Kinetic Simulation of Methacrolein and Lactone Production from the Catalytic Oxidation of Isobutane over Lanthanide Phosphomolybdates

Abstract

Eight lanthanum- (La₀.₂₅H₂.₂₅[PMo₁₂O₄₀], La₀.₅H₁.₅[PMo₁₂O₄₀], La₀.₇₅H₀.₇₅[PMo₁₂O₄₀], La[PMo₁₂O₄₀]) and cerium- (Ce₀.₂₅H₂.₂₅[PMo₁₂O₄₀], Ce₀.₅H₁.₅[PMo₁₂O₄₀], Ce₀.₇₅H₀.₇₅[PMo ₁₂O₄₀], Ce[PMo₁₂O₄₀]) containing phosphomolybdate catalysts have been synthesized and analysed using a low pressure steady state technique. The products from isobutane oxidation using the catalysts were water, methacrolein, carbon dioxide and lactone. Methacrylic acid is not detected under the low-pressure molecular-flow conditions; lactone is postulated to be intermediary in methacrylic acid production. The methacrolein and lactone data were simulated using two different theoretical models in order to determine kinetic parameters. The activation barriers for methacrolein formation vary substantially throughout each lanthanum and cerium series, however the most active catalyst is determined to be Ce[PMo₁₂O₄₀]. Only three of the eight catalysts produced significant quantities of lactone (La₀.₇₅H₀.₇₅ [PMo₁₂O₄₀], La[PMo₁₂O₄₀] and Ce[PMo₁₂O₄₀]) and this activity is correlated with the most active catalysts for methacrolein formation. The trends in selective oxidation activity must be due to the acidity and redox properties, as well as the structural phases, but it is difficult to quantify in all cases.