Conversão da celulose e da glicose em presença de catalisadores sólidos ácidos a base de MoO3/TiO2 em insumos químicos

Abstract

The chemical catalysis of the cellulose conversion reaction via hydrolysis / solubilization and degradation and conversion of glucose via dehydration, the basis of heterogeneous solid acid catalysts has aroused great interest due to the great potential in terms of activity and selectivity or the possibility of development of chemical products and / or processes (Green chemistry) associated with the use of clean technologies. Thus, this work proposes the synthesis and characterization of TiO2 - based catalytic systems followed by wet impregnation of molybdenum oxide and catalytic tests against the conversion of cellulose and glucose in order to obtain fermentable sugars and other products of interest in fine chemistry. The work was divided in two topics where the first study the variation of the concentration of MoO3 in TiO2. Initially, TiO2 catalysts were synthesized by the sol-gel method and MoO3/TiO2 (with different concentrations of molybdenum oxide) by the wet impregnation method and calcined at 550 ° C for 4 hours under atmospheric conditions. Subsequently, different characterizations were made in order to know the structure and the acid nature of these catalysts. These catalysts were used in reaction tests of cellulose conversion under the conditions of 190 ° C, at 1, 2 and 4 hours and with varying amount of catalyst. The catalysts showed catalytic activity against cellulose conversion, with the catalyst having 25% MoO3/TiO2, which presented the highest conversion percentage (21%) in the test at 190 ° C / 4 h. The higher conversion observed when using the 25% MoO3/TiO2 catalyst may be associated with a greater amount of available Lewis and Brönsted acidic sites and their available acid strength as shown by absorption spectroscopy analysis in the infrared region with adsorbed pyridine and programmed ammonia desorption temperature, respectively. Therefore, this catalyst was chosen for reuse studies and did not present activity after the first test under the condition of 190 ° C, at 2 hours. As well as, alteration of the calcination temperature to see its influence on the structural properties, and consequently, on the catalytic activity of the same. This will be investigated in the second topic of this paper. In the second topic, new catalysts (TiO2-300 and 25% MoO3/TiO2-300) were synthesized without MoO3 anchoring and another with 25% MoO3 anchored to TiO2, both calcined at 300 ° C under the same synthetic methods. They were characterized by different techniques and carried out tests of conversion of cellulose and glucose, in order to observe the evolution of the formation of the products. However, the change from the anatase phase to rutile of TiO2, predominantly, and consequent alteration in the catalytic activity was observed. Therefore, the catalyst with an anatase phase based on TiO2 calcined at 300 ° C showed higher activity than the rutile phase with a TiO2 base calcined at 550 ° C. In this context, it is important to note that after the impregnation of molybdenum, changes in the texture properties occurred, as well as the change in the calcination temperature altered the morphological properties of the catalysts, presenting a variation in the crystalline phases of MoO3 (orthorhombic and monoclinic). In this context, it is important to note that the relationship between Lewis acid sites and the Bronsted acid sites was verified, where a higher amount of Lewis acid sites was verified for calcined at 300 ° C. Thus, the catalysts that presented higher relative acidity provided higher conversions of cellulose and glucose with formation of sugars and acetic acid, respectively.