Patent ID: 8242306

Claim:
A process for producing acrylic acid by catalytically oxidizing acrolein or an acrolein-containing gas at gas phase, with molecular oxygen or a molecular oxygen-containing gas, which comprises conducting the reaction in the presence of 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.