Kinetic Analysis of Methacrolein and Lactone Formation over Lanthanide Phosphomolybdate Catalysts

Eight lanthanum (La{0.25}H{2.25}[PM{o12}O{40}], La{0.5}H{1.5}[Pmo{12}O{40}], La{0.75}H{0.75}[Pmo{12}O{40}], La[Pmo{12}O{40}]) and cerium (Ce{0.25}H{2.25}[Pmo{12}O{40}], Ce{0.5}H{1.5}[Pmo{12}O{40}], Ce{0.75}H{0.75}[Pmo{12}O{40}], Ce[Pmo{12}O{40}]) 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. 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[Pmo{12}O{40}]. Only three of the eight catalysts produced significant quantities of lactone (La{0.75}H{0.75}[Pmo{12}O{40}], La[Pmo{12}O{40}] and Ce[Pmo{12}O{40}]) and its formation is correlated with methacrolein. The correlation between lactone and methacrolein formation is likely due to the presence of a distinct structural phase.