Síntese hidrotermal de catalisadores nanoestruturados de nióbio aplicados na conversão de frutose, glicose, glicerina e na degradação de contaminantes orgânicos

Abstract

This work reports the synthesis of two new classes of catalysts based on niobium and their application in both the conversion of molecules from biomass and the oxidation of organic contaminants. The first class was synthesized from the precursor Filter Cake (FC), used in the process of obtaining Nb2O5.nH2O. The second class was obtained from the niobium phosphate (NbOPO4.nH2O), which is recognized by its high acidity. Hydrothermal treatment in the presence of different agents (oxalic acid or hydrogen peroxide) provided the alteration of properties associated with morphology, porosity, and acidity. Carbohydrate conversion catalytic tests were carried out under different conditions and demonstrated that the two new classes of catalysts showed significant catalytic potential in aqueous dehydration reactions of fructose in order to obtain 5-HMF (5-hydroxymethyl-2-Furancarboxaldehyde) and/or levulinic acid (4-oxopentanoic acid). They are important inputs for the petrochemical industry. The use of the PH12h catalyst allowed a 5-HMF yield of up to 22 % in aqueous media. By using the FOSFPH4h catalyst, yields of 42 % to 5-HMF and 97 % conversion were obtained. In addition, the latter proved to be more stable in relation to in natura niobium phosphate and could be reused for up to 3 times with only a small reduction in its catalytic activity. Studies on the conversion of crude glycerin (residue from biodiesel production) using the catalysts based on niobium phosphate were also carried out. The results were expressive and a conversion of up to 80 % was obtained using the catalyst FOSFPH4h. Formic acid was obtained as the main product, which is very desirable since it is an important petrochemical feedstock. Finally, the activity of Filter Cake (FC), AO4h and PH12h materials was evaluated in the decomposition of methylene blue (MB) in aqueous solution. The heterogeneous Fenton and Photocatalysis processes were used for this purpose. A removal of 87 % of MB was achieved in only 30 minutes using the AO4h catalyst in a Fenton-type reaction system with a dye concentration of 50 ppm. Photocatalysis employing UV radiation provided 86 % removal of MB after 5 hours using the AO4h catalyst.