摘要:
A catalyst for purifying exhaust gases includes a porous support; a cerium oxide or a solid solution of a cerium oxide and a zirconium oxide in a state of mutual solid solution, loaded on the porous support; and a noble metal element loaded on the porous support. The cerium oxide or the solid solution has an average particle diameter of from 5 to 100 nm. The cerium oxide is present in the solid solution in an amount of from 0.2 to 4.0 by molar ratio with respect to the zirconium oxide therein. The catalyst can be prepared by: coating and calcinating on a support substrate a slurry of a cerium oxide sol, a cerium oxide sol and a zirconium oxide sol, on a solid solution powder of a cerium oxide and a zirconium oxide in a state of mutual solid solution; and loading a noble metal element thereon. The cerium oxide or its solid solution has a surface area large enough to effect an oxygen storage function, and has an average particle diameter large enough to prevent the same from entering deeply into fine pores of a porous support, thereby providing a catalyst fully exhibiting both of the oxygen storage capability and the catalytic activity.
摘要:
A solid solution particle of oxides contains a solid solution of oxides in which one oxide is dissolved into the other oxide, and in which the degree of dissolution of one oxide into the other oxide is not less 50%, and in which an average diameter of crystallite is not more than 100 nm. The solid solution particle of oxides has small average diameter of a crystallite and large specific surface area, and it improves capacities such as an oxygen storage ability due to high degree of dissolution. A catalyst for purifying exhaust gases has excellent purifying performance by employing the solid solution comprising ceria and zirconia which has large OSC and high oxygen adsorption and discharge speed.
摘要:
A method for producing a catalyst having high catalytic activity even at high temperatures of 1200.degree. C. or higher. Fine alumina particles, of which 50% by weight or more have a particle size of 100 nm or less, are mixed with a catalytic component and a substance of inhibiting the sintering of fine alumina particles to form a slurry mixture. This slurry is dried and then calcined to obtain a porous catalyst. The fine alumina particles in the porous catalyst have a large specific surface area even at high temperatures and therefore the porous catalyst maintains its high catalytic activity even at high temperatures of 1200.degree. C. or higher.
摘要:
An exhaust gas purifying catalyst for oxidizing HC and CO and for reducing NOx is provided, which comprises at least one oxide of rare earth element, rhodium, and at least one of platinum and palladium loaded on alumina grains. The major amount of rhodium is dispersed on the oxide of rare earth element. Thus, the rhodium solidification into the alumina grains is prevented. Further, when cerium oxide accompanying lanthanum oxide, neodymium oxide or a mixture thereof is used as the oxide of rare earth element, the sintering of cerium oxide or palladium at a high temperature is suppressed since it forms a complex oxide with lanthanum oxide, neodymium oxide or a mixture thereof. Additionally, when stabilized alumina grains in which a rare earth element and an alkali earth element are present in a solid solution state are used, the deterioration of NOx purifying activity of the catalyst at a high temperature is suppressed. The exhaust gas purifying catalyst of this invention has high durability as well as high activity at a high temperature.
摘要:
This composite oxide powder can secure a large pore volume even after calcination at high temperature and, when a catalyst is formed by loading a noble metal on this composite oxide powder, noble metal grain growth can be suppressed. The composite oxide powder comprises particles of an oxide of a metal M1 and an oxide of a metal M2 which does not dissolve in the oxide of the metal M1, the oxide of the metal M1 and the oxide of the metal M2 being dispersed at the nanometer level. Since different oxides serve as a barrier to each other, sintering is suppressed. Therefore, in the case of composite oxide powder comprising Ce as a metal M1 and Al as a metal M2, grain growth is small even after exposed to high temperature and pores of 3.5-100 nm secure a volume of 0.07 cc/g or more after calcination at 600° C. for 5 hours and a volume of 0.04 cc/g or more after calcination at 800° C. for 5 hours.
摘要:
A composite oxide includes CeO2, ZrO2 and a metallic oxide being free from reacting with CeO2 and ZrO2 at 700° C. or more, preferably at 900° C. or more and further preferably at 1,000° C. or more. The composite oxide has a regulatory oriented phase, such as a pyrochlore phase, etc., in which at least a part of Ce cations and Zr cations are oriented regularly. The composite oxide makes a catalytic support. The CeO2—ZrO2 composite oxide and the reaction-free metallic oxide make barriers each other which suppress the granular growth when the composite oxide is subjected to high-temperature heat in a reducing heat treatment to form the regulatory oriented phase. The regulatory oriented phase improves the oxygen storage-and-release capability of the catalytic support. Thus, it is possible to simultaneously attain a large a specific surface area and a high oxygen storage-and-release capability.
摘要:
A metal oxide which has a large pore volume, and is very useful as a catalyst support. An alkaline material is added to an aqueous solution in which a compound of a metal element for composing an oxide is dissolved, a resultant mixture is co-precipitated, an obtained precipitate is washed, a washed precipitate is stirred in water along with a surfactant, and is calcined. By adding the surfactant after washing, the pH is not changed so that the adding effect of the surfactant is achieved to its upper most limit, thereby obtaining a metal oxide which has a large pore volume and a large mean diameter of secondary particles, and exhibits excellent gas diffusion properties.
摘要:
A catalyst for the steam reforming of hydrocarbons into gases such as methane, hydrogen and carbon monoxide and a method of preparing the same. The catalyst which comprises cerium oxide and rhodium supported on a carrier can maintain high catalytic activity and durability for steam reforming without any carbon deposition on its surface.
摘要:
A catalyst for purifying an exhaust gas includes a support and a noble metal loaded on the support. The support includes a mixture containing a porous oxide and a composite oxide. The composite oxide is expressed by the following formula: (Al2O3)a(CeO2)b(ZrO2)1−b in which the values “a” and “b” are molar ratios and the value “a” falls in a range of from 0.4 to 2.5 and the value “b” falls in a range of from 0.2 to 0.7. The support includes a particle having a particle diameter of 5 &mgr;m or more in an amount of 30% by volume or more. With the thus arranged support, even when the catalyst is subjected to such a severe durability test that it is heated at 1,000° C. for 10 to 20 hours, it exhibits a high purifying activity, and its coating layer is inhibited from cracking or coming off.
摘要:
Exhaust gas purifying method and apparatus for internal combustion engines in which the temperature of an exhaust gas purifying catalyst is detected and, as desired, oxygen content of exhaust gas is further detected, and in which the actual air-fuel ratio is varied toward the higher air-fuel ratio side and the lower air-fuel ratio side with respect to the theoretical air-fuel ratio, in accordance with the frequency and amplitude preset dependent on the kind of the catalyst and set based on these measured values.