A honeycomb structure including: a pillar-shaped honeycomb structure portion having an outer peripheral wall and partition walls disposed on an inner side of the outer peripheral wall and defining a plurality of cells extending from one end face to another end face to form flow paths; and at least an electrode portion disposed on an outer surface of the outer peripheral wall of the pillar-shaped honeycomb structure portion, wherein the pillar-shaped honeycomb structure portion is formed of ceramics containing either or both of Si and SiC, the electrode portion contains either or both of a metal and a metal compound in addition to an oxide, and a volume ratio of the oxide on an inner peripheral side of the electrode portion is higher than a volume ratio of the oxide on an outer peripheral side of the electrode portion.

A honeycomb structure includes: an outer peripheral wall; and partition walls disposed on an inner side of the outer peripheral wall, the partition walls defining a plurality of cells, each of the plurality of cells extending from one end face to the other end face to form a flow path for a fluid. The partition walls and the outer peripheral wall include ceramics containing at least silicon. A content of silicon in the ceramics is 30% by mass or more. A concentration of at least one dopant in the silicon is from 10.sup.16 to 510.sup.20/cm.sup.3.

A combustion system operated at low cost is provided. A combustion system 1 includes a combustion device 10 that burns fuel, an exhaust line L1 through which exhaust gas flows, the exhaust gas being generated through combustion of the fuel in the combustion device 10, an air preheater 30 that is disposed in the exhaust line L1 and that recovers heat from the exhaust gas, and a denitration device 40 that is disposed in the exhaust line L1 and that removes nitrogen oxide from the exhaust gas using a denitration catalyst. The denitration device 40 is disposed downstream from the air preheater 30 in the exhaust line L1, and the denitration catalyst contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more.

An electrical resistor includes borosilicate particles, Si-containing particles, and pore parts. The pore parts are constituted by gaps between the borosilicate particles and the Si-containing particles and surround the borosilicate particles and the Si-containing particles. A honeycomb structure includes the electrical resistor. An electric heating catalytic device has the honeycomb structure.

A fluid feed ring (5), a substrate coating apparatus (1) and a method are provided for coating a substrate (2) with a catalyst component. The fluid feed ring (5) comprises an annular body (40) having an inner face (45) bounding a central bore of the fluid feed ring. A fluid feed port (47) receives the liquid and a plurality of outlet apertures (50) on the inner face of the annular body discharge the liquid onto a piston face (23) of the substrate coating apparatus (1). A distribution channel (51) extending at least part-way around the annular body (40) provides fluid communication between the fluid feed port (47) and the plurality of outlet apertures (50).

An electric heating support includes a honeycomb structure having an outer peripheral wall and interior porous partition walls defining a plurality of cells forming a flow path. A pair of electrode layers are disposed on a surface of the outer peripheral wall so as to face each other across a central axis of the honeycomb structure. Protective layers cover the electrode layers, respectively, such that at least a part of each electrode layer is exposed. A pair of metal terminals are provided on the electrode layers. Each electrode layer is composed of a metal-ceramic mixed member. A portion of each electrode layer that is exposed from the protective layer is electrically connected to each of the pair of metal terminals.

There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of spraying an aqueous solution with a pH of 7 or more onto a used denitration catalyst while the denitration catalyst is set in a denitration device to remove a surface of the denitration catalyst. The denitration catalyst contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more. The denitration catalyst after recycling is used for denitration at 200 C. or lower.

There is provided a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A denitration catalyst is obtained by coating a substrate with a catalyst component. The catalyst component contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more. The denitration catalyst is used for denitration at 200 C. or lower.

There is provided a method for recycling a catalyst that exhibits a high denitration efficiency at a relatively low temperature and does not cause oxidation of SO.sub.2 in a selective catalytic reduction reaction that uses ammonia as a reducing agent. A method for recycling a denitration catalyst includes a step of removing a used denitration catalyst from a denitration device and then coating the used denitration catalyst with a catalyst component. The catalyst component contains 43 wt % or more of vanadium pentoxide and has a BET specific surface area of 30 m.sup.2/g or more, and the denitration catalyst after recycling is used for denitration at 200 C. or lower.

Provided are catalyst particles for treating vehicle exhaust gas, containing semiconductor nanoparticles supported by noble metals.