Alan B. Levy

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 e-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 (Bronsted-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.

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

A combined electronic structure computational and X-ray absorption spectroscopy study was used to investigate the nature of the active sites responsible for catalytic synergy in Co-Ti bimetallic nanoporous frameworks. Probing the nature of the molecular species at the atomic level has led to the identification of a unique Co-O-Ti bond, which serves as the loci for the superior performance of the bimetallic catalyst, when compared with its analogous monometallic counterpart. The structural and spectroscopic features associated with this active site have been characterized and contrasted, with a view to affording structure-property relationships, in the wider context of designing sustainable catalytic oxidations with porous solids.

Understanding the role of designed solid acid sites in the low-temperature production of ϵ-Caprolactam

Modern society is placing increasing demands on commodity chemicals, driven by the ever‐growing global population and the desire for improved standards of living. As the polymer industry grows, a sustainable route to ϵ‐caprolactam, the precursor to the recyclable nylon‐6 polymer, is becoming increasingly important. To this end, we have designed and characterized a recyclable SAPO catalyst using a range of characterization techniques, to achieve near quantitative yields of ϵ‐caprolactam from cyclohexanone oxime. The catalytic process operates under significantly less energetically demanding conditions than other widely practiced industrial processes.

Theoretical insights into the nature of synergistic enhancement in bimetallic CoTiAlPO-5 catalysts for ammonia activation

Bimetallic catalytic synergy, the concurrent action of two different metal ions in the same material, has resulted in improved efficiency in many catalytic systems and for a range of chemical processes. Via a computational mechanistic study, we investigate the catalytic benefits of the bimetallic CoTiAlPO-5 material in comparison to the monometallic CoAlPO-5 system, on the activation of NH3. The presence of Ti in a framework site adjacent to Co stabilises the Co(II) oxidation state, and increases the Co(III)/Co(II) reduction potential. We show that this change lowers the activation barrier for the homolytic H extraction from NH3 by Co(III), from 162 kJ mol−1 in the monometallic CoAlPO-5 catalyst to 140 kJ mol−1 in the bimetallic CoTiAlPO-5 (175 and 111 kJ mol−1 respectively when considering both dispersion and free energy corrections). Elucidation of mechanistic details through computational studies can make significant contributions to the rational design of catalytic materials.