Synthesis and application of waste egg shell derived CaO supported W-Mo mixed oxide catalysts for FAME production from waste cooking oil: Effect of stoichiometry

The solid bifunctional tungsten molybdenum supported calcium mixed oxide catalyst (W-x-Mo-y/CaO 0.3 <= x, 0.7 <= y) was synthesized by simple wet impregnation method. The prepared catalyst has successfully transesterified waste cooking oil to biodiesel in a single step reaction process, owing to its acid-base bifunctional capacity. Presence of acid and basic sites of the catalyst was believed to promote the catalytic activity for the transesterification reaction of high FFA waste cooking oil. The stoichiometric effect of transition bimetallic oxide loading on acid-base properties, surface area and porosity of the catalyst were studied. The catalytic activity of the catalyst for transesterification reaction increases with the increase in the W molar weight ratio over Mo from 0.3 to 0.7. The W0.6-Mo0.4/CaO catalyst recorded the highest biodiesel yield of 96.2% under reaction conditions of 15:1 methanol to oil molar ratio, 70 degrees C reaction temperature, 2 wt% catalyst loading and 2 h reaction time. The newly synthesized catalysts were characterised by X-ray diffraction (XRD), BET surface area, vapour pressure scanning electron microscope (VP-SEM), temperature programmed desorption of CO2 and NH3 and thermal gravimetric analysis (TGA).