The commercially available zeolite HY and its desilicated analogue were subjected to a classical wet impregnation procedure with NHVO to produce catalysts differentiated in acidic and redox properties. Various spectroscopic techniques (in situ probe molecules adsorption and time-resolved propane transformation FT-IR studies, XAS, V MAS NMR, and 2D COS UV-vis) were employed to study speciation, local coordination, and reducibility of the vanadium species introduced into the hierarchical faujasite zeolite. The acid-based redox properties of V centres were linked to catalytic activity in the oxidative dehydrogenation of propane. The modification of zeolite via caustic treatment is an effective method of adjusting its basicity-a parameter that plays an important role in the ODH process. The developed mesopore surface ensured the attachment of vanadium species to silanol groups and formation of isolated (SiO)(HO)V=O and (SiO)V=O sites or polymeric, highly dispersed forms located in the zeolite micropores. The higher basicity of HY, due to the presence of the Al-rich shell, aided the activation of the C-H bond leading to a higher selectivity to propene. Its polymerisation and coke formation were inhibited by the lower acid strength of the protonic sites in desilicated zeolite. The Al-rich shell was also beneficial for anchoring V species and thus their reducibility. The operando UV-vis experiments revealed higher reactivity of the bridging oxygens V-O-V over the oxo-group V=O. The (SiO)V=O species were found to be ineffective in propane oxidation when temperature does not exceed 400 °C.

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http://www.ncbi.nlm.nih.gov/pmc/articles/PMC9142926PMC
http://dx.doi.org/10.3390/ijms23105584DOI Listing

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