Passive NOx adsorber

Use of a passive NOx adsorber (PNA) comprising an LTL Framework Type molecular sieve and a first noble metal to adsorb NOx at or below a low temperature and release the adsorbed NOx at temperatures above the low temperature. The low temperature may be 250 °C. The first noble metal can be palladium, platinum, rhodium, gold, silver, iridium, ruthenium, osmium or mixtures thereof. The molecular sieve may be an aluminosilicate zeolite, an aluminophosphate zeolite, a silicoaluminophosphate(SAPO) zeolite, a metal-substituted aluminosilicate or a aluminophosphate zeolite, such as zeolite L, gallosilicate L, LZ-212, LTL-type SAPO or perlialite zeolite. The adsorber can either be coated onto or extruded, to form a flow-through or filter substrate. The adsorber may also contain a second molecular sieve catalyst, of a second noble metal and a second molecular sieve that does not have an LTL Framework Type. The second noble metal can also be palladium and the second molecular sieve may have an AEI or CHA framework type. The passive NOx adsorber may be arranged by having a first layer that comprises the first noble metal and LTL Framework Type molecular sieve, and a second layer comprising the second molecular sieve catalyst.