Obtenção de zeólita MCM-22 impregnada com cério a partir de resíduos agroindustriais

Abstract

The development of technologies to obtain materials that can replace polluting approaches with renewable options is a growing theme in the current research scenario. In this context, the reuse of agro-industrial waste, such as rice husk, is gaining attention. Rice husk is a by-product of the rice processing industry, that is, a product of plant origin, and it consists of cellulose, protein, fat, fiber, oil and inorganic compounds. Notably, this residue contains a high content of silica (13%) when compared to residues from other crops (corn and sugarcane bagasse). It can therefore be used as a raw material for the synthesis of materials for application in various catalytic processes. In this context, the aim of this study was to synthesize MCM-22 zeolite using silica from rice husk waste and cerium oxide impregnation, with a view to future application in catalytic oxidation processes. Initially, the rice husk was subjected to heat treatment to obtain silica. The zeolite was synthesized with an Si/Al molar ratio of 25 the SDA used was HMI, at 135º C for 7 days of crystallization and impregnated with cerium (Ce) or cerium oxide (CeO2) (5% and 10% m/m) using the wet impregnation method. The materials obtained were characterized by thermogravimetric (TG) analysis, X-ray fluorescence (XRF) spectrometry, X-ray diffractometry (XRD), infrared (IR) spectroscopy, N2 physisorption at low temperature, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and diffuse reflectance spectroscopy (DRS) in the UV-Vis region. The TG results showed the decomposition of the organic matter present in the rice husk and the XRF analysis revealed that the material had a silica content of 92.52%. XRD analysis confirmed the formation of MCM-22 zeolite from the amorphous rice husk silica. The TG analysis of the lamellar precursor indicated the occlusion of SDA molecules in the microporous channels of the zeolite, confirming the success of the synthesis. Cerium oxide impregnation resulted in a decrease in the specific surface area, indicating the deposition of cerium oxide particles on the surface of the materials. The deposition of cerium oxide on silica from rice husk and of MCM-22 zeolite impregnated with 5% and 10% cerium had particle sizes of approximately 3-4, 3 and 6 nm, respectively. The use of the UV-Vis technique verified that the oxidation states of the cerium oxide species were +3 and +4. From the results obtained, it can be confirmed that the synthesis and impregnation of cerium oxide was successful.