Rationalising the role of solid-acid sites in the design of versatile single-site heterogeneous catalysts for targeted acid-catalysed transformations

A versatile design strategy for rationalising the role of well-defined and isolated multifunctional solid-acid active centres, employing Mg(ii)Si(iv)AlPO-5 nanoporous architectures has been demonstrated, with a view to affording structure-property correlations compared to its corresponding mono-substituted analogues (Mg(ii)AlPO-5 and Si(iv)AlPO-5). The simultaneous incorporation of Mg(ii) and Si(iv) ions, as isomorphous replacements for Al(iii) and P(v) ions in the microporous architecture, plays an important role in modulating the nature and strength of the solid-acid active sites in the industrially-important, vapour-phase Beckmann rearrangement of cyclohexanone oxime to produce ε-caprolactam (the precursor for renewable nylon-6) and in the isopropylation of benzene to cumene. The structural integrity, coordination geometry and local environment of the active (Brønsted-acid) sites could be rationalised at the molecular level, using in situ spectroscopic techniques, for tailoring the catalytic synergy by adroit design of the framework architecture.