NOx reduction from gas stream by selective non-catalytic reduction (SNCR) using urea as a reducing agent was performed in this study. A Pilot-scale experimental system was designed and constructed to evaluate the NOx reduction efficiency and temperature window of the process. Particularly, different types of additives were added during SNCR process to improve NOx reduction efficiency and enlarge temperature window. The addition of additives was based on organic compounds like alcoholic group (CH3OH, C2H5OH and C3H7OH) and metallic compounds like alkali metals (NaOH, KOH and LiOH). Some newly introduced additives, such as surfactants and different blends of alkali metal NaOH (1%) with organic group or surfactants were also added to assess the effect of these mixed additives on NOx reduction efficiency and reaction temperature window during SNCR process. Main focus was laid on surfactants as an additive because of their cost: effectiveness and availability. Basically, surfactants have both organic and metallic parts which provide OH free radicals from both ends (organic and metallic) to enhance the reaction mechanism and improve the NOx reduction at low temperature. Different types of surfactants (anionic, cationic, amphitricha, long chain, short chain and with different functional groups attached to chains) were tested as an additive during SNCR process. Anionic surfactants (SPES, APS, LAS and SPS) gave maximum efficiency for NOx reduction and provided maximum range for the temperature window. (C) 2011 Elsevier Ltd. All rights reserved.