Pd-Based Catalyst on Alumina with Perovskite (La0.67Fe0.83Cu0.17O3) to Reduce Ammonia Content in Natural Gas Exhaust

La0.67Fe0.83Cu0.17O3 with perovskite structure was prepared by sol-gel method, and 1.5 wt% Pd/Al2O3 was prepared by initial wet impregnation method. Pd/Al2O3 and perovskite prepared above were mixed by mechanical ball-milling with mass ratios of 10:1, 5:1 and 3:1, respectively, and represented by 10Pd/Al-La, 5Pd/Al-La and 3Pd/Al-La. Pd/Al refers to Pd/Al2O3 catalyst. In theoretical air-fuel ratio conditions (lambda=1), the simulation of chemical metering of natural gas vehicle exhaust gas mixture on the catalysts were tested. The results showed that the perovskite could significantly reduce the ammonia formation in the exhaust gas. Moreover, the three-way catalytic performance of Pd/Al and 3Pd/Al-La were also tested in the feeds without water, CH4 or CO. The results demonstrated that the perovskite greatly reduced the ammonia content in the three exhaust gases. However, the ammonia content over bare Pd/Al was much higher in the presence of CO, and almost no ammonia was generated in the absence of CH4. The catalysts were also investigated by N-2-physisorption, CO-chemisorption, XRD, EDX mapping and XPS techniques. The results showed that the perovskite may promote the reaction of NO and CO towards high N-2 selection in the presence of CH4 and H2O, resulting in lower ammonia formation. Our work provided a new method for reducing ammonia formation over TWC catalysts for stoichiometric natural gas vehicles. Graphic

Automated summary

The perovskite synthesized showed a significant reduction in ammonia formation in the exhaust gases, and also improved the three-way catalytic performance of Pd/Al and 3Pd/Al-La catalysts. The presence of perovskite greatly decreased the ammonia content in the exhaust gases, with particularly notable results in the absence of CH4.