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

Engineering two cooperative sites into a catalyst impliesthe onsetof synergistic effects related to the existence of short-range electronicinteractions between two metal components. However, these interactionsand the relative structure-property correlations are oftendifficult to obtain. Here we show that hyperfine spectroscopy hasthe potential to reveal the presence of V4+-O-Mo6+ linkages assessing the degree of spin density transfer fromparamagnetic V4+ species to proximal oxo-bridged Mo6+ metal ions. The dimer species were prepared by adsorptionof Mo-(CO)(6) in the pores of SAPO-5, followed by thermaldecomposition and oxidation and subsequent grafting of anhydrous VCl4(g) followed by hydrolysis and dehydration. The metal speciesreact with SAPO protons during the exchange process and generate newLewis acid sites, which act as redox centers. X- and Q-band EPR andHYSCORE experiments have been employed to monitor the local environmentof V4+ species obtaining direct evidence for spin delocalizationover Al-27, P-31, Mo-95, and Mo-97 nuclei, demonstrating the presence of bimetallic V-O-Mowell-defined structures.