Oxidation pillared clay catalysts

These clays have been hybridized with diverse structural types of components such as nanoparticles, clusters, complex compounds, polymers, molecules, and ions. Their potential apphcations are found in many fields as inorganic catalysts, adsorbents, ceramics, coatings, and even drug delivery carriers. Various preparation methods have been developed such as pillaring, intercalation, and delamination techniques. The representative examples include organic-clay hybrids," metal oxide-pillared clays, " and bioclay hybrids. ... 

Guelou, E., Tatibouet, J. and Barrault, J. (2010). Fe-Al-Pillared Clays Catalysts for Wet Peroxide Oxidation of Phenol, in A. Gil, S. Korili, R. TmjiUano, et al. (eds). Pillared Clays and Related Catalysts, Springer, Heidelberg, Germany, pp. 201—224. 

Achma, R., Ghorbel, A., Dafinov, A., et al. (2008). Copper-supported Pillared Clay Catalysts for the Wet Hydrogen Peroxide Catalytic Oxidation of Model Pollutant Tyrosol, Appl. Catal. A General, 349, pp. 20-28. 

The superior activity of a new type of catalyst with respect to conventional SCR catalysts is often claimed in the literature. Long et al. [40], for example, claimed the superiority of pillared clay catalysts for SCR of nitrogen oxides to control power plant emissions by comparing Ce-Fe-Ti02-PILC (Pillared InterLayer Clay) with a V205-W03/Ti02 catalyst. There are many more examples of this type of claim in the literature. 

Long, R.Q., Yang, R.T., and Zammit, K.D. Superior pillared clay catalysts for selective catalytic reduction of nitrogen oxides for power plant emission control. J. Air Waste Manag. Assoc. 2000, 50, 436-442. 

The hydroamination of alkenes has been performed in the presence of heterogeneous acidic catalysts such as zeolites, amorphous aluminosilicates, phosphates, mesoporous oxides, pillared interlayered clays (PILCs), amorphous oxides, acid-treated sheet silicates or NafioN-H resins. They can be used either under batch conditions or in continuous operation at high temperature (above 200°C) under high pressure (above 100 bar). 

Tertiary butylhydroperoxide (TBHP) is a popular oxidizing agent used with certain catalysts. Because of its size, TBHP is most effective with catalysts containing large pores however, it can also be used with small-pore catalysts. Using first-row transition metals, Cr and V, impregnated into pillared clays, TBHP converts alcohols to ketones, epoxidizes alkenes, and oxidizes allylic and benzylic positions to ketones.83-87... 

N anomaterials have been around for hundreds of years and are typically defined as particles of size ranging from 1 to 100 nm in at least one dimension. The inorganic nanomaterial catalysts discussed here are manganese oxides and titanium dioxide. Outside the scope of this chapter are polymers, pillared clays, coordination compounds, and inorganic-organic hybrid materials such as metal-organic frameworks. 

Heterogeneous catalysts for liquid phase oxidations can be divided into three different categories (a) supported metals (e.g. Pd/C), (b) supported metal ions (e.g. ion exchange resins, metal ion exchanged zeolites) and (c) supported oxometal (oxidic) catalysts (e.g. Ti1v/SiOg, redox zeolites, redox pillared clays). This division of the various catalyst types will be used as a framework for the ensuing discussion. 

Redox pillared clays as shape selective oxidation catalysts... 

Such regioselectivities are unique and suggest that redox pillared clays may have broad scope and utility as selective, heterogeneous catalysts for liquid phase oxidations. Indeed, V-PILC also catalyzes the oxidation of benzyl alcohol (to a mixture of benzoic acid and benzylbenzoate) whilst a-methyl benzylalcohol is left completely untouched.71 Similarly, p-substituted benzyl alcohols are oxidized whilst o-substituted benzyl alcohols are inert.71... 

The book explores various examples of these important materials, including perovskites, zeolites, mesoporous molecular sieves, silica, alumina, active carbons, carbon nanotubes, titanium dioxide, magnesium oxide, clays, pillared clays, hydrotalcites, alkali metal titanates, titanium silicates, polymers, and coordination polymers. It shows how the materials are used in adsorption, ion conduction, ion exchange, gas separation, membrane reactors, catalysts, catalysts supports, sensors, pollution abatement, detergency, animal nourishment, agriculture, and sustainable energy applications. 

Catalyst discovery research—metal oxides and supports, shape selective and hetero metal substituted molecular sieves, pillared clays, biomimetic, methan-otropic and other bio systems and combinatorial catalytic screening techniques, liquid phase homogeneous systems. 

Nanosized sulfated tin oxide (STO) particles dispersed in the micropores of Al-pillared clay (STO/Al-P), were used by Mishra and co-workers [91] as an environmentally benign, recyclable and efficient catalyst for the solvent-free synthesis of 3,4-dihydropyrimidin-2(l//)-ones 42 using a domestic microwave oven. The protocol offers advantages in terms of simple experimentation, reusable catalyst, excellent yields, short reaction times, and preclusion of toxic solvents (Scheme 31). 

In order to improve the textural properties of particle-clay nanohybrids, bulky organic cations are intercalated as a kind of template into particle-intercalated clays before stabilization procedures. Intercalation of the organic cations results in the removal of some of the intercalated nanoparticles and/or in their rearrangement. Subsequent calcination leads to formation of additional pore space that is highly correlated to the geometry and size of the templates. This technique allows fine tuning of textural properties in the preparation of particle-clay nanohybrids. The clay nanohybrids intercalated with metals, oxides, and complexes have a broad range of applications. In particular, metal oxide particle-pillared clays have excellent potentials as catalysts, catalyst supports, selective adsorbents, etc. " ... 

Another approach to designing shape-selective heterogeneous oxidation catalysts was to use redox metal oxides as the pillaring agents in the preparation of pillared clays. These redox pillared clays have been used for a number of selective oxidations. Chromium pillared montmorillonite (Cr-PILC) is an effective catalyst for the selective oxidation of alcohols with tert-butyl hydroperoxide. 7 Primary aliphatic and aromatic alcohols are oxidized to the aldehydes in very good yields. Secondary alcohols are selectively oxidized in the presence of a primary hydroxy group of a diol to give keto alcohols in excellent yields (Eqn. 21.12). 2... 

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