Catalyst Technology Satisfying Low Emission of Natural Gas Vehicle 970744
To develop catalysts for natural gas vehicles the effects of precious metal, washcoat and catalysts combination on the removal of methane (CH4), non methane hydrocarbon (NMHC), CO and NOx were investigated. The precious metal formula studied were Pt/Rh, Pd/Rh, Pt/Pd/Rh (trimetal) and Pd only. Two types of washcoats with different compositions and coating structures were used. Model gas tests were carried out for eight kinds of catalysts and dual catalysts consisted of two single catalysts. Through FTP75 vehicle test, three 50,000 miles approximate aged catalytic converters with dual beds were evaluated.
The experimental results showed that Pd only and trimetal catalysts had good catalytic performance over the CH4-CO-NO simulated gas composition. Dual bed catalysts had better CH4, CO and NO conversion performance and light off characteristics than single bed catalysts. From the vehicle tests, NOx emission levels were far below ULEV standard regardless of catalytic converter, but only the converter with Pd front and Pt/Rh rear bed cleared the ULEV standards of NMOG (non methane organic gases), CO and NOx simultaneously.