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This is a follow-up report about the development of a cost-effective Palladium (Pd) zeolite-based (HC/NOx trap type) cold-start catalyst (CSC) [1] to meet the future more stringent Chinese vehicle tailpipe emission standard. The impacts of Pd /stabilizer combination within zeolite for the HC/NOx trapping efficiency, the high temperature aging and the durability of the CSCs will be demonstrated by the laboratory results within this paper. The feasibility of a Cu zeolite, a popular non-precious metal ion- zeolite CSC for vehicle applications with respect to cost saving options will be demonstrated. A more complete picture of the effects of PGM/stabilizer within the zeolite to the functions of a CSC will also be summarized in this paper. All results indicate clearly that without the PGM/stabilizer within the zeolite, it would be difficult for the zeolite-based HC/NOx trap type CSC catalyst to be practically used for a vehicle application.

A state of art Pd-zeolite based cold-start catalyst (CSC) or HC/NOx trap type of catalyst was codeveloped between Geely Automotive Company and Ningbo Kesen Exhaust Gas Cleaner Manufacturing CO. LTD. This CSC catalyst was added to the downstream of an existing catalyst system (TWC+CGPF) of a China 6b conventional passage car which was powered by a 1.5L turbo charge direct injection (1.5L GTDI) engine. The CSC significantly converted cold-start tailpipe NMHC emission and enabled the tailpipe emissions to meet the engineering targets of the projected next more stringent Chinese vehicle tailpipe emission standards in WLTC cycles. The vehicle tailpipe emission results with the addition of the laboratory simulated 120K km aged CSC also met the projected emission engineering targets of a fresh catalyst. Both the vehicle and laboratory results demonstrated the excellent ammonia adsorption and oxidation function of this CSC catalyst as a very efficient natural ammonia slip catalyst (ASC).

Future LEV-III tailpipe (TP) emission regulations pose an enormous challenge forcing the fleet average of light-duty vehicles produced in the 2025 model year to perform at the super ultralow emission vehicle (SULEV-30) certification levels (versus less than 20% produced today). To achieve SULEV-30, regulated TP emissions of non-methane organic gas (NMOG) hydrocarbons (HCs) and oxygenates plus oxides of nitrogen (NOx) must be below a combined 30 mg/mi (18.6 mg/km) standard as measured on the federal emissions certification cycle (FTP-75). However, when flex-fuel vehicles use E85 fuel instead of gasoline, NMOG emissions at cold start are nearly doubled, before the catalytic converter is active. Passive HC traps (HCTs) are a potential solution to reduce TP NMOG emissions. The conventional HCT design was modified by changing the zeolite chemistry so as to improve HC retention coupled with more efficient combustion during the desorption phase.

In the development of HC traps (HCT) for reducing vehicle cold start hydrocarbon (HC)/nitrogen oxide (NOx) emissions, zeolite-based adsorbent materials were studied as key components for the capture and release of the main gasoline-type HC/NOx species in the vehicle exhaust gas. Typical zeolite materials capture and release certain HC and NOx species at low temperatures (<200°C), which is lower than the light-off temperature of a typical three-way catalyst (TWC) (≥250°C). Therefore, a zeolite alone is not effective in enhancing cold start HC/NOx emission control. We have found that a small amount of Pd (<0.5 wt%) dispersed in the zeolite (i.e., BEA) can significantly increase the conversion efficiency of certain HC/NOx species by increasing their release temperature. Pd was also found to modify the adsorption process from pure physisorption to chemisorption and may have played a role in the transformation of the adsorbed HCs to higher molecular weight species.

Passive in-line catalyzed hydrocarbon (HC) traps have been used by some manufacturers in the automotive industry to reduce regulated tailpipe (TP) emissions of non-methane organic gas (NMOG) during engine cold-start conditions. However, most NMOG molecules produced during gasoline combustion are only weakly adsorbed via physisorption onto the zeolites typically used in a HC trap. As a consequence, NMOG desorption occurs at low temperatures resulting in the use of very high platinum group metal (PGM) loadings in an effort to combust NMOG before it escapes from a HC trap. In the current study, a 2.0 L direct-injection (DI) Ford Focus running on gasoline fuel was evaluated with full useful life aftertreatment where the underbody converter was either a three-way catalyst (TWC) or a HC trap. A new HC trap technology developed by Ford and Umicore demonstrated reduced TP NMOG emissions of 50% over the TWC-only system without any increase in oxides of oxygen (NOx) emissions.

Diesel NOx emissions control utilizing combined Lean NOx Trap (LNT) and so-called passive or in-situ Selective Catalytic Reduction (SCR) catalyst technologies (i.e. with reductant species generated by the LNT) has been the subject of several previous papers from our laboratory [ 1 - 2 ]. The present study focuses on hydrocarbon (HC) emissions control via the same LNT+SCR catalyst technology under FTP driving conditions. HC emissions control can be as challenging as NOx control under both current and future federal and California/Green State emission standards. However, as with NOx control, the combined LNT+SCR approach offers advantages for HC emission control over LNT-only aftertreatment. The incremental conversion obtained with the SCR catalyst is shown, both on the basis of vehicle and laboratory tests, to result primarily from HC adsorbed on the SCR catalyst during rich LNT purges that reacts during subsequent lean engine operation.

This study extends research previously reported from our laboratory [SAE 2009-01-0285] on diesel NOx control utilizing a new generation of Lean NOx Trap (LNT) plus in-situ Selective Catalytic Reduction (SCR) catalyst systems. Key findings from this work include 1) evidence for a “non-ammonia” reduction pathway over the SCR catalyst (in addition to the conventional ammonia pathway), 2) high NOx conversions utilizing LNT formulations with substantially lower platinum group metal (PGM) loadings than utilized in earlier systems, 3) ability of the downstream SCR catalyst to maintain high overall system NOx efficiency with aged LNTs, and 4) effectiveness of both Cu- and Fe-zeolite SCR formulations to enhance overall system NOx efficiency. FTP NOx conversion efficiencies in excess of 95% were obtained on two light-duty vehicle platforms with lab-aged catalyst systems, thus showing potential of the LNT+SCR approach for achieving the lowest U.S. emissions standards

An alumina-based LNT is being developed through laboratory studies, for diesel vehicle applications. This LNT provides high NOx conversion efficiency at low temperature (150 to 350°C, especially below 200°C), which is very important for the exhaust-gas after-treatment of diesel passenger vehicles. Addition of 2 to 4 wt% of alkaline-earth metal oxide or other metal oxides to the alumina LNT formulation improves NOx reduction activity at the high end of its active temperature window. More significantly, the alumina-based LNT can undergo the de-SOx process (the process of removing sulfur from the catalytic surfaces) very efficiently: within 1 minute at the relatively low temperature of 500 to 650°C under slightly rich conditions (λ = 0.98 to 0.987). Such a mild de-SOx process imposes minimal thermal exposure, causing almost no thermal damage to the LNT, and helps minimize the associated fuel penalty.

Catalyst poisoning from engine oil additives is a complicated process that depends in part on the pathway by which the oil is consumed in the engine. Engine studies were conducted to assess the relative impact of three major modes of oil consumption - through the PCV system, past the piston rings, and through the valve guides. Minimal phosphorus poisoning was observed with oil consumed through the PCV system and piston rings, whereas oil consumed through the intake valve guides demonstrated severe catalyst poisoning. The former produces effects characteristic of complete combustion of the ZDDP additive previously shown to produce relatively innocuous washcoat overlayers of porous zinc phosphate. In contrast, the latter produces effects characteristic of incomplete combustion (i.e., spray of oil additive into the exhaust and, most notably a washcoat pore-plugging effect accompanied by a marked decrease in washcoat surface area.

Diesel exhaust systems equipped with selective catalytic reduction (SCR) catalysts based on urea were subjected to an aging process where the exhaust gas temperature was below 300°C. Solid deposits related to urea injection were found on the wall of the exhaust pipe down stream of the urea injector and on a urea mixer in front of the SCR catalyst. In laboratory tests, an aqueous solution of urea (1.5wt%) was dripped onto an SCR catalyst core in a simulated lean gas mixture at a rate corresponding to a 1:1 NH3-to-NOx ratio (NOx = 350ppm) and a space velocity (SV) of 15,000 h-1 at various temperatures. At 300°C and below, urea-related deposits appeared on the SCR catalyst surface and totally plugged the SCR catalyst monolith within 250 hours. When the aging temperature was 350°C or above, no deposits were observed on the SCR catalyst core.

Selective Catalytic Reduction (SCR) of NOx with aqueous urea and a Catalyzed Diesel Particulate Filter (CDPF) has been considered as one of the emission control systems for diesel vehicles required to meet Federal Tier 2 and California LEVII emission standards. At Ford Motor Company, a DOC-SCR-CDPF system containing a copper / zeolite SCR catalyst was aged to 120k mi on the engine dynamometer using an aging cycle that mimicked both city and highway driving modes. A total of 643 CDPF regenerations occurred during the aging that raised the SCR catalyst to a temperature of up to 650°C on a regular basis. A series of lab analyses including activity tests, ammonia thermal desorption, BET surface area, XRF, XRD, and EPMA was conducted on cores taken from the 120k mi engine aged SCR catalyst brick. The lab post-mortem characterizations revealed the changes of catalyst properties, and the deterioration profile of the SCR catalyst brick after undergoing real aging conditions.