Biodiesel synthesis over the CaO-ZrO2 solid base catalyst prepared by a urea-nitrate combustion method

CaO-ZrO2 solid base catalysts with Ca/Zr ratios varying from 4/6 to 9/1 were prepared via a urea-nitrate combustion method and used in the transesterification of soybean oil with methanol to produce biodiesel. The catalysts were characterized using N-2 adsorption, XRD, SEM and CO2-TPD techniques, and tested for biodiesel synthesis. The results show that a new phase of CaZrO3 has been formed for the investigated CaO-ZrO2 catalysts. With the increase in Ca/Zr molar ratio, the total basic sites over the catalyst increase and a maximum is obtained over the CaO-ZrO2 catalyst with a Ca/Zr ratio of 8/2. A similar variation trend of biodiesel yield is observed, suggesting that the catalytic activity correlates well with the total basic sites on the catalyst surface. Furthermore, the turnover frequency (TOF) has been calculated for various CaO-ZrO2 catalysts and the result revealed that the catalytic activity also depends on the strength of basic sites. The urea-nitrate combustion method was demonstrated to be a simple, fast and effective method for the preparation of CaO-ZrO2 solid base catalysts, which could be effectively applied for biodiesel synthesis.