In addition to many experimental techniques, computational chemistry methods have become a standard tool which is used nowadays to characterize solid catalysts. The theoretical approach is helpful in interpretation of spectroscopic data and provides a complementary description of surface sites, not fully available by experimental methods. However, modeling amorphous catalytic materials is still a challenging task. There are two different ways to model solid surface and catalyst active sites, the molecular approach (cluster models) and the solid-state chemistry approach (periodic slab models). In this talk, the results of periodic and cluster DFT studies of chromium, molybdenum and tungsten oxide species supported on amorphous silica are presented. The theoretically predicted structures, relative energies and vibrational frequencies of various surface metal species are discussed in relation to experimental data. The systems studied are important catalysts for many chemical processes. Among others, CrOx/SiO2 is the well-known Phillips catalyst for ethene polymerization, whereas MoOx/SiO2 and WOx/SiO2 are active in alkene metathesis. In all these cases, in-situ formation of the active sites from the oxide precursors has to occur, however, the respective mechanisms are still not well established. Based on the cluster calculations performed in our group, the possible pathways for reduction of the surface metal oxide species by alkene and/or their transformation into the active sites are discussed.

Computational insights into structure and catalytic properties of group VI metal oxides on amorphous silica

256th National Meeting (2018)

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