Methyl methacrylate is widely used in the polymer industry. This precursor is predominately synthesized via an environmentally hazardous route known as the Acetone Cyanohydrin Process. The deleterious aspects of this procedure include the use of the reactant hydrogen cyanide, the formation of acetone cyanohydrin as an intermediate, and the production of contaminated ammonium sulfate. These significant drawbacks have prompted research into different production methods, with several companies now employing molybdenum based catalysts and selective isobutane oxidation to manufacture methyl methacrylate.

For this work, four lanthanum and four cerium salts were synthesized via ion exchange with phosphomolybdic acid: La_0.25H_2.25[PMo₁₂O₄₀], La_0.5H_1.5[PMo₁₂O₄₀], La_0.75H_0.75[PMo₁₂O₄₀], La[PMo₁₂O₄₀], Ce_0.25H_2.25[PMo₁₂O₄₀], Ce_0.5H_1.5[PMo₁₂O₄₀], Ce_0.75H_0.75[PMo₁₂O₄₀] and Ce[PMo₁₂O₄₀]. The phosphomolybdates were then analysed by temperature-programmed oxidation experiments using isobutane in a low-pressure steady-state apparatus. The products formed from the isobutane oxidation were water, carbon dioxide, methacrolein and 3-methyl-2-oxetanone, a rare lactone species.

A comprehensive mathematical model has been developed to determine the Arrhenius parameters associated with low-pressure steady-state heterogeneous catalytic reactions. Included in this model are principles from kinetic gas theory, transition state theory and the Langmuir adsorption isotherm. This model has been successfully applied to the oxidation experiments involving the lanthanum and cerium catalysts with isobutane. Accurate apparent activation energies for methacrolein production from each of the catalysts have been determined. The most active toward methacrolein formation is Ce[PMo₁₂O₄₀] with an activation energy of 64.7 ± 0.4 kJ mol^-1, however other phosphomolybdates analysed in this study exhibited activation energies of more than 200 kJ mol^-1.