Vanadia/titania aerogel catalyst for selective oxidation of ammonia

Abstract

Ammonia is an important source of malodor associated with the transportation, processing and storage of organic, biological wastes; power plants and new diesel engine vehicles. In this study, supported catalysts including vanadia/titania catalysts and bifunctional catalysts, as well as their aerogel catalysts were designed, prepared, modified and tested for selective catalytic oxidation of Ammonia (NH₃-SCO). Vanadia supported on titania catalysts were tested via the reactions with a wide concentration range of NH₃ from 40 ppm to 2175 ppm in synthetic air at temperatures ranging from 25 ℃ to 250 ℃. The results showed a near 100% conversion for low concentrations of NH₃ (40 ppm) and a still high reaction rate with moderate conversion for high concentrations of NH₃ (2175 ppm). Vanadia supported on titania presented a monolayer form of supported catalyst when the surface vanadium coverage approached and even surpassed the theoretical vanadium atom monolayer coverage (7-8 V/nm^-2) using Micro-Raman, XRD and XPS. The mechanism of NH₃-SCO over vanadia/titania catalysts was demonstrated to follow a direct oxidation pathway involving hydrazinium-type intermediate. Vanadia/titania aerogel catalysts of large surface area (800 cm²/g) obtained using the ethanol supercritical drying method presented a much higher ammonia reaction rate with the same selectivity of N₂ (100 %) at each reaction temperature. More importantly, hydrophobic aerogel catalysts maintained reactivity for NH₃-SCO under a highly humid reaction condition compared with vanadia/titania catalysts. Bifunctional catalysts based on copper-vanadia/titania and ceria-vanadia/titania were also studied for NH₃-SCO, and showed promoted catalysis involving both direct oxidation and internal selective catalytic reduction (iSCR) pathways. Supported catalysts including vanadia/titania catalysts and bifunctional catalysts, as well as their aerogel catalysts, are able to convert NH₃ to N₂ at lower temperatures (< 100 ℃). This work provides a series of high catalytic selective catalysts for ammonia remediation at low temperatures and humid conditions, which are suitable for environmental applications for both indoor malodor treatments and practical situations such as landfills, lavatories and drainage.

Date of Award	2015
Original language	English
Awarding Institution	The Hong Kong University of Science and Technology