ZrO₂-supported alkali metal (Li, Na, K) catalysts for biodiesel production

We studied the effect of the alkali metal type (Li, Na, and K) and the calcination temperature (500, 600 and 700 °C) in the activity for biodiesel production of catalysts prepared by impregnation method, with constant metal content of 10%w/w using ZrO₂ as support. The results of the catalytic activity allowed to find an activity sequence regarding the alkali tested metals: Na > Li > K, with this sequence remaining constant independent of the calcination temperature. The high activity of the Na/ZrO₂ system, and slightly lower activity of Li/ZrO₂, can be explained by the fact that higher calcination temperatures promote the formation of alkali-based zirconate species, M₂ZrO₃ (M = Na or Li). The presence of these species is correlated with the higher activity of these catalysts, specifically with the Na and Li-based catalyst calcined at high temperatures (600-700 °C). These M₂ZrO₃ species show higher basicity respect to other alkali metal oxide species, as was demonstrated with CO₂-TPD results. The higher activity corresponded to 10% Na supported on ZrO₂ and calcined at 700 °C, which reached full conversion within just 30 minutes of reaction, which makes this system a promising heterogeneous replacement for the regular homogeneous systems.