Heterogeneous Catalysts for Liquid-Phase Oxidations:  Philosophers' Stones or Trojan Horses?

Sheldon, Roger A.; Wallau, Martin; Arends, Isabel W. C. E.; Schuchardt, Ulf

doi:10.1021/ar9700163

Cited by 948 publications

(616 citation statements)

References 74 publications

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“…22 The lower activity of catalyst SGMo II could be ascribed to diffusion, expected to be more difficult owing to its smaller surface area and pore volume (0.15 cm 3 g -1 , compared with 0.24 cm 3 g -1 for catalyst SGMo I; both systems are microporous). Leaching experiments 23 carried out with catalyst SGMo I suggested that catalysis was ca. 50% homogeneous.…”

Section: Entrapment Via the Sol-gel Methodsmentioning

confidence: 99%

“…Leaching experiments proved that catalysis was indeed heterogeneous. 23 The performance of these systems with other substrates was tested using an aged (and previously used) catalyst 4, keeping an [alkene]/[Re] molar ratio of 175. With styrene, no conversion was observed even after 24 h; in the same reaction time, 1-octene gave a TON = 28, and norbornene gave 84, both with 100% selectivity.…”

Section: [Rech 3 O 3 ] Entrapped In Silica Matrices Via the Solgel Mementioning

confidence: 99%

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Heterogenization of alkene epoxidation catalysts

Buffon¹,

Schuchardt²

2003

J. Braz. Chem. Soc.

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Este trabalho descreve nosso esforço em heterogeneizar catalisadores para epoxidação. Tanto o molibdênio ancorado quanto o engaiolado pelo método de sol-gel mostraram grande seletividade, mas possuem suas atividades fortemente reduzidas. Por outro lado, silicatos de molibdênio foram muito ativos e estáveis até a formação de diols na mistura reacional. Catalisadores heterogeneizados de rênio foram menos ativos, mas permitiram o uso do peróxido de hidrogênio anidro como oxidante. Contudo, o alto custo e a dificuldade de regeneração impedem a aplicação industrial destes catalisadores. Durante estas investigações, descobrimos que a alumina sozinha é ativa para epoxidação com peróxido de hidrogênio anidro, fornecendo boas conversões para epóxidos com alta seletividade. Mais pesquisa é necessária para esclarecer a natureza dos grupos hidroxilas responsáveis pela atividade catalítica, para produzir materiais que permitem a obtenção de epóxidos com alta seletividade em condições industriais.This account describes our efforts to heterogenize epoxidation catalysts. Anchored and sol-gel entrapped molybdenum were shown to be very selective, but had a strongly reduced activity. On the other hand, molybdenum silicates were very active and stable as long as no diols were present in the reaction mixture. Heterogenized rhenium catalysts were less active but allowed the use of anhydrous hydrogen peroxide as oxidant. However, the high cost and difficult regeneration prevents the industrial use of these catalysts. During these investigations, we found that alumina alone is active in the epoxidation with anhydrous hydrogen peroxide, giving good conversions to epoxides with high selectivity. More research is needed in order to clarify the nature of the hydroxyl groups responsible for its catalytic activity and thus to produce an appropriate material which would allow the obtention of epoxides with high selectivity under industrial conditions.

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Section: Entrapment Via the Sol-gel Methodsmentioning

confidence: 99%

Section: [Rech 3 O 3 ] Entrapped In Silica Matrices Via the Solgel Mementioning

confidence: 99%

Heterogenization of alkene epoxidation catalysts

Buffon¹,

Schuchardt²

2003

J. Braz. Chem. Soc.

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“…This includes the use of metal complexes, 196 metal oxides 197,198 metal nanoparticles, 199,200 and investigation of both liquid and gas phase systems. 201 For example, the oxidation of cyclohexane over MoO 3 in gas phase, investigated by means of EPR spin trapping in aerobic and anaerobic conditions, showed evidence of a Mars and Van Krevelen mechanism.…”

Section: Cyclohexane Oxidation: An Exploited Case Of Autoxidationmentioning

confidence: 99%

Catalytic oxygen activation versus autoxidation for industrial applications: a physicochemical approach

Liu

Ryabenkova

Conte

2015

Phys. Chem. Chem. Phys.

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The activation and use of oxygen for the oxidation and functionalization of organic substrates is among the most important reactions in a chemist's toolbox. Nevertheless, despite the vast literature on catalytic oxidation, the phenomenon of autoxidation, an ever-present background reaction that occurs in virtually every oxidation process, is often neglected. In contrast, autoxidation can affect the selectivity to a desired product, to those dictated by pure freeradical chain pathways, thus affecting the activity of any catalyst used to carry out a reaction.This critical review compares catalytic oxidation routes by transition metals versus autoxidation, particularly focusing on the industrial context, where highly selective and "green" processes are needed. Furthermore, the application of useful tests to discriminate between different oxygen activation routes, especially in the area of hydrocarbon oxidation, with the aim of an enhanced catalyst design, is described and discussed. In fact, one of the major targets of selective oxidation is the use of molecular oxygen as ultimate oxidant, combined with the development of catalysts capable to perform the catalytic cycle in a real energy and cost effective manner on a large scale. To achieve this goal, insights from metallo-proteins that could find application in some areas of industrial catalysis are presented, as well as considering the physicochemical principles that are at the fundament of oxidation and autoxidation processes.3

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“…This exciting concept 108 can now be potentially extended to other systems to facilitate one-pot cascade reactions with high activities and selectivities. These initial studies and many others [103][104][105][106][107][108] that underpin the potential application of hierarchical molecular sieves in catalysis, have been promising and have highlighted the ability of the hierarchical systems to circumvent the mass-transfer problems that have plagued catalytically promising microporous molecular sieves. Recent advances 3,67,71,75,97 in creating well-defined, multifunctional single-sites at the atomic level on microporous architectures need to be suitably integrated and adapted for the design and synthesis of hybrid hierarchical systems.…”

Section: Computational Design Of Active Sitesmentioning

confidence: 99%

Predictive design of engineered multifunctional solid catalysts

2014

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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.

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Heterogeneous Catalysts for Liquid-Phase Oxidations: Philosophers' Stones or Trojan Horses?

Cited by 948 publications

References 74 publications

Heterogenization of alkene epoxidation catalysts

Heterogenization of alkene epoxidation catalysts

Catalytic oxygen activation versus autoxidation for industrial applications: a physicochemical approach

Predictive design of engineered multifunctional solid catalysts

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