Abstract: A catalyst that is used for a method of reduction removal of NOx in a exhaust gas by using ammonia as a reducing agent and has been deteriorated in activity by aggregation of vanadium oxide as an active component through long term use at a high temperature is washed with an acid aqueous solution having pH of 6 or less, and preferably 4 or less. The washing operation dissolves and removes away mainly the vanadium oxide as the aggregated active component, and then vanadium oxide as the active component is re-deposited thereon. The method of the invention enables regeneration of a thermally deteriorated catalyst, which has conventionally been impossible. The washing operation with the acid aqueous solution or an alkali aqueous solution does not influence the mechanical strength of the catalyst.

Abstract: The invention is to provide a method for regenerating a deteriorated denitration catalyst by an easy and simple procedure. A catalyst that is used for reduction removal of NOx contained in a exhaust gas by using ammonia as a reducing agent and has been deteriorated in activity through long term use is washed with an acid aqueous solution having pH of 4 or less, and preferably 2 or less, containing vanadium and/or tungsten. The washing operation dissolves away mainly an alkali metal, an alkaline earth metal, arsenic and sulfur, which are deteriorating components, and vanadium and tungsten having been deteriorated in activity, and simultaneously vanadium and/or tungsten as an active component is deposited thereon. Examples of the alkali metal include potassium and sodium, and examples of the alkaline earth metal include calcium.

Abstract: The invention provides a process for removing NOx which is free of impairment in denitration efficiency at a reaction temperature of up to 300° C. even when the component molar ratio of NOx in the gas to be treated is NO2>NO. For use in removing NOx from the gas to be treated and containing NO2 in a larger amount than NO, that is, having a (NO2)/NOx ratio in excess of 0.5, by selective reduction with use of ammonia serving as a main reducing agent in the presence of a denitration catalyst, the process of the invention for removing NOx comprises adding to the denitration reaction system a substance for removing an excess of oxygen accumulating on catalyst active sites by selectively reducing the oxygen at not higher than 300° C., for example, at 300 to 150° C., in other words, a substance which reacts with the excess of oxygen on the catalyst active sites and becomes oxidized at not higher than 300° C.

Abstract: The present invention provides a nitrogen dioxide absorbent for the exhaust gas purifying facility designed to remove by absorption or adsorption of NO2 from a gas (such as ventilation gas from road tunnels) containing NOx in low concentrations. The absorbent is composed of a porous carrier and a basic amino acid and/or organic amine compound supported thereon. The absorbent is produced by impregnating a porous carrier sequentially with two aqueous solutions each containing in an amount of, for example, 0.5-3.0 mol/l (preferably 1.0-2.0 mol/l) of basic amino acid and 0.5-3.0 mol/l (preferably 1.0-2.0 mol/l) of organic amine compound, or impregnating a porous carrier with a solution containing 0.5-3.0 mol/l (preferably 1.0-2.0 mol/l) of basic amino acid and/or 0.5-3.0 mol/l (preferably 1.0-2.0 mol/l) of organic amine compound.

Abstract: The present invention relates to a Mn-added titania carrier obtained by adding a Mn salt to amorphous titania and baking the titania. The invention also relates to an NOx adsorbent comprising the above-mentioned titania carrier and adsorbing components comprising oxides of Ru and/or Ce supported on the carrier. The invention also relates to an NOx adsorbent comprising the above-mentioned titania carrier and adsorbing components comprising oxides of Ru and/or Ce and an oxide of at least one metal among Ag, Cu and Mn supported on the carrier. The NOx adsorbents embodying the invention are effectively used for efficiently adsorbing and removing NOx from gases which contain much moisture and low-concentration, for example, a few ppm NOx such as gases discharged by ventilation from highway tunnels.

Abstract: The invention discloses a NOx adsorption and removal apparatus employed in the method of passing NOx containing gas into the adsorber 1 filled with NOx adsorbent to adsorb a specific volume of NOx on the adsorbent, passing hot air into the adsorber to desorb NOx, and regenerating the adsorbent, wherein the adsorber is divided in plural zones arranged parallel in the gas flow direction. In this invention, by regenerating after adsorbing NOx in each zone, the regenerating apparatus can be reduced in size, and the energy may be saved by effective utilization of preheat.

Abstract: The invention provides first to fourth adsorbents for removing low-concention nitrogen oxides. The first adsorbent comprises a carrier of gamma-alumina, and ruthenium supported-thereon. The second adsorbent comprises a carrier of anatase-type titania, and ruthenium supported thereon. The third adsorbent comprises ceramic paper retaining a carrier of anatase-type titania thereon, and ruthenium supported on the ceramic paper. The fourth adsorbent comprises ceramic paper retaining a carrier of anatase-type titania thereon, and a ruthenium halide and a halide of addition metal which are co-supported on the ceramic paper. These adsorbents are free of the influence of moisture and therefore usable without necessitating energy-consuming dehumidification or only with dehumidification on a reduced scale.

Abstract: The invention provides first to fourth adsorbents for removing low-concentration nitrogen oxides. The first adsorbent comprises a carrier of gamma-alumina, and ruthenium supported thereon. The second adsorbent comprises a carrier of anatase-type titania, and ruthenium supported thereon. The third adsorbent comprises ceramic paper retaining a carrier of anatase-type titania thereon, and ruthenium supported on the ceramic paper. The fourth adsorbent comprises ceramic paper retaining a carrier of anatase-type titania thereon, and a ruthenium halide and a halide of addition metal which are co-supported on the ceramic paper. These adsorbents are free of the influence of moisture and therefore usable without necessitating energy-consuming dehumidification or only with dehumidification on a reduced scale.

Abstract: Disclosed is a method of adsorbing and removing NOx, by washing with water a gas discharged by ventilation from highway tunnels in a washing tower as pretreatment, and then adsorbing NOx in the gas with a rotary NOx adsorption unit. The washed gas may be heated by a heater which is placed between the washing tower and the rotary NOx adsorption unit.