Unraveling the real active site of reaction-induced trivalent vanadium ion in VOx/Al2O3 catalysts for boosting photothermal catalytic propane non-oxidative dehydrogenation

Nano-Hierarchical SSZ-13-Supported Low-Polymerized VOX as Highly Efficient Catalysts for Propane Dehydrogenation

“…The absence of VO X particles or clusters in the TEM and HAADF-STEM images can be ascribed to the low contrast between Al and V as well as the small size of VO X particles. 28 This observation is consistent with the XRD results which show that no bulk VO X species are formed. Notably, a large number of bright areas are observed in the TEM image, which indicates the presence of intracrystalline mesopores with random distribution in the 5V/SSZ catalyst, in line with the N 2 adsorption/desorption results.…”

“…In general, the LMCT bands centered at 245, 271, and 296 nm are attributed to highly dispersed isolated and V–O–V bridged low-polymerized VO X species in tetrahedral environment. ,, In agreement with previous reports, ,, these absorption bands shift to higher wavelengths with the increasing V loading. The relatively weak LMCT bands at 387 nm are attributed to high-polymerized VO X species in tetrahedral or distorted octahedral coordination. ,, The high intensity of the LMCT bands at 271 nm and the relatively weak band at 387 nm imply that isolated and low-polymerized vanadium species are the main VO X species in the 5V/SSZ catalyst. Additionally, there are no obvious LMCT bands exceeding 450 nm, proving the absence of bulk V 2 O 5 crystals and the high dispersion of VO X species on the zeolite surface, which is in line with the XRD and Raman results.…”

“…The real loading of V (4.89 wt %) analyzed by ICP (Table ) is close to the designed value of 5 wt %. The absence of VO X particles or clusters in the TEM and HAADF-STEM images can be ascribed to the low contrast between Al and V as well as the small size of VO X particles . This observation is consistent with the XRD results which show that no bulk VO X species are formed.…”

“…As exhibited in Figure 2, like SSZ-13 zeolite, no bands are observed for the 1V/SSZ catalyst in the range 200− 1200 cm −1 , indicating that isolated VO 4 species are dominant. 15,28 Both 5V/SSZ and 12V/SSZ exhibit characterized Raman bands at 332, 480, and 1030 cm −1 , which are attributed to V−O−V stretching vibrations of polymerized VO X species, 17,29 V−O−V bending vibrations of polymerized VO X species, 30−32 and V�O stretching vibrations of the isolated and low-polymerized VO X species. 28,33,34 Compared to 5V/SSZ, the obvious increment in the intensity of all of the Raman bands for 12V/SSZ can be ascribed to the aggregation of more VO X species on the surface of SSZ-13 zeolite.…”

“…15,28 Both 5V/SSZ and 12V/SSZ exhibit characterized Raman bands at 332, 480, and 1030 cm −1 , which are attributed to V−O−V stretching vibrations of polymerized VO X species, 17,29 V−O−V bending vibrations of polymerized VO X species, 30−32 and V�O stretching vibrations of the isolated and low-polymerized VO X species. 28,33,34 Compared to 5V/SSZ, the obvious increment in the intensity of all of the Raman bands for 12V/SSZ can be ascribed to the aggregation of more VO X species on the surface of SSZ-13 zeolite. 34,35 The absence of sharp band at approximately 990 cm −1 assigned to the V�O stretching vibration of crystalline V 2 O 5 excludes the formation of bulk V 2 O 5 crystalline on all xV/SSZ catalysts.…”