Óxidos nanoestruturados contendo alumina aplicados a conversão de glicerol: efeito da adição de promotores básicos ao suporte

Abstract

Catalysis plays a crucial role in the chemical industry, being essential for most industrial and biological chemical reactions. Nanostructured oxides, especially γ-alumina, stand out as catalytic supports due to their textural properties, thermal stability, and chemical versatility. The modification of γ-alumina with basic promoters such as ZnO, MgO, and La2O3 can enhance its catalytic efficiency in glycerol acetylation reactions. This work synthesized and characterized nanostructured catalysts based on γ-alumina modified with basic promoters and impregnated with Ni and Co, evaluating their efficiency in the glycerol acetylation reaction. The synthesis methods included sol-gel and nanocasting, allowing precise control over the catalysts' properties. Characterization techniques included XRD, FTIR, Raman spectroscopy, SEM coupled with EDS, BET, BJH, EPR, TPD-NH3, TEM, and XPS. X-ray diffraction patterns showed structural characteristics of the supports after incorporating the promoters, indicating the formation of mixed oxides. The modification of γ-alumina aimed to reduce the acidity of the catalysts, minimizing unwanted by-products and increasing catalytic efficiency. Nanocomposites containing Ni and Co were significantly more active in the esterification of glycerol with acetic acid due to the redox properties of Ni2+ and Co3+/Co2+ and moderate surface acidity. Reaction tests showed that NiCo-based catalysts achieved glycerol conversions between 12% and 36% with high selectivity for triacetin. The stability of NiCo catalysts, especially those promoted by La, was highlighted by their reusability in multiple reaction cycles without significant loss of activity. The synthesis of graphene-based nanocomposites using the nanocasting method proved effective in creating nanostructured metal oxides with the γ-Al2O3 phase among graphene nanosheets. The addition of basic promoters such as La, Mg, and Zn showed varied results, with La incorporation favoring catalyst stability and reuse, while Mg and Zn resulted in lower stability due to the leaching of metallic species during the reaction. Nanocomposites containing Ni and Co resulted in excellent stabilization of active sites, preventing leaching and increasing catalytic efficiency. Recyclability studies indicated that NiCo-based nanocomposites, especially those promoted by La, maintained good activity and stability in prolonged reaction cycles, highlighting the excellent reusability of the NiCo@MA catalyst, reusable at least four times for the production of glycerol esters.