Development And Mechanism Study Of Non-precious Metal Passive No_x Adsorber(Non-PM PNA)

In this paper,Co-SSZ-13 served as a non-PM PNA was developed to solve the problem of NO_x emission during cold start of vehicles.Cobalt species and NO_x storage/desorption process of this catalyst were studied.And the storage/desorption mechanism was proposed.High-load Co-SSZ-13 catalyst can be prepared by multiple ion exchange method using Co（Ac）₂ solutions.The low-temperature NO_x storage capacity of this catalyst is27.3μmol/gcat,which is 60%of that of precious metal PNA（Pd-SSZ-13）reported in the literature.The desorption temperature of NO_x is above 250 ^oC,which is appropriate for downstream NH₃selective catalytic reduction catalysts.Besides,Co-SSZ-13 still has a stable NO_x storage capacity after repeat runs of catalyst evalation in a synthetic gas mixture simulating the cold start exhaust emissions.And Reduction inactivation resistance has also been observed.In summary,Co-SSZ-13 served as a non-PM PNA can be adopted as a promising alternative to platinum-based adsorbers to solve the problem of NO_x pollution emissions during cold start.In addition,cobalt species and the NO storage/desorption process were also investigated.Multiple cobalt species coexist in Co-SSZ-13 catalyst,including cobalt oxides,Co²⁺ions on exchange sites of zeolites and cobalt phyllosilicate.At the beginning of the NO storage stage,Co-（NO）₂ is formed immediately due to the strong interaction between NO molecules and Co²⁺on exchange sites of zeolites,which is responsible for the excellent NO_x storage capacity.With O₂ or cobalt oxides served as oxidants,Co-（NO）₂ is further converted into Co-NO₃ and ZEO―（NO）.This conversion process could increase the desorption temperature of NO.Co-NO₃ and ZEO―（NO）decomposes at 350 ^oC and 180 ^oC respectively,corresponding to two different NO_x desorption temperatures.