David R. Monroe

THE EFFECT OF SULFUR ON THREE-WAY CATALYSTS

Abstract Both pelleted and monolithic catalysts have been tested in a laboratory reactor under conditions designed to simulate the operation of the catalyst in a vehicle. The warmed-up and light-off performances of both types of catalyst were deteriorated by the sulfur. The monolithic catalyst rapidly recovered all of the lost activity when sulfur was removed from the feed gas, but the pelleted catalyst only recovered a portion of the lost activity. Examination of the effect of sulfur on Pt, Pd, and Rh indicated that both Pt and Rh rapidly recovered all of its lost activity when sulfur was removed from the feed, but Pd did not. Additionally, a pelleted Pt/Rh catalyst which did not contain any Ce also rapidly recovered all lost activity when sulfur was removed from the feed, but a similar catalyst which contained Ce did not. Hence, the slow recovery from sulfur poisoning is related both to the the high Ce surface area seen in pelleted catalysts and to the presence of Pd. The impact of the sulfur decreased when the cycling frequency was increased and the cycling amplitude decreased, indicating that sulfur will have less of an effect on cars with better A/F control. This result was confirmed in tests which used engine exhaust.

The redispersion of sintered Pt, Rh, and Pt/Rh catalysts

Abstract Sintered Pt/alumina catalysts can be readily redispersed by treatment with chlorine, chlorine/air mixtures, or bromine at temperatures above 400 °C. The redispersion of Pt has been verified by hydrogen chemisorption, high resolution transmission electron microscopy, and catalytic activity measurements. Sintered Rh/alumina catalysts can be redispersed by a chlorine treatment at 500 °C, but only when this treatment is preceded by a hydrogen treatment at or above 700 °C. Sintered bimetallic PtRh/alumina catalysts can be partially redispersed by direct treatment with chlorine at 500 °C and more completely redispersed if the chlorine treatment is preceded by a hydrogen treatment at 700 °C. However, unlike Pt/alumina, improvements in the catalytic activity of Rh/alumina or PtRh/alumina do not necessarily accompany improvements in dispersion. For these catalysts, activity appears to be dominated by the recent oxidation or reduction history of the catalyst.

FUEL SULFUR EFFECTS ON THE PERFORMANCE OF AUTOMOTIVE THREE-WAY CATALYSTS DURING VEHICLE EMISSIONS TESTS

Vehicle exhaust emissions tests, using the Federal Test Procedure, were conducted to deter mine the effect of gasoline sulfur content on the performance of three-way catalysts. The test fuels had sulfur concentrations of 0.01, 0.03, and 0.09 per cent. An increase in the fuel sulfur content from 0.01 to 0.09 percent reduced the conversion of hydro carbons, carbon monoxide, and oxides of nitrogen, resulting in higher tailpipe emissions. The effects were generally small, but statistically significant. The lower conversion was due to poisoning of the catalyst by sulfur species in the exhaust. The poison ing was reversible.

The effect of Pt and Rh loading on the performance of three-way automotive catalysts

The activities of three-way catalysts containing various Pt and Rh loadings have been tested in a laboratory reactor. These tests were performed on the catalysts both when they were fresh and following aging in engine exhaust. Increasing the Pt and Rh loadings from 0.1 wt% and 0.01 wt%, respectively, to 0.2 wt% and 0.02 wt%, respectively, resulted in improved catalyst lightoff and improved warmed-up performances during A/F ratio cycling for both the fresh and the aged catalysts. Increasing only the Rh loading of these bimetallic catalysts resulted in a greater improvement in the lightoff and warmed-up NO conversion efficiencies than resulted from increasing only the Pt loading. Increasing the Pt loading, however, resulted in a greater improvement in the warmed-up CO conversion efficiencies than did increasing the Rh loading. Increasing either the Pt or the Rh loading resulted in similar improvements in the warmed-up HC conversion efficiencies.

THE PERFORMANCE OF PD, PT, AND PD-PT CATALYSTS IN LEAN EXHAUST

A matrix of pelleted catalysts composed of Pt, Pd, Pt co- impregnated with Pd, and Pt physically mixed with Pd supported on Al2O3 were compared with the same noble metal formulations supported on CeO2/Al2O3 for lightoff and warmed-up performance in net lean exhaust. These catalysts were tested as prepared (fresh) and following a relatively severe thermal aging treatment (cycled between net lean and net rich environment at 1000 degrees C for 4 h). Pd showed better lightoff performance than Pt for catalyzing the oxidation of propylene, while Pt showed better lightoff and warmed-up performance than Pd for catalyzing the oxidation of propane. Having both Pt and Pd present as a result of co-impregnation or physical mixture results in good lightoff and warmed-up performance for the conversion of both types of hydrocarbons. The presence of CeO2 generally decreases lightoff performance for most of these catalysts. (A) For the covering abstract see IRRD 858138.

Dynamic Measurement of Carbon Monoxide Concentrations in Automotive Exhaust Using Infrared Diode Laser Spectroscopy

Infrared diode laser spectroscopy was used to make the first measurements of carbon monoxide (CO) concentration in automotive exhaust with a time response fast enough to be useful in the analysis of engine and emission control system dynamics. Carbon monoxide concentrations were measured before and after a three-way catalytic converter. The response time of the laser system (for a change in amplitude of 10%-90% of fullscale) was 25 ms, more than adequate to resolve all CO transients of interest. The instrument was capable of resolving concentration changes on the order of 0.1 vol % before the catalyst and 0.02 vol % after it. A minicomputer was used to simultaneously collect data on CO concentrations before and after the catalyst, and also the output of an oxygen sensor located in the exhaust line.

Axial Characterization of Lightoff and Underfloor Catalytic Converters Vehicle-Aged on a 5.7 L Corvette

Catalysts taken from the lightoff and underfloor converters of two 1986 Corvette exhaust systems which had been vehicle-aged for 100,000+ miles were cut into 1 inch thick sections along their axis and characterized for lean lightoff and warmed-up performance using a laboratory reactor. Sections were then treated to remove the poisons, and the characterization was repeated. An axial gradient in both lightoff and warmed-up conversion efficiency for HC and CO was, detected within the first 2 inches of both lightoff converters for both vehicles. This activity gradient is in agreement with the gradient in the phosphorus and zinc concentrations found in the front 2--3 inch sections of the lightoff converters. Comparison of these data sets with those obtained after removal of the P and Zn poisons led the authors to conclude that a significant part of the total deterioration of activity can be attributed to phosphorus and zinc poisoning for the front 1 inch (and to a lesser extent for the second 1 inch section) of the lightoff converters.