Karanja oil transesterification using green synthesized bimetallic oxide catalyst, gCaO-CeO2: Comparative investigations with the monometallic oxide catalysts on the catalytic efficacy and stability

[Display omitted] •Waste egg shells and P. juliflora leaves extract based mixed oxide catalyst synthesized.•Crude karanja oil extracted and their transesterification performed using synthesized heterogeneous catalyst and compared with the monometallic oxide catalysts.•Biodiesel produced was characterized and confirmed with ASTM D6571 standards. In the present study, a novel plant-mediated approach was reported to synthesize a bimetallic oxide (BMO, gCaO-CeO2) catalyst from waste egg shells. Previously, an equi-molar mixture of cerium nitrate and shell recovered calcium nitrate was considered as precursor for Prosopis juliflora mediated green synthesis. The prepared gCaO-CeO2 was characterized by means of FT-IR, TG/DTA, XRD and surface area analyzer. X-ray diffraction results showed that the gCaO-CeO2 is thermally stable even after the calcination process at 800 °C as the peaks for the cubic fluorite of cerium oxide (CEO) and cubic nature of calcium oxide (CO) were observed intact. Batch transesterification of karanja oil showed an improved catalytic activity for gCaO-CeO2 than monometallic oxides due to the increased basicity of the catalysts with the reduced temperature maxima. The highest fatty acid ethyl ester (FAEE) content of 96.17 % was attained for 6:1 mol ratio of ethanol-karanja oil over 4% (weight basis) of gCaO-CeO2 catalyst at 65 °C in 5 h. Further, the physico-chemical parameters of the transesterified products were found consistent with ASTM D6751 biodiesel standards. The study also reported the potential reuse of gCaO-CeO2 catalyst upto 6 operations with no appreciable loss in catalytic activity during transesterification.