Methods and systems are provided for an emissions aftertreatment device. In one example, the emissions aftertreatment device may include a catalyst and a high entropy oxygen storage material formed of at least five metal oxides in equal molar proportions. The at least five metal oxides includes one or more rare earth metals as well as other metals with similar chemical properties as the rare earth metals.

A denitration catalyst for removing nitrogen oxide in an exhaust gas is represented by the following chemical formula: Ba.sub.3Y.sub.(4-x)A.sub.xO.sub.9, wherein A is an element selected from the group consisting of Bi, Sn, Ga, Mn, Ti, and Al; and X is 0.4 or more and 2 or less. A denitration device has the denitration catalyst for removing nitrogen oxide in an exhaust gas discharged from an exhaust gas generation source including a gas engine, a gas turbine, a melting furnace, or a boiler.

A denitration catalyst for removing nitrogen oxide in an exhaust gas is represented by the following chemical formula: Ba.sub.3Y.sub.(4-x)A.sub.xO.sub.9, wherein A is an element selected from the group consisting of Bi, Sn, Ga, Mn, Ti, and Al; and X is 0.4 or more and 2 or less. A denitration device has the denitration catalyst for removing nitrogen oxide in an exhaust gas discharged from an exhaust gas generation source including a gas engine, a gas turbine, a melting furnace, or a boiler.

A denitration catalyst for removing nitrogen oxide in an exhaust gas is represented by the following chemical formula: Ba.sub.3Y.sub.(4-x)A.sub.xO.sub.9, wherein A is an element selected from the group consisting of Bi, Sn, Ga, Mn, Ti, and Al; and X is 0.4 or more and 2 or less. A denitration device has the denitration catalyst for removing nitrogen oxide in an exhaust gas discharged from an exhaust gas generation source including a gas engine, a gas turbine, a melting furnace, or a boiler.

A denitration catalyst for removing nitrogen oxide in an exhaust gas is represented by the following chemical formula: Ba.sub.3Y.sub.(4-x)A.sub.xO.sub.9, wherein A is an element selected from the group consisting of Bi, Sn, Ga, Mn, Ti, and Al; and X is 0.4 or more and 2 or less. A denitration device has the denitration catalyst for removing nitrogen oxide in an exhaust gas discharged from an exhaust gas generation source including a gas engine, a gas turbine, a melting furnace, or a boiler.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

Disclosed are ruthenium-based catalyst systems, hafnium-based catalyst systems, and yttrium-based catalyst systems for use in ammonia decomposition. Catalyst systems include ruthenium, hafnium, and/or yttrium optionally in combination with one or more additional metals that can be catalytic or catalyst promoters. Hafnium-based and yttrium-based catalyst systems can be free of ruthenium. The catalyst systems also include a support material. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.

In general, disclosed herein are methods for forming hydrogen by use of an ammonia decomposition catalyst system. For instance, a method can include contacting a catalyst system with an ammonia source at a temperature of about 450? C. or lower. The catalyst systems can include a support material and a trimetallic catalyst component carried on the support material and within a reactor. Disclosed catalyst systems can decompose ammonia at relatively low temperatures and can provide an efficient and cost-effective route to utilization of ammonia as a carbon-free hydrogen storage and generation material.