Watling, T., Lopez, Y., Pless, J., Sukumar, B. et al., "Removal of Hydrocarbons and Particulate Matter Using a Vanadia Selective Catalytic Reduction Catalyst: An Experimental and Modeling Study," SAE Int. J. Engines 6(2):882-897, 2013, doi:10.4271/2013-01-1071.
The use of vanadia selective catalytic reduction (V-SCR) catalysts for NOX reduction from diesel engine exhaust is well known. These catalysts are also active for hydrocarbon (HC) and particulate matter (PM) oxidation. This dual functionality (oxidation and reduction) of V-SCR catalysts can help certain applications achieve the legislative limits with an improved margin.In this work, NOX reduction, HC and CO oxidation over V-SCR were studied independently and simultaneously in microreactor tests. The effect of various parameters (HC speciation, concentration, ANR, and NO₂/NOX ratio) was investigated and the data was used to develop a kinetic model. Oxidation of CO, C₃H₆, and n-C₁₀H₂₂ is first order in CO/HC, while C₇H₈ oxidation is less than first order in C₇H₈. All these reactions were zero order in O₂. Oxidation activity decreased in order: C₇H₈ ≻ n-C₁₀H₂₂ ≻ C₃H₆ ≻ CO. HC oxidation was inhibited by NH₃. The presence of HCs was found to inhibit NOX conversion, but only after the HC had started to react. This can be explained by NOX reduction being inhibited not by the HC itself, but by the CO produced from partial oxidation of the HC.The V-SCR catalyst was also tested on a diesel engine in the absence of an upstream DOC and DPF to investigate its performance. The results confirm that V-SCR can remove HC and PM effectively: for temperatures above 230°C, V-SCR showed 45-75% HC conversion and 20-60% PM removal, under the specific engine conditions tested. This data was used to validate the kinetic model.