Toward achieving selective catalytic reduction of NO (x) by hydrocarbons at low temperatures (especially lower than 200 A degrees C), C2H2 selective reduction of NO (x) was explored on H-mordenite (H-MOR) catalysts in dielectric barrier discharge (DBD) plasma. This work reported significant synergistic effects of DBD plasmas and H-MOR catalysts for C2H2 selective reduction of NO (x) at low temperatures (100-200 A degrees C ) and across a wide range of O-2 content (0-15%). At 100 A degrees C, NO (x) conversions were 3.3, 11.6 and 66.7% for the plasma alone, catalyst alone and in-plasma catalysis (IPC) cases (with a reactant gas mixture of 500 ppm NO, 500 ppm C2H2, 10% O-2 in N-2, GHSV = 12,000 h(-1) and input energy density of 125 J L (-1)), respectively. At 200 A degrees C, NO (x) conversions were 3.8, 54.0 and 91.4% for the above three cases, respectively. Also, strong signals of hydrogen cyanide (HCN) byproduct were observed in the catalyst alone system by an on-line mass spectrometer. By contrast, almost no HCN was detected in the IPC system.