Doubly promoted platinum group metal catalysts for emission control

摘要

Catalysts are made from supports which are doubly promoted with ceria and an alkali metal oxide by adding these promoters and the catalytic noble metal components in a specified order. The ceria is first applied to the support. It can be applied in a salt form such as cerous nitrate. This impregnated support is then calcined to form a deposit of ceria. Next, solutions bearing the noble metals are applied to the ceria-promoted support and with these solutions the alkali metal component is applied. After subsequent elevated temperature activation, the alkali metal component is converted to an alkali metal oxide and the noble metals are converted into their metallic or oxide form. When lithium is chosen as the alkali metal promoter, it can alternatively be applied to the support along with the initial ceria promoter. After calcining the support to yield the ceria and lithia promoters, the noble metals can then be deposited and subsequently activated at an elevated temperature. Using this process it is possible to have the noble metals deposited on the support so that their penetration depth is less than 300 microns as measured by the SnCl2 solution staining method to provide an effective three-way catalyst suitable for use in auto emission control.