Provided are a composite material that has lower volume resistivity in comparison with SiC, SiC—Si, and the like, which are materials for forming constituent elements of an EHC, has low temperature dependence of volume resistivity, and thus is able to form a constituent element of a high-performance EHC; an electrode film, an electrode terminal, and a honeycomb substrate that are constituent elements of an EHC formed with such composite material, and a method for producing them. The composite material contains MoSi.sub.2 and at least one of Si or SiC, and is a material for forming a constituent element of an electrically heated catalytic converter. An electrode film 2, an electrode terminal 3, and a substrate 1 are produced from such composite material.

Provided are a composite material that has lower volume resistivity in comparison with SiC, SiC—Si, and the like, which are materials for forming constituent elements of an EHC, has low temperature dependence of volume resistivity, and thus is able to form a constituent element of a high-performance EHC; an electrode film, an electrode terminal, and a honeycomb substrate that are constituent elements of an EHC formed with such composite material, and a method for producing them. The composite material contains MoSi.sub.2 and at least one of Si or SiC, and is a material for forming a constituent element of an electrically heated catalytic converter. An electrode film 2, an electrode terminal 3, and a substrate 1 are produced from such composite material.

A method of reducing a gaseous carbon oxide includes reacting a carbon oxide with a gaseous reducing agent in the presence of an intermetallic or carbide catalyst. The reaction proceeds under conditions adapted to produce solid carbon of various allotropes and morphologies, the selective formation of which can be controlled by means of controlling reaction gas composition and reaction conditions including temperature and pressure. A method for utilizing an intermetallic or carbide catalyst in a reactor includes placing the catalyst in a suitable reactor and flowing reaction gases comprising a carbon oxide with at least one gaseous reducing agent through the reactor where, in the presence of the catalyst, at least a portion of the carbon in the carbon oxide is converted to solid carbon and a tail gas mixture containing water vapor.

A method of reducing a gaseous carbon oxide includes reacting a carbon oxide with a gaseous reducing agent in the presence of an intermetallic or carbide catalyst. The reaction proceeds under conditions adapted to produce solid carbon of various allotropes and morphologies, the selective formation of which can be controlled by means of controlling reaction gas composition and reaction conditions including temperature and pressure. A method for utilizing an intermetallic or carbide catalyst in a reactor includes placing the catalyst in a suitable reactor and flowing reaction gases comprising a carbon oxide with at least one gaseous reducing agent through the reactor where, in the presence of the catalyst, at least a portion of the carbon in the carbon oxide is converted to solid carbon and a tail gas mixture containing water vapor.

A honeycomb structure includes: a honeycomb structure body; and a convex part that protrudes outward from a part of circumference of the honeycomb structure body. The convex part surrounds the circumference of the honeycomb structure body like a ring. The convex part is of a tapered shape at least at one end having a tapered face. The convex part has a circumference coating layer making up the tapered face. The convex part has a maximum thickness of 1 to 20 mm, and a rough-face region on the tapered face, the rough-face region having surface roughness of 5 to 70 μm. The rough-face region has a total of a rough-face region angle of 108° or more. An inclination angle formed between the tapered face and the extending direction of the cells is 10 to 80 degrees.

A honeycomb structure includes: a honeycomb structure body; and a convex part that protrudes outward from a part of circumference of the honeycomb structure body. The convex part surrounds the circumference of the honeycomb structure body like a ring. The convex part is of a tapered shape at least at one end having a tapered face. The convex part has a circumference coating layer making up the tapered face. The convex part has a maximum thickness of 1 to 20 mm, and a rough-face region on the tapered face, the rough-face region having surface roughness of 5 to 70 μm. The rough-face region has a total of a rough-face region angle of 108° or more. An inclination angle formed between the tapered face and the extending direction of the cells is 10 to 80 degrees.

Provided are a porous silicon carbide nanocomposite structure comprising nanowires that are self-formed, a preparation method thereof, and a catalyst comprising the same, in which the catalyst with excellent activity may be prepared by uniformly supporting a catalytically active component in meso-macro pores and nanowires.

A honeycomb structure is formed of a porous ceramic material and has pores in the structural body, wherein cerium dioxide is present in a state that it is incorporated in the structural body in the ceramic material, and at least a part of cerium dioxide particles is exposed on pore surfaces of the pores. The ceramic material includes cordierite or silicon carbide as a major component, the ratio of the cerium dioxide to the ceramic material is in the range of from 1.0% by mass to 10.0% by mass, and at least a part of catalyst particulates of a platinum group element such as platinum or palladium is loaded by the cerium dioxide particles.

A honeycomb filter includes a honeycomb structure body having porous partition walls defining a plurality of cells which become through channels for fluid, plugging portions disposed in open ends of the cells, and a protective layer disposed to cover at least the surface of the honeycomb structure body, each of the honeycomb structure body and the plugging portion has a structure constituted of aggregates made of silicon carbide and a bonding material which bonds the aggregates to one another, the protective layer is a layer in which silicon is present as much as 40 mass % or more and oxygen is present as much as 40 mass % or more and a thickness is 0.5 μm or more, and an outer end face of both end faces of the plugging portion has an exposed region in which the protective layer is not disposed.

A honeycomb filter includes a honeycomb structure body having porous partition walls defining a plurality of cells which become through channels for fluid, plugging portions disposed in open ends of the cells, and a protective layer disposed to cover at least the surface of the honeycomb structure body, each of the honeycomb structure body and the plugging portion has a structure constituted of aggregates made of silicon carbide and a bonding material which bonds the aggregates to one another, the protective layer is a layer in which silicon is present as much as 40 mass % or more and oxygen is present as much as 40 mass % or more and a thickness is 0.5 μm or more, and an outer end face of both end faces of the plugging portion has an exposed region in which the protective layer is not disposed.