Molybdenum impregnated HZSM-5 zeolite catalysts With MoO3 loading from 1 to 8 wt.% were studied in detail for the selective catalytic reduction (C2H2-SCR) of NO by acetylene. A 83.9% of NO could be removed by the reductant at 350 degrees C under 1600 ppm of NO, 800 ppm Of C2H2 and 9.95% of O-2 in He over 2%MoO3/HZSM-5 catalyst with a specific activity of 0.09 mmol h(-1) g(cat)(-1) in NO elimination and the competitiveness factor (c.f.) of 33.6% for the reductant. The NO elimination level and the c.f. value were ca. 3-4 times as high as those using methane or propene as reductant over the catalyst in the same reaction condition. About same reaction rate was estimated in NO oxidation as that in the NO reduction over each xMoO(3)/HZSM-5 (x = 0-8%) catalyst, which confirms that NO2 is a crucial intermediate for the aimed reaction over the catalysts. Appropriate amount of Mo incorporation to HZSM-5 considerably enhanced the title reaction, both by accelerating the intermediate formation and by strengthening the adsorption NOx on the catalyst surface under the reaction conditions. Rather lower adsorption tendency of acetylene compared with propene on the catalysts explains the catalyst's steady performance in the C2H2-SCR of NO and rapid deactivation in the C3H6-SCR of NO. (C) 2006 Elsevier B.V. All rights reserved.