Modeling the framework stability and catalytic activity of pure and transition metal-doped zeotypes

Corà, Furio; Alfredsson, Maria; Barker, Chris; Bell, R. G.; Foster, Martin D.; Saadoune, Iman; Simperler, Alexandra; Catlow, C. Richard A.

doi:10.1016/s0022-4596(03)00275-5

Cited by 51 publications

(46 citation statements)

References 105 publications

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“…The structure of undoped AlPO-5, with lattice parameters a = b = 13.75 Å, c = 8.35 Å and individual Al-O and P-O bond lengths of 1.74 ± 0.02 and 1.54 ± 0.01 Å is in good agreement with literature values (Table S4 and S5). 22,24 On isomorphously substituting a Co 2+ ion for Al 3+ (and introducing the appropriate charge-balancing proton) both the high spin and low spin d 7 electronic configurations were investigated. The high-spin state was found to be the stable electronic state, as expected for a first row transition element four coordinated by electron donor ligands.…”

Section: Resultsmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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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 structureproperty relationships, in the wider context of designing sustainable catalytic oxidations with porous solids.

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Section: Resultsmentioning

confidence: 99%

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

et al. 2015

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“…50 The periodic DFT calculations were performed using the CRYSTAL software package. 51,52 Two structures representative of monomeric V centers in the AlPO-5 framework, and compatible with the experimental findings, were investigated.…”

Section: Methodsmentioning

confidence: 99%

Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

et al. 2014

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“…Extensive measurements, as well as ab initio quantum computational studies (19)(20)(21)(22), reveal that the Brönsted acidity of a particular kind of isolated site varies as a function of the actual open structure in a manner that is rather complicated. For example, tetrahedrally bound Mg II ions in MAlPO-5 and also in other MAlPO frameworks (23) generate stronger Brönsted acid sites than Mg II ions in MAlPO-36.…”

Section: Methodsmentioning

confidence: 99%

Design of a “green” one-step catalytic production of ε-caprolactam (precursor of nylon-6)

Thomas

Raja

2005

Proc. Natl. Acad. Sci. U.S.A.

123

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The ever-increasing industrial demand for nylon-6 (polycaprolactam) necessitates the development of environmentally benign methods of producing its precursor, -caprolactam, from cyclohexanone. It is currently manufactured in two popular double-step processes, each of which uses highly aggressive reagents, and each generates substantial quantities of largely unwanted ammonium sulfate as by-product. Here we describe a viable laboratory-scale, single-step, solvent-free process of producing -caprolactam using a family of designed bifunctional, heterogeneous, nanoporous catalysts containing isolated acidic and redox sites, which smoothly convert cyclohexanone to -caprolactam with selectivities in the range 65-78% in air and ammonia at 80°C. hydroxylamine ͉ single-site heterogeneous catalysts (SSHC) ͉ ammoximation A precursor to nylon-6, -caprolactam, is manufactured on a massive scale through the agency of two currently favored methods, each of which starts from cyclohexanone, 1 (Scheme 1). In one, the oxidant that forms the intermediate cyclohexanone oxime, 2, is hydroxylamine sulfate, and ammonia is used to neutralize the liberated acid. In the other, a far less environmentally aggressive oxidant, aqueous H 2 O 2 is used in conjunction with a solid redox catalyst, a titanosilicate known as TS-1 (Fig. 1) to ammoximize the ketone. However, both methods entail the use of oleum to effect the Beckmann rearrangement of the oxime to the lactam, 3, and the former method generates very large quantities of low-value ammonium sulfate as by-product.Here, we describe a route that produces 3 without generating unwanted ammonium sulfate in an environmentally benign, solvent-free manner using air as oxidant and nanoporous solid catalysts. These nanoporous acid catalysts (1, 2) are bifunctional because they also have within them isolated redox centers (Co III , Mn III , or Fe III ions tetrahedrally coordinated to oxygen) (3) at which air (or oxygen) in the presence of ammonia forms hydroxylamine in situ. Because the open structure of the bifunctional catalysts contain pores large enough to facilitate the diffusion of reactants, intermediates, and products within them, the parent ketone is sequentially and smoothly converted to the lactam when it, air, and ammonia are brought into contact with one another within the solid catalysts. The solids designed for this purpose, like those that we have used to effect other environmentally benign oxidations, such as the conversion of cyclohexane in air to adipic acid with 65% selectivity (4) (thereby circumventing the production of N 2 O, a greenhouse gas that also depletes the ozone layer), are single-site heterogeneous catalysts (SSHCs).SSHCs are those in which the active centers are spatially isolated from one another [and uniformly distributed through the solid (5)] such that each site has the same energy of interaction between it and the incoming reactant (6). Moreover, that energy remains constant when all of the sites participate in catalytic turnover. SSHCs possess the supreme advanta...

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Modeling the framework stability and catalytic activity of pure and transition metal-doped zeotypes

Cited by 51 publications

References 105 publications

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Spectroscopic and Computational Insights on Catalytic Synergy in Bimetallic Aluminophosphate Catalysts

Structure of the Catalytic Active Sites in Vanadium-Doped Aluminophosphate Microporous Materials. New Evidence from Spin Density Studies

Design of a “green” one-step catalytic production of ε-caprolactam (precursor of nylon-6)

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