# Mo(VI) Complexes Immobilized on SBA-15 as an Efficient Catalyst for 1-Octene Epoxidation
###### Abstract
An option for overcoming problems associated with zeolites (low pore size) and polymers (low porosity and stability) could be using ordered mesoporous silicas for anchoring molybdenum species. However, suitable immobilization procedures must be applied for these catalyst supports, as conventional grafting procedures on silica do not allow preserving the interaction between organic ligands and molybdenum sites, decreasing the catalytic activity or, if the silica is previously functionalized with organic binding groups, the metal loading is usually rather low [12; 13; 14]. In a previous work, we proposed a possible solution to these disadvantages by functionalizing mesostructured silicas (SBA-15) with polymer chains containing numerous molybdenum grafting points (consisting on polyglycidylmethacrylate treated with 2-aminomethyl pyridine to form the binding groups, which can coordinate to metal centers) [15]. These new catalysts combine the properties of both kinds of materials, i.e. a large number of anchoring points and the ability to control the environment of the metal sites in polymers along with the open porous structure of mesostructured materials with high surface areas. Catalytic results were very promising, but mass transfer limitations had an effect on these hybrid systems due to the fact that polymer incorporation on SBA-15 surface drastically reduced its porosity. Therefore, it seems that the best option will be a less bulky organic moiety containing numerous anchoring points (and able for tuning the molecular environment of the molybdenum centers), which must be efficiently grafted onto large surface-area silicas. Some recently reported works have been focused on this approach [3; 6; 16; 17; 18; 19; 20; 21]. A remarkable example is the investigation of [PERSON] et al. [3], who described the behavior of 8-quinolin complexes of dioxo-molybdenum(VI) covalently attached onto mesoporous SBA-15 silica in epoxidation reactions. According to their results, organic ligands containing two nitrogen atoms (as electron donors) lead to more efficient and stable molybdenum sites than ligands bearing only one nitrogen. Thus, more stable coordination of the environment of active sites and less metal leaching during the epoxidation reaction are the main consequences. Taking these facts into account and our previous experience on the modification of polyglycidylmethacrylate with 2-aminomethyl pyridine to generate stable binding sites for metal coordination, herein we present the facile synthesis, characterization, and olefin epoxidation behavior of an efficient and highly porous Mo(VI) catalyst supported onto mesostructured SBA-15 silica. Metal anchoring points on SBA-15 surface were produced by silica functionalization with (3-glycidyloxypropyl)trimethoxysilane followed by subsequent reaction with 2-aminomethylpyridine, opening epoxy groups and leading to a Schiff base (with two nitrogen donor atoms). Bis(acetylacetonate)dioxomolybdenum(VI) (MoO\({}_{2}\)(acac)\({}_{2}\)) was selected as metal source. The influence of different reaction variables, such as the catalyst to olefin molar ratio, the type of solvent and the type of hydroperoxide used as oxidant were evaluated in the catalytic performance assessment of these materials in 1-octene epoxidation. Likewise, a spectroscopic study of the molybdenum environment in both fresh and used catalysts was carried out to propose a detailed mechanism of the active sites performance during the epoxidation of 1-octene by using tert-butyl hydroperoxide as oxidant.