Selective catalytic reduction of nitric oxide over cerium-doped activated carbons

• The potential of 3 types of cerium-doped carbons is studied to reduce NO with NH3.
• Catalyst physical/chemical properties were examined with and without Ce-doping.
• Catalyst activity experiments were conducted from 100–400 °C and 150–500 ppm NO.
• 78% NO gets reduced by Ce-doped granular activated carbon for 150 ppm NO concentration
• For 500 ppm NO, Ce-doped multiwall carbon nanotubes reduced NO by 85%.

An affordable selective catalytic reduction (SCR) catalyst for nitrogen oxides (NOx) from diesel engines is needed, which is effective at low as well as high temperatures. The contribution of this study was to directly compare the effectiveness of cerium-doped activated carbons as potential diesel SCR catalysts, via testing under similar conditions. Unmodified and cerium-doped granular activated carbon (GAC), activated carbon fiber (ACF), and multiwall carbon nanotubes (MWCNTs) were tested in a fixed bed column from 100–400 °C for 150 and 500 ppm concentration NO. For 150 ppm NO, CeGAC (with the highest cerium surface weight percent) achieved the highest reduction efficiencies over all temperatures. It maintained these efficiencies over 12 h of durability testing. However, CeGAC was only thermally stable to 310 °C, and its reduction efficiency did not increase at 500 ppm NO, due to limited accessibility of internal pore space. For high NOx conditions, CeMWCNTs (thermally stable until 412 °C) achieved the highest efficiencies above 280 °C (85% at 300 °C). Additional research is needed to extend the thermal stability of CeGAC or CeACF to higher temperatures, or increase the reduction efficiencies of CeMWCNTs at lower temperatures.

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