Vanadia–zirconia and vanadia–hafnia catalysts for utilization of volatile organic compound emissions

Utilization is a sustainable and interesting alternative for the destructive treatment of volatile organic compounds due to avoided CO₂ emission. This work concentrates on the development of active and sulfur-tolerant catalysts for the utilization of contaminated methanol. Impregnated and sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were thoroughly characterized by N₂ sorption, analytical (S)TEM, elemental analysis, XRD and Raman spectroscopy, and their performances were evaluated in formaldehyde production from methanol and methanethiol mixture. The results showed higher activity of the sol–gel prepared catalysts due to formation of mono-and polymeric vanadia species. Unfortunately, the most active vanadia sites were deactivated more easily than the metal-mixed oxide HfV₂ O₇ and ZrV₂ O₇ phases, as well as crystalline V₂ O₅ observed in the impregnated catalysts. Metal-mixed oxide phases were formed in impregnated catalysts through formation of defects in HfO₂ and ZrO₂ structure during calcination at 600^◦ C, which was evidenced by Raman spectroscopy. The sol–gel prepared vanadia–zirconia and vanadia–hafnia catalysts were able to produce formaldehyde from contaminated methanol with high selectivity at temperature around 400^◦ C, while impregnated catalysts required 50–100^◦ C higher temperatures.