiO2. In contrast, on the Ni12P5/SiO2 catalyst, there were two main competitive pathways producing C15 and C16, one of which mainly proceeded via the decarbonylation (DCO) to form C15 accompanying water formation, and the other pathway produced C16 via the dehydration of hexadecanol intermediate, and the yield of C15 was approximately twofold that of C16. Over the Ni2P/SiO2 catalyst, two main deoxygenation pathways formed C15, one of which was mainly the DCO pathway and the other was dehydration accompanying the hexadecanal intermediate and then direct decarbonylation without water formation. The turn over frequency (TOF) followed the order: Ni12P5/SiO2 > Ni/SiO2 > Ni2P/SiO2.
Highlights
Research on alternative resources for hydrocarbon fuel has received wide attention due to diminishing fossil fuel reserves and the environmental crisis during the past decades [1,2,3,4,5,6]
Increased attention has been focused on biomass conversion into hydrocarbon fuel [8,9,10,11,12,13,14,15]
Palmitic acid from palm oil has often been chosed as model compound to investigate the conversion pathway into hydrocarbon fuel by deoxygenation
Summary
Research on alternative resources for hydrocarbon fuel has received wide attention due to diminishing fossil fuel reserves and the environmental crisis during the past decades [1,2,3,4,5,6]. Hydrocarbon fuel from biomass can directly substitute for that from coal, natural gas and petroleum in the current energy system. Biomass-based oil is abundant, and it has the potential to significantly displace petroleum in the production of fuels for the transportation sector. Increased attention has been focused on biomass conversion into hydrocarbon fuel [8,9,10,11,12,13,14,15]. Palmitic acid from palm oil has often been chosed as model compound to investigate the conversion pathway into hydrocarbon fuel by deoxygenation. Three approaches have been used to remove oxygen from fatty acids, that is, decarboxylation (DCO2 ), decarbonylation (DCO) and hydrodeoxygenation (HDO) as shown in Scheme 1 [3,15,16,17,18], where the degree of H2 consumption follows the order of DCO2 < DCO < HDO. The HDO pathway was characterized by the sequential
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