The effect of lanthanum doping on activity of Zn-Al spinel for transesterification

The transesterification of soybean oil with methanol to biodiesel using lanthanum doped zinc aluminate with spinel structure as catalyst is studied. The catalyst was characterized by X-ray diffraction (XRD), N-2 adsorption/desorption, temperature programmed desorption of CO2 (CO2-TPD) and infrared spectroscopy of CO2 adsorption (CO2-IR). The results of CO2-IR show that the basic sites of La doped zinc aluminate are surface isolated O2- anions and OH- groups. The results of CO2-TPD show that the total amount of basic sties of the catalyst improves with the increase of the La doping amount until which is to 18.5 wt%. Doping La also enlarges the pore volume and diameter of zinc aluminate. It gets the largest pore volume (0.30 cm(3) g(-1)) and pore diameter (7.9 nm) when doped with 5.5 wt% La. Zinc aluminate doped with 5.5 wt% La (5.5% La/ZnAl2O4) exhibits the highest activity, with which the biodiesel yield exceeds 95% at 160 degrees C, 2.0 MPa and 0.9h(-1). Furthermore, the transesterification reaction of about 500h in a fixed-bed reactor was carried out over 5.5% La/ZnAl2O4 catalyst. No deactivation and leaching of catalyst components were happened on the catalyst in reaction. (C) 2013 Elsevier B.V. All rights reserved.