The nonthermal plasma generated in a shielded sliding discharge reactor was used to reform diesel for the hydrocarbon-selective catalytic reduction (HC-SCR) of NOx on Ag/Al2O3 catalysts. Compared with raw diesel, the reformed diesel enhanced the NOx reduction efficiency, mitigated hydrocarbon poisoning of the catalyst and reduced the fuel penalty for the HC-SCR reaction. The NOx conversion values obtained with a commercial Ag/Al2O3 catalyst exceeded that of a 2.0 wt% Ag/Al2O3 catalyst prepared by wet impregnation. A significant amount of NH3 was produced as a by-product during the HC-SCR reaction, which suggests that further NOx conversion enhancement can be achieved by placing a second NH3-SCR catalyst in series with the Ag/Al2O3 catalyst.