J.C. Summers

Durability of Palladium Only Three-way Automotive Emisson Control Catalysts

The noble metal palladium (Pd) has the capability of simultaneously converting significant quantities of HC, CO and NO/sub x/ in automotive exhaust. Primary interests in using palladium-containing TWC catalysts are overall noble metal cost reduction, reduction in rhodium usage and important performance advantages. Dynamometer aging experiments comparing palladium and platinum/rhodium catalysts were conducted under a variety of operating conditions. Vehicle evaluation of these aged catalysts under U.S. FTP-75, European ECE-15 and Japan 10-Mode conditions indicate that palladium-only TWC technology is vaiable for achieving high levels of three-way control. Vehicle aging studies (25K miles) were also conducted. The results of these studies are discussed in this work.

Catalytic control issues associated with the use of reformulated gasolines

The adoption of significantly more stringent tailpipe emission standards is leading the domestic car manufacturers and oil companies to reexamine the composition of commercial gasolines. One offshoot of this examination is a cooperative inter-industry Auto/Oil Air Quality Improvement Research Program. This study will attempt to determine the potential reductions in total vehicle emissions and resultant improvements in air quality from the use of reformulated gasolines. One important aspect of the program is to determine the effect of variable aromatic and olefinic hydrocarbon content as well as variable levels of oxygenates on emission levels from a statistically-designed vehicle program. Much laboratory, engine and vehicle emission data has been generated over the past two decades that is potentially useful in interpreting the tailpipe emission patterns associated with proposed fuel composition changes. For sake of completeness, the role of fuel sulfur on tailpipe emissions will also be examined. This paper examines these experimental data in order to provide guidelines for interpretation of fleet generated emission data and to predict general directions of catalytic control strategy that should be considered when contemplating a change in gasoline composition. In addition, some new experimental data presented in this paper that relate to these general goals.

DESIGN AND PERFORMANCE EVALUATION OF AUTOMOTIVE EMISSION CONTROL CATALYSTS

Abstract The performance of a series of single noble metal automobile emission catalysts was determined as a function of washcoat composition and aging conditions. The use of catalysts containing individual noble metals allowed the contributions of each type of noble metal to be identified, and revealed the role of the alumina supports containing cerium. Each noble metal was found to have a washcoat which optimized its performance under a given set of conditions. Addition of Ce to Pt and Pd-only catalysts improved performance after aging, but Ce did not improve Rh performance at 450 °C. The individual contributions of Pt, Pd, and Rh for aged three-way performance indicate significant advantages of using Pd-Ce over Pt-Ce, however when they are combined the predominant contribution to TWC activity comes from Rh. The influence of CO concentration in the feedstream on the light-off activity was determined for single noble metal catalysts on an alumina/ceria washcoat. Increasing the CO content of the feedstream led to an increase in light-off temperature for all three noble metal catalysts. The light-off characteristics varied with the noble metal, and are thought to be related to the stability of the noble metal oxides.

Improvements In Converter Durability and Activity via Catalyst Formulation

This paper is concerned with the impact of different washcoat systems on both the catalytic and physical durabilities of porous cellular ceramic monoliths for automotive emissions control. A key objective of the paper is to optimize the washcoat formulation from systems point of view to help meet the stringent NO x and hydrocarbon emission standards for the 1990s

Catalysts for natural gas emission control applications

Abstract Several parameters that affect catalytic methane oxidation on a natural gas vehicle were investigated with laboratory aged noble metal catalysts and a simulated vehicle exhaust. These include the air/fuel control strategy, the noble metal loading, the role of base metals and the exhaust hydrocarbon composition. The catalytic performance of several formulations was compared both slightly fuel-rich of the stoichiometric point and under extreme lean conditions. Catalyst formulations different from those used near the stoichiometric point appear to be required if the vehicle is run under extreme lean conditions, such as those found with diesel engines. Under diesel conditions low exhaust temperatures may pose a challenge, since methane requires relatively high temperatures for catalytic oxidation. Spark ignition lean burn engines might offer a higher temperature exhaust, but NOx conversion becomes more problematic in this environment. Increasing the Pd load improves methane and NOx conversions near the stoichiometric point and methane activity under lean conditions. Ce addition was found to be beneficial for aged catalyst performance and increasing the Ce loading resulted in improved methane activity over Pd near the stoichiometric point. For natural gas vehicles run under closed loop control near the stoichiometric point, the composition of the controlled exhaust will modulate around the set point. The effect of the amplitude and frequency of these modulations on methane oxidation was explored. Increasing the frequency or decreasing the amplitude of exhaust modulations results in improved methane conversions, especially near the maximum methane conversion point. The effect of natural gas fuel composition was investigated with feedstreams containing various hydrocarbon mixtures. Small amounts of propane in the feedstream led to increased hydrocarbon conversions lean of the stoichiometric point. This improvement may be due to propane reacting with and removing surface oxygen species, which otherwise block methane adsorption on the catalyst surface. Larger amounts led to improvements in hydrocarbon conversion rich of the stoichiometric point as well, due to the easier oxidation of propane. The information gained from the above studies was used to design a catalyst for a natural gas vehicle tested by the U. S. EPA. With this catalyst, the vehicle achieved California Ultra Low Emmission Vehicule standards.

Performance of Copper Base Metal Catalysts in Stoichiometric Automotive Exhausts

Durability performance characteristics of copper-containing base metal catalysts and base metallow noble metal catalysts have been determined in laboratory and engine aging conditions under well controlled stoichiometric closed-loop AF operation. Cu-Cr base metal formulations yield significant HC and CO conversions under stoichiometric operation after aging at 620/sup 0/C, but deteriorate rapidly at high-temperature (750/sup 0/C inlet) stoichiometric operation. Incorporation of Rh into the base metal formulation substantially improved NO/sub x/ performance, a major weakness of base metal catalysts. The addition of Cu-Cr base metals substantially improves CO oxidation over Pt, Pd, and Rh catalysts but was accompanied by some loss of HC conversion over Pt and Rh. A Cu-CrPd catalyst, however, also had better HC conversions as well as significantly improved light-off performance when compared to a Pd-only catalyst. The stoichiometric operating strategy and performance envelope for base metal catalysts were probed in engine dynamometer and vehicle studies. The aged performance of the Cu containing catalysts is significantly lowered by lean AF preconditioning due probably to sulfur poisoning of Cu at low-temperature lean operating conditions.