The catalyst module is designed for use in an emission control system of an industrial scale combustion system. It comprises a stack frame, in which several mounting units, especially element boxes are inserted. Each of these is provided with several catalysts. In order to make a simple installation possible and, at the same time, a reliable sealing, the stack frame is assembled from side frame parts, which are connected and especially bolted to one another via mechanical connecting elements, a sealing element, which is inserted during the installation before the connection of the at least one side frame part and pressed against at least one element box with the help of the connecting element, being present at least at a side frame part.

A composite heat storage material includes a heat storage material and an inorganic material. The heat storage material is made of a strongly correlated electron material that stores and dissipates heat via solid-solid phase transition. The inorganic material is different from the material of the heat storage material. The heat storage material and the inorganic material are mixed. The composite heat storage material can have characteristics of both the heat storage material and the inorganic material.

A honeycomb structure includes: a honeycomb structure body including a plurality of cells; and a plugging portion to alternately plug open end parts of the plurality of cells on one side as an inflow side of the exhaust gas and open end parts on the other side as an outflow side of the exhaust gas. The partition wall is loaded, on the side of the outflow cells, with an oxidation catalyst made of a transition metal oxide to oxidize NO gas or an oxidation catalyst made of a transition metal oxide loaded at CeO.sub.2 to oxidize NO gas. The partition wall has porosity of 70% or less, the oxidation catalyst has a particle diameter of more than 1 μm and less than 50.0 μm, and the loading amount of the oxidation catalyst is 5.0 g/L or more and 50 g/L or less.

A reducing agent injection device includes a honeycomb structure and a urea spraying device spraying a urea water solution in mist form. In addition, the reducing agent injection device includes a carrier gas inlet that introduces carrier gas f between the urea spraying device and the honeycomb structure. The exhaust gas treatment method of the present invention supplies the urea water solution from the urea spraying device into the cells from the first end face of the honeycomb structure body to generate the ammonia, while introducing the carrier gas f from the carrier gas inlet, and injecting the ammonia to the outside to treat exhaust gas containing NO.sub.X.

A reducing agent injection device includes a honeycomb structure and a urea spraying device spraying a urea water solution in mist form. A pair of electrode members is formed in the honeycomb structure. The honeycomb structure of the reducing agent injection device, the hydraulic diameter HD, defined as HD=4×S/C, when the area of the cross section of one of the cells in the cross section perpendicular to the cell extending direction is S, and the peripheral length of the cross section of one of the cells is C, is 0.8 to 2.0 mm. Also, the open frontal area OFA of the honeycomb structure in the cross section perpendicular to the cell extending direction is 45 to 80%.

A honeycomb structure includes: a honeycomb structure body including a plurality of cells defined by a partition wall and serving as a through channel of fluid; and a plugging portion to alternately plug open end parts of the plurality of cells on one side as an inflow side of the exhaust gas and open end parts on the other side as an outflow side of the exhaust gas. The partition wall is loaded, on the side of the outflow cells, with an oxidation catalyst made of a transition metal oxide at least including Fe and Mn to oxidize NO gas or an oxidation catalyst made of a transition metal oxide loaded at CeO.sub.2 and at least including Fe and Mn to oxidize NO gas. The loading amount of the oxidation catalyst is 5.0 g/L or more and 50 g/L or less.

A reducing agent injection device includes a first honeycomb structure and a urea spraying device spraying a urea water solution in mist form. A pair of electrode members is formed in the first honeycomb structure. The ratio L/D of length L in the cell extending direction of the honeycomb structure body to diameter D of the cross section perpendicular to the cell extending direction is 0.5 to 1.2. Also, it is preferable that a urea hydrolysis catalyzer is provided in the second end face side of the honeycomb structure body, with a gap from the second end face.

A heater includes: a plate-like first heater substrate; an electrical heating wire that is provided on a first surface of the first heater substrate in a parallel circuit; electrodes that are connected to the electrical heating wire to allow current to flow in the electrical heating wire; and a plate-like cover substrate that covers the first surface of the first heater substrate, the electrical heating wire, and the electrodes with a second surface thereof. The electrical heating wire of the heater generates heat, so that the amount of heat is supplied. A honeycomb structure includes at least one heater that is provided so as to surround an outer wall thereof.

The honeycomb structure includes a honeycomb structure body having porous partition walls, and a plugging portion disposed in one of open ends of each cell, a thickness of the partition walls is 0.30 mm or more and 0.51 mm or less, a cell density is 30 cells/cm.sup.2 or more and 93 cells/cm.sup.2 or less, a filtration area (cm.sup.2) of inflow cells included per cm.sup.3 of the honeycomb structure body is defined as an inflow side filtration area G (cm.sup.2/cm.sup.3), a value obtained by dividing a pore volume Vp (cm.sup.3) formed in the partition walls by a total volume Va (L) including the cells is defined as a pore volume ratio A (cm.sup.3/L), and in this case, a product of the inflow side filtration area G (cm.sup.2/cm.sup.3) and the pore volume ratio A (cm.sup.3/L) is 1800 cm.sup.2/L or more and 3200 cm.sup.2/L or less.

A honeycomb structure includes a honeycomb structure body including porous partition walls defining a plurality of cells serving as fluid passages extending from an inflow end face to an outflow end face. A porosity of the partition walls is from 45 to 65%, an open frontal area of pores having an equivalent circle diameter of 10 um or more is from 20 to 40%, a pore density of pores having an equivalent circle diameter of 10 μm or more is from 350 to 1,000 pores/mm.sup.2 and a median opening diameter of the pores having an equivalent circle diameter of 10 μm or more is from 40 to 60 μm, where the median opening diameter is the median value of the equivalent circle diameters.