Desenvolvimento e aplicação de catalisadores heterogêneos a base de caulim e nióbio para formação de produtos de valor agregado a partir de açúcares obtidos de biomassa lignocelulósica da Amazônia

Abstract

The region comprising the Brazilian Legal Amazon extends over approximately 5 million km² and encompasses a vast array of natural resources, ranging from biodiversity to strategically important minerals of industrial relevance. In this context, kaolin and niobium stand out, with Brazil holding 98% of the world’s niobium reserves. Parallel to this mineral wealth, the territory hosts approximately 14,000 plant species, with particular emphasis on the Bromeliaceae and Arecaceae families. However, the commercial exploitation of fruits such as Açaí and Tucumã generates a critical environmental burden: Tucumã residues can represent up to 98% of the fruit mass, while Açaí seeds account for up to 85% of its total volume. Thus, the pursuit of full biomass valorization not only mitigates environmental impacts but also aligns directly with the United Nations Sustainable Development Goals (SDGs) 13 and 17. From this perspective, residues derived from pineapple (Ananas comosus), Açaí (Euterpe oleracea), and Tucumã (Astrocaryum aculeatum) emerge as valuable feedstocks, containing cellulose contents of up to 46.8%, in addition to a hemicellulosic fraction rich in sugars such as glucose, xylose, and mannose. Accordingly, the chemical conversion of these sugars via heterogeneous catalysis represents a promising technological route to produce high value-added bioproducts, including 5-hydroxymethylfurfural (5-HMF), levulinic acid, formic acid, and furfural. Regarding the experimental results, sugar extraction from the investigated biomasses demonstrated high efficiency, yielding elevated concentrations of xylose and rhamnose, with glucose reaching a significant 56 wt% of the cellulose fraction in pineapple leaves. To enable the conversion of these monomers, heterogeneous catalysts were developed through wet impregnation followed by calcination, using kaolin from Manaus (BR-174) and Nb₂O₅·nH₂O. The resulting materials exhibited favorable textural properties, with surface areas of up to 168 m²/g, as well as the strategic coexistence of Brønsted and Lewis acid sites. As a direct consequence of this configuration, the catalysts demonstrated activity, converting glucose into formic acid (47%), and levulinic acid (19%) within 2 h at 180 °C. The data therefore indicate that the synergy between Amazonian kaolin and niobium generates promising catalytic matrices, with particular emphasis on the TMCNb20 catalyst due to its high catalytic performance and economic feasibility. In conclusion, the integration of regional minerals and agro-industrial residues from the Amazon constitutes a realistic and sustainable strategy for the national bioeconomy. The application of these catalysts not only addresses the issue of solid waste disposal but also establishes a technological production chain capable of transforming environmental liabilities into essential chemical inputs, thereby strengthening Brazilian industrial autonomy in the face of global climate challenges.