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

摘要

Eight lanthanum- (La0.25H2.25[PMo12O40], La0.5H1.5[PMo12O40], La0.75H0.75[PMo12O40],nLa[PMo12O40]) and cerium- (Ce0.25H2.25[PMo12O40], Ce0.5H1.5[PMo12O40], Ce0.75H0.75[PMon12O40], Ce[PMo12O40]) containing phosphomolybdate catalysts have been synthesized and anal-nysed using a low pressure steady state technique. The products from isobutane oxidation us-ning the catalysts were water, methacrolein, carbon dioxide and lactone. Methacrylic acid is notndetected under the low-pressure molecular-flow conditions; lactone is postulated to be interme-ndiary in methacrylic acid production. The methacrolein and lactone data were simulated usingntwo different theoretical models in order to determine kinetic parameters. The activation barri-ners for methacrolein formation vary substantially throughout each lanthanum and cerium series,nhowever the most active catalyst is determined to be Ce[PMo12O40]. Only three of the eight cat-nalysts produced significant quantities of lactone (La0.75H0.75 [PMo12O40], La[PMo12O40] andnCe[PMo12O40]) and this activity is correlated with the most active catalysts for methacrolein for-nmation. The trends in selective oxidation activity must be due to the acidity and redox properties,nas well as the structural phases, but it is difficult to quantify in all cases.