Patent ID: 7960308

Claim:
An oxide catalyst containing molybdenum as an essential component, wherein the relative standard deviation of its particle size as determined according to the following formula (1): relative ⁢ ⁢ standard ⁢ ⁢ deviation ⁢ ⁢ of ⁢ ⁢ particle ⁢ ⁢ size = standard ⁢ ⁢ deviation ⁢ ⁢ of ⁢ ⁢ particle ⁢ ⁢ size ⁢ / ⁢ average ⁢ ⁢ particle ⁢ ⁢ size ⁢ ⁢ wherein ⁢ ⁢ the ⁢ ⁢ standard ⁢ ⁢ deviation ⁢ ⁢ of ⁢ ⁢ particle ⁢ ⁢ size = ⁢ ⁢ N ⁢ ⁢ Σ ⁢ ⁢ Xn 2 - ( Σ ⁢ ⁢ Xn ) 2 N ⁡ ( N - 1 ) ( 1 ) (N is the number of particles whose size is measured; Xn is the size of each particle in terms of triaxial average diameter which is the average value of diameters measured in three directions of each particle); and the average particle size is the arithmetic mean of particle sizes of N particles is at least 0.04 and no more than 0.20, and wherein the oxide catalyst is represented by the following formula (3): Mo 12 V g W h Cu i E j F k G l H m O y (3) wherein Mo is molybdenum, V is vanadium, W is tungsten, Cu is copper, E is at least an element selected from cobalt, nickel, iron, lead and bismuth, F is at least an element selected from antimony, niobium and tin, G is at least an element selected from silicon, aluminum, titanium and zirconium, H is at least an element selected from alkali metals, and O is oxygen; g, h, i, j, k, l, m and y are respective atomic ratios of V, W, Cu, E, F, G, H and O, which are, respectively, 2≦g≦15, 0≦h≦10, 0<i≦6, o≦j≦30, 0≦k≦6, 0≦l≦60, 0≦m≦6, and y is a numerical value determined by the state of oxidation of respective elements.