Abstract: An exhaust gas containing a nitrogen oxides is passed at a temperature of 250.degree. to 550.degree. C. in the presence of a reducing agent through a catalyst bed filled with a molded denitration catalyst comprising at least the following three catalyst components(A) an oxide of at least one metallic element selected from the group consisting of Ti, Si and Zr,(B) an oxide of at least one metallic element selected from the group consisting of Mo and W, and(C) an oxide of Vsuch that the concentrations of the oxide (B) and/or the oxide (C) in the exhaust gas inlet site of the catalyst bed are higher than in the other site thereof.The molded denitration catalyst is also described.

Abstract: A catalyst for denitrizing nitrogen oxides contained in waste gas which contains a substantial amount of arsenic compounds therein, which comprises:(a) titanium, and(b) at least one element selected from the group consisting of arsenic and manganese. The catalyst is resistant to deactivation by arsenic compounds and retains high denitrizing activity over a long period of time. The catalyst may further contain at least one base metal selected from the group consisting of V, W, Mo, Cu, Fe, Cr, Co, Ni, Zn and Sn.

Abstract: A process for removing nitrogen oxides from an exhaust gas containing the nitrogen oxides and an arsenic compound, which comprises bringing said exhaust gas into contact with a reducing gas in the presence of a catalyst to reduce the nitrogen oxides in the exhaust gas and render them nontoxic. There are disclosed two types of catalysts: (1) a catalyst comprising (A) an oxide of titanium, (B) an oxide of at least one metal selected from tungsten and molybdenum, (C) an oxide of vanadium, and (D) an oxide and/or a sulfate of at least one metal selected from the group consisting of yttrium, lanthanum, cerium and neodymium, and (2) the above (A), (B), (C) components and (D)' at least one metal selected from the group consisting of yttrium, lanthanum, cerium, neodymium, copper, cobalt, manganese and iron, the component (D)' being deposited on zeolite.

Abstract: A catalyst for removing nitrogen oxides in an exhaust gas, said catalyst containing a first group of many pores having a diameter of 1.times.10.sup.2 .ANG. to less than 1.times.10.sup.3 .ANG. and a second group of many pores having a diameter of 1.times.10.sup.3 .ANG. to 1.2.times.10.sup.5 .ANG., the pore volume of the first group being at least 10% based on the total pore volume of the first group and the second group, and said catalyst comprising titanium and at least one metal selected from molybdenum, tungsten and vanadium as metal elements of catalytically active ingredients.

Abstract: Here is provided an adsorbent for adsorbing and removing an arsenic compound which becomes a catalyst poison in a selective contact reduction process for removing nitrogen oxides (NOx) from a combustion exhaust gas by the use of an ammonia as a reducing agent and a denitrating catalyst.The adsorbent of the present invention comprises a material in which the total volume of pores is 0.2 to 0.7 cc/g and the volume of the pores having a pore diameter of 300 .ANG. or more is 10% or more with respect to the total pore volume, and the material is a specific element, its oxide, an ion-exchanged zeolite or the like.In addition, the present invention is directed to a method for removing the arsenic compound from the combustion exhaust gas by injecting the adsorbent into the flow of the gas on the upstream side of the denitrating catalyst.

Abstract: A process for removing nitrogen oxides from an exhaust gas containing the nitrogen oxides and an arsenic compound, which comprises bringing said exhaust gas into contact with a reducing gas in the presence of a catalyst to reduce the nitrogen oxides in the exhaust gas and render them nontoxic. There are disclosed two types of catalysts: (1) a catalyst comprising (A) an oxide of titanium, (B) an oxide of at least one metal selected from tungsten and molybdenum, (C) an oxide of vanadium, and (D) an oxide and/or a sulfate of at least one metal selected from the group consisting of yttrium, lanthanum, cerium and neodymium, and (2) the above (A), (B), (C) components and (D)' at least one metal selected from the group consisting of yttrium, lanthanum, cerium, neodymium, copper, cobalt, manganese and iron, the component (D)' being deposited on zeolite.

Abstract: A denitration catalyst comprising an oxide of titanium, an oxide of tungsten and an oxide of vanadium as catalytically active ingredients and having a specific surface area, measured by the BET method, of 80 to 200 m.sup.2 /g and a pore volume, measured by the mercury penetration method, of 0.1 to 0.5 cc/g.