Patent ID: 8402754

Claim:
An apparatus for purifying exhaust gas, comprising: a catalyzed particulate filter (CPF) device mounted downstream of an engine and including a first diesel oxidation catalyst (DOC) therein, the catalyzed particulate filter (CPF) device firstly oxidizing hydrocarbon (HC) and carbon monoxide (CO) in the exhaust gas by using the first diesel oxidation catalyst (DOC), and trapping and regenerating particulate material (PM) so as to increase nitrogen dioxide (NO2) required for soot regeneration; a second diesel oxidation catalyst (DOC) device mounted downstream of the CPF device, secondarily oxidizing the HC and the CO in the firstly oxidized exhaust gas by using the second DOC, and oxidizing nitrogen monoxide (NO) into nitrogen dioxide (NO2) so as to increase amount of nitrogen dioxide (NO2) supplied to a selective catalytic reduction (SCR) device by using the second DOC; a nozzle mounted downstream of the DOC device, and dosing a reducing agent to exhaust gas secondarily oxidized by the second DOC device; and the selective catalytic reduction (SCR) device mounted downstream of the nozzle, and reducing nitrogen oxide (NOx) in the exhaust gas into nitrogen gas (N2) by using the NO2 generated in the second DOC device and the reducing agent; wherein the first DOC comprises a noble metal; wherein the noble metal of the first DOC comprises platinum (Pt) and palladium (Pd); wherein a ratio of the platinum to the palladium in the first DOC is 2:1 to 12:1; wherein the second DOC comprises a noble metal; wherein the noble metal of the second DOC comprises platinum and palladium; and wherein a ratio of the platinum to the palladium in the second DOC is 1:0 to 2:1.