4.7 Article

Modulation of ODH Propane Selectivity by Zeolite Support Desilication: Vanadium Species Anchored to Al-Rich Shell as Crucial Active Sites

Journal

Publisher

MDPI
DOI: 10.3390/ijms23105584

Keywords

vanadium; oxidative dehydrogenation; hierarchical zeolites; XAS; V-51 MAS NMR; in situ IR; in situ UV-vis; 2D COS UV-vis

Funding

  1. National Science Centre, Poland

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This study used various spectroscopic techniques to study the properties of vanadium species introduced into different zeolites, finding that basicity plays a critical role in the catalytic activity of the oxidative dehydrogenation of propane. Modifying zeolite through caustic treatment can adjust its basicity, aiding in the adsorption of vanadium species and increasing selectivity to propene.
The commercially available zeolite HY and its desilicated analogue were subjected to a classical wet impregnation procedure with NH4VO3 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-51 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)(2)(HO)V=O and (SiO)(3)V=O sites or polymeric, highly dispersed forms located in the zeolite micropores. The higher basicity of HYdeSi, 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)(3)V=O species were found to be ineffective in propane oxidation when temperature does not exceed 400 degrees C.

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