Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Patent
1994-10-24
1996-12-03
Beck, Shrive
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
502350, 502439, B01J 802
Patent
active
055805337
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a catalyst according to the preamble of claim 1 for purifying diesel gases. The invention also relates to a method for the manufacture of a catalyst and to a method for purifying diesel exhaust gases.
2. Description of the Background
The exhaust gases of diesel engines contain nitrogen oxides, carbon monoxide, and hydrocarbons. In addition, diesel exhaust gas contains small amounts of SO: gas, which in the operating conditions of an exhaust gas catalyst tends to form, for example, sulphates, which, when depositing on a surface containing noble metals, will weaken the efficiency of the exhaust gas catalyst. Other compounds which are detrimental for the functioning of a catalyst are lead compounds and phosphorus compounds.
Sulphur dioxide gas in itself does not hamper the functioning of a catalyst. However, in the exhaust gas catalysts in diesel engines, sulphur dioxide gas tends to oxidize, whereby sulphur trioxide is formed, and in a moist environment further sulphate. This, in turn, results in the accumulation of sulphur on the catalyst surface and a weakening of the catalytic action. The accumulation of sulphur on the surface of the catalyst is a serious problem in diesel exhaust gas catalysts.
U.S. Pat. No. 5,000,929 discloses a catalyst in which diesel exhaust gases are purified by using the oxides of palladium, praseodymium, neodymium and samarium, and as a support inorganic oxides. These inorganic oxides include active aluminum oxide, silica, titanium dioxide, zirconium oxide, etc., mentioned in the patent. The operating conditions of the above-mentioned catalyst are a high temperature and an oxidizing atmosphere.
EPO publication 0 377 290 discloses a catalyst which is silica-based and removes impurities from diesel exhaust gases by oxidizing carbon monoxide and hydrocarbons into carbon dioxide and water. Both noble metals and promoters are added to the silica support layer. The promoters include gold chloride, silver nitrate, cerium chloride, etc. By means of the invention, the oxidation of SO.sub.2 to SO.sub.3 is decreased to a rather low level.
Patent publication WO-90/00439 discloses a method for lowering the light-off temperature of diesel soot. On the surface of the soot filter there is produced a support layer in which, for example, titanium dioxide is used. The surface of the titanium dioxide is impregnated with a noble metal, which may be Pt, Pd or Rh. The light-off temperature of the soot was lowered by means of such a filter.
Patent publication EP-214 085 discloses a method for the production of a catalyst intended for the elimination of NO.sub.x gases. According to the method, the support is prepared by sintering a mixture of orthotitanic acid and silicic acid. Thereby a TiO.sub.2 with very small crystals is formed. Instead of silicic acid, or in addition to it, a compound of tungsten or molybdenum may be used in the method. By the use of a catalyst which contains no noble metals and which cannot be used for the purification of diesel exhaust gases, NO.sub.x gases can be removed while the oxidation of SO.sub.2 remains insignificant.
The state-of-the-art methods for the manufacture of catalysts have the deficiency that they do not enable production of a noble metal catalyst which would have simultaneously both an efficient conversion of CO and HC gases and a low binding of sulphur, i.e. oxidation of SO.sub.2.
SUMMARY OF THE INVENTION
The object of the present invention is to provide a catalyst in which the binding of the sulphur present in diesel exhaust gas to the catalyst is inhibited and which has an effective conversion of CO and HC gases. A further object is a catalytic unit in which the support adheres well to the metal foil. These objects are achieved by means of the catalyst according to the invention, which is mainly characterized in the facts stated in the characterizing clause of claim 1.
According to the invention there is also provided a method for the manufacture of such a catalyst, in
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Dialog Information Services, File 351, World Patent Index 81-93, Dialog accession No. 009218221,, WPI acession no. 92-345643/42, Cataler Kogyo KK: "Catalysts for reducing diesel particulates discharge--comprises catalyst supporting layer comprising titanium dioxide and e.g. yttrium oxide formed on support base material, and oxidising catalyst", JP 4250848, A, 920907, 9242 (Basic) (Date Unknown).
H ark onen Matti
Kivioja Matti
Maunula Teuvo
Ravola Sointu
Slotte Thomas
Beck Shrive
Kemira Oy
Meeks Timothy H.
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