CATALYST FOR PREPARATION OF AN UNSATURATED CARBOXYLIC ACID BY GAS PHASE OXIDATION OF AN UNSATURATED ALDEHYDE

What is described is a catalyst for preparation of an .alpha.,.beta.-unsaturated carboxylic acid by gas phase oxidation of an a,? -unsaturated aldehyde, comprising a shaped support body with an active composition applied thereto, wherein the active composition coverage q is at most 0.3 mg/mm2, where Q is the active composition content of the catalyst in % by weight and Sm is the specific geometric surface area of the shaped support body in mm2/mg. Also described are a process for preparing the catalyst and a process for preparing an a,? -unsaturated carboxylic acid by gas phase oxidation of an a,? -unsaturated aldehyde over a fixed catalyst bed comprising a bed of the catalyst. The catalyst, with constantly high conversion of acrolein, reduces overoxidation to COx and increases the selectivity of acrylic acid formation.