Short-Range Electronic Interactions between Vanadium and Molybdenum in Bimetallic SAPO-5 Catalysts Revealed by Hyperfine Spectroscopy.

Engineering two cooperative sites into a catalyst implies the onset of synergistic effects related to the existence of short-range electronic interactions between two metal components. However, these interactions and the relative structure-property correlations are often difficult to obtain. Here we show that hyperfine spectroscopy has the potential to reveal the presence of V 4+ -O-Mo 6+ linkages assessing the degree of spin density transfer from paramagnetic V 4+ species to proximal oxo-bridged Mo 6+ metal ions. The dimer species were prepared by adsorption of Mo(CO) 6 in the pores of SAPO-5, followed by thermal decomposition and oxidation and subsequent grafting of anhydrous VCl 4 (g) followed by hydrolysis and dehydration. The metal species react with SAPO protons during the exchange process and generate new Lewis acid sites, which act as redox centers. X- and Q-band EPR and HYSCORE experiments have been employed to monitor the local environment of V 4+ species obtaining direct evidence for spin delocalization over 27 Al, 31 P, 95 Mo, and 97 Mo nuclei, demonstrating the presence of bimetallic V-O-Mo well-defined structures.