Search Results

Prototype metallic and electrically heated metallic catalysts (EHC) are being evaluated on a gasoline fueled vehicle. The vehicle used for this evaluation is a 5.0L Mustang equipped with an emissions control system which includes mass air, and sequential electronic fuel injection (SEFI). FTP tests are performed to evaluate non-heated metallic and electrically heated metallic catalysts in both production and close-coupled configurations. The objective of the evaluation is to determine light-off characteristics of both the non-heated metallic and the EHCs and their effect on cold-start emissions (Bag 1). FTP results are compared to those obtained from conventional ceramic catalysts in the same configurations. Initial data show some emissions benefits for the prototype EHC converter during the first 60 seconds or so of the FTP. From 60 seconds on in the FTP cycle, the ceramic catalyst was slightly more efficient, leading to overall FTP emissions about the same for the two systems.

Automotive three-way catalysts (TWC) were characterized using temperature-programmed reduction (TPR), x-ray diffraction (XRD), Raman spectroscopy, chemisorption measurements and laboratory activity measurements. Capabilities and limitations of these standard analytical techniques for the characterization of production-type automotive catalysts are pointed out. With the exception of chemisorption techniques, all appear to have general utility for analyzing exhaust catalysts. The techniques were used to show that the noble metals and ceria in fresh Pt/Rh and Pd/Rh catalysts are initially highly dispersed and contain a mixture of interacting and non-interacting species. Thermal aging of these catalysts (in the reactor or vehicle) caused both precious metal and ceria particles to sinter, thereby decreasing the interaction between the two.

Rhodium supported catalysts capable of withstanding temperatures above 600°C under oxidizing conditions while maintaining a resistance to chemical poisons have been developed by reducing the undesirable interaction of Rh2O3, with γ-alumina support material. The impregnation of Rh on a zirconia (ZrO2) washcoat provides a well dispersed, thermally-stable active phase. When the Rh/ZrO2 phase is in turn supported on a high surface area γ-Al2O3 washcoated monolith, the resulting (Rh/ZrO2)/γ-Al2O3 catalyst also has sufficient surface area for dispersion of other active metals, as well as to provide a sink for fuel-and oil-derived contaminants. Upon heating at 850°C in air, the Rh area is decreased by 95% when supported on γ-Al2O3 but is lowered only by 15% when ZrO2 is used to separate Rh from γ-Al2O3.

Ruthenium-containing catalysts have good activity and selectivity for the reduction of the nitric oxides in automobile exhaust. Although designed to be operated under reducing conditions, these catalysts lose Ru by volatilization when subjected to lean transients. Attempts were made to stabilize these catalysts against volatilization by forming stable ruthenates. This paper deals with durability testing of stabilized ruthenate catalysts on a laboratory bench set-up, dynamometers, and vehicles. Post-mortem analysis of the durability-tested catalysts are presented showing the extent of stabilization. The results show that the Ru loss from ruthenate catalysts in present vehicle systems is in excess of acceptable limits. These losses can be minimized further, but at a cost of reduced selectivity in the NO reduction. Substantial further improvements are needed to achieve the required performance characteristics. Another problem is the poisoning by S, Pb and P.

The performance of three way and NOx catalysts was evaluated on vehicles utilizing non-feedback fuel control and electronic feedback fuel control. The vehicles accumulated 80,450 km (50,000 miles) using fuels representing the extremes in hydrogen-carbon ratio available for commercial use. Feedback carburetion compared to non-feedback carburetion improved highway fuel economy by about 0.4 km/l (1 mpg) and reduced deterioration of NOx with mileage accumulation. NOx emissions were higher with the low H/C fuel in the three way catalyst system; feedback reduced the fuel effect on NOx in these cars by improving conversion efficiency with the low H/C fuel. Feedback had no measureable effect on HC and CO catalyst efficiency. Hydrocarbon emissions were lower with the low H/C fuel in all cars. Unleaded gasoline octane improver, MMT, at 0.015g Mn/l (0.06 g/gal) increased tailpipe hydrocarbon emissions by 0.05 g/km (0.08 g/mile).

This is the third and final communication in this series of laboratory evaluation of three-way catalysts. The effect of inlet NO concentration and temperature on the NH3 formation over fresh, pulsator-aged and dynamometer-aged three-way catalysts of the current generation has been investigated under temperatures and exhaust compositions of practical interest. In spite of differences in aging procedures employed, both the pulsator and dynamometer-aged catalysts show similar selectivity behavior. The effect of SO2 in feed-gas on gross NO conversion and NH3 formation was studied over Pt-Rh and Pt-Rh-Ru types of three-way catalysts. A strong dependence of the gross NO conversion on the SO2 concentration in exhaust gas mixtures was noted. A simultaneous suppression of gross NO conversion and NH3 formation, in presence of SO2 in feed-gas, is attributed to the poisoning of Pt sites on aged three-way catalysts.

Post-mortem analyses of 50,000 mi (80,000 km) vehicle-aged catalysts revealed that the use of 0.125g Mn/gal (33 mg/L) as MMT (methyl-cyclopentadienyl manganese tricarbonyl) significantly reduces phosphorus and zinc retention levels at the catalyst inlets by ~20-fold and ~5-fold, respectively. In subsequent laboratory pulsator experiments the presence of 0.016 to 0.157g Mn (as MMT)/gal (4 to 41 mg/L) isooctane fuel containing a 10-fold excess of ZDP (zinc dialkyldithiophosphate, source of oil P and Zn) similarly reduced the retention of P and Zn on TWCs by proportional amounts, while the TWCs maintained significantly higher 3-way conversions than in the absence of MMT. The combustion of Mn from MMT to very stable Mn3O4 probably serves as a scavenger in the exhaust for transporting away fuel- and oil-derived catalyst poisons such as P, Zn, and Pb. The utility of the laboratory results will require verification in vehicle studies.

A comprehensive laboratory evaluation was carried out on recent three-way catalyst formulations. The evaluation of selectivity characteristics was made in a synthetic exhaust mixture where “window” widths and positions for three-way conversion and their change after durability runs were determined. The durability runs were made in combusted gases from laboratory pulse-flame exhaust generators using both contaminant-free fuel and fuels with 1975 levels of Pb, P and S. A thorough evaluation of the “oxygen-storage” capability of the catalysts was performed and the results correlated with engine dynamometer experiments designed to utilize this property of three-way catalysts which allows a wider A/F ratio tolerance. A new technique which involves intentional modulation of the A/F ratio was found to extend the usefulness of such catalysts.

This is a continuation of our earlier paper on the laboratory evaluation of three-way catalysts, SAE 76201. A number of recent 3-way catalyst formulations were evaluated in a laboratory flow-reactor when fresh, after 25,000 simulated miles on a pulse-flame reactor and after 100 or 200 hours of accelerated AMA dynamometer durability. A comparison was made of the effects of contaminant levels on the performance of pulsator - and dynamometer-aged selected catalysts. The 4-fold decrease in contaminant (lead and phosphorus) levels in 76/77 certification fuel compared with the 75/76 fuel significantly improved the durability of 3-way catalysts. The problems of increased NH3 formation on pulsator - and dynamometer-aged catalysts which contain base-metal oxides as oxygen-storage or water-gas shift components is attributed to S-poisoning. An inverse relationship between NH3 formation and the amount of rhodium on aged 3-way catalysts was noted.

The durability of automotive three-way catalysts (TWCs) for European applications were investigated as a function of higher temperatures encountered in autobahn driving modes over extended periods of time, potentially higher residual lead (Pb) levels anticipated in European marketed unleaded fuels, and occasional misfueling with leaded fuels. In laboratory durability and dynamometer aging studies, platinum-rhodium (Pt-Rh) TWCs at higher loadings than currently used in US applications maintained substantial three-way conversions when aged under rich conditions (λ ∼ 0.9) at maximum temperatures of ∼ 900 to 1000°C with 3 mg Pb/L fuel levels. Increasing maximum catalyst aging temperatures from 730°C to 1000°C resulted in ∼50% reduction in BET surface area which increased stoichiometric hydrocarbon light-off temperatures, but improved net NO and HC conversions after light-off due to lower Pb retention on the TWC.

On occasions automotive fuels have been contaminated by adventitious admixtures of silicon (Si)-containing compounds which have deleterious effects on automotive catalysts and oxygen sensors. The deactivation of monolithic automotive catalysts by fuel-derived silicon is due to deposition of crystalline silica (∝-SiO2) on the catalyst surface which causes mass transfer limitations and may ultimately result in plugging of the monolith. Stoichiometric conversions efficiency of three-way catalysts (TWCs) from various low-mileage vehicles were significantly deteriorated; e.g., from typical three-way efficiencies of −95% conversion to <50% conversion at 550°C after only 1500 mi of vehicle use. Laboratory aging of a TWC exposed to combustion products of isooctane fuel containing 20 ppm Si resulted in a continual decline in three-way conversions to <40% after 15,000 simulated miles.

A novel non-phosphorus antiwear additive, NP-1, was evaluated as a partial substitute for zinc dialkyldithiophosphate (ZDTP). ZDTP, an antiwear/antioxidant engine oil additive may under certain conditions cause three way catalyst (TWC) deactivation due to formation of an amorphous zinc pyrophosphate, Zn2P2O7, glaze. Antiwear and antioxidant properties of NP-1 alone and in combination with ZDTP were compared with ZDTP only containing formulations. The effects of NP-1 on TWC activity during pulsator modulation and steady-state conditions showed that the TWC maintained good overall activity during 24,000 simulated miles.

The deactivation of automotive catalysts by engine oil-derived components of phosphorus and zinc can occur by the formation of an amorphous zinc pyrophosphate (Zn2P2O7) that is impervious to gas diffusion. The catalyst poison, derived from antiwear oil additive zinc dialkyl dithiophosphate (ZDP) in low-temperature exhaust environments, appears as glassy, amorphous deposits on catalysts as shown by scanning electron microscopy (SEM). Laboratory studies were performed to understand the effects of exhaust stoichiometry, temperature, rate of oil burn, and chemical form of P and Zn compounds on glaze formation. The formation of the amorphous deposits using a laboratory pulsator apparatus showed that noncombusted ZDP causes the glaze formation. Electron microprobe studies indicated the association of P with Zn on precious metal films exposed to ZDP combustion products. Secondary ion mass spectrometry (SIMS) confirmed a similar P to Zn correspondence on the vehicle-aged catalysts.

Poisoning of a typical platinum-rhodium (Pt-Rh) automotive three-way catalyst (TWC) was determined as a function of lead (Pb), sulfur (S) and phosphorus (P) fuel levels, thermal aging and sulfur dioxide (SO2) content in the evaluation fuel. In laboratory studies catalysts were durability tested in pulse-flame reactors followed by flow-reactor activity measurements. Engine dynamometer-aged catalysts were evaluated on a slave vehicle. For Pt-Rh TWCs the activities for nitric oxide (NO), carbon monoxide (CO) and hydrocarbon (HC) conversions were poisoned by trace levels of 1-6 mg Pb/gal (0.3 - 1.6 g/m3). When the peak temperature in the aging cycle was increased from 730 to 870°C (1346 to 1598°F), the activities improved significantly. In an attempt to mimic the effect on TWCs of misfueling with Pb levels typical of commercially available leaded fuels, TWC activities were severely poisoned.