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 HfV₂O₇ and ZrV₂O₇ phases, as well as crystalline V₂O₅ 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.