Development of modified KIT-6 and SBA-15-spherical supported Rh catalysts for N2O abatement: From powder to monolith supported catalysts

In the chemical industry, nitric acid and adipic acid plants are the main producers of nitrous oxide (N2O), a greenhouse gas that damages the ozone layer and leads to environmental problems. In this work, mesoporous silica KIT-6 and SBA-15-spherical, materials have been modified by post salt addition and the incorporation of aluminum (Al), in order to increase their stability and produce more acidic sites on the surface. The potential of these modified mesoporous silica supported Rh (1 wt.%) powder catalysts has been examined in a small laboratory scale reactor under specific N2O decomposition conditions to investigate the properties of these materials for this kind of application. Modified KIT-6 or SBA-15-spherical supported Rh catalysts not only showed better activity, but also very good stability compared to the non-modified mesoporous silica supported Rh catalysts that were investigated. The higher catalytic activity was due to the improved acidic sites on the supports and the long-term stability might be due to the thicker wall of the materials caused by the post salt addition. The role of O-2, CO and NO has also been explored to establish the promoting or inhibiting effect on these catalysts. It has been found that O-2 and NO inhibited and suppressed the activity, whereas CO promoted the N2O decomposition activity at lower temperatures. The final optimized catalysts (Rh/Al-KIT-6 post salt treated and Si/Al = 5, and Rh/Al-SBA-15-S post salt treated and Si/Al = 20) have also shown better activity than the commercial alumina supported Rh catalysts. Finally, the optimized powder catalysts were deposited on a cordierite type monolith and tested in a laboratory-scale pilot-plant reactor, also showed good activity and hydrothermal stability, which means they can be considered promising candidates for this application. (C) 2013 Elsevier B.V. All rights reserved.