An innovative nanocatalyst α-Fe2O3/AlOOH processed from gibbsite rubbish ore for efficient biodiesel production via utilizing cottonseed waste oil

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A novel dispersed α-Fe2O3 on AlOOH (Fe2+/Fe3+/AlOOH) acid catalyst synthesized via utilizing a deposition hydrothermal route and thoroughly characterized using XRD, SAED-TEM, FTIR, N2 sorptiometry and XPS measurements was employed for biodiesel production via trans-esterification of waste cooking cottonseed oil (WCO). The resulting catalysts own high surface texturing and acid sites loading characteristics especially 12% Fe2+/Fe3+/AlOOH that owns the highest surface area value (323 m2 g−1), uniform 4 nm mesopores, and high total acid sites loading of 0.45 mmol g−1. The optimum conditions for the transesterification of waste cooking oil (WCO) of the latter catalyst were 60 °C, methanol:WCO molar ratio of 6:1, 3% catalyst mass ratio, and 180 min reaction time to achieve 95% FAME yield. This catalyst exhibited high reusability and enabled facile separation and production of high quality biodiesel comparable to the universal ASTM standards. XPS results indicated that the catalytic reaction is promoted on the 12% catalyst when Fe3+/Fe2+ atomic ratios equal 4:1 is combined with AlOOH of appreciable OH bonds. Although 8% catalyst exposed 100% ratio of AlOOH as the 12% catalyst however, the strong interaction exhibited in the later catalyst besides boosting the ratio of Fe3+ that owns two surface active sites; in front of only one on the former, appears to enhance the FAME yield. The calculated activation energy of the reaction indicates a value of 51.54 KJ mol−1 and from the thermodynamic parameters (ΔH‡, ΔS‡ and ΔG‡) the reaction appears to be non-spontaneous and thus accommodated endothermicity beside an entropy decrease.