Study Of Pd-only Three-way Catalysts Preparation Technology And Interaction Mechanism Among Different Components

In order to satisfy the increasing strict regulations on emission of vehicle exhausts, development of advanced automobile three-way-catalyst (TWCs) have been widely investigated. For the purpose of promoting the activities, optimizing preparation technology of TWCs is considered as the sticking point to advance efficient solutions. In this work, to obtain catalyst with excellent thermal stability and high catalytic properties, different preparation technologies were studied. The results show the best preparation method is: CeO2–ZrO2–Al2O3 supports are obtained by precursor mixing co-precipitation, and Pd is supported on the supports by the incipient wetness method.Pd/Ce0.7Zr0.3O2 samples prepared by various Pd support methods have different interaction between components on different level. The sample obtained by co-precipitation which possesses intimate interaction between Pd and Ce0.7Zr0.3O2 has high thermal stability but few Pd active sites; the sample obtained by incipient wetness has most Pd active sites, outstanding oxygen storage/release capability and catalytic activity.Obtained by precursor mixing co-precipitation, strong interaction between Ce0.7Zr0.3O2 and Al2O3 exists in mixed ceria-zirconia-alumina oxides. With most incorporation of Al3+ into the lattices of Ce0.7Zr0.3O2 indicates the essential of the interaction between Ce0.7Zr0.3O2 and Al2O3. This sample has the smallest crystallites and highest surface area confirmed through BET and XRD measurements. Meanwhile, EPR detected increasing Ce3+ and OSC is obviously enhanced by intimate interaction between ceria-zirconia and alumina. The results show that the intimate interaction between ceria-zirconia and alumina could modify the structural properties,improve thermal stability and enhance OSC.Moreover, to induce the interactive effect between Pd and different supports, a series Pd-loaded sample was designed to obtain different interaction forms. The results show that the interaction between Pd and Al2O3 benefits the conversion of HC and NO under stoichiometric air/fuel condition. Pd tends to exist on Al2O3 with large particles and metallic state, which improves the adsorption of HC, N-O bond rupture and N-N bond recombination. Meanwhile, Pd loaded on Ce0.7Zr0.3O2 with small Pd particle size and high Pd dispersion is in favor of CO elimination.