Robert Raja

Design and control of Lewis acid sites in Sn-substituted microporous architectures

Co-reporter:Khaled M. H. Mohammed, Arunabhiram Chutia, June Callison, Peter P. Wells, Emma K. Gibson, Andrew M. Beale, C. Richard A. Catlow and Robert Raja

Journal of Materials Chemistry A 2016 vol. 4(Issue 15) pp:5706-5712

Publication Date(Web):21 Mar 2016

DOI:10.1039/C5TA10283A

Monometallic and bimetallic tin-containing framework architectures have been prepared by hydrothermal methods. Structural and spectroscopic techniques were used to probe the nature of the solid-acid sites, at the molecular level, using a combination of XRD, DR UV-Vis, solid state MAS NMR (119Sn, 27Al and 31P) and XAFS. The nature and strength of the solid-acid sites were experimentally probed by FT-IR spectroscopy using CD3CN as a probe molecule. To elucidate further the local-structure, the structural characteristics of the Sn sites were probed using DFT calculations, with a view to rationalising the experimental findings. These detailed structural and spectroscopic studies revealed the presence of multiple Sn environments, with the monometallic SnAlPO-5 catalyst displaying a greater number of tetrahedral Sn(IV) active centres. These framework Sn(IV) centres generated strong Lewis acid sites, when compared with their bimetallic Co–Sn analogue, thereby affording attractive possibilities for modulating catalytic reactivity.

Utilisation of gold nanoparticles on amine-functionalised UiO-66 (NH2-UiO-66) nanocrystals for selective tandem catalytic reactions

Co-reporter:Christopher S. Hinde, William R. Webb, Benny K. J. Chew, Hui Ru Tan, Wen-Hua Zhang, T. S. Andy Hor and Robert Raja

Chemical Communications 2016 vol. 52(Issue 39) pp:6557-6560

Publication Date(Web):11 Apr 2016

DOI:10.1039/C6CC02169G

Colloidal deposition of gold nanoparticles (Au NPs) onto NH2-UiO-66 nanocrystals has been demonstrated with the resulting hybrid catalyst proving robust and versatile for one-pot, heterogeneous conversions involving the selective oxidation of primary alcohols in tandem with Knoevenagel condensation reactions. Within these systems, structure–property correlations have been established to confirm that the active sites for the oxidation and condensation reactions are intrinsically correlated with the Au NPs and pendant amine groups respectively.

The curious effects of integrating bimetallic active centres within nanoporous architectures for acid-catalysed transformations

Co-reporter:Matthew E. Potter, Danni Sun and Robert Raja

Catalysis Science & Technology 2016 vol. 6(Issue 8) pp:2616-2622

Publication Date(Web):12 Jan 2016

DOI:10.1039/C5CY02061A

The resourceful combination of distinct Mg, Zn and Si active-sites within a single aluminophosphate framework, via simultaneous isomorphous substitution, has afforded unique bimetallic nanoporous heterogeneous catalysts. Unique site-specific interactions have been engineered, at the molecular level, to facilitate catalytic modifications and optimize product yield. By the dextrous incorporation of individual transition-metal active centres, we are able to intricately control the precise nature of the Brønsted acid sites, thereby influencing their catalytic behaviour for the industrially relevant acid-catalysed Beckmann rearrangement of cyclohexanone oxime and isopropylation of benzene.

Cover Picture: Design of Highly Selective Platinum Nanoparticle Catalysts for the Aerobic Oxidation of KA-Oil using Continuous-Flow Chemistry (ChemSusChem 5/2016)

Co-reporter:Arran M. Gill;Dr. Christopher S. Hinde;Dr. Rowan K. Leary;Dr. Matthew E. Potter;Andrea Jouve;Dr. Peter P. Wells; Paul A. Midgley; John M. Thomas;Dr. Robert Raja

ChemSusChem 2016 Volume 9( Issue 5) pp:

Publication Date(Web):

DOI:10.1002/cssc.201600245

Design of Highly Selective Platinum Nanoparticle Catalysts for the Aerobic Oxidation of KA-Oil using Continuous-Flow Chemistry

Co-reporter:Arran M. Gill;Dr. Christopher S. Hinde;Dr. Rowan K. Leary;Dr. Matthew E. Potter;Andrea Jouve;Dr. Peter P. Wells; Paul A. Midgley; John M. Thomas;Dr. Robert Raja

ChemSusChem 2016 Volume 9( Issue 5) pp:

Publication Date(Web):

DOI:10.1002/cssc.201600246

Abstract

Invited for this month′s cover is the group of Dr. Robert Raja at the University of Southampton, UK. The image shows the origin of spatially isolated and well-defined platinum nanoparticles, within a microporous framework architecture, for the selective aerobic oxidation of KA-oil to cyclohexanone, which is an important precursor in the manufacture of nylon-6. The Communication itself is available at 10.1002/cssc.201501264.

Design of Highly Selective Platinum Nanoparticle Catalysts for the Aerobic Oxidation of KA-Oil using Continuous-Flow Chemistry

Co-reporter:Arran M. Gill;Dr. Christopher S. Hinde;Dr. Rowan K. Leary;Dr. Matthew E. Potter;Andrea Jouve;Dr. Peter P. Wells; Paul A. Midgley; John M. Thomas;Dr. Robert Raja

ChemSusChem 2016 Volume 9( Issue 5) pp:423-427

Publication Date(Web):

DOI:10.1002/cssc.201501264

Abstract

Highly active and selective aerobic oxidation of KA-oil to cyclohexanone (precursor for adipic acid and ɛ-caprolactam) has been achieved in high yields using continuous-flow chemistry by utilizing uncapped noble-metal (Au, Pt & Pd) nanoparticle catalysts. These are prepared using a one-step in situ methodology, within three-dimensional porous molecular architectures, to afford robust heterogeneous catalysts. Detailed spectroscopic characterization of the nature of the active sites at the molecular level, coupled with aberration-corrected scanning transmission electron microscopy, reveals that the synthetic methodology and associated activation procedures play a vital role in regulating the morphology, shape and size of the metal nanoparticles. These active centers have a profound influence on the activation of molecular oxygen for selective catalytic oxidations.

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Co-reporter:Matthew E. Potter; A. James Paterson; Bhoopesh Mishra; Shelly D. Kelly; Simon R. Bare; Furio Corà; Alan B. Levy

Journal of the American Chemical Society 2015 Volume 137(Issue 26) pp:8534-8540

Publication Date(Web):June 15, 2015

DOI:10.1021/jacs.5b03734

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.

Elucidating Structure–Property Relationships in the Design of Metal Nanoparticle Catalysts for the Activation of Molecular Oxygen

Co-reporter:Christopher S. Hinde, Davide Ansovini, Peter P. Wells, Gillian Collins, Sivan Van Aswegen, Justin D. Holmes, T. S. Andy Hor, and Robert Raja

ACS Catalysis 2015 Volume 5(Issue 6) pp:3807

Publication Date(Web):May 14, 2015

DOI:10.1021/acscatal.5b00481

A novel synthetic strategy for the design of metal nanoparticles by extrusion of anionic chloride precursors from a porous copper chlorophosphate framework has been devised for the sustainable aerobic oxidation of vanillyl alcohol (4-hydroxy-3-methoxybenzyl alcohol) to vanillin (4-hydroxy-3-methoxybenzaldehyde) using a one-step, base-free method. The precise nature of the Au, Pt, and Pd species has been elucidated for the as-synthesized and thermally activated analogues, which exhibit fascinating catalytic properties when subjected to diverse activation environments. By employing a combination of structural and spectroscopic characterization tools, it has been shown that analogous heat treatments have differing effects on extrusion of a particular metal species. The most active catalysts in this series of materials were the extruded Pt nanoparticles that were generated by reduction in H2, which exhibit enhanced catalytic behavior, when compared to its Au or Pd counterparts, for industrially significant, aerobic oxidation reactions.Keywords: aerobic oxidation; catalysis; EXAFS; nanoparticle; structure−property correlations; vanillin; vanillyl alcohol

Expanding Beyond the Micropore: Active-Site Engineering in Hierarchical Architectures for Beckmann Rearrangement

Co-reporter:Stephanie H. Newland, Wharton Sinkler, Thomas Mezza, Simon R. Bare, Marina Carravetta, Ibraheem M. Haies, Alan Levy, Scott Keenan, and Robert Raja

ACS Catalysis 2015 Volume 5(Issue 11) pp:6587

Publication Date(Web):September 29, 2015

DOI:10.1021/acscatal.5b01595

The ability to engineer discrete solid-acid centers within hierarchically porous architectures that contain micropores with interconnected mesopores offers the potential to overcome the spatial restraints and diffusional limitations imposed by conventional microporous zeotype catalysts, which often lead to decreased catalyst lifetimes and restricted substrate scope. By employing a one-step soft-templating approach, coupled with detailed physicochemical and spectroscopic characterization, isolated, solid-acid sites can be suitably tailored and discretely modulated within the micropores and mesopores. The design strategy facilitates a synergistic enhancement in catalytic activity, selectivity, substrate versatility, and longevity, compared to analogous microporous zeotypes that have been extensively employed in the chemical industry, as solid-acid catalysts, for the production of ε-caprolactam (precursor for Nylon-6).Keywords: Beckmann rearrangement; hierarchically porous; silicoaluminophosphates; soft-templating; solid-acid catalysis

Highly effective design strategy for the heterogenisation of chemo- and enantioselective organocatalysts

Co-reporter:Stephanie H. Newland, David J. Xuereb, Enrica Gianotti, Leonardo Marchese, Ramon Rios and Robert Raja

Catalysis Science & Technology 2015 vol. 5(Issue 2) pp:660-665

Publication Date(Web):04 Sep 2014

DOI:10.1039/C4CY00895B

We have demonstrated that the covalent heterogenisation of two homogeneous organocatalysts, cinchonine and 1,4-diazabicyclo[2.2.2]octane, onto the inner walls of mesoporous silica supports results in highly active and selective solid catalysts that are easily recoverable and recyclable. We have further highlighted the efficacy of our design rationale and its amenability for tailoring the nature of the active site via meticulous choice of pore-aperture and hydrophobicity to create a superior heterogenised analogue for Michael addition and Baylis Hillman reactions. It is envisaged that this immobilisation strategy could be rationally extended to the heterogenisation of a plethora of organocatalysts.

Spectroscopic chemical insights leading to the design of versatile sustainable composites for enhanced marine application

Co-reporter:Agnieszka S. Dzielendziak, James I. R. Blake, Richard Bounds, Karl A. Wilkinson, Marina Carravetta, Alan R. Chambers, Chris-Kriton Skylaris and Robert Raja

RSC Advances 2015 vol. 5(Issue 122) pp:101221-101231

Publication Date(Web):17 Nov 2015

DOI:10.1039/C5RA19197A

The viability of a novel sustainable polymeric composite material, based on photocurable linseed oil resin was explored, with a view to exploiting its potential in marine environments. The study focused on a UV-curable resin subjected to setting through photoinitiated cationic polymerisation. Deployment of heterogeneous solid catalysts, containing isolated Brønsted acid centres, further improved the efficiency of cationic polymerisation, leading to enhanced thermal stability and water resistance. These features are highly desirable in the design of composite resins for marine applications. A wide range of spectroscopic, calorimetric and thermogravimetric methods as well as computational simulations have been employed to study the physico-chemical characteristics of the resin and its resistance to black and grey waste, UV resistance and hygrothermal ageing. The findings have revealed that, unlike conventional epoxy resins, the ELO resin demonstrated no decrease in glass transition temperature, Tg, despite having been exposed to different methods of ageing. In addition, the water molecules that are absorbed by the resin during hygrothermal ageing have been found to be structurally-bound through hydrogen bonding, which is supported by initial computational studies. The structure–property correlations that have been derived help to better understand the ageing process, which could be beneficial in predicting the lifetimes of these sustainable polymeric composite materials and consequently developing novel chemical methods for improving their durability and stability.

Frontispiece: Utilizing Benign Oxidants for Selective Aerobic Oxidations Using Heterogenized Platinum Nanoparticle Catalysts

Co-reporter:Christopher S. Hinde;Arran M. Gill;Dr. Peter P. Wells; T. S. Andy Hor;Dr. Robert Raja

ChemPlusChem 2015 Volume 80( Issue 8) pp:

Publication Date(Web):

DOI:10.1002/cplu.201580861

Utilizing Benign Oxidants for Selective Aerobic Oxidations Using Heterogenized Platinum Nanoparticle Catalysts

Co-reporter:Christopher S. Hinde;Arran M. Gill;Dr. Peter P. Wells; T. S. Andy Hor;Dr. Robert Raja

ChemPlusChem 2015 Volume 80( Issue 8) pp:1226-1230

Publication Date(Web):

DOI:10.1002/cplu.201500195

Abstract

By using platinum nanoparticle catalysts that are generated in situ by extrusion from a porous copper chlorophosphate framework, the role of oxidants in the selective oxidation of benzyl alcohol to benzaldehyde was evaluated, with a view to establishing structure–property relationships. With a detailed study of the kinetic properties of the oxidation reaction, it has been determined that the aerobic oxidation pathways progress with lower levels of product selectivity and higher activation energies (72.4 kJ mol⁻¹) than the peroxide-based ones (23.6 kJ mol⁻¹); affording valuable insights in the design of solid catalysts for selective oxidation reactions. Furthermore, through the use of X-ray absorption spectroscopy, the effect of calcination temperature on the degree of extrusion and its influence on nanoparticle formation have been evaluated, leading to the establishment of structure–activity correlations between the observed activation energies and the proportion of nanoparticle species generated.

Role of Isolated Acid Sites and Influence of Pore Diameter in the Low-Temperature Dehydration of Ethanol

Co-reporter:Matthew E. Potter, Mary E. Cholerton, Julija Kezina, Richard Bounds, Marina Carravetta, Maela Manzoli, Enrica Gianotti, Michael Lefenfeld, and Robert Raja

ACS Catalysis 2014 Volume 4(Issue 11) pp:4161

Publication Date(Web):October 10, 2014

DOI:10.1021/cs501092b

Silicoaluminophosphates, SAPO-5 and SAPO-34, differ not only in their pore diameters and structural topology but also in their preferred mechanism of silicon substitution into the framework, which subsequently influences the nature of the acid sites for solid-acid-catalyzed transformations. This study combines 29Si NMR, FTIR, and DFT calculations for probing the nature of the isolated acid sites, thereby affording structure–property correlations, in the low-temperature catalytic dehydration of ethanol to ethylene.Keywords: 29Si NMR; ethanol dehydration; SAPO; single-site; solid-acid; structure−activity relationships; synergy

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

Co-reporter:Enrica Gianotti, Maela Manzoli, Matthew E. Potter, Vasudev N. Shetti, Danni Sun, James Paterson, Thomas M. Mezza, Alan Levy and Robert Raja

Chemical Science 2014 vol. 5(Issue 5) pp:1810-1819

Publication Date(Web):31 Jan 2014

DOI:10.1039/C3SC53088D

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.

Predictive design of engineered multifunctional solid catalysts

Co-reporter:Robert Raja, Matthew E. Potter and Stephanie H. Newland

Chemical Communications 2014 vol. 50(Issue 45) pp:5940-5957

Publication Date(Web):18 Mar 2014

DOI:10.1039/C4CC00834K

The ability to devise and design multifunctional active sites at the nanoscale, by drawing on the intricate ability of enzymes to evolve single-sites with distinctive catalytic function, has prompted complimentary and concordant developments in the field of catalyst design and in situ operando spectroscopy. Innovations in design-application approach have led to a more fundamental understanding of the nature of the active site and its mechanistic influence at a molecular level, that have enabled robust structure–property correlations to be established, which has facilitated the dextrous manipulation and predictive design of redox and solid-acid sites for industrially-significant, sustainable catalytic transformations.

Iridium–Bismuth Cluster Complexes Yield Bimetallic Nano-Catalysts for the Direct Oxidation of 3-Picoline to Niacin

Co-reporter:Richard D. Adams, Mingwei Chen, Gaya Elpitiya, Matthew E. Potter, and Robert Raja

ACS Catalysis 2013 Volume 3(Issue 12) pp:3106

Publication Date(Web):November 18, 2013

DOI:10.1021/cs400880k

The reaction of Ir3(CO)9(μ3-Bi), 1, with BiPh3 has yielded a iridium–bismuth cluster complex Ir5(CO)10(μ3-Bi)2(μ4-Bi), 2. The first examples of bimetallic iridium–bismuth nanoparticles have been subsequently synthesized from 1 and 2, and these have been securely anchored onto the inner walls of mesoporous silica. These isolated, bimetallic iridium–bismuth nanoparticles display a superior catalytic performance, when compared to their analogous monometallic counterparts and equivalent physical mixtures, in the C–H activation of 3-picoline to yield niacin.Keywords: anchored nanoparticles; catalytic synergy; C−H activation; iridium−bismuth; nanocluster; niacin; selective oxidation

Probing the origin of in situ generated nanoparticles as sustainable oxidation catalysts

Co-reporter:Christopher S. Hinde, Sivan Van Aswegen, Gillian Collins, Justin D. Holmes, T. S. Andy Hor and Robert Raja

Dalton Transactions 2013 vol. 42(Issue 35) pp:12600-12605

Publication Date(Web):14 May 2013

DOI:10.1039/C3DT50606A

A novel method for the in situ generation of catalytically active small metal nanoparticles, by anion extrusion on a parent porous copper chloropyrophosphate framework, has been developed to generate gold, platinum and palladium nanoparticles for sustainable catalytic oxidations using molecular oxygen as the oxidant. Transmission electron microscopy coupled with detailed structural and physico-chemical characterisation, in combination with in-depth kinetic analysis have afforded profound insights into the nature of the active site for facilitating structure–property correlations.

Investigating site-specific interactions and probing their role in modifying the acid-strength in framework architectures

Co-reporter:Matthew E. Potter, Danni Sun, Enrica Gianotti, Maela Manzoli and Robert Raja

Physical Chemistry Chemical Physics 2013 vol. 15(Issue 32) pp:13288-13295

Publication Date(Web):23 May 2013

DOI:10.1039/C3CP51182K

The ability to adroitly tailor acid-strength using specifically-engineered bimetallic nanoporous materials has been investigated with a view to exploiting their potential in solid-acid catalysed transformations. Further, it has been demonstrated that through site-specific interactions, extra-framework zinc ions can suitably modify the acidity of Brønsted acid sites, to stimulate diverse catalytic responses, when combined with isomorphously-substituted framework metal cations within porous architectures, for the Beckmann rearrangement of cyclohexanone oxime and in the isopropylation of benzene.

Transition Metal versus Heavy Metal Synergy in Selective Catalytic Oxidations

Co-reporter:Matthew E. Potter, A. James Paterson, and Robert Raja

ACS Catalysis 2012 Volume 2(Issue 12) pp:2446

Publication Date(Web):October 19, 2012

DOI:10.1021/cs300404u

Simultaneous framework incorporation of heavy metal ions such as Ru(III) and Sn(IV) into aluminophosphate architectures generates novel bimetallic active sites, which facilitate synergistic interactions, affording high degrees of selectivity and activity in the catalytic oxidations as compared with analogous bimetallic systems, in which transition metals, such as Co(III) and Ti(IV), have been similarly incorporated.Keywords: catalytic synergy; microporous solids; multifunctional active sites; oxidation; redox catalysts

Design strategies for engineering selectivity in bio-inspired heterogeneous catalysts

Co-reporter:David J. Xuereb and Robert Raja

Catalysis Science & Technology 2011 vol. 1(Issue 4) pp:517-534

Publication Date(Web):11 Mar 2011

DOI:10.1039/C0CY00088D

In an era where the requirement for greener chemical processes is so exigent, the growing need for developing novel routes to environmentally benign and sustainable catalytic procedures is highly desirable. Heterogenising bio-inspired transition-metal complexes on a diverse range of porous supports provides a viable alternative for achieving some of these goals, particularly in terms of reducing waste and by increasing efficiency and selectivity in industrially significant catalytic processes. Choosing an appropriate spatial-restricting support is vital for facilitating enhancements in rate and stereoselectivity, as this plays a pivotal role in optimising the orientation of desired transition-states through varying confinement effects, by utilising a myriad of pore-window apertures for regulating diffusion of organic molecules. The nature of the active site can also be further attuned by adopting an appropriate encapsulation strategy, which could eventually assist in maximising the hydrophilic/hydrophobic character of the support. The nature of the active site and its involvement in the catalytic process can be characterised by using a wide-range of physico-chemcial spectroscopic techniques, which provide valuable insights for drawing mechanistic relationships, which in turn facilitates structure–property correlations.

Spectroscopic investigation into the nature of the active sites for epoxidation reactions using vanadium-based aluminophosphate catalysts

Co-reporter:Muthusamy Vishnuvarthan, A. James Paterson, Robert Raja, Andrea Piovano, Francesca Bonino, Enrica Gianotti, Gloria Berlier

Microporous and Mesoporous Materials 2011 Volume 138(1–3) pp:167-175

Publication Date(Web):February 2011

DOI:10.1016/j.micromeso.2010.09.010

VAlPO-5 and VAlPO-11 catalysts were synthesized and their structural features characterized by a range of spectroscopic techniques (UV–Vis, Raman and IR spectroscopies) revealing valuable information on the nature of the incorporated vanadium species. A preliminary investigation into the catalytic potential of these catalysts was carried out by studying the epoxidation of cyclopentene to its corresponding epoxide using a solid source of “active” oxygen, acetylperoxyborate (APB) as the oxidant. UV–Vis spectra showed strong bands in the 40,000–35,000 cm−1 range, that can be assigned to isolated Td-like oxovanadium(V) (V5+ = O vanadyls), along with a component around 35,000 cm−1 due to a small fraction of Td V5+ = O in di- or oligomeric VxOy clusters. The V5+ = O ions were reversibly transformed to V4+ = O species by reduction, and could also change their coordination (to octahedral geometry) in the presence of water molecules. The presence of isolated V5+ = O was confirmed by resonant Raman studies. IR spectroscopy of adsorbed probes (CO and NO) revealed the presence of two families of framework V4+ = O ions with different Lewis acidity VA4+andVB4+ forming monocarbonyls (bands at 2192 cm−1 and 2184 cm−1) and di-nitrosyls (bands at 1905–1755 cm−1 and 1835–1680 cm−1). Small differences in the local environment of the vanadyl ions (symmetry, defects), that can have an influence over their Lewis acidity, did not play a major role in influencing the overall product selectivity, whilst the differences in rate and turnover frequency could be explained on the basis of the differing pore diameters of the two catalysts.Graphical abstractVanadyls ions in AlPOs framework: On the basis of a combined FTIR, DR UV–Vis, and Raman characterization, we propose that the active sites for the highly selective oxidation of cyclopentene to the corresponding epoxide are framework incorporated oxovanadium ions, that can undergo reversible V5+=O⇌V4+=OV5+=O⇌V4+=O (left and right, respectively) transformation.Research highlights► DR UV–Vis, resonant Raman and IR characterization of VAPO-5 and VAPO-11 catalysts. ► Evidence for reversible V5+=O⇌V4+=OV5+=O⇌V4+=O transformation. ► Changes from tetrahedral to octahedral coordination upon ligands interaction. ► High activity and selectivity in the epoxidation of cyclopentene with acetylperoxyborate.

The role of isolated active centres in high-performance bioinspired selective oxidation catalysts

Co-reporter:Joanna Dzierzak, Emanuela Bottinelli, Gloria Berlier, Enrica Gianotti, Eugen Stulz, Radoslaw Michal Kowalczyk and Robert Raja

Chemical Communications 2010 vol. 46(Issue 16) pp:2805-2807

Publication Date(Web):02 Mar 2010

DOI:10.1039/B926721B

Transition-metal complexes containing amino acids encapsulated within solid supports generate isolated active centres that function as effective selective oxidation catalysts using benign oxidants such as air and display high turnovers and selectivity in industrially significant oxidation reactions.

New Catalytic Liquid-Phase Ammoxidation Approach to the Preparation of Niacin (Vitamin B3)

Co-reporter:Robert Raja, Richard D. Adams, Douglas A. Blom, William C. Pearl , Jr., Enrica Gianotti and John Meurig Thomas

Langmuir 2009 Volume 25(Issue 13) pp:7200-7204

Publication Date(Web):May 22, 2009

DOI:10.1021/la900803a

New highly dispersed bimetallic nanoscale catalysts based on rhenium combined with antimony or bismuth have been shown to be highly effective for the ammoxidation of 3-picoline to nicotinonitrile (precursor for vitamin B3) under mild conditions in the liquid phase.

Exploiting Nanospace for Asymmetric Catalysis: Confinement of Immobilized, Single-Site Chiral Catalysts Enhances Enantioselectivity

Co-reporter:John Meurig Thomas and Robert Raja

Accounts of Chemical Research 2008 Volume 41(Issue 6) pp:708

Publication Date(Web):May 28, 2008

DOI:10.1021/ar700217y

In the mid-1990s, it became possible to prepare high-area silicas having pore diameters controllably adjustable in the range ca. 20−200 Å. Moreover, the inner walls of these nanoporous solids could be functionalized to yield single-site, chiral, catalytically active organometallic centers, the precise structures of which could be determined using in situ X-ray absorption and FTIR and multinuclear magic angle spinning (MAS) NMR spectroscopy. This approach opened up the prospect of performing heterogeneous enantioselective conversions in a novel manner, under the spatial restrictions imposed by the nanocavities within which the reactions occur. In particular, it suggested an alternative method for preparing pharmaceutically and agrochemically useful asymmetric products by capitalizing on the notion, initially tentatively perceived, that spatial confinement of prochiral reactants (and transition states formed at the chiral active center) would provide an altogether new method of boosting the enantioselectivity of the anchored chiral catalyst. Initially, we anchored chiral single-site heterogeneous catalysts to nanopores covalently via a ligand attached to Pd(II) or Rh(I) centers. Later, we employed a more convenient and cheaper electrostatic method, relying in part on strong hydrogen bonding. This Account provides many examples of these processes, encompassing hydrogenations, oxidations, and aminations. Of particular note is the facile synthesis from methyl benzoylformate of methyl mandelate, which is a precursor in the synthesis of pemoline, a stimulant of the central nervous system; our procedure offers several viable methods for reducing ketocarboxylic acids. In addition to relying on earlier (synchrotron-based) in situ techniques for characterizing catalysts, we have constructed experimental procedures involving robotically controlled catalytic reactors that allow the kinetics of conversion and enantioselectivity to be monitored continually, and we have access to sophisticated, high-sensitivity chiral chromatographic facilities and automated high-throughput combinatorial test rigs so as to optimize the reaction conditions (e.g., H2 pressure, temperature, time on-stream, pH, and choice of ligand and central metal ion) for high enantioselectivity. This Account reports our discoveries of selective hydrogenations and aminations of synthetic, pharmaceutical, and biological significance, and the findings of other researchers who have achieved similar success in oxidations, dehydrations, cyclopropanations, and hydroformylations. Although the practical advantages and broad general principles governing the enhancement of enantioselectivity through spatial confinement are clear, we require a deeper theoretical understanding of the details pertaining to the phenomenology involved, particularly through molecular dynamics simulations. Ample scope exists for the general exploitation of nanospace in asymmetric hydrogenations with transition metal complexes and for its deployment for the formation of C−N, C−C, C−O, C−S, and other bonds.

Toward Less Dependence on Platinum Group Metal Catalysts: The Merits of Utilizing Tin

Co-reporter:Richard D. Adams, Douglas A. Blom, Burjor Captain, Robert Raja, John Meurig Thomas and Eszter Trufan

Langmuir 2008 Volume 24(Issue 17) pp:9223-9226

Publication Date(Web):August 9, 2008

DOI:10.1021/la801759d

Minute stoichiometric bimetallic clusters rich in tin (PtSn2, RhSn2, and RuSn2) are powerful selective hydrogenation catalysts: these “molecular metallic” entities, supported on mesoporous silica and characterized by aberration-corrected electron microscopy, yield high percentages of cyclododecene (CDE) at fractional conversions ranging from 0.45 to 0.70 of the parent cyclododecatriene (CDT) at modest temperatures and under solvent-free conditions.

Facile, One-Step Production of Niacin (Vitamin B3) and Other Nitrogen-Containing Pharmaceutical Chemicals with a Single-Site Heterogeneous Catalyst

Co-reporter:Robert Raja Dr.;JohnMeurig Thomas Sir;Michael Greenhill-Hooper Dr.;StevenV. Ley ;FilipeA. AlmeidaPaz Dr.

Chemistry - A European Journal 2008 Volume 14( Issue 8) pp:2340-2348

Publication Date(Web):

DOI:10.1002/chem.200701679

Abstract

Niacin (3-picolinic acid), which is extensively used as vitamin B₃ in foodstuffs and as a cholesterol-lowering agent, along with other oxygenated products of the picolines, 4-methylquinoline, and a variety of pyrimidines and pyridazines, may be produced in a single-step, environmentally benign fashion by combining single-site, open-structure, heterogeneous catalysts with a solid source of active oxygen, namely acetyl peroxyborate (APB), in the absence of an organic solvent. The high activities, selectivities, and the relatively mild conditions employed with this single-site heterogeneous catalyst, coupled with ease of transport, storage, and stability of the solid oxidant, augurs well for the future use of APB in conjunction with other open-structure, single-site catalysts for fine-chemical, pharmaceutical, and agrochemical applications.

Cover Picture: Facile, One-Step Production of Niacin (Vitamin B3) and Other Nitrogen-Containing Pharmaceutical Chemicals with a Single-Site Heterogeneous Catalyst (Chem. Eur. J. 8/2008)

Co-reporter:Robert Raja Dr.;JohnMeurig Thomas Sir;Michael Greenhill-Hooper Dr.;StevenV. Ley ;FilipeA. AlmeidaPaz Dr.

Chemistry - A European Journal 2008 Volume 14( Issue 8) pp:

Publication Date(Web):

DOI:10.1002/chem.200890023

A high-performance selective oxidation system for the facile production of fine chemicals

Co-reporter:Robert Raja, John Meurig Thomas, Mike Greenhill-Hooper and Violeta Doukova

Chemical Communications 2007 (Issue 19) pp:1924-1926

Publication Date(Web):19 Apr 2007

DOI:10.1039/B618090F

MnIIIAlPO-5 and CrVIAlPO-5 redox (microporous) catalysts are effective, in the presence of dissolved acetylperoxyborate (APB) under mild conditions (333–373 K), and much superior to the titanosilicate, TS-1 (also a single-site heterogeneous catalyst), in the selective oxidation of primary, secondary, benzylic and other unsaturated alcohols, p-cymene, methyl cyclohexene and other speciality organics which are of value in the fine-chemical and pharmaceutical industries.

Bimetallic Ru–Sn Nanoparticle Catalysts for the Solvent-Free Selective Hydrogenation of 1,5,9-Cyclododecatriene to Cyclododecene

Co-reporter:Richard D. Adams Dr.;Erin M. Boswell;Burjor Captain Dr.;Ana B. Hungria Dr.;Paul A. Midgley Dr. Dr.;John Meurig Thomas Sir

Angewandte Chemie 2007 Volume 119(Issue 43) pp:

Publication Date(Web):20 SEP 2007

DOI:10.1002/ange.200702274

Zwei Metalle mit Wirkung: Neue RuSn-Nanopartikelkatalysatoren, die durch thermische Behandlung der Carbonylcluster [Ru₄(μ₄-SnPh)₂(μ-SnPh₂)_4−x(CO)_12−x] (x=0, 2, 3, 4) auf Silicaträgern präpariert wurden (siehe Beispiel; Ru grün, Sn blau, O rot), sind aktive Katalysatoren für die hoch selektive Hydrierung von 1,5,9-Cyclododecatrien zu Cyclododecen unter milden Bedingungen.

Bimetallic Ru–Sn Nanoparticle Catalysts for the Solvent-Free Selective Hydrogenation of 1,5,9-Cyclododecatriene to Cyclododecene

Co-reporter:Richard D. Adams Dr.;Erin M. Boswell;Burjor Captain Dr.;Ana B. Hungria Dr.;Paul A. Midgley Dr. Dr.;John Meurig Thomas Sir

Angewandte Chemie International Edition 2007 Volume 46(Issue 43) pp:

Publication Date(Web):20 SEP 2007

DOI:10.1002/anie.200702274

Tin(n)y catalysts: Bimetallic RuSn supported nanoparticle catalysts (see picture; Ru green, Sn blue, O red), prepared from the carbonyl-cluster precursors [Ru₄(μ₄-SnPh)₂(μ-SnPh₂)_4−x(CO)_12−x] (x=0, 2, 3, 4) are shown to be active catalysts for the highly selective hydrogenation of 1,5,9-cyclododecatriene to cyclododecene under mild conditions.

Predictive design of engineered multifunctional solid catalysts

Co-reporter:Robert Raja, Matthew E. Potter and Stephanie H. Newland

Chemical Communications 2014 - vol. 50(Issue 45) pp:NaN5957-5957

Publication Date(Web):2014/03/18

DOI:10.1039/C4CC00834K

The ability to devise and design multifunctional active sites at the nanoscale, by drawing on the intricate ability of enzymes to evolve single-sites with distinctive catalytic function, has prompted complimentary and concordant developments in the field of catalyst design and in situ operando spectroscopy. Innovations in design-application approach have led to a more fundamental understanding of the nature of the active site and its mechanistic influence at a molecular level, that have enabled robust structure–property correlations to be established, which has facilitated the dextrous manipulation and predictive design of redox and solid-acid sites for industrially-significant, sustainable catalytic transformations.

Highly effective design strategy for the heterogenisation of chemo- and enantioselective organocatalysts

Co-reporter:Stephanie H. Newland, David J. Xuereb, Enrica Gianotti, Leonardo Marchese, Ramon Rios and Robert Raja

Catalysis Science & Technology (2011-Present) 2015 - vol. 5(Issue 2) pp:NaN665-665

Publication Date(Web):2014/09/04

DOI:10.1039/C4CY00895B

We have demonstrated that the covalent heterogenisation of two homogeneous organocatalysts, cinchonine and 1,4-diazabicyclo[2.2.2]octane, onto the inner walls of mesoporous silica supports results in highly active and selective solid catalysts that are easily recoverable and recyclable. We have further highlighted the efficacy of our design rationale and its amenability for tailoring the nature of the active site via meticulous choice of pore-aperture and hydrophobicity to create a superior heterogenised analogue for Michael addition and Baylis Hillman reactions. It is envisaged that this immobilisation strategy could be rationally extended to the heterogenisation of a plethora of organocatalysts.

Design and control of Lewis acid sites in Sn-substituted microporous architectures

Co-reporter:Khaled M. H. Mohammed, Arunabhiram Chutia, June Callison, Peter P. Wells, Emma K. Gibson, Andrew M. Beale, C. Richard A. Catlow and Robert Raja

Journal of Materials Chemistry A 2016 - vol. 4(Issue 15) pp:NaN5712-5712

Publication Date(Web):2016/03/21

DOI:10.1039/C5TA10283A

Monometallic and bimetallic tin-containing framework architectures have been prepared by hydrothermal methods. Structural and spectroscopic techniques were used to probe the nature of the solid-acid sites, at the molecular level, using a combination of XRD, DR UV-Vis, solid state MAS NMR (119Sn, 27Al and 31P) and XAFS. The nature and strength of the solid-acid sites were experimentally probed by FT-IR spectroscopy using CD3CN as a probe molecule. To elucidate further the local-structure, the structural characteristics of the Sn sites were probed using DFT calculations, with a view to rationalising the experimental findings. These detailed structural and spectroscopic studies revealed the presence of multiple Sn environments, with the monometallic SnAlPO-5 catalyst displaying a greater number of tetrahedral Sn(IV) active centres. These framework Sn(IV) centres generated strong Lewis acid sites, when compared with their bimetallic Co–Sn analogue, thereby affording attractive possibilities for modulating catalytic reactivity.

Utilisation of gold nanoparticles on amine-functionalised UiO-66 (NH2-UiO-66) nanocrystals for selective tandem catalytic reactions

Co-reporter:Christopher S. Hinde, William R. Webb, Benny K. J. Chew, Hui Ru Tan, Wen-Hua Zhang, T. S. Andy Hor and Robert Raja

Chemical Communications 2016 - vol. 52(Issue 39) pp:NaN6560-6560

Publication Date(Web):2016/04/11

DOI:10.1039/C6CC02169G

Colloidal deposition of gold nanoparticles (Au NPs) onto NH2-UiO-66 nanocrystals has been demonstrated with the resulting hybrid catalyst proving robust and versatile for one-pot, heterogeneous conversions involving the selective oxidation of primary alcohols in tandem with Knoevenagel condensation reactions. Within these systems, structure–property correlations have been established to confirm that the active sites for the oxidation and condensation reactions are intrinsically correlated with the Au NPs and pendant amine groups respectively.

The role of isolated active centres in high-performance bioinspired selective oxidation catalysts

Co-reporter:Joanna Dzierzak, Emanuela Bottinelli, Gloria Berlier, Enrica Gianotti, Eugen Stulz, Radoslaw Michal Kowalczyk and Robert Raja

Chemical Communications 2010 - vol. 46(Issue 16) pp:NaN2807-2807

Publication Date(Web):2010/03/02

DOI:10.1039/B926721B

Transition-metal complexes containing amino acids encapsulated within solid supports generate isolated active centres that function as effective selective oxidation catalysts using benign oxidants such as air and display high turnovers and selectivity in industrially significant oxidation reactions.

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

Co-reporter:Enrica Gianotti, Maela Manzoli, Matthew E. Potter, Vasudev N. Shetti, Danni Sun, James Paterson, Thomas M. Mezza, Alan Levy and Robert Raja

Chemical Science (2010-Present) 2014 - vol. 5(Issue 5) pp:NaN1819-1819

Publication Date(Web):2014/01/31

DOI:10.1039/C3SC53088D

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.

The curious effects of integrating bimetallic active centres within nanoporous architectures for acid-catalysed transformations

Co-reporter:Matthew E. Potter, Danni Sun and Robert Raja

Catalysis Science & Technology (2011-Present) 2016 - vol. 6(Issue 8) pp:NaN2622-2622

Publication Date(Web):2016/01/12

DOI:10.1039/C5CY02061A

The resourceful combination of distinct Mg, Zn and Si active-sites within a single aluminophosphate framework, via simultaneous isomorphous substitution, has afforded unique bimetallic nanoporous heterogeneous catalysts. Unique site-specific interactions have been engineered, at the molecular level, to facilitate catalytic modifications and optimize product yield. By the dextrous incorporation of individual transition-metal active centres, we are able to intricately control the precise nature of the Brønsted acid sites, thereby influencing their catalytic behaviour for the industrially relevant acid-catalysed Beckmann rearrangement of cyclohexanone oxime and isopropylation of benzene.

Design strategies for engineering selectivity in bio-inspired heterogeneous catalysts

Co-reporter:David J. Xuereb and Robert Raja

Catalysis Science & Technology (2011-Present) 2011 - vol. 1(Issue 4) pp:NaN534-534

Publication Date(Web):2011/03/11

DOI:10.1039/C0CY00088D

In an era where the requirement for greener chemical processes is so exigent, the growing need for developing novel routes to environmentally benign and sustainable catalytic procedures is highly desirable. Heterogenising bio-inspired transition-metal complexes on a diverse range of porous supports provides a viable alternative for achieving some of these goals, particularly in terms of reducing waste and by increasing efficiency and selectivity in industrially significant catalytic processes. Choosing an appropriate spatial-restricting support is vital for facilitating enhancements in rate and stereoselectivity, as this plays a pivotal role in optimising the orientation of desired transition-states through varying confinement effects, by utilising a myriad of pore-window apertures for regulating diffusion of organic molecules. The nature of the active site can also be further attuned by adopting an appropriate encapsulation strategy, which could eventually assist in maximising the hydrophilic/hydrophobic character of the support. The nature of the active site and its involvement in the catalytic process can be characterised by using a wide-range of physico-chemcial spectroscopic techniques, which provide valuable insights for drawing mechanistic relationships, which in turn facilitates structure–property correlations.

Probing the origin of in situ generated nanoparticles as sustainable oxidation catalysts

Co-reporter:Christopher S. Hinde, Sivan Van Aswegen, Gillian Collins, Justin D. Holmes, T. S. Andy Hor and Robert Raja

Dalton Transactions 2013 - vol. 42(Issue 35) pp:NaN12605-12605

Publication Date(Web):2013/05/14

DOI:10.1039/C3DT50606A

A novel method for the in situ generation of catalytically active small metal nanoparticles, by anion extrusion on a parent porous copper chloropyrophosphate framework, has been developed to generate gold, platinum and palladium nanoparticles for sustainable catalytic oxidations using molecular oxygen as the oxidant. Transmission electron microscopy coupled with detailed structural and physico-chemical characterisation, in combination with in-depth kinetic analysis have afforded profound insights into the nature of the active site for facilitating structure–property correlations.

Investigating site-specific interactions and probing their role in modifying the acid-strength in framework architectures

Co-reporter:Matthew E. Potter, Danni Sun, Enrica Gianotti, Maela Manzoli and Robert Raja

Physical Chemistry Chemical Physics 2013 - vol. 15(Issue 32) pp:NaN13295-13295

Publication Date(Web):2013/05/23

DOI:10.1039/C3CP51182K

The ability to adroitly tailor acid-strength using specifically-engineered bimetallic nanoporous materials has been investigated with a view to exploiting their potential in solid-acid catalysed transformations. Further, it has been demonstrated that through site-specific interactions, extra-framework zinc ions can suitably modify the acidity of Brønsted acid sites, to stimulate diverse catalytic responses, when combined with isomorphously-substituted framework metal cations within porous architectures, for the Beckmann rearrangement of cyclohexanone oxime and in the isopropylation of benzene.

A high-performance selective oxidation system for the facile production of fine chemicals

Co-reporter:Robert Raja, John Meurig Thomas, Mike Greenhill-Hooper and Violeta Doukova

Chemical Communications 2007(Issue 19) pp:

Publication Date(Web):

DOI:10.1039/B618090F