Synergistic Effect of Cu/CeO₂ and Pt–BaO/CeO₂ Catalysts for a Low-Temperature Lean NO_x Trap

Abstract

A lean NO x trap (LNT) catalyst has been widely used for removing NO x exhaust from lean-burn engines. However, the operation range of LNT has been limited because of the poor activity of LNT catalysts at low temperatures (≤300 °C), especially in urban driving conditions. To increase NO x removal efficiency during lean–rich cycle operation, a Cu/CeO2 (CC) catalyst was added to a Pt–BaO/CeO2 (PBC) catalyst. In comparison to PBC- or CC-only catalysts, the physical mixture of PBC and CC catalysts (PBC + CC) exhibited a significant synergy for both NO x storage and reduction efficiencies. In particular, low-temperature activity below 200 °C was greatly enhanced. A Pt–BaO–Cu/CeO2 (PBCC) catalyst, which was synthesized by depositing Pt and Cu together on a ceria support, showed poorer NO x removal efficiency. The origin of the synergistic effect over PBC + CC was investigated. Under lean conditions, the CC showed much better activity for NO oxidation, allowing for faster NO x storage on PBC. Under rich conditions, H2 was generated in situ on the CC by a water–gas shift reaction then accelerated the reduction of NO x , which had been stored on PBC, with a higher selectivity to N2. This simple modification in the catalyst can provide an important clue to enhance low-temperature activity of the commercial LNT system.

Highly Water-Resistant La-Doped Co3O4 Catalyst for CO Oxidation

“…Figure c shows XPS O 1s peaks of the catalysts that were deconvoluted into three components at ∼529.5, 531.2, and 533.2 eV, assigned to lattice oxygen (O latt ), adsorbed oxygen (O ads ), and oxygen in molecular water or hydroxyl species adsorbed on the catalyst surface (O w ), respectively. − The O w /O latt ratios and Δ T 90 , which indicate the difference in T 90 under dry and wet conditions, were plotted as a function of the La contents in Figure d. While bare Co 3 O 4 showed the O w /O latt ratio of 0.25, the O w /O latt ratio was reduced greatly in all La-doped Co 3 O 4 catalysts.…”

Roles of Oxygen Vacancies in the Bulk and Surface of CeO2 for Toluene Catalytic Combustion

“…Transitional metal oxides exhibited comparative activities and versatile surface modification possibility and are one of the research hot spots for their R&D process . CeO 2 has been extensively used as active components due to its outstanding redox property and oxygen storage capacity (OSC). , Nonstoichiometric CeO 2 exhibits excellent combustion activity in pollutant removal. , …”

“…5 CeO 2 has been extensively used as active components due to its outstanding redox property and oxygen storage capacity (OSC). 6,7 Nonstoichiometric CeO 2 exhibits excellent combustion activity in pollutant removal. 8,9 Oxygen vacancies display crucial roles for originating superior catalytic activity.…”

Investigation of the modes of NO adsorption in Pd/H-CHA

“…One way to reduce NO x emissions during cold-start is to adsorb NO together with CO and unburned hydrocarbons, and then to desorb these gases so that NO can be reduced in the catalytic converter once it reaches a temperature of 523-573 K. This can be done using a passive NO x adsorber (PNA), a device placed upstream of the catalytic converter that adsorbs NO x emissions while the converter is heating up [3]. The PNA consists of a metal dispersed on a high surface area support, such as a zeolite or mixed oxide [4]. Pd has been identified as a particularly attractive adsorbent for PNAs because of its high capacity for NO x storage as molecular NO or as intermediates such as nitrites [5][6][7].…”