Impacts of Reductants on Hydrocarbon Deactivation of a Hydrocarbon SCR Catalyst

To comply with Tier II Bin 5 light-duty or 2010 heavy-duty NOx emission standards, all diesel engines require some sort of NOx control device. Selective Catalytic Reduction of NOx with hydrocarbons (HC-SCR) to reduce NOx from diesel exhaust emissions is an attractive technology for lean NOx control, especially when diesel fuel is used as the reductant. However, it has been reported that when diesel fuel is used as the reductant catalyst deactivation occurred (1).

In a companion paper, we demonstrated that the HC-deactivation is caused by the mismatch of the adsorption and desorption processes of either the reactants or the products of a normal SCR reaction (2). In this paper, we probe the nature of the catalyst deactivation with various reductants. Both hydrocarbons and oxygenates were used as the reductants.

The deactivation or the mismatch in adsorption and desorption rates is molecular size or chain length dependent. Small molecules or short-chain molecules have no or low tendencies to deactivate the catalyst. Conversely, large molecules or long-chain molecules are more prone to have mismatched adsorption and desorption rates.