Catalisadores de Pt e Ni suportados em HY e SiO2- Al2O3modificadas com Nb2O5 sulfatado para obtenção decombustíveis drop-in

Abstract

The increase in demand for fuels and concerns related to the intensification of greenhouse gases have led to the search for alternative fuel sources. Drop-in fuels are a class of biofuels that have been receiving attention. They consist of liquid biohydrocarbons functionally equivalent to fossil fuels. One of the routes for obtaining drop-in fuels is the hydroprocessing of fatty acids and esters derived from triglycerides. The reactions involved in obtaining drop-in fuels include deoxygenation (hydrodeoxygenation, decarbonylation, and decarboxylation), cracking, and isomerization. Bifunctional catalysts containing metallic sites and Lewis and Brønsted acid sites can be applied for their production. In this sense, the objective of this work was to evaluate the performance of Ni catalysts, 5% (w/w), and Pt, 0.5% (w/w), supported on pure HY and silica-alumina (SiAl) and modified with Nb2O5, 10% (w/w), sulfated (SNb-HY and SNb-SiAl) in the hydroprocessing of oleic acid. Sulfation was employed to increase the acidity of the catalysts and was carried out using (NH4)2SO4 as an eco-friendly sulfation agent, which is an alternative to H2SO4, which, besides being highly corrosive, causes dealumination of HY. The sulfate group was identified using infrared spectroscopy techniques, thermogravimetric analysis, and temperature programmed reduction with H2 (TPR-H2), demonstrating the efficiency of the synthesis methodology. XRD analyses indicated that the sulfation procedure preserved the structures of HY and SiAl. From the RTP-H2 analyses, it was found that NiO was reduced at a lower temperature for the sulfated catalysts. Through ultraviolet-visible diffuse reflectance spectroscopy analyses (UV-vis-DRS), absorption bands of NiAl2O4 were observed for Ni-supported catalysts in SiAl, which were not observed in sulfated catalysts. The sulfated catalysts showed an increase in acidity, which was verified by analyses of temperature programmed desorption of NH3 (TPD-NH3) and adsorption and desorption of pyridine followed by infrared spectroscopy analysis (Py-FTIR). Furthermore, the sulfated catalysts showed an increase in the proportion of Brønsted acid sites. Catalytic tests revealed that the reaction system reached a steady state after 360 minutes of reaction, remaining stable thereafter. HY, SiAl, SNb-HY, and SNb-SiAl showed high conversion of oleic acid. However, the main product obtained was elaidic acid, indicating low performance in deoxygenation in the absence of metallic sites. The bimetallic catalysts were evaluated in the deoxygenation of oleic acid, and the main products observed were heptadecenes, heptadecane, elaidic acid, and stearic acid. Sulfated catalysts showed an increase in hydrocarbon formation compared to non-sulfated ones. The hydrocarbons obtained correspond to the diesel range. Thus, Ni and Pt catalysts supported on HY and SiAl modified with sulfated Nb2O5 show potential application for obtaining drop-in fuels.