An ammonia decomposition catalyst contains a carrier containing a composite oxide of cerium (Ce) and praseodymium (Pr), and ruthenium (Ru), and the content of the composite oxide is 70 mass % or more with respect to the entire catalyst, and the molar ratio between Ce and Pr in the composite oxide is Ce:Pr=99:1 to 10:90.

The invention relates to a method for converting a gas into methane (CH.sub.4) which includes: a step of activating a catalytic material including praseodymium oxide (Pr.sub.6O.sub.11) associated with nickel oxide (NiO) and alumina (Al.sub.2O.sub.3), the respective proportions of which are, relative to the total mass of these three compounds: Pr.sub.6O.sub.11: 1 wt % to 20 wt %, NiO: 1 wt % to 20 wt %, and Al.sub.2O.sub.3: 60 to 98 wt %; and a step of passing a gas including at least one carbon monoxide (CO) over the activated catalytic material.

The invention relates to a method for converting a gas into methane (CH.sub.4) which includes: a step of activating a catalytic material including praseodymium oxide (Pr.sub.6O.sub.11) associated with nickel oxide (NiO) and alumina (Al.sub.2O.sub.3), the respective proportions of which are, relative to the total mass of these three compounds: Pr.sub.6O.sub.11: 1 wt % to 20 wt %, NiO: 1 wt % to 20 wt %, and Al.sub.2O.sub.3: 60 to 98 wt %; and a step of passing a gas including at least one carbon monoxide (CO) over the activated catalytic material.

An after treatment method is disclosed. The after treatment method may include: operating an engine at a lean air/fuel ratio; calculating an amount of NH.sub.3 stored in an SCR catalyst; calculating an amount of NOx which will flow into the SCR catalyst; determining whether conversion to a rich air/fuel ratio is desired; calculating, when the conversion to the rich air/fuel ratio is desired, a rich duration for which the rich air/fuel ratio is maintained and a target air/fuel ratio; and operating the engine at the target air/fuel ratio for the rich duration.

An after treatment method is disclosed. The after treatment method may include: operating an engine at a lean air/fuel ratio; calculating an amount of NH.sub.3 stored in an SCR catalyst; calculating an amount of NOx which will flow into the SCR catalyst; determining whether conversion to a rich air/fuel ratio is desired; calculating, when the conversion to the rich air/fuel ratio is desired, a rich duration for which the rich air/fuel ratio is maintained and a target air/fuel ratio; and operating the engine at the target air/fuel ratio for the rich duration.

The present invention discloses a rare-earth-manganese/cerium-zirconium-based composite compound, a method for preparing the same, and a use thereof. The composite compound is of a core-shell structure with a general formula expressed as: A RE.sub.cB.sub.aO.sub.b-(1-A)Ce.sub.xZr.sub.(1-x-y)M.sub.yO.sub.2-z, wherein 0.1≤A≤0.3, preferably 0.1≤A≤0.2; a shell layer has a main component of rare-earth manganese oxide with a general formula of RE.sub.cMn.sub.aO.sub.b, wherein RE is a rare-earth element or a combination of more than one rare-earth elements, and B is Mn or a combination of Mn and a transition metal element, 1≤a≤8, 2≤b≤18, and 0.25≤c≤4; and a core has a main component of cerium-zirconium composite oxide with a general formula of Ce.sub.xZr.sub.(1-x-y)M.sub.yO.sub.2-z, wherein M is one or more non-cerium rare-earth elements, 0.1≤x≤0.9, 0≤y≤0.3, and 0.01≤z≤0.3. The composite compound enhances an oxygen storage capacity of a cerium-zirconium material through an interface effect, thereby increasing a conversion rate of a nitrogen oxide.

The present invention discloses a rare-earth-manganese/cerium-zirconium-based composite compound, a method for preparing the same, and a use thereof. The composite compound is of a core-shell structure with a general formula expressed as: A RE.sub.cB.sub.aO.sub.b-(1-A)Ce.sub.xZr.sub.(1-x-y)M.sub.yO.sub.2-z, wherein 0.1≤A≤0.3, preferably 0.1≤A≤0.2; a shell layer has a main component of rare-earth manganese oxide with a general formula of RE.sub.cMn.sub.aO.sub.b, wherein RE is a rare-earth element or a combination of more than one rare-earth elements, and B is Mn or a combination of Mn and a transition metal element, 1≤a≤8, 2≤b≤18, and 0.25≤c≤4; and a core has a main component of cerium-zirconium composite oxide with a general formula of Ce.sub.xZr.sub.(1-x-y)M.sub.yO.sub.2-z, wherein M is one or more non-cerium rare-earth elements, 0.1≤x≤0.9, 0≤y≤0.3, and 0.01≤z≤0.3. The composite compound enhances an oxygen storage capacity of a cerium-zirconium material through an interface effect, thereby increasing a conversion rate of a nitrogen oxide.

The purpose of the present invention is to provide a zirconia-based composite oxide for making it possible to form a catalyst layer which, despite having a reduced thickness, has a sufficient quantity of catalyst to function in exhaust gas treatment on a wall of a honeycomb structure. The purpose of the present invention is also to provide a method for manufacturing said zirconia-based composite oxide. The present invention relates to a zirconia-based composite oxide characterized in that the tap bulk density thereof is 0.75 g/mL or greater, and the specific surface area thereof after heat treatment for three hours at 1000° C. is 45 m.sup.2/g or greater.

The purpose of the present invention is to provide a zirconia-based composite oxide for making it possible to form a catalyst layer which, despite having a reduced thickness, has a sufficient quantity of catalyst to function in exhaust gas treatment on a wall of a honeycomb structure. The purpose of the present invention is also to provide a method for manufacturing said zirconia-based composite oxide. The present invention relates to a zirconia-based composite oxide characterized in that the tap bulk density thereof is 0.75 g/mL or greater, and the specific surface area thereof after heat treatment for three hours at 1000° C. is 45 m.sup.2/g or greater.

Disclosed are novel catalyst compositions, catalyst precursors, processes for making catalyst precursors, processes for making catalyst compositions, and processes for converting syngas. The catalytic component in the catalyst composition can comprise a metal carbide and/or a metal nitride. This disclosure is particularly useful for converting syngas via the Fischer-Tropsch reactions to make olefins and/or alcohols.