Catalyst for preparing methacrylic acid by oxidation of methylacrolein and preparation method of catalyst

The invention relates to a heteropolyacid catalyst for preparing methacrylic acid by oxidation of methylacrolein and a preparation method of the catalyst. According to the catalyst, phosphorus molybdenum cesium metavanadate or phosphorus molybdenum ammonium metavanadate with high thermal stability serves as a kernel; phosphorus molybdenum ammonium metavanadate or phosphorus molybdenum cesium metavanadate serves as a secondary outer layer; phosphorus molybdenum vanadate with a catalytic active site coats the outermost layer. The catalyst has high catalytic activity and long catalytic life in preparation of the methacrylic acid by gas-phase oxidation of the methylacrolein.