New Titania Materials with Improved Stability and Activity for Vanadia-Based Selective Catalytic Reduction of NOx 2010-01-1179

Selective Catalytic Reduction (SCR) of NO

using reductants such as urea continues to be of high interest to meet impending regulations. Vanadia supported on anatase titania is a well-established catalyst for stationary and heavy-duty-diesel truck deNO

applications. However, traditional anatase titania-based materials are regarded to have limited thermal stability in the most demanding applications such as those where the SCR catalyst is located downstream of a regenerating DPF, in which the catalyst could be exposed to very high temperatures. More recently, state-of-the-art titania-based vanadia catalysts have shown good cold-start performance and are capable of surviving accelerated aging treatments of up to 64 hrs at 670°C, good performance in a configuration upstream of a DOC/DPF, good low temperature NO

conversion on par with Cu-zeolite SCR catalysts and superior resistance to sulfur poisoning. We report here new, highly engineered titania-based materials with substantially improved stability and/or activity compared to the state-of-the-art commercial titania-based vanadia SCR catalysts. New synthetic approaches were used to prepare catalyst support materials that are predominantly anatase TiO₂ in composition. The thermal and hydrothermal stabilities of the new materials were characterized using a combination of x-ray powder diffraction with Rietveld Refinement, transmission and scanning electron microscopies, and N₂ porosimetry. Vanadia-loaded catalysts in powder form were thermally or hydrothermally aged and evaluated for NO conversion activity and selectivity in model-gas bench-scale reactors using NH₃ as the reductant, and were compared to commercial titania-based vanadia powders. The new materials fall into two classes. In the first, the materials exhibit substantially improved thermal stability, anatase phase stability and higher porosity, while exhibiting deNO

activity comparable to commercial materials. In the second class, the activity and stability of the new materials can be tuned to yield higher deNO

activity, particularly after exposure to high temperatures, while maintaining crystal phase stability and porosity at least as good as that of state-of-the art commercial titania-based vanadia catalysts. In a bench test under severe conditions that simulate lifetime catalyst exposure, no detectable vanadium is lost from the new catalysts to the vapor phase. The new, highly engineered materials should provide the catalyst formulator with new options to achieve robust and active SCR systems.