Structural transformation of vanadate nanotubes into vanadate oxides nanostructures during the dry reforming of methane (original) (raw)

2020, Molecular Catalysis

The metal-containing vanadate nanotubes namely MeVO-NT (Me = Ni, Co or Pt) were in situ transformed into vanadate oxides nanostructures i.e., MeV x O y , during the methane dry reforming. All the experimental observations through Raman, HRTEM, XRD, XPS, SEM-EDS, TG-FTIR and elemental analysis, strongly suggested that the VO x (MeV 2 O 7 , V 2 O 5 and VO 2) support contained the metal species that were involved in the dry reforming of methane (DRM) reaction. The pristine VO-NT catalyst exhibited a fairly low activity in DRM due to its degradation. In the case of CoVO-NT, the Co 3 O 4 /VO 2 , Co 3 O 4 /Co 2 V 2 O 7 and Co 3 O 4 /V 2 O 5 phases were deactivated by oxidation of the Co particles, instead of being deactivated by sintering and coking, as well. In contrast to CoVO-NT, PtVO-NT having PtO x /V 2 O 5 , PtO x /VO 2 or even PtO x /V 2 O 7 phases inhibited heavy carbonaceous deposition on surface, but sintering was not avoided. The NiVO-NT was active due to the stability of the Ni°/ Ni 2 V 2 O 7 active phase in hindering heavy whisker and filamentous carbonaceous deposits on such catalyst. Using Halgren-Lipscomb algorithm in the frame of density functional theory (DFT), transition states energy for all three catalysts were obtained. It was found that PtVO-NT energy profile was lower than CoVO-NT and NiVO-NT counterparts. This suggested that the Pt sites dispersed on VO x structure was catalytic active during the methane activation in DRM whereas the CoVO-NT and CoVO-NT solids were prone to perform side reactions.