Catalysts smart

Smallpox vaccine Smalt Smaltite SMA resins SMART Smart catalysts Smart gels Smart hydrogels Smart material Smart materials... 

Hill, C. L. and Zhang, X. A smart catalyst that self-assembles under turnover conditions, Nature, 373 (1995), 324-326... 

In most cases the catalytically active metal complex moiety is attached to a polymer carrying tertiary phosphine units. Such phosphinated polymers can be prepared from well-known water soluble polymers such as poly(ethyleneimine), poly(acryhc acid) [90,91] or polyethers [92] (see also Chapter 2). The solubility of these catalysts is often pH-dependent [90,91,93] so they can be separated from the reaction mixture by proper manipulation of the pH. Some polymers, such as the poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) block copolymers, have inverse temperature dependent solubihty in water and retain this property after functionahzation with PPh2 and subsequent complexation with rhodium(I). The effect of temperature was demonstrated in the hydrogenation of aqueous allyl alcohol, which proceeded rapidly at 0 °C but stopped completely at 40 °C at which temperature the catalyst precipitated hydrogenation resumed by coohng the solution to 0 °C [92]. Such smart catalysts may have special value in regulating the rate of strongly exothermic catalytic reactions. 

One class of smart catalysts is based on homogeneous rhodium-based polytalkcnc oxidos, in particular those with a poly(cthylcnc oxide) backbone. Traditionally chemical catalyzed reactions proceed in a manner in which the catalysts become more soluble and active as the temperature is raised. This can lead to exothermal runaw ays. thus, posing both safety and yield problems. The behavior of these smart catalysts is different from that of traditional catalysts. As the temperature increases, they become less soluble, thus precipitating out of solution and becoming inactive. As the reaction mixture cools down, a smart catalyst redissolves and becomes active again. 

Smart catalyst, complex polyanion cluster a-[(Coll)PWn039] assembles itself from four precursor species... 

In a first approximation, the new methods correspond to the conventional solvent techniques of supported catalysts (cf Section 3.1.1.3), liquid biphasic catalysis (cf Section 3.1.1.1), and thermomorphic ( smart ) catalysts. One major difference relates to the number of reaction phases and the mass transfer between them. Owing to their miscibility with reaction gases, the use of an SCF will reduce the number of phases and potential mass transfer barriers in processes such as hydrogenation, carbonylations, oxidation, etc. For example, hydroformylation in a conventional liquid biphasic system is in fact a three-phase reaction (g/1/1), whereas it is a two-phase process (sc/1) if an SCF is used. The resulting elimination of mass transfer limitations can lead to increased reaction rates and selectiv-ities and can also facilitate continuous flow processes. Most importantly, however, the techniques summarized in Table 2 can provide entirely new solutions to catalyst immobilization which are not available with the established set of liquid solvents. 

Olsen, C., Krenzke, L.D., and Watkins, B. Sulfur removal from diesel fuel optimizing HDS activity through the SMART catalyst system. Proceedings of the Fifth International Conference on Refinery Processing, AIChE Spring National Meeting. New Orleans, LA, 2002. 

The compound was used as a catalyst for the hydrogenation of olefins. No rhodium was lost. This type of polymer shows inverse temperature solubility. When the temperature was raised, the polymeric catalyst separated from solution for easy recovery and reuse. This type of smart catalyst will separate from solution if the reaction is too exothermic. The catalytic activity ceases until the reaction cools down and the catalyst redissolves. Poly (A i sop ropy lacrylamide) also shows inverse temperature solubility in water. By varying the polymers and copolymers used, the temperature of phase separation could be varied (e.g., from 25 to 80°C).214 A terpolymer of 2-isopropenylan-thraquinone, A-isopropylacrylamide, and acrylamide has been used in the preparation of hydrogen peroxide instead of 2-ethylanthraquinone.215 The polymer separates from solution when the temperature exceeds 33 C to allow re-... 

Hill. C.L. Zhang. X. A smart catalyst that self-assembles... 

Poly(A alkyl acrylamide)s and poly(7V-isopropylacrylamide) in particular are the other type of LCST polymers our group has studied. Poly(iV-isopropylacrylamide) is soluble below 31 C in water but insoluble above that temperature. Our group has used this temperature induced phase change has been used as a way to isolate, recover and reuse water-soluble polymer-bound catalysts. It is also a way to make a smart catalysts, catalysts that can turn off an exothermic reaction without external temperature control. Such on/off behavior is seen for both catalysts and substrates. 

While the development of new 3-D self-assembled metallocyclic architectures has thrown up some topological challenges, it undoubtedly constitutes an increasingly important avenue of research. As the field grows, more ambiguities of greater complexity can be anticipated. However, these should not obscure the practical potential that 3-D metallocycles hold in areas as diverse as smart catalysts or molecular information storage systems. 

Stiebels S (2011) Reducing Emissions with Smart Catalyst Technologies. Paper presented at the SAE Light Duty Diesel Emissions Control Symposium, Ann Arbor, MI, 2011... 

The distinctive features of spherical polyelectrolyte brushes (SPB) as ideal nanoreactors are discussed. SPB containing colloidal particles on which polyelectrolyte chains have been densely grafted offer a wide range of potential applications. They are ideally suited for the generation and immobilization of metal or metal oxide nanoparticles, which can be applied as smart catalysts in chemical industry. SPB can also be used for immobilization of proteins and enzymes. The response to external stimuli makes SPB unique in the field of nanoreactors. 

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