Abstract: A catalyst for purifying an exhaust gas for simultaneously removing carbon monoxide, hydrocarbons and nitrogen oxides contained in the exhaust gas under an oxygen rich atmosphere, comprising a carrier composed of a porous material, and barium oxide, lanthanum oxide and platinum supported on the carrier, and a method for purifying an exhaust gas by bringing the exhaust gas under an oxygen rich atmosphere into contact with the above-mentioned catalyst.

Abstract: An exhaust gas purification device of an engine providing a NO.sub.x absorbent arranged in the exhaust passage. An O.sub.2 sensor is arranged in the engine exhaust passage downstream of the NO.sub.x absorbent. The degree of deterioration of the NO.sub.x absorbent is detected from the output signal of the O.sub.2 sensor. The cycle for making the air-fuel ratio of the air-fuel mixture rich for causing the release of the NO.sub.x from the NO.sub.x absorbent and the rich time at that time are shortened the greater the deterioration of the NO.sub.x absorbent.

Abstract: An exhaust purification device of an engine providing a NO.sub.x absorbent arranged in the exhaust passage. An O.sub.2 sensor generating a current proportional to the air-fuel ratio is arranged in the engine exhaust passage downstream of the NO.sub.x absorbent. The amount of NO.sub.x actually absorbed in the NO.sub.x absorbent at the time of release of the NO.sub.x is calculated on the basis of the output signal of this O.sub.2 sensor. On the basis of this calculated amount of NO.sub.x, correction is made so that the estimated amount of NO.sub.x represents the actual amount of absorption of NO.sub.x. When this corrected estimated amount of NO.sub.x reaches a set value, the action of releasing the NO.sub.x from the NO.sub.x absorbent is carried out.

Abstract: A device for detecting deterioration of a NO.sub.x absorbent arranged in the exhaust passage of an engine. An O.sub.2 sensor generating a current proportional to the air-fuel ratio is arranged in the exhaust passage downstream of the NO.sub.x absorbent. When the amount of NO.sub.x absorbed in the NO.sub.x absorbent is almost zero or after the amount of NO.sub.x absorbed in the NO.sub.x absorbent is made almost zero, the air-fuel ratio of the air-fuel mixture is changed from lean to rich, and the amount of oxygen stored in the NO.sub.x absorbent is detected from the output signal of the O.sub.2 sensor at this time. Further, the NO.sub.x absorbing capability is found by using this detected oxygen amount.

Abstract: An exhaust purification device which is capable of detecting the degree of deterioration of the NOx absorbent or the three-way catalyst arranged in the exhaust passage of an engine. An O.sub.2 sensor whose output current or output voltage is proportional to the air-fuel ratio is arranged inside the exhaust passage downstream of the NOx absorbent or three-way catalyst. The air-fuel ratio of the air-fuel mixture is temporarily changed from lean to rich or from rich to lean to enable the degree of deterioration of the NOx absorbent or three-way catalyst to be detected from the peak value of the output current or voltage of the O.sub.2 sensor during the time when the air-fuel ratio is changed.

Abstract: An NO.sub.x absorber (18) is arranged in an exhaust passage of an internal combustion engine. The NO.sub.x absorber (18) absorbs the NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorber (18) is lean while releases the absorbed NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorber (18) becomes the stoichiometric air-fuel ratio or rich. An air-fuel ratio sensor (22) is arranged in the exhaust passage downstream of the NO.sub.x absorber (18). When the air-fuel ratio detected by the air-fuel ratio sensor (22) is switched from lean to rich after the air-fuel ratio of the exhaust gas flowing into NO.sub.x absorber (18) is switched from lean to rich, it is decided that the releasing action of NO.sub.x from the NO.sub.x absorber (18) is completed.

Abstract: An engine comprising an exhaust passage having therein a NO.sub.x absorbent which absorbs the NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent is lean and releases the absorbed NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent becomes the stoichiometric air-fuel ratio or rich. A sulphur trapping device for trapping SO.sub.x contained in the exhaust gas is arranged in the exhaust passage upstream of the NO.sub.x absorbent.

Abstract: A NO.sub.x absorbent (17) is disposed in an exhaust passage of an internal combustion engine. This NO.sub.x absorbent (17) absorbs the NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent (17) is lean and releases the absorbed NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent (17) becomes rich. When making the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent (17) rich to release the NO.sub.x from the NO.sub.x absorbent (17), the degree of richness is made larger and the time the ratio is made rich is made shorter the higher the temperature of the NO.sub.x absorbent (17).

Abstract: An engine comprising an exhaust passage having therein a NO.sub.x absorbent which absorbs the NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent is lean and releases the absorbed NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent becomes the stoichiometric air-fuel ratio or rich. When the air-fuel ratio of the air-fuel mixture should be changed over from lean to the stoichiometric air-fuel ratio, the air-fuel ratio of the air-fuel mixture is temporarily made rich and is then made the stoichiometric air-fuel ratio.

Abstract: A NO.sub.x absorbent (18) which absorbs the NO.sub.x when the air-fuel ratio of the exhaust gas flowing into the NO.sub.x absorbent (18) is lean and releases the absorbed NO.sub.x when the oxygen concentration of the exhaust gas flowing into the NO.sub.x absorbent (18) is lowered, is arranged in the exhaust passage of the engine. The amount of alkali metals, alkali-earth metals or rare-earth metals contained in the NO.sub.x absorbent (18) positioned on the downstream side, is made lower than the amount of alkali metals, alkali-earth metals or rare-earth metals contained in the NO.sub.x absorbent (18) positioned on the upstream side, to increase a reducing ability of the NO.sub.x absorbent (18) positioned on the downstream side as compared to the reducing ability of the NO.sub.x absorbent (18) positioned on the upstream side.

Abstract: An NOx absorbent is installed in an exhaust conduit of an internal combustion engine capable of fuel combustion at lean air-fuel ratios. An oxygen concentration is repeatedly or continuously decreased by, for example, switching the air-fuel from the lean air-fuel ratio to a stoichiometric or rich air fuel ratio when the exhaust gas temperature is higher than 550.degree. C. or when NOx absorbent temperature is higher than 500.degree. C. As a result, the SOx absorbed in the NOx absorbent during lean air-fuel ratio, low temperature operation is released from the NOx absorbent, and the SOx-poisoned NOx absorbent is recovered.

Abstract: An exhaust gas purification system includes a transition metal/zeolite first catalyst, a three-way second catalyst, and a noble metal-type third catalyst arranged in that order in the direction of exhaust gas flow in an exhaust conduit of an internal combustion engine capable of fuel combustion at lean air-fuel ratios. NOx which has not been purified by the transition metal/zeolite first catalyst is oxidized by the three-way second catalyst into NO.sub.2, which the noble metal-type third catalyst can easily decompose into N.sub.2 and O.sub.2.