Studies of Catalyst Degradation in Automotive Emission Control Systems

Hunter, Joseph E.

doi:10.4271/720122

Cited by 27 publications

(2 citation statements)

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“…Sulfur dioxide poisoning is a serious problem both in the oxidation of CO and hydrocarbons and reduction of NO over base metal oxide catalysts (Hunter, 1972;Fishel, et al, 1973; Leech and Campbell, 1974). In reduction by noble metal alloy catalysts the effect of SO2 is less dramatic in lowering the pollutant conversions as illustrated by data in Figure 2, a plot of pollutant conversions vs. time for Pd-Ru.…”

Section: Resultsmentioning

confidence: 99%

Reduction of Nitric Oxide by Monolithic-Supported Palladium-Nickel and Palladium-Ruthenium Alloys

Bartholomew¹

1975

Product R&D

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added to the feed stream. This experiment simulates the conditions as they would exist halfway through the reactor and bears directly on the question of ammonia intermediacy since it determines the efficiency of the catalyst to remove ammonia under reaction conditions (Bemstein, et al., 1973).The results for the ammonia addition experiments are dramatically different for the two states of the catalyst (Figure 7). Thus, most of the ammonia passes through the reactor unchanged when the catalyst is in the reduced state. In contrast for the oxidized catalyst, the ammonia did not pass through the reactor but was efficiently removed at temperatures above 350°C. The presence of only 350 ppm of NH3 in the product a t -250°C is due to our inability to analyze for NH3 in the presence of large amounts of NO. An NH3-NO reaction over the Pt catalyst used t u oxidize NH3 back to NO for the NH3 analysis results in a decrease in the amount of NH3 determined. This problem does not exist at higher temperatures where all the N O is reacted. These additional ammonia experiments strongly support the intermediacy of ammonia for oxygen-treated Ru-Al203. The fact that the added ammonia does not affect the temperature of NO removal ( Figure 7) argues against a change in the mechanism for NO removal with the added "3.It has been suggested though that an NO-NH3 mechanism may operate at low temperature to some extent all the time (Otto and Shelef, 1973).In both states ruthenium is very selective in the conversion of nitric oxide to molecular nitrogen. The unique selectivity of ruthenium catalysts in NO reduction is undoubtedly related to the unique chemistry of ruthenium with nitrogen ligands (Cotton and Wilkinson, 1972). Thus, the strong NO-ruthenium bonding as well as the remarkable interactions of Nz with ruthenium are consistent with the Nz selectivity of ruthenium catalysts in NO reduction.Ammonia intermediacy does not appear to be involved in NO reduction over reduced Ru-Alz03 (Taylor and Klimisch, 1973) and is only a minor pathway to nitrogen over the oxygen treated Ru-Al203 catalyst. Acknowledgment of Mr. R. M. Sinkevitch in all aspects of this work. Literature CitedThe authors acknowledge the indispensable assistanceThe effect of reaction parameters such as temperature, space velocity, and pollutant concentration on the performance of monolithic-supported Pd-Ni and Pd-Ru alloys in reduction of NO has been studied in a laboratory reactor. Freshly prepared Pd-Ni and Pd-Ru catalysts convert 100% NO (1000 ppm) with less than 5% ammonia formation in 0.4% 0 2 (1% CO and 250 ppm of C3H6) at 600 and 480°C, respectively. Conversions of NO, CO, and C3H6 decrease slightly with increasing space velocity. The effect of dynamic exposure to 100 ppm of SO2 is to lower slightly but reversibly the NO and C3H6 conversions while significantly and irreversibly lowering conversion of CO. After 100 hr of exposure in a reducing en ine exhaust the conversions of NO, CO, and C3H6 over monolithic-supported Pd-Ru/AlzOp and Pd-NiaNiAlz04 are lowered 5-20% c...

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Section: Resultsmentioning

confidence: 99%

Reduction of Nitric Oxide by Monolithic-Supported Palladium-Nickel and Palladium-Ruthenium Alloys

Bartholomew¹

1975

Product R&D

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“…In addition to the requirement of high intrinsic activity, automotive catalysts must resist the irreversible loss of active sites in order to meet durability requirements. Three serious site deactivating conditions common to the automotive situation, thermal aging (Aykan et al, 1973), SO2 poisoning (Hunter, 1972), and reaction of catalyst with AI2O3 support material (Summers and Klimisch, 1973) were examined. The thermal aging treatment led, in varying degrees, to the deactivation of all catalysts.…”

Section: Discussionmentioning

confidence: 99%

Lanthanum Lead Manganite Catalyst for Carbon Monoxide and Propylene Oxidation

Katz¹,

Croat²,

Laukonis³

1975

Product R&D

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The activity of single crystal lanthanum lead manganite (La0.7Pbo.3Mn03) was compared to Pt/Al203, Co304, and CuO under conditions important to automotive emission control. In simulated automotive exhaust ambients, the observed order of activity of fresh catalyts toward both CO and C3H6 oxidation was found in general to be: Pt/Al203 > Co304 > La0.7Pbo.3Mn03 > CuO. Pt/Al203 remained the most active of the materials throughout tests In which the susceptibility of catalysts to various modes of deactivation, namely, high temperature exposure, S02 poisoning and reaction with -203, was measured. The results for the single crystal manganite catalyst showed it to be susceptible to thermal deactivation but resistant to S02 poisoning. Manganite was also found to react extensively with • 203 at 1000°C suggesting potential difficulties with supported catalysts.Basic differences were found between the properties of single crystal and polycrystalline forms of La0.7Pbo.3Mn03. They showed different oxidation kinetics and the specific catalytic activity of the single crystals was found to be roughly 100 times higher than the polycrystalline materials. The data suggest that the enhanced activity might be due to the presence of small quantities of Pt. In addition to single crystal LaojPbo.sMnOs and Pt/ AI2O3, two base metal catalysts, C03O4 and CuO, were included in the study to broaden the scope by which the activity of manganite catalysts could be assessed. The activity of polycrystalline Lao^Pbo.sMnOs materials was also investigated. Experimental SectionMaterials. A total of four manganite samples were investigated. These included two samples of crushed Lao.7Pbo.3Mn03 single crystals (37-250 µ ) which were grown from a lead borate flux in a Pt crucible and subsequently etched 3-5 min in hot (80°C) 20% nitric acid (Voorhoeve et al., 1973). The two samples were prepared at different laboratories. The first (sample A) was obtained from J. P. Remeika (Bell Telephone Laboratories), and the second (sample B) was prepared by the authors. The remaining samples were polycrystalline. Sample C was prepared from coprecipitated hydroxides which were calcined in A1203 crucibles for 24 hr at 600°C and etched 5 min in hot (50°C) 15% nitric acid (Voorhoeve et al., 1973). Testing was conducted on particles in the 149-250-µ range. Samples A-C were found by X-ray diffraction analysis to be single phase material with well defined perovskite structures.

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Catalytic automotive exhaust aftertreatment

Koltsakis

1997

Progress in Energy and Combustion Science

316

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Studies of Catalyst Degradation in Automotive Emission Control Systems

Cited by 27 publications

References 1 publication

Reduction of Nitric Oxide by Monolithic-Supported Palladium-Nickel and Palladium-Ruthenium Alloys

Reduction of Nitric Oxide by Monolithic-Supported Palladium-Nickel and Palladium-Ruthenium Alloys

Lanthanum Lead Manganite Catalyst for Carbon Monoxide and Propylene Oxidation

Catalytic automotive exhaust aftertreatment

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