Methods for Quantifying the Release of Vanadium from Engine Exhaust Aftertreatment Catalysts

Titanium dioxide supported vanadium oxide catalysts have been successfully utilized for the selective catalytic reduction (SCR) of nitrogen oxides emitted from both stationary and mobile sources. Because of their cost and performance advantages in certain applications, vanadium-based SCR catalysts are now also being considered for integration into some U.S. Tier IV off-highway aftertreatment systems. However, concern exists that toxic vanadium compounds, such as vanadium pentoxide, could be released from these catalysts as a result of mechanical attrition or high temperature volatility. An experimental study has been conducted to compare various techniques for measuring the release of particle and vapor-phase vanadium from SCR catalysts. Previous research has utilized a powder reactor-based method to measure the vapor-phase release of vanadium, but there are inherent limitations to this technique. A new method developed in this study utilizes a core reactor to measure the vapor-phase release of vanadium from commercially available SCR monolith cores in order to simulate real-world catalyst applications. The vanadium release results from this study were compared to engine-based measurements and previously published data from powder reactor experiments. Both reactor-based (i.e., powder and core) vanadium measurement techniques detected lower levels of vanadium than engine-based measurements. The increased level of vanadium release determined by the engine-based approach can be attributed to that method's ability to measure particle-phase and particle bound vanadium as well as the fraction of vapor-phase vanadium which was adsorbed onto particulate matter.