Synthesis and characterization studies of γ-Al2O3 -supported, V-Zr mixed oxidecatalysts prepared from OV(OEt)3 and Zr(OnBu)4

Abstract

Steam reforming of hydrocarbons is one of the methods widely used to produce clean hydrogen for fuel cells. In previous studies in this group, a nickel-containing, V₂O_x-ZrO₂ co-grafted catalyst on γ-Al₂O₃, prepared from a solution of OV(OⁱPr)₃ and Zr(OⁿBu)₄ (precursor feed of 1 V nm⁻² : 4 Zr nm⁻²) was found to generate significant turnover rates in the production of hydrogen from steam-reforming of alkanes and light alcohols. To investigate the influence of change in vanadium precursor ligand and other reaction conditions including time, temperature, concentration of co-grafting solution etc. on the surface optimization of these supported mixed oxides a compositional range of V₂O_x-ZrO₂ samples were synthesized using co-grafting solutions of OV(OEt)₃ and Zr(OⁿBu)₄. Temperature Programmed reduction (TPR) and X-ray Photoelectron Spectroscopy (XPS) studies furnished further insight into the red-ox behavior of the catalysts under steam-reforming conditions. It was observed that a V⁵⁺/V⁴⁺ red-ox couple was involved in this catalytic process. Zirconium was observed to be present only in the +4 oxidation state irrespective of temperature and other reduction conditions. Based on this premise it was concluded that the refractory nature of the Zr⁴⁺ species on the surface was responsible in preventing the vanadyl groups from sintering at temperatures above 600 °C, thereby stabilizing the red-ox active species during the steam-reforming process.