This paper is interested in mechanism of lactic acid (LA) adsorption and dehydration into acrylic acid (AA) over tin and iron beta zeolite (Sn- and Fe-BEA) catalysts. The electronic structure of clusters was calculated by ab initio density functional theory (DFT) method. The M₂Si₁₂O₃₉H₂₂ (hierarchical zeolite) and M₂Si₂₂O₆₄H₃₂ (ideal zeolite) clusters (M=Al, Si, Sn) were used in the LA dehydration reaction. The stabilization of the dimeric complex M-O_b-M (where M= Sn or Fe) in the BEA, ideal and hierarchical structure, was investigated. Possible modes of interaction of lactic acid with different cations (Si, Al, Fe or Sn) in the BEA zeolite framework as well as with added iron and tin dimers were considered. The interaction of lactic acid was only observed above the M-O_b-M dimer. The direct mechanism of lactic acid dehydration into acrylic acid was found over metal M-O_b-M dimers deposited at the BEA zeolite.