Abordagem quimiométrica da oxidação de glicerol sobre nanopartículas de ouro suportadas em carvão ativado

Abstract

The effects of the catalyst synthesis conditions and of the reaction conditions on the efficiency of glycerol oxidation over H2O2 and gold nanoparticles supported on activated carbon were studied. The reaction was monitored by mass spectrometry with electrospray ionization, and the studies supported by chemometric methods. Catalysts prepared with lower poly(vinyl alcohol)/gold ratio and lower gold content favored the glycerol conversion and selectivity to glycerate and tartronate. The use of more concentrated HAuCl4 solution on the catalyst preparing resulted in larger nanoparticles, favoring the selectivity to glycolate. The temperature of the reaction was the parameter that most influenced the oxidation. Major conversions and selectivity to glycerate and tartronate were obtained at lower temperatures and lower glycerol/gold ratio. Increased selectivity to glycolate was obtained using higher OH/glycerol ratio. The selectivity to glyceraldehyde was higher under unfavorable conditions to formation of other oxidation products. The H2O2/glicerol ratio presented no significant influence on the reaction performance. In the kinetic study it was found to stabilize the process with four hours of reaction, with 70% conversion and selectivity of 65% for glycerate, 15% for glyceraldehyde and 10% for glycolate and tartronate. Blank experiments indicated that the presence of the catalyst and promoter base (NaOH) was indispensable for the occurrence of the oxidation. During the reaction, there was no lixiviation of gold nanoparticles, even after five reuses of the catalyst. However, after two batches of reaction, the catalyst lost its activity.