Comments on the paper “Low-bromide containing MC catalyst for the autoxidation of para-xylene” by B. Saha and J.H. Espenson [J. Mol. Catal. A 271 (2007) 1–5]

p-Xylene Oxidation to Terephthalic Acid: A Literature Review Oriented toward Process Optimization and Development

“…Above the minimum formation of CO x shows a less steep trend. This observation is consistent with a need for a balance between bromine and metals: metals in their trivalent oxidation state react with bromide ions to form bromide atoms, which will abstract hydrogen atoms from methyl groups to yield radicals; however, competitive degradation of carboxylic groups of both product and solvent molecules to carbon oxides is favored by a high concentration of metals, in particular cobalt, which has a well-known ability to decarboxylate acids. , Co 3 + + CH 3 CO 2 normalH ⇄ Co 2 + + CH 3 CO 2 • + normalH + Co 3 + + CH 3 CO 2 • → CH 3 CO 2 normalH Co 2 + + CO 2 + CH 3 CO 2 CH 3 + normalH + Thus, as a result of these two competitive reactions, one can expect an optimum Br/metals ratio to achieve greater catalyst selectivity with respect to carbon oxides formation.…”

“…Comparison of methane formation with CO 2 and CO formation with increasing metal concentration at constant air flow. Adapted from ref .…”

“…Comparison of methane formation with carbon dioxide formation with increasing air flow/metal ratio. Adapted from ref .…”

Production of NMSBA from the oxidation of NMST in the homogeneous Co/Mn/Br/H3PMoxW12−xO40 catalytic system

“…As a chain initiator in NMST oxidation, bromine concentration has a very important effect on this catalytic reaction process. The main role of bromine in the reaction [ 27 ] is that it reacts with high‐valence metal ions (Mn 3+ and Co 3+ ) and itself is turned into a bromine‐free radical (Br·), which causes methyl dehydrogenation to generate a methyl free radical and promote the reaction. In addition, bromine also forms a complex with Co 3+ (Mn 3+ ) and weakens the decarboxylation abilities of Co 3+ and Mn 3+ .…”