In this book hydrotalcite catalysts, silver alumina and Cu-ZSM5 catalyst are used to reduce NOx using CO as a reducing agent. Catalysts are prepared by carbonate co-precipitation method and by partial substitution of cations. Catalysts activity for NOx reduction was performed in a fixed bed tubular reactor under the following conditions: wt of catalyst = 100mg, ratio of gas mixture used = 0.13 NO, 2.50 CO, 1.36 O 2, 96.00 Ar, total flow rate = 60 ml/min, temperature = 50-450o C and pressure = 1 atm. The compositions of inlet and outlet gases were measured with the help of an online gas chromatograph and NO analyser. CO and CO2 concentrations were GC equipped with porapack q-column/molecular sieve 5-A, methanizer and FID/TCD detector.