Method for preparing unsaturated acid by oxidation of unsaturated aldehyde

The invention relates to a method for preparing unsaturated acid by oxidation of unsaturated aldehyde, and solves the problems of low yield and selectivity of unsaturated acid in the prior art. According to the invention, unsaturated aldehyde selected from acrolein or methacrolein, and oxygen-containing gas selected from air or oxygen are adopted as raw materials, and the raw materials are allowed to contact a catalyst to prepare acrylic acid or methacrylic acid at a temperature of 220-340 DEG C and an air speed of 800-1800 h , wherein the molar ratio of oxygen in oxygen-containing gas to unsaturated aldehyde is 0.4-0.9, at least one of SiO2, Al2O3, or TiO2 is adopted as the catalyst carrier, and the catalyst contains an active ingredient represented by the following general formula: Mo12VaCubXcYdZeOx, in which X is selected from at least one of W, Cr, and Nb; Y is selected from at least one of Fe, Bi, Sb, Ce, La, Zr, and Th; and Z is selected from at least one of alkali metals or alkaline earth metals. The invention provides a solution, which is useful in the industrial production of preparing unsaturated acid from alpha-beta unsaturated aldehyde.