The extensive emission of anthropogenic carbon dioxide resulted from the widespread usage of fossil fuels has been confirmed as the main cause leading to the global warming and extreme weather events. Consequently, the development of economically and environmentally friendly fuel alternatives from renewable resources to replace fossil fuels has become the focus of extensive research works. One of these alternative fuels is fatty acid methyl/ethyl esters (FAME/FAEE), aka biodiesel. Biodiesel is obtained mostly via the esterification of free fatty acids (FFAs) or the transesterification of triglycerides including vegetable oils, animal fats and waste cooking oils, in excess methanol or ethanol in presence of proper catalysts. However, the high oxygen content in biodiesel has been detrimental in long-term storage and, thus, has limited their applications in cold environment. For example, biodiesel can be clouding and even gel-like so as to clog the fuel lines during cold months. The application of FAMEs as aviation turbine fuels becomes almost impossible owing to the very low fluidity in cold environment at high altitude. As the result, the catalytic hydrotreatment of these renewable fatty acids and triglycerides is proposed to produce liquid alkane fuels with less oxygen content [1, 2, 3].

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In our group, zeolite-supported Ni-M catalysts (M = none or Mo) were prepared and studied for their applications in the catalytic processing of fatty acids and triglycerides to liquid fuels, mainly via hydrodeoxygenation (HDO) and hydroisomerization (HI) process. In brief, zeolite ZSM-5 from Zeolyst (CBV 3024E) was used as support, and no precious metals were used as active catalysts in this work. A Ni-content about 10 wt% of zeolite ZSM-5 support with various Mo-contents was found on these Ni-Mo/ZSM5 catalysts. Prior to the hydrogenation reaction, catalysts were generally reduced in the stream of 5% H2/Ar (100 mL/min) at 500°C for at least 3 hours. Both HDO and HI of palmitic acid and soybean oil were carried out at 280–350°C and under the H2 pressure up to 70 bar. The GC-MS was employed to qualitatively analyze the products, which include methylbenzene, dimethyl-heptane, tetramethyldecane, t-butylphenol etc. (Figure 1). The catalyzed HDO reaction of palmitic acid was carried out in a batch autoclave (Parr 4560) at 573 K with an initial pressure of hydrogen at 35 bar at this temperature. The loadings of catalyst were maintained as 25 wt% of palmitic acid. With Ni/ZSM5 catalyst, the conversion of palmitic acid reach ca. 60% in 12 h. In contrast, the complete conversion of palmitic acid was almost achieved, near 99%, in 4h with Ni-Mo/ZSM5 catalysts. Presence of molybdenum really improved the HDO reaction of palmitic acid. Furthermore, a significant portion of isomerized alkanes were obtained in the product as revealed by GC-MS. That is, both HDO and HI reactions took place conjointly with Ni-Mo/ZSM5 catalysts. As the HDO of palmitic acid proceeded, the yields of short-chain alkanes would increase, accordingly. Therefore, an optimal strategy in catalytic hydrotreatment of fatty acids and triglycerides has to be implemented.