Development of metal oxyde nanophase catalysts for emission control

Exploitable results

Adequate know-how has been obtained on the following items regarding the novel TWEHC: 1) Formulation of Pd/perovskite active phases and ways of tailoring their properties. The catalysts based on these formulations exhibit comparable light-off and 3-way efficiency with commercial exhaust catalysts. Their catalytic activity is due to strong synergism between the two components. 2) A simple method has been developed for preparing and coating the active phases with adequate adhesion, conductance and activity. Future improvements in the coating quality are considerd. 3) The novel catalysts exhibit multi-function features in exhaust emissions control: 3a) Operation as light-off or main 3-way catalysts. Under-floor or close-coupled operation positions are assessed to be feasible. An intermediate operation position offers advantages with respect to 3-way performance, SO2 resistance and lifetime. 3b) Operation as effective Electrically Heated Catalysts with very low electrical power consumption. This is due to selective heating of the active phase (i.e. current passage through the active phase only). 3c) Effective and relatively simple diagnosis of the light-off characteristics through monitoring of the relative conductance change during cold-start. 4d) Potential multi-fuel use (e.g. gasoline and natural gas). Selective active phase heating can be considered for lowering the light-off temperature of methane. Introduction of these catalysts into the market is estimated to result in a significant reduction of the exhaust aftertreatment cost. This is due to increased durability of the catalyst, due to reduced amount of noble metals, and also because of integration and simplicity of the aftertreatment and diagnosis system. This cost reduction is expected to compensate for any cost increase because of the stricter environmental regulations. The benefit of car, catalyst and automotive component manufacturers from such a development is obvious.

The achievements of the project can be summarized as follows: 1. CeO(2) doped nanopowders with Ca, Mg, Mn, Zr and Nd doping have been synthesized by controlled co-precipitation and evaluated in terms of oxygen storage capacity and thermal stability. The combination of Nd and Zr doping leads to maximum oxygen storage capacity and enhances catalytic activity. The synthesis process of such compounds by controlled co-precipitation was optimised. In parallel, sol-gel techniques were employed to produce Ca, Mg and Zr doped CeO(2). Very encouraging results were achieved both by aqueous and polymeric routes. CeO(2) particles are thermally stabilized by their dispersion in an Al(2)O(3) matrix. The sol-gel technique permits for the dispersion of Pd in the sol state as well as for direct deposition of the wash coat on the support from the liquid state. The particle size of the ceria-doped powders prepared by this way is under 30nm. Samples of catalytic monoliths were assessed in terms of redox properties and catalytic activity. The catalytic activity measured on the optimised formulation 0.25CeO(2)-0.73Al(2)O(3)-0.0(2)CaO and with 1.5%wt noble metal inserted directly in the sol state (polymeric route) with much lower precious metal content than the reference commercial catalyst showed equivalent catalytic activity with it. Although the deposition process was not optimised, the catalytic activities of coated monoliths were very promising. Significant catalytic activity very similar to the reference catalyst was measured even with negligible precious metal content and small amounts of nanomaterials. 2. Pd/Perovskite formulations with optimised synthesis were prepared for the development of TWEHC. These formulations represent a new family of precious-metal/metal-oxide catalysts with activity not depending on high surface area materials but on strong synergism between the two components, a fact that provides higher thermal stability. This feature allows the catalyst operation at an optimised close-coupled position that offers advantages with respect to light-off, 3-way performance and SO(2) poisoning. Furthermore, operation under slightly rich conditions induces a significant improvement in the overall catalyst performance. The feasibility of electrical heating for cold start emissions reduction has been proved, since the light-off time can be reduced to about 50% by applying low electrical power. Catalytic performance and ageing studies showed comparable results with a reference commercial catalyst for both gasoline and natural gas exhaust gas. Moreover, the new catalysts combine the advantages of low precious metal loading, cold start emissions control and capability of on board diagnostics by measuring the relative conductance changes during operation. 3. Deposition studies with respect coating of nanomaterials on the ceramic support were carried out with the aim to improve coating quality in terms of homogeneity and adhesion. Although good quality coatings were obtained, the deposition process needs further optimisation in order to increase the wash coat loading and the homogeneity of the coating across the monolith channels. 4. New tielite-mullite composites with improved thermo-mechanical properties were developed for the construction of honeycomb supports. Extensive characterization and ageing studies led to the optimum composition in terms of tielite stability at high temperatures combined with high mechanical strength. The new materials developed, combine high refractoriness; very low thermal expansion coefficient with increased mechanical strength. The processing conditions for the construction of honeycomb structures were optimised and real size monoliths with 400 cells/in2 were fabricated.

Exploitable results

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