The method for suppressing formation of a high-melting-point pipe-clogging substance includes disposing a urea-solution supply pipe (6) configured to supply pressurized air and a urea solution into a pipe through which exhaust gas flows, connecting a urea-solution spray nozzle (7) near a tip of the urea-solution supply pipe (6), providing a mixing section (8) configured to mix the exhaust gas flowing through the pipe and a sprayed urea solution sprayed from the urea-solution spray nozzle (7), circumferentially providing a metal sheet (9) on all or part of an inner wall surface of the pipe in a belt-like manner around the mixing section (8), and forming a hydrolysis catalyst layer (10) configured to promote hydrolysis of urea on an inner surface of the metal sheet (9).

A reductant injecting device, including: a honeycomb structure including: a pillar shaped honeycomb structure portion having partition wall that defines a plurality of cells each extending from a fluid inflow end face to a fluid outflow end face; and at least one pair of electrode portions arranged on a side surface of the honeycomb structure portion; an outer cylinder having an inlet side end portion and an outlet side end portion, the inlet side end portion comprising a carrier gas introduction port being configured to introduce a carrier gas, the outlet side end portion comprising an injection port being configured to inject ammonia; a urea sprayer arranged at one end of the outer cylinder; and a spray direction switcher configured to be able to switch a spray direction of the aqueous urea solution.

A monolith filter unit for exhaust gas cleaning combines urea hydrolysis with particle filtering.

A monolith filter unit for exhaust gas cleaning combines urea hydrolysis with particle filtering.

The present invention discloses a method of preparing a catalyst for low-temperature synergistic catalytic purification of NO.sub.x and HCN in a flue gas, and the use thereof. Citric acid is dissolved in ethanol to obtain a citric acid/ethanol solution; tetrabutyl titanate is added, mixed uniformly to obtain a tetrabutyl titanate-citric acid/ethanol solution; glacial acetic acid is added dropwise to react for 30-40 min to obtain a solution A; the metal salt solution was added dropwise into the solution A, mixed uniformly and added with nitric acid, ammonium hydroxide is added dropwise to adjust the pH value and the temperature is raised at a constant speed to obtain a gel B; dried and then then baked at a temperature of 300-500 C. for 3-4 h, cooled in the furnace, pulverized, tableted and sieved to obtain the catalyst for the low-temperature synergistic catalytic purification of NO.sub.x and HCN in the flue gas.

A method for treatment of a gas having 10 to 0.5% by volume of at least one of COS and CS.sub.2, and 30 ppm to 5% by volume of unsaturated hydrocarbons: a) hydrogenation of organic compounds unsaturated with respect to paraffins by contacting the gas with a hydrogenation catalyst in the presence of hydrogen at 100 to 400 C., to provide an effluent that is low in unsaturated hydrocarbon compounds, the hydrogenation catalyst having at least one metal that is palladium, platinum, nickel, or cobalt deposited on a porous substrate. b) catalytic hydrolysis-hydrogenation in the presence of water of COS and/or CS.sub.2 present in the effluent of a) to provide an H.sub.2S-rich effluent by bringing the effluent from a) into contact with a hydrolysis-hydrogenation catalyst.

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.

An exhaust gas purification material according to the present invention is provided with a particulate filter 10 that traps particulate matter in exhaust gas and contains an SCR catalyst for adsorbing ammonia and reducing NOx in the exhaust gas. A maximum allowable adsorption amount of ammonia adsorbable by the filter 10 differs between an upstream portion 10a of the filter 10 including an exhaust gas inlet-side end 10c, and a downstream portion 10b of the filter 10 including an exhaust gas outlet-side end 10d. The SCR catalyst contained in the upstream portion 10a and the SCR catalyst contained in the downstream portion 10b are qualitatively different. A ratio (B/A) of a maximum allowable adsorption amount of ammonia A in the upstream portion 10a and a maximum allowable adsorption amount of ammonia B in the downstream portion 10b satisfies the relationship 1.1(B/A)2.

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%.

The present invention relates to a new strategy for capturing NO.sub.x using a two-step process.