The adsorption and skeletal isomerization of m-xylene to p-xylene on the nanostructure H-ITQ-22 catalyst, modeled with a nano-cluster of 42T where T represents Si or Al atoms, has been studied with the M06-2X/6-31g(d,p) approach.  The adsorption energy of m-xylene is evaluated to be -23.9 kcal/mol, which is within the range of experimental data. The mechanism of isomerization for m-xylene to p-xylene in H-ITQ-22 was proposed to proceed in three steps namely: 1) the protonation of m-xylene, 2) the methyl shift of protonated m-xylene and 3) the proton back to zeolite and desorption of p-xylene.  Their activation energies are calculated to be 29.3, 15.1 and 2.0 kcal/mol, respectively, indicating that the protonation of m-xylene is the rate determining step. Our findings provide not only detailed understanding for the adsorption and reaction mechanism of xylene isomerization in the H-ITQ-22 zeolite, but also suggest that H-ITQ-22 is one of the potential candidate catalysts for this industrially important chemical process.

Isomerization mechanism of <i>m</i>-xylene to <i>p</i>-xylene on H-ITQ-22: A DFT mechanistic study

243rd National Meeting (2012)

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Isomerization mechanism of m-xylene to p-xylene on H-ITQ-22: A DFT mechanistic study