Caracterização de catalizadores de SnO2 e Nb2O5 sintetizados pelo método Pechini para utilização em conversão de biomassa

Abstract

The use of lignocellulosic biomass has stood out in recent years to address a growing demand for essential products. The conversion of fructose emerges as a viable alternative for the generation of chemical feedstocks. Among the various products that can be obtained, 5-hydroxymethylfurfural (5-HMF) is considered a crucial building block for obtaining other chemical products. In this process, homogeneous catalysts are commonly used (e.g., sulfuric acid, phosphoric acid, and hydrochloric acid), although their use is associated with problems such as corrosion generated by their extensive use and the separation limitation. Therefore, the usage of heterogeneous catalysts is more attractive, presenting advantages such as being less corrosive, the reuse, and the possibility of recovery. Among them, oxides stand out due to their high stability in aqueous media and the diversity of acidic sites. Thus, this work aims to synthesize and characterize tin or niobium oxides for the application of fructose conversion. All catalytic systems were obtained by the Pechini method using glycerol and ethylene glycol as polyalcohols, and the materials were named SnO2(G), Nb2O5(G), SnO2(EG) e Nb2O5(EG), respectively. The catalysts were characterized by X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and infrared absorption spectroscopy using pyridine as a probe (FTIR-pyridine), thermogravimetric analysis (TG) and nitrogen physisorption analysis using the Brunauer, Emmett and Teller Method (BET). With the described techniques, it was observed that all systems presented characteristic bands of the different vibrational modes of the metal with oxygen. For tin and niobium oxides, the presence of the orthorhombic/pseudo-hexagonal phase and tetrahedral rutile phase, respectively, was observed. Additionally, in all cases, when using glycerol as a polyalcohol, there was an increase in the surface area, indicating the positive effect of this matrix and the diversity of Lewis and Bronsted acidic sites. The systems proved be selective to 5-HMF with conversions ranging from 30% to more than 70%.