▎ 摘　　要

The use of heterogeneous catalyst for biodiesel production can reduce the price of separation process and therefore minimize the biodiesel cost. ZnCuO/N-doped graphene (NDG) catalyst synthesized by facile mechanochemical procedure was tested in the transesterification of waste cooking oil (WCO) with methanol to produce biodiesel. The effects of catalyst loading (0-15 wt%), weight percentage of NDG (10-100%), methanol to oil molar ratio (6:1-18:1), reaction time (210 h) and reaction temperature (120-200 degrees C) were systematically studied at the optimal conditions. Additionally, the properties of the fabricated catalysts were assessed via XRD, FTIR, N-2 sorption studies, HRTEM, TGA and Raman spectroscopy. It was found that the ZnCuO/(X%)NDG nanocomposites exhibit enhanced catalytic performance when compared with the ZnCuO catalyst (without NDG) under the identical conditions. The efficacy of the ZnCuO/(X%)NDG nanocomposites has improved owing to the inclusion of NDG in the catalytic system, which in-turn enhanced the properties of the mixed metal oxides (MMO's) such as surface area, defective sites to a great extent. The ZnCuO/(30%)NDG catalyst displayed a highest catalytic activity towards transesterification of WCO (97.1%) at the optimized conditions of 10 wt% catalyst loading, 15:1 methanol:oil molar ratio, 8 h reaction time and 180 degrees C reaction temperature. Moreover, the recovered catalyst was successfully reused six cycles with no discernible loss in its activity. (C) 2020 Published by Elsevier B.V. on behalf of King Saud University.