Probing Molybdenum Active Sites during In Situ Photoreduction of the Mo6+/SiO2 Catalyst

Abstract

The photoreduction of the Mo6+/SiO2 system with CO was investigated in situ, employing a recently developed experimental setup allowing for the acquisition of transmission FT-IR spectra under simultaneous UV irradiation. Carbon monoxide, besides acting as a reducing agent in such processes, is also a useful probe molecule able to detect coordinatively unsaturated sites exposed on the surface. The unprecedented quality of the spectroscopic data, obtained as a function of the reduction time, allowed us to better rationalize the different mechanisms previously proposed for the photoreduction process. These results, coupled with UV-Vis spectroscopic data, shed light on the oxidation state and surface structure of supported molybdenum species, which are key active sites for several important reactions, such as selective oxidation, polymerization, hydrodesulfurization, epoxidation and olefin metathesis.

Non-aqueous synthesis of homogeneous molybdenum silicate microspheres and their application as heterogeneous catalysts in olefin epoxidation and selective aniline oxidation

“…Based on the previous investigations of different molybdenum complexes, it can be assumed that the peak at 263 nm is associated with ligand-to-metal charge transfers (LMCT) of highly dispersed tetrahedral molybdenum species (Mo 6+ /SiO2 (Td) isolated dioxo-species) [51,69,70]. The band raised at 303 nm can be attributed to the octahedral geometry of isolated molybdenum species [71].…”

Design, Characterization and Applications of Functional Nanomaterials

“…Other contributions in the energy field come from papers by Rorabeck et al [ 9 ] and Santalucia et al [ 10 ]. The first research paper showed the fabrication of nanostructured composite electrodes based on Mn 3 O 4 and multiwalled carbon nanotubes (MWCNTs) by using the salting-out method, which makes the particle transfer from an aqueous synthesis medium to a 2-propanol suspension possible.…”

“…The authors observed an increase in capacitance during the cycling of the fabricated electrodes together with good capacitance retention at high scan rates and cyclic stability. Santalucia et al [ 10 ], in their paper, investigated the in-situ photoreduction of Mo 6+ /SiO 2 in the presence of CO by means of FT-IR and UV-vis diffuse reflectance spectroscopies. Combining these complementary techniques, they were able to monitor the changes of Mo oxidation states and coordination over time.…”