EP0970165B1

EP0970165B1 - Method for reducing emissions from a gasoline engine equipped with a three-way catalytic converter

Info

Publication number: EP0970165B1
Application number: EP98908457A
Authority: EP
Inventors: Jeremy D. Peter-Hoblyn; James M. Valentine; Barry N. Sprague
Original assignee: Clean Diesel Technologies Inc
Current assignee: Clean Diesel Technologies Inc
Priority date: 1997-01-31
Filing date: 1998-01-30
Publication date: 2004-11-24
Anticipated expiration: 2018-01-30
Also published as: WO1998033871A1; DE69827778D1; TW499475B; EP0970165A1; ES2232936T3; EP0970165A4; DE69827778T2; ATE283333T1; US20010001354A1

Abstract

Gasoline engines equipped with three-way catalysts emit less NOx, hydrocarbons and carbon monoxide when operated on fuels containing a bimetallic catalyst comprising rhodium acetylacetonate and a fuel-soluble platinum compound such as diphenyl cyclooctadiene platinum(II) or platinum acetyl acetonate. The total metals in the additive will be dosed at a concentration of less than about 2 ppm (milligrams of metal to liter of gasoline) based on the amount of gasoline burned in the engine. Preferred dosages will be from about 0.15 to about 1.5 ppm, with a ratio of platinum to rhodium of from about 3:1 to about 15:1.

Description

The invention relates to methods that enable reduction of emissions while permitting a gasoline engine to operate efficiently.

The use of three-way catalytic converters for gasoline-powered engines has become the standard. The life of these converters is often less than the life expected of the vehicles in which they are installed, due to attrition, poisoning, masking, sintering and mechanical damage. But, even when they lack the requisite activity to meet regulatory compliance, they still contain significant amounts of catalytic metals. Replacement is expensive and wasteful. And, unfortunately, many vehicles are and will continue to be driven long after they become environmental hazards.

The art has endeavored to provide an additive for gasoline, which could be used for an entire fleet to maintain a suitable level of catalyst activity. It has further looked for a specific additive that could be added to gasoline at a suitable dosage to renew the activity of a catalytic converter that has lost vigor. This search has been difficult because effectiveness for one purpose must be balanced with other factors such as chemical composition necessary to deliver the catalyst to the catalytic converter at a cost that is practical and safe in terms of toxicity and handling. This cost has been found to be a matter of initial synthesis as well as to the presence of incompatible chemical species. Other factors that need to be balanced include the requirement that the added chemical compositions not damage or alter in a negative way components and functions of the engine and its emission control system.

Moreover, the search for effective catalytic fuel additives for improving the operation of a catalytic converter is a difficult technical problem because treatment of the various gaseous exhaust species presents conflicting requirements. For example, lowering emissions of hydrocarbons and carbon monoxide are chemical oxidation problems while lowering emissions of NO_x is a chemical reduction problem.

There is a current need for an effective gasoline additive that can be produced and utilized at reasonable cost to maintain and/or restore the effectiveness of a catalytic converter while avoiding problems of the prior art.

Catalytic converters are standard on gasoline-powered automobiles in countries where regulators are aggressively attempting to control air quality. Many attempts have been made to balance their cost and effectiveness over reasonable periods of operation and the determination of effective catalyst compositions has progressed to the point that it is generally understood that combinations of platinum, palladium and rhodium are required. The procedures for catalyzing new catalytic converters are also fairly well worked out. In addition, several attempts have been made to renew them during operation. To this end several gasoline additives have been mentioned.

In U. S. Patent No. 5,034,020, Epperly, et al., disclose a variety of fuel-soluble platinum group metal fuel additives, adding to the materials disclosed in earlier Bowers, et al., U. S. patents 4,892,562 for diesel fuel and 4,891,050 for gasoline. In the Epperly, et al., patent, it was noted that the additives could provide improved operation of a catalytic converter; however, all of the compounds referenced appear to require expensive synthesis procedures.

In WO 94/2293, Shustorovich, et al., noted that the Bowers' disclosure in U. S. Patent No. 4,891,050 tested only compounds containing ligands with unsaturated C-C bonds, and asserted that it did not teach any catalytic effect outside of the combustion chamber. As their solution to the problem, they disclosed that both noble precious metals (e.g., platinum, palladium, gold, rhodium) and non-noble metals (preferably, rhenium) could be directly dissolved in gasoline (from a solid preform) to catalyze a catalytic converter. The metal compounds have polar metal-ligand bonds, preferably formed by purely inorganic ligands such as halogens, oxygen, etc. The preferred compounds of platinum "are alkali salts of platinum hydrochloric acid X₂PtCl₆, where X is" potassium, rubidium or cesium. Applicants have determined, however, that the chlorides have several disadvantages, among which are a corrosive effect on the exhaust system, including certain catalyst supports, and a tendency to release catalyst metals from a catalyst support due to a decrease in the vapor pressure of the metal compounds. In addition, chlorides can present negative health and safety issues. Moreover, the concept of modulating concentration by varying the surface contact appears problematic in view of an expected variation of solubility with temperature and fuel composition.

Despite the industry's successful work on providing effective catalytic converters with creditable durability, there has not been the same degree of success with the identification of a specific bimetallic catalyst rejuvenator that could be directly added to gasoline for effective and economical effect.

It is an object of the invention to enable owners of old, but reliable vehicles with an easy and effective means for maintaining regulatory compliance.

It is a further object of the invention to provide a method for maintaining or renewing the activity of a three-way catalytic converter.

These and other objects are achieved by the present invention, which provides a process for maintaining or renewing the activity of a three-way catalytic converter.

The method for renewing or improving the performance of a three-way catalytic converter operated on a gasoline engine according to the invention comprises: feeding a gasoline composition, comprising a blend of rhodium acetylacetonate and a fuel-soluble organo-platinum compound comprising diphenyl cyclooctadiene platinum(II) and/or platinum acetylacetonate, the platinum and rhodium compounds being present in amounts sufficient to provide a ratio of platinum to rhodium within the range of from 3:1 to 15:1, to a combustion chamber of the engine where the fuel is combusted and the organic portions of the rhodium and platinum compounds are oxidized, thereby releasing the rhodium and platinum as active catalyst species in exhaust gases generated by the combustion; and
passing the exhaust gases through the catalytic converter whereby rhodium and platinum are deposited in the catalytic converter to thereby renew it in terms of the ability to oxidize hydrocarbons and carbon monoxide and to reduce nitrogen oxides.

The invention will be better understood and its advantages will be more apparent when the following detailed description is read in light of the accompanying drawings, wherein:

The Figure is a graphical presentation of the results of engine tests run with the gasoline additive of the invention.

The invention relates to gasoline engines equipped with three-way catalytic converters. This type of catalyst has become standard in the United States and many other countries for reducing the emissions of gaseous hydrocarbons, carbon monoxide and NO_x. They typically have functions effective for both chemical reduction of the NO_x and chemical oxidation of the hydrocarbons and carbon monoxide. They are required by various regulatory bodies to meet specific standards. Those numerical limits are not intended to limit the definition of the "three-way catalytic converter" as set forth above.

Gasoline is defined herein to have its usual meaning and to include those fuels defined as such by the ASTM and European standards and is intended to include all fuels capable of operating an engine of the Otto type. Typically, these will be hydrocarbon fuels which are characterized as having a boiling point within the gasoline fraction range, e.g., from 32,22 to 104,44°C (90 to 220° F), and will typically contain additives to increase the oxygen content, improve octane and maintain the engine free of deposits that would tend to decrease engine performance.

Gasoline engines equipped with three-way catalysts emit less NO_x hydrocarbons and carbon monoxide when operated on fuels containing a bimetallic catalyst comprising rhodium acetylacetonate and a fuel-soluble platinum compound comprising diphenyl cyclooctadiene platinum(II) and/or platinum acetyl acetonate. The total metals in the additive will be dosed at a concentration of less than about 2 ppm (e.g., 0.01 to 2 ppm based on the weight of metal in milligrams to volume of fuel in liters). Higher doses, e.g., up to about 10 ppm can be employed for shock treatments. The additives will contain the appropriate concentrations of the metal compounds to give the appropriate dosage based on the amount of gasoline burned in the engine. Preferred dosages will be from about 0.15 to about 1.5 ppm, with a ratio of platinum to rhodium of from about 3:1 to about 15:1. In addition to the catalytic metal compositions, the compositions of the invention will preferably include a gasoline-miscible solvent such as mineral spirits, toluene and isopropyl alcohol.

The preparation of the ligand-containing materials identified above is set out in the above patents to Bowers, et al., and Epperly, et al. The disclosures of these patents are incorporated herein by reference. The rhodium and platinum acetylacetonate compounds are commercially available and easily synthesized. Preferably, the composition will be temperature stable, and substantially free of phosphorus, arsenic, antimony, or halides.

To achieve the advantages of the invention, a gasoline engine is fed a gasoline composition including the bimetallic catalyst composition of the invention. The gasoline is combusted in a combustion chamber of the engine and the organic portions of the rhodium and platinum compounds are oxidized, thereby releasing the rhodium and platinum as active catalyst species in exhaust gases generated by the combustion. The resulting exhaust gases are then passed through the catalytic converter whereby rhodium and platinum are deposited in the catalytic converter in active form.

Tests with several gasoline-powered engines having exhaust systems equipped with three-way catalytic converters showed improved emissions reductions when the fuel contained a bimetallic catalyst additive containing rhodium acetyl acetonate and a fuel-soluble platinum compound.

EXAMPLE

This example is presented to further illustrate and explain the invention and is not to be taken as limiting in any regard. Unless otherwise indicated, all parts and percentages are by weight.

Four automobiles equipped with three-way catalytic converters were operated on a gasoline composition according to the invention containing rhodium acetylacetonate (0.15 ppm) and diphenyl cyclooctadiene platinum(II) (0.80 ppm). The results are reported graphically in the attached Figure.

Rhodium acetylacetonate is a commercially available material, and is unexpectedly effective when used in combination with a fuel-soluble platinum compound in the composition and method of the invention.

The above description is for the purpose of teaching the person of ordinary skill in the art how to practice the present invention, and it is not intended to detail all of those obvious modifications and variations of it which will become apparent to the skilled worker upon reading this description. It is intended, however, that all such obvious modifications and variations be included within the scope of the present invention which is defined by the following claims.

Claims

A method for renewing or improving the performance of a three-way catalytic converter operated on a gasoline engine, comprising:

feeding a gasoline composition, comprising a blend of rhodium acetylacetonate and a fuel-soluble organo-platinum compound comprising diphenyl cyclooctadiene platinum(II) and/or platinum acetylacetonate, the platinum and rhodium compounds being present in amounts sufficient to provide a ratio of platinum to rhodium within the range of from 3:1 to 15:1, to a combustion chamber of the engine where the fuel is combusted and the organic portions of the rhodium and platinum compounds are oxidized, thereby releasing the rhodium and platinum as active catalyst species in exhaust gases generated by the combustion; and

passing the exhaust gases through the catalytic converter whereby rhodium and platinum are deposited in the catalytic converter to thereby renew it in terms of the ability to oxidize hydrocarbons and carbon monoxide and to reduce nitrogen oxides.