Pillared clay supports

The use of pillared clays as metal supports has also been reported. The more defined interlamelar spacing available with these supports should give a more predictable shape selectivity to the resulting supported metal catalysts. Further, since the pillars prevent the collapse of the layers on drying and further heating, the pillared clay supported metals salts can be calcined and reduced under conditions that can give the best metal dispersion without any concern for a change in the structure of the support. ... 

Qi, G., Yang, R.T. and Thompson, L.T. (2004) Catalytic reduction of nitric with hydrogen and carbon monoxide in the presence of excess oxygen by Pd supported on pillared clays, Appl. Catal. A 259, 261. 

A small increase of the (d 001) basal spacing is observed for the Li containing Zr pillared clays. However, the thermal stability of these solids drastically decrease. At high temperature, the collapse of the strucutre is also supported by the decrease of the surface area which is, at 700°C, almost identical to those measured for the montmorillonite. Different hypothesis may be proposed to explain the increase of the interlayer distance at low temperature (i) a better polymerization of the intercalated complex (ii) a modification of the distribution of the pillars (iii) a lower interaction between the pillar and the silica layer. The first hypothesis may easily be eliminated since the small variation of the height of the pillars (less than 1 A) cannot be explained by structural changes of the... 

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. 

The similarities in catalytic reactivity between Cr3 53-montmorillonite and chromia supported on alumina suggest that the structure of the intercalated chromia particles may resemble the structure of the bulk oxide. In order to obtain structural information for the chromia aggregates in pillared clays, we have initiated structural studies of these materials. Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy is being recognized as an effective tool for determining the local structure of a variety of materials. The basic principles and utility of this technique have been discussed elsewhere (18.). ... 

Abbreviations AD, asymmetric dihydroxylation BPY, 2,2 -bipyridine DMTACN, 1,4-dimethyl-l,4,7-triazacyclonane EBHP, ethylbenzene hydroperoxide ee, enantiomeric excess HAP, hydroxyapatite LDH, layered double hydroxide or hydrotalcite-type structure mCPBA, meta-chloroperbenzoic acid MTO, methyltrioxorhenium NMO, A-methylmorpholine-A-oxide OMS, octahedral molecular sieve Pc, phthalocyanine phen, 1,10-phenantroline PILC, pillared clay PBI, polybenzimidazole PI, polyimide Por, porphyrin PPNO, 4-phenylpyridine-A-oxide PS, polystyrene PVP, polyvinylpyridine SLPC, supported liquid-phase catalysis f-BuOOH, tertiary butylhydroperoxide TEMPO, 2,2,6,6-tetramethyl-l-piperdinyloxy TEOS, tetraethoxysilane TS-1, titanium silicalite 1 XPS, X-ray photoelectron spectroscopy. 

The above examples of shape selective reactions show the complexity of such systems and that several factors need to be considered before shape selective control can be realized. The use of other porous supports besides zeolites such as carbon molecular sieves, clays, pillared clays and related materials to catalyze shape selective reactions appears to be growing. Molecular modeling of the spatial constraints of various pores is also an area of increased research effort. 

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. 

The data of Figure 1 clearly show that irradiation of the titania pillared clay systems leads to an enhancement in the moles of Cl produced during photodegradation of dichloromethane. Prolonged pre-irradiation leads to lower conversion than shorter periods of pre-Irradlatlon. This is a general result and was found for all supported systems studied here. 

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. " ... 

The decrease in the activity of the rhodium catalyst supported on the pillared clay (Rh/BENPIL) after the reaction was carried out at 100 °C is significant. 

The activity of rhodium catalyst samples was monitored at 100 C for 7 hours, during which period the activity declined. All the catalysts reach a constant activity after 200 minutes fi om the start of the reaction approximately (Fig. 3). The percentage of residual activity (percentage of the final activity versus the maximum value reached) for the catalysts supported on zeolites (Rh/ZEDIP, 71% Rh/ZESEP, 83 % Rh/ZEDIX, 76% and Rh/ZESEX, 57%) indicates the resistance to poisoning. The deactivation of Rh/BENPIL (36%) is relatively rapid particularly during the first hour of reaction as mentioned, and this can be related to the formation of heavy secondary products formed in the MIBK formation route [20]. These molecules remain within the pores of the pillared clay sample, and therefore they block the access of the reactant to the active centres, hence causing a decrease in the activity of the catalyst. 

Vanadia doped sulfated Ti-pillared clays were prepared and characterized by BET, XRD, XPS, TPD-NH3 and compared with sulfated Ti-pillared clays and vanadia-doped unsulfated Ti-pillared clays. When sulfated Ti-pillared clay was doped with vanadia, the BET surface areas decrease whereas the diffraction line (001) are not significantly affected. The acidic properties of sulfated catalysts are higher than vanadia doped sulfated samples. The comparison of the activity of the catalysts in the selective catalytic reduction (SCR) of NO by ammonia in presence of oxygen show that vanadia doped sulfated Ti-pillared clay were highly active for the SCR NO. Therefore sulfated Ti-pillared clay appears as a good support for vanadia catalysts for the SCR reaction. 

The role of catalysis in the petroleum industry has been equally revolutionary. Meta I-supported systems (e.g. of Topsoe and Shell) for catalytic reforming, hydrodesulfurization and hydrodenitrification, alkylation catalysts and shape selective systems (e.g. zeolites and pillared clays) for catalytic cracking (FCC) and production of gasoline from methanol (Mobil MTG) all represent significant technical and commercial achievements. 

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