Abstract: <P><FONT face=Verdana>Mn/γ-Al<SUB>2</SUB>O<SUB>3</SUB>cataly</FONT><FONT face=Verdana>st was prepared by isopyknic soaking method,using γ-Al<SUB>2</SUB>O<SUB>3</SUB> as supporter.3-pentanone was synthesized by acid-decarboxylation method in fixed bed reactor with propionic acid as raw material.Influences of preparation conditions on catalyst activity were researched.Results showed that the optimal preparing conditions were as follows:loading amount of Mn was 10%~13%(mass fraction);impregnation time was 5 h;and calcination temperature was between 450~600 ℃.Under these conditions the percent conversion of propionic acid was over 95% and selectivity was over 90%.Catalyst life test indictated that the life of Mn/γ-Al<SUB>2</SUB>O<SUB>3</SUB>reached 80 h.FT-IR characterization of catalyst showed that Mn entered into crystal lattices of Al<SUB>2</SUB>O<SUB>3</SUB> and new chemical bond Mn—O—Al was formed.</FONT></P>