According to the present invention, there is provided an exhaust gas purification device for an engine having an exhaust passage, the device comprising a catalyst arranged in the exhaust passage and having an upstream end and a downstream end, a purification ratio of exhaust gas by the catalyst becoming more than a predetermined ratio when a temperature of the catalyst is within a predetermined temperature range, cooling means for cooling the upstream end of the catalyst, heating means for heating the downstream end of the catalyst, and control means for controlling the cooling means and the heating means to maintain the temperature of a portion of the catalyst, which portion is positioned between the upstream end and the downstream end, in the predetermined temperature range.

An exhaust gas purification device for an internal combustion engine

An exhaust gas-purifying catalyst includes a substrate, and a catalytic layer facing the substrate and including a precious metal, alumina, an oxygen storage material, and a sulfate of an alkaline-earth metal having an average particle diameter falling within a range of 0.01 to 0.70 μm, the average particle diameter being obtained by observation using a scanning electron microscope. Another exhaust gas-purifying catalyst includes a substrate, and a catalytic layer formed on the substrate using slurry containing a precious metal, alumina, an oxygen storage material, and a sulfate of an alkaline-earth metal having an average particle diameter falling within a range of 0.01 to 0.70 μm, the average particle diameter being obtained by observation using a scanning electron microscope.

Exhaust gas purifying catalyst

The exhaust gas purification device according to the present invention utilizes two NO x absorbents in order to remove NO x from the exhaust gas of an engine operated at a lean air-fuel ratio. The NO x absorbents are disposed, in series, in the exhaust passage of the engine and a nozzle for supplying a reducing agent is disposed in the exhaust passage at a position between the two NO x absorbents. Further, the device includes switching valves for changing the direction of the exhaust gas flow in the exhaust gas passage. When the switching valves are set to direct the exhaust gas flow to one direction, the exhaust gas first flows through one of the NO x absorbents (first NO x absorbent), and after passing through the first NO x absorbent, the reducing agent is supplied to the exhaust gas before it flows into the other NO x absorbent (second NO x absorbent). Thus, the first NO x absorbent absorbs NO x in the exhaust gas, and the NO x absorbed by the second NOabsorbent is released from the second NO x absorbent. When the switching valves are switched, the exhaust gas flows in the opposite direction, and flows through the second NO x absorbent and the first NO x absorbent in this order. In this case, the second NO x absorbent absorbs NO x in the exhaust gas, and the NO x absorbed by the first NO x absorbent is released and reduced to N 2 . Therefore, by reversing the direction of the exhaust gas periodically, the absorbing operation of NO x and releasing/reducing operation of NO x are performed by two NO x absorbents alternately. Thus, it becomes possible to remove NO x in the exhaust gas continuously while the NO x absorbents are prevented from being saturated by the absorbed NO x .

Exhaust gas purification device for an engine

In the present invention, the exhaust gas from the engine (1) is divided into a first (4a) and a second branch (4b) exhaust passages after it passes through a three-way reducing and oxidizing catalyst (11), and the two branch exhaust passages merge into an exhaust gas outlet passage (5). In the first branch exhaust passage (4a), an oxidizing catalyst (13) is disposed, and in the exhaust gas outlet passage (5), a denitrating and oxidizing catalyst (15) is disposed. NOX in the exhaust gas from the engine is all converted to N₂ and NH₃ by the three-way reducing and oxidizing catalyst (11) and a part of the NH₃ generated by the three-way catalyst flows into the first branch exhaust passage (4a) and is converted to NOX again by the oxidizing catalyst (13). The amount of NOX produced by the oxidizing catalyst (13) and the amount of NOX flowing through the second branch exhaust passage (4b) is determined by the flow distribution ratio of the first and the second branch exhaust passages. In this invention, the flow ratio is determined in such a manner that the amount of the NOX produced by the oxidizing catalyst (13) and the amount of the NH₃ passing through the second branch exhaust passage (4b) are stoichiometric to produce N₂ and H₂O. Therefore, when these exhaust gases flow into the denitrating and oxidizing catalyst (15) after they mix with each other in the exhaust gas outlet passage (5), all the NOX and the NH₃ are converted to N₂ and H₂O by the denitrating and oxidizing catalyst (15) without producing any surplus NOX or NH₃.

An exhaust gas purification device for an engine

An engine (1) has first and second cylinder groups (1a) and (1b). The first cylinder group (1a) is connected to a three way (TW) catalyst (8a). The second group (1b) and the TW catalyst (8a) are connected, via an interconnecting duct (13) to an NH3 adsorbing and oxidizing (NH3-AO) catalyst (14a). The first group (1a) performs the rich operation, and the second group (1b) performs the lean operation. In the TW catalyst (8a), NO x exhausted from the first group (1a) is converted to NH3, and the NH3 reduces the NO x exhausted from the second group (1b) in the NH3-AO catalyst (14a). A NO x occluding and reducing (NO x-OR) catalyst (11a) is arranged in the exhaust passage between the second group (1b) and the interconnecting duct (13), to thereby suppress the NO x amount flowing into the NH3-AO catalyst (14a).

Method and device for purifying exhaust gas of engine

A METHOD IS PROPOSED FOR THE REDUCTION OF NITROGEN OXIDES IN EXHAUST GASES FROM INTERNAL COMBUSTION ENGINES TO SELECTIVELY FORM NITROGEN AS SUBSTANTIALLY THE ONLY NITROGEN-CONTAINING PRODUCT. THE METHOD COMPRISES CONTACTING AN EXHAUST GAS FROM AN INTERNAL COMBUSTION ENGINE AT AN ELEVATED TEMPERATURE IN A REDUCING ATMOSPHERE WITH RHODIUM AND RUTHENIUM.

B Taylor

Papers

Process for reducing the content of nitrogen oxides in the exhaust gases from internal combustion engines