Removal of Hydrocarbons and Particulate Matter Using a Vanadia Selective Catalytic Reduction Catalyst: An Experimental and Modeling Study 2013-01-1071

The use of vanadia selective catalytic reduction (V-SCR) catalysts for NO_X 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, NO_X 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/NO_X 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 NO_X conversion, but only after the HC had started to react. This can be explained by NO_X 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.