Síntese do carbonato de glicerol catalisada por óxidos mistos de Zn-Al promovidos por Zr, Ce e La

Abstract

A series of Zn-Al mixed oxides promoted by Ce, La or Zr (X) obtained by thermal decomposition at 550 ° C of hydrotalcite-like precursors was tested as heterogeneous basic catalysts for glycerol carbonate synthesis - a promising alternative for glycerol recovering from biodiesel industry. The mixed oxides present Zn/Al molar ratio set at 2, while the X/Al molar ratios were set at 0.02 or 0.3. The mixed oxides physical-chemical and basic properties were investigated by inductive coupled plasm emission spectroscopy (ICP-OES), X-ray diffraction (XRD), N2 adsorption-desorption at -196 °C, thermogravimetry - differential scanning calorimetry (TG-DTG-DSC) and temperature programmed desorption of CO2 (TPD-CO2). The mixed oxides catalytic activities were evaluated for glycerol carbonate (CG) synthesis from transcarbonatation reactions of dimethyl carbonate (DMC) with glycerol (molar ratio 4: 1) under mild reaction conditions (100 °C, atmospheric pressure). Catalytic tests showed that the strength and the density of basic sites are directly linked to the mixed oxides ability to synthesize CG. All catalysts were 100 % selective to GC under the studied conditions. The Zn-Al mixed oxide promoted by La at the molar ratio La/Al = 0.3 showed the best performance among the tested catalysts, reaching 15 % yield after 2.5 h of reaction. The incorporation of Zr as a promoter resulted in active sites with reduced basic strength and lower CG yields. Mixed oxides promoted by Ce showed no correlation between their basic properties and their catalytic performances.