# Conversion of Stearic Acid into Bio-Gasoline over Pd/ZSM-5 Catalysts with Enhanced Accessibility
## 1 Introduction  
Oleaginous biomass, consisting mainly of triglycerides and fatty acids, is the major component in different products obtained from plants, animals, and microorganisms. Due to their relatively low oxygen content, oleaginous biomass resources are viewed as promising raw materials for obtaining biofuels and/or bio-based chemicals. Accordingly, a number of routes have been developed and investigated for biofuels production from oleaginous biomass, such as transesterification, catalytic cracking, and hydrodeoxygenation. Fatty acid methyl esters (FAMEs), generated by transesterification of triglycerides with methanol, are known under the conventional denomination of biodiesel and have already reached the commercial scale [1; 2; 3]. However, FAMEs present several drawbacks when used in internal combustion engines: high viscosity, low thermal and oxidation stability, and a trend to polymerize, limiting the content of biodiesel up to a maximum of 7 vol% [4; 5]. These problems are provoked by the relatively large molecular weight of the triglyceride molecules, as well as by their oxygen content. Therefore, several alternative pathways have been devised to produce fuels from oleaginous biomassresulting in their transformation into hydrocarbon mixtures, that in terms of both molecular weight and composition, are very similar to petroleum-derived transportation fuels, mainly within the diesel range. These products are usually named as green or renewable diesel to differentiate them from FAME biodiesel and present the advantage of not having any limitations when blending with diesel obtained from petroleum for application in internal combustion engines. Catalytic cracking of free fatty acids or triglycerides results in gasoline and diesel hydrocarbons. Catalytic cracking of oils under an inert atmosphere has been reported using conventional acid catalysts such as zeolites [6; 7], mesoporous aluminosilicates [8], microporous/mesoporous composites [9; 10] or bifunctional metallic/acidic catalysts [11]. Typically, catalytic cracking usually proceeds at high temperatures in the vapor phase, which promotes the occurrence of severe cracking reactions and the extensive deposition of coke over the catalyst. Hydrodeoxygenation of oleaginous feedstocks involves their treatment under moderate temperatures and high hydrogen pressure in order to remove most of their oxygen content, which is released as water. Both the hydrogen consumption and the high pressures required affect quite negatively to the economy of these processes. Hydrodeoxygenation was initially investigated over conventional hydrotreated sulfide catalysts, which have the drawback of requiring a continuous input of sulfur to the reaction medium to remain active [12; 13]. Alternatively, the use of transition metals, such as Ni, Mo, Co, W or their combinations, has also been reported [14; 15]. Moreover, some interesting results in hydrodeoxygenation processes have been recently disclosed using supported metal phosphide catalysts [16; 17]. On the other hand, although quite less investigated, deoxygenation of fatty acids by decarboxylation has been reported over noble metals catalysts (mainly Pd and Pt) [18; 19; 20]. Deoxygenation of the feedstock occurs over the metallic phase because the metal accomplishes the preferential adsorption of the fatty acid via the formation of a metal-carboxylate complex along with hydrogen-transfer reactions. A variety of supports have been employed to hike the dispersion of the metal particles in order to increase the exposed surface [21; 22]. In this regard, small metal nanoparticles are usually formed over carbonaceous supports, hence, Pd on carbon has become a reference catalyst for free fatty acid decarboxylation [23; 24; 25]. More recently, other supports have also been investigated in these types of reactions. In this way, [PERSON] et al.