Chemical deactivation of commercial vanadium SCR catalysts in diesel emission control application

• Phosphorous and zinc were the primary chemical contaminants on Field returned vanadium SCR catalysts.
• NOx conversion during the NH3-SCR reaction was lowered and altered by chemical contamination.
• Chemical deactivation was mainly caused by NH3 storage capability reduction and oxidation activity modification.

Irreversible chemical deactivation of state-of-the-art vanadium selective catalytic reduction (SCR) catalysts was investigated using an aftertreatment system from a heavy-duty diesel vehicle for general haulage application. Elemental analysis revealed that Field returned vanadium SCR catalysts had higher phosphorous and zinc concentrations than those from a fresh catalyst. Phosphorous concentration dropped significantly from catalyst inlet to outlet, while zinc concentration remained almost constant. Broadened infrared intensity from V5+O and W6+O bonds were observed from contaminated vanadium SCR samples. Anatase phases and crystallite size remained unchanged in the presence of chemical contaminants.Chemical contamination monotonically reduced NH3 storage capability but non-linearly modified acid site distribution and oxidation activity, causing differences in NOx reduction behaviors. Low chemical contamination on vanadium SCR catalyst reduced NOx conversion below 450 °C due to the decrease in NH3 storage capacity and oxidation activity. NOx conversion over a sample with high phosphorus concentration was lowered by the weakened NH3 storage capacity below 350 °C and the enhanced parasitic NH3 oxidation above 400 °C. High levels of phosphorus increased low-temperature NOx conversion compared to low levels of phosphorus due to increase in oxidation capability.

Figure optionsDownload as PowerPoint slide