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Selective Catalytic Reduction (SCR) systems will be widely used to meet the Heavy Duty Diesel (HDD) Euro IV emissions legislation. Reports on a number of demonstrations of such systems have already been published, but the long-term durability of such systems is still to be proven. The potential catalyst deactivation induced by oil-derived species and thermal processes have, up to now, received very little attention, despite the fact that these HDD emission control systems will need to be durable for distances of the order of 500,000 km or more. This paper describes the development and performance of a new family of SCR catalyst with very high thermal durability and poison resistance. The thermal durability of the catalyst was initially demonstrated within long-term, high temperature engine bench ageing studies.

The tightening of Heavy Duty Diesel (HDD) emissions legislation throughout the world is leading to the development of emission control devices to enable HDD engines to meet the new standards. One system which has shown great promise in controlling PM emissions is the Continuously Regenerating Trap (CRT®) system. This system will be referred to as the CR-DPF for the remainder of this paper. Stringent durability requirements will be introduced alongside the new legislative emission limits, so it is essential that DPF systems are made to be as robust as possible. In Europe the systems are expected to need to meet a durability target of 500,000 km, while in the US this will be approximately 700,000 km (435,000 miles). This paper reports on the development of a greatly improved oxidation catalyst for these CR-DPF applications. Field and engine bench studies revealed that the previous catalyst could be poisoned by sulfur build-up during prolonged operation at low temperatures.