Conventional vs. hybrid methods for dispersion of MgO over magnetic MgeFe mixed oxides nanocatalyst in biofuel production from vegetable oil Shervin Alaei a, b , Mohammad Haghighi a, b, * , Behgam Rahmanivahid a, b , Reza Shokrani a, b , Hossein Naghavi a, b a Chemical Engineering Faculty, Sahand University of Technology, P.O.Box 51335-1996, Sahand New Town, Tabriz, Iran b Reactor and Catalysis Research Center (RCRC), Sahand University of Technology, P.O.Box 51335-1996, Sahand New Town, Tabriz, Iran article info Article history: Received 11 February 2019 Received in revised form 17 January 2020 Accepted 7 March 2020 Available online 9 March 2020 Keywords: MgO/MgFe 2 O 4 Nanocatalyst Combustion Precipitation Ultrasonic Biodiesel Vegetable oil abstract In this research, MgO/MgFe 2 O 4 heterogeneous magnetic nanocatalyst was used in biodiesel production and to study its structural and morphological characteristics, various methods have been used in MgO addition on the support. Impregnation, Precipitation, Precipitation e Hydrothermal, Precipitation e Ultrasonic and Combustion methods were utilized to add the MgO on the MgFe 2 O 4 to find the suitable surface structure and catalytic activity. Combustion synthesis was used as a facile and low cost prepa- ration route for fabrication of all nanocatalysts’ support because of suitable porosity for the biodiesel production reaction. For this purpose, the samples were analysed by XRD, FESEM, EDX, BET-BJH, and FTIR and then used in the transesterification reaction. Results indicate the sheet like morphology in precip- itation and precipitation-hydrothermal methods and lower particle size in combustion synthesized nanocatalyst. Suitable surface structure and proper pore size and volume caused the combustion pre- pared sample to score the highest yield of 92.9% in biodiesel production from sunflower oil. This sample showed proper stability and reusability potential while the structure remained intact after five times being used in the reaction. Due to the magnetic characteristic of the support the catalyst separation was easy and this caused negligible catalyst loss. © 2020 Elsevier Ltd. All rights reserved. 1. Introduction Nowadays, energy, water and the environmental issues are among the most important global challenges. Environmental pollution caused by the increasing use of fossil fuels has caused problems such as global warming, cancer and climate change in which they motivate the researchers to develop green fuels as a substitute [1 ,2]. Biodiesel is proposed as a proper candidate which can be produced from renewable sources and generates less pol- lutants [3e5]. Biodiesel is a blend of long chained mono alkyl esters and is obtained from transesterification of triglycerides with the pres- ence of an alcohol and a catalyst [6e8]. Conventional catalysts which are commonly used in this process can be categorized into homogeneous and heterogeneous groups [6,9, 10]. Homogeneous catalysts have some advantages such as reasonable operating conditions, high catalytic activity, suitable prices and availability, given that they have some problems such as difficult separation and sensitivity to FFAs and water which leads to the formation of soap [11]. Heterogeneous catalysts have some benefits like easy separation, reusability and lower costs [12e14]. However, they still suffer some challenges such as leaching of the active phase, high cost and long reaction times [15e17]. The heterogeneous catalysts are divided into acidic and basic types [18e20]. Some of the heterogeneous acid catalysts that are capable of simultaneous transesterification and esterification reactions [21], include SO 4 2 / ZrO 2 [22] and Fe(HSO 4 ) 3 . The solid basic catalysts such as CaO [23] and MgO which are the most common and best functional catalysts of this type, act better in the transesterification process. Therefore, lots of researches have focused on developing these catalysts [24,25]. * Corresponding author. Reactor and Catalysis Research Center, Sahand University of Technology, P.O. Box 51335-1996, Sahand New Town, Tabriz, Iran. E-mail address: haghighi@sut.ac.ir (M. Haghighi). URL: http://rcrc.sut.ac.ir Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene https://doi.org/10.1016/j.renene.2020.03.039 0960-1481/© 2020 Elsevier Ltd. All rights reserved. Renewable Energy 154 (2020) 1188e1203