Exhaust gas purification method and exhaust gas purification system and the exhaust gas purifying ca

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PROBLEM TO BE SOLVED : To provide a method for removing NOx in a high efficiency. SOLUTION : An NOx removal catalyst obtd. by carrying at least Rh and Pt selected from the platinum group metals such as Pt, Rh and Pd, Ca, Ti and at least one rare earth metal selected from rare earth metals on a porous carrier is disposed in the exhaust gas passage of an internal combustion engine and a lean exhaust gas and a stoichiometric or rich exhaust gas are allowed to flow alternately into the catalyst to remove NOx in the exhaust gases. The catalyst contains 0.1-3.0 pts.wt. Pd, 1.0-6.0 pts.wt. Pt, 0.2-1.0 pt.wt. Rh, 20-50 pts.wt. Ca, 3-20 pts.wt. Ti and 15-40 pts.wt. rare earth metal based on 100 pts.wt. porous carrier and an SOx capturing material may be incorporated into the catalyst.