TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preparation (Claimed): Preparing monolithic catalyst comprises (a) mixing solution of soluble cobalt ion (Co2+) and chromium ion (Cr3+) or mixing solution of soluble cobalt ion (Co2+), chromium ion (Cr3+) and doped metal ion (Mn+), where n+ is the valence of the doped metal, (Co2+)+ (Cr3+) is 1-2 mole/l, or (Co2+)+ (Cr3+)+ (Mn+) is the mixing solution, vacuum extracting and filtering the mixing solution, then drying at 100-120 degrees C, conse-2 mole/l, regulating the mixing solution the pH value to 7-9.5 by ammonia water solution of 10 wt.%, then stirring for roasting the material for 2 hours or more at 450-600 degrees C to obtain a metal-doped cobalt/chromium composite metal oxide CoxCry-M, (b) mixing gamma -aluminum oxide with CoxCry-M for forming a mixture, then adding mixture into deionized water, stirring uniformly for obtaining turbid liquid, regulating the added amount of the deionized water for regulating the solid content of the turbid liquid to 30-40%, ball-milling the turbid liquid, controlling the granularity D90 at less than 50 mu for obtaining slurry, adding into a palladium nitrate solution with 10 wt.% of palladium, regulating the pH value to 3-7 by nitric acid or acetic acid to obtain the coating slurry, (c) soaking the cordierite honeycomb ceramic carrier in the coating slurry, pulling out the carrier at a constant speed, and blowing the barrier, and (d) performing drying and roasting of the material by drying the cordierite honeycomb ceramic carrier coated with the coating slurry at 100-120 degrees C, then repeating until the coating amount of the cordierite honeycomb ceramic carrier reaches 20-40%, and roasting the carrier for 2-5 hours at 450-700 degrees C. Preferred Composition: The mesh of the cordierite honeycomb ceramic carrier is 300-600 meshes. The mole ratio (x:y) of cobalt to chromium in CoxCry is 1:2. The coating is 20-40 wt.% of the honeycomb carrier, where the ratio of the components (Pd: CoxCry-M: Al2O3) is 70-100:\10-20:0.2-1. Preferred Method: The doped metal M in step (a) is cerium, lanthanum, iron, nickel or zirconium, the metal salt solution is nitrate, when the doped metal M is manganese, and the metal salt solution is manganese acetate. The metal salt solution in step (a) is nitrates of cobalt. In step (a), the mixing solution is nitrates of cobalt and chromium. In step (b), the added palladium nitrate is directly introduced into the coating slurry and is coated on the cordierite honeycomb carrier together with the slurry. In step (c), the honeycomb ceramic carrier remains in the slurry for 1-3 seconds, and then the honeycomb ceramic carrier is pulled out at a constant speed of 30-60 mm/seconds.