Catalytic properties/performance evolution during sono-hydrothermal design of nanocrystalline ceria over zinc oxide for biofuel production

Abstract

The main objective of this study was to produce biodiesel from waste oil by bifunctional acid-base CeO2(x%)/ZnO nanocatalysts. CeO2 was loaded over mesoporous ZnO in different percentages (X = 5, 10, 20, 30 and 50) to reach the optimum acid-base balance, and remove the internal mass transfer resistance. Ultrasonication was adopted as an efficient approach to synthesize the nanocatalysts with modified features. XRD, FESEM, TEM, EDX, BET-BJH, FTIR TPR-H2, and TPD-NH3 characterization analyses were carried out to identify the as-fabricated nanocatalysts. Bi-metallic nanocatalysts were tested in one-pot biodiesel production from a high free fatty acid containing model of waste oil. In each cycle, the conversion of esterification and transesterification reactions, as well as the overall conversion were estimated, and the superior activity was achieved over sonoassisted designed CeO2 = 20% nanocatalyst (FFA conversion = 80%, TG conversion = 97% and total conversion = 93%). According to the results of analyses, this outcome is depended on the uniform dispersion of active components, high SBET, and pore volume, as well as the suitable acid site density and strength. The promotion effect of ultrasonic waves on CeO2 dispersion not only increased the activity of nanocatalysts but also yielded satisfactory stability. Sono-designed sample with CeO2 = 20% exhibited the most stable nanocatalyst that maintained its performance after five cycles. Moreover, CeO2 = 20% showed high performance without deactivation in the presence of NaCl which is one of the impurity elements in waste cooking oil.