# Mesoporous Niobium Oxyhydroxide Catalysts for Cyclohexene Epoxidation Reactions
## 1 Introduction  
The use of molecular sieves has been of great industrial interest, since they direct the reactions due to their defined porous structure, being able to promote a greater selectivity for the product of interest. Two classes of well-defined and widely studied porous materials are the microporous zeolites [1] and the mesoporous silicates known as Mobil Composition of Mater (MCM) [2]. Moreover, the incorporation of transition metals, such as those of group V, in these porous materials can generate materials with high catalytic activity and good selectivity [1]. The presence of mesopores allows compounds of higher kinetic volume to access the active sites deposited in the cavities, which is difficult when using supports with smaller pores, such as the microporous. Niobium compounds stand out among those of neighboring elements because of their bifunctional properties, since they may have high acidity and ability to form highly oxidizing species in the presence of H\({}_{2}\)O\({}_{2}\) by the formation of peroxo (Nb-O-OH) surface groups [3]. This allows their oxides to be widely used in heterogeneous catalysis in several types of reactions [4]. In addition, the bifunctional character of niobium oxides has been explored in reactions that require dehydration/oxidation properties of the substrate [5]. The niobium oxides commonly used have low specific area and low mesoporous [6], which diminishes their activity as catalysts in reactions of total or partial oxidation involving molecules with higher kinetic volume. Selective oxidation reactions are less thermodynamically favored than those that promote total oxidation, necessitating a suitable catalyst to direct the formation of the product of kinetic interest [7].  
Epoxidation of olefins is a selective oxidation reaction, especially in the production of various raw materials, as well as in the synthesis of intermediates for the production of chemical andpharmaceutical products [8; 9; 10; 11]. Epoxidation may occur via homogeneous catalysis, but the greatest disadvantage of this process is the recovery of the catalyst, increasing interest in the development of heterogeneous catalysts capable of performing this reaction [12]. In the literature there are several studies on the epoxidation of olefin model molecules, and V and Nb compounds have been widely used but supported on porous materials. Using porous materials [PERSON] et al., obtained near 100% conversion of the toluene oxidation reactions [13]. [PERSON] et al., employing vanadium-titania catalysts obtained conversion of 94% for the epoxidation of a variety of alkenes with organic solvent extracted TBHP as the oxidant [14]. In another work, [PERSON] et al. employing catalysts based on niobium metallocenes deposited into mesoporous silica showed conversion of 58% and high selectivity to limonene epoxide >98% [15]. Works using niobium compounds are scarce, mainly dealing with synthetic compounds where their textural properties can be modulated, in order to obtain high activity in epoxidation reactions.  
Thus, it is understood that it is of great technological interest to obtain catalysts based on niobium compounds that can be efficiently used in selective oxidation reactions of olefins, aiming at the production of compounds of high added value that are of interest to the petrochemical industry. Different niobium catalyst synthesis methods are mentioned in the literature [16; 17; 18; 19; 20] as well as studies on the activity of these materials [21]. Therefore, we propose the synthesis of niobium oxyhydroxide from NbCl\({}_{5}\) using a surfactant to increase the hydrophobicity of the catalysts in order to improve their interaction with the non-polar substrate, and we test these materials for their ability to realize the epoxidation of cyclohexene used as a model molecule.