Abstract
The passive NOx adsorber (PNA) material has been considered an effective candidate for the control of NOx from diesel exhaust during the engine cold start stage, and Pd/SSZ-13 attracts peoples’ attention mainly due to its superior hydrothermal stability and sulfur resistance. However, chemical poisoning tolerance of Pd/SSZ-13 is another key parameter to its practical application and future development. Herein, we prepared potassium-loaded Pd/SSZ-13 and evaluated the influence on NOx adsorption ability. The characterization results revealed that the loading of potassium could not destruct the structure of SSZ-13 but impaired the BET surface area and pore structure through the sintering of Pd species to PdO. Meanwhile, the grown PdO phase restrained the NOx adsorption ability and promoted the generation of NO2 at high temperatures. Moreover, the presence of H2O could also impair the NOx adsorption ability due to the competitive adsorption between H2O and NOx. This work verifies that the design of Pd/SSZ-13 sample with stable Pd species and excellent hydrophobicity is significant for its further application under harsh conditions.
Highlights
The release of nitrogen oxides (NOx) from mobile sources brings huge damage to both the environment and human health; diesel exhaust purification is a long-term and severe challenge in this field [1,2,3]
No distinct Pd species are observed in all samples, probably due to the Pd phases that usually overlap with the CHA characteristic peaks [9,21]
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Summary
The release of nitrogen oxides (NOx) from mobile sources brings huge damage to both the environment and human health; diesel exhaust purification is a long-term and severe challenge in this field [1,2,3]. Unremitting efforts are still being taken to meet the increasingly rigorous requirement for the NOx emission, especially during the engine cold start period [4,5,6,7]. The exhaust temperature is almost below 200 ◦C during the cold start stage, which is a short time of 1~3 min upon engine starting [6,7,8]. Such low temperature could not guarantee the decomposition of urea (>180 ◦C) and the operation of NH3-SCR process (>200 ◦C). Stricter demands for NOx emission have been raised by Europe, USA and China in recent years [12,13,14], so it is extremely essential and urgent to reduce the NOx emitted in the cold start period
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