Desenvolvimento de catalisadores bifuncionais a base de fosfato e suas aplicações catalíticas

Abstract

The development of bifunctional acid catalysts is an area of heterogeneous catalysis in intense growth, mainly due to the possibility of performing consecutive reactions using a single catalyst and a single reactor. In this sense, bifunctional acid catalysts, containing Lewis and Brönsted acid sites, based on phosphates, are promising materials to catalyze different classes of chemical reactions. Thus, the work sought the synthesis and characterization of phosphates, oxides and oxides of phosphated Sn, Ti and Zr. In addition, a synthesis methodology was developed to obtain aluminophosphates with zeolitic structure (MAPOs) modified with Sn, Ti and Zr (M = Sn, Ti or Zr). The characterization of the materials was obtained by analysis of XRD, Physisorption of N2, TPD-NH3, FTIR-NH3, UV-Vis; XRF, ICP-OES and 31P and 27Al -MAS-RMN. Which, in the case of phosphates, phosphate oxides and oxides of Sn, Ti and Zr showed that the synthesized materials present structures that resemble metallic oxyphosphates and phosphated metallic oxides. In the case of MAPOs, structures with a purely AFI topology with the heteroatom tetrahedrally coordinated to the aluminophosphate structure were obtained, evidencing the effectiveness of the developed synthesis procedure. The activity of the catalysts was evaluated in two different reactions, in the reaction of biomass conversion (glucose and xylose) and in the condensation between ketones and aldehydes to form the chalcone. In the conversion of glucose and xylose, the synthesized catalysts showed medium results, with the maximum formation of fructose and HMF, from xylulose and fufural, from xylose 40%, respectively. However, excellent results were obtained for the reactions of chalcone formation, with Zr(PO4)x presenting yields above 80%, which are similar to the reactions catalyzed in a homogeneous basic medium. In addition, it was observed that Zr(PO4)x maintains its structure and activity unchanged during 5 reuses, evidencing high stability of the material. In addition, another important result was the development of milder procedures, using p-cymene or carrying out the reaction in the absence of solvent, without compromising the TOFinitial of chalcone formation or consumption of acetophenone, demonstrating the potential of this system. Finally, Zr(PO4)x was also active for the formation of chalcones containing different substituents, through the use of aldehydes and centones containing different functional groups.