It is presented herein heterogeneous catalysts comprised of strontium and nickel oxides synthesized using a coprecipitation method. They were applied for the preparation of biodiesel from macaw palm oil. The catalysts were characterized by X-ray diffraction (XRD), adsorption and desorption of nitrogen by Brunauer-Emmett-Teller (BET) and Barrett-Joyner-Halenda (BJH) methods, scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and differential thermogravimetric analysis (TG-DTA). The conversion was determined by gas chromatography with flame detector (GC-FID). The best activity was obtained when the catalyst was calcined at 1100 °C for 3 hours. The highest conversion was reached (97%) when the following conditions were used: 5 hours, 2% of metal loading, 65 °C and oil/alcohol molar ratio of 1:9. Keywords: heterogeneous catalyst, coprecipitation, biodiesel, macaw oil IntroductionThe large increase in global petroleum consumption has caused huge environmental impacts and economic issues. In order to provide a future reduction of the world oil dependence, the development of renewable fuels like biodiesel is quite attractive 1,2 since the main advantages of biodiesel include biodegradability, high flash point and low emissions of carbon monoxide and other pollutants. 3,4 According to Agência Nacional do Petróleo, Gás Natural e Biocombustíveis (ANP) resolution 14/2012 5 and law number 11.097, 6 which deals with the introduction of sustainable fuel in the Brazilian energy matrix, biodiesel refers to renewable fuels derived from raw materials meant to be used in internal combustion compression ignition engines; they may partially or totally replace fossil feedstock. Usually, these compounds are made by chemically reacting triglyceride molecules present in vegetable oils and animal fats with methanol or ethanol in the presence of a suitable catalyst to form alkyl esters of fatty acids and glicerol. 7,8 Industrial biodiesel production uses homogeneous alkaline catalysts (KOH, NaOH and NaOCH 3 ) due to its low cost and high yield of the final products.9-11 Although these catalysts are effective, the serious environmental problems they cause has driven the development of more active and selective heterogeneous catalysts lately. 12,13 The application of heterogeneous catalysts in transesterification reactions is considered a green technology as the catalysts are easily separated from the products and can be recycled. Moreover, the reaction method utilizes less water than the homogeneous catalysts processes.14,15 Thus, the development of efficient and low cost heterogeneous catalysts raises the possibility of their commercially utilization on biodiesel production. 16 Many heterogeneous catalysts have been widely investigated for vegetable oils transesterification such as alkali and alkaline earth metal oxides and transition metal hydroxides compounds supported on alumina, zeolites, hydrotalcites and ion exchange resins. [17][18][19][20][21][22] In accordance to Zabeti et al. 23 strontium oxide...