Pillars montmorillonite clay

A Ti02 pillared montmorillonite clay (Ti-PILC) has recently been investigated as photocatalyst for the selective oxygenation of several alkylaromatics [53]. As shown in Table 1, accumulation of valuable carbonylic derivatives is possible since their over-oxidati(Mi to CO2 is negligible. In particular, proper reaction conditions are found for obtaining carbonylic compounds with about 90% selectivity, a value... 

Polymer-supported tetrabromooxomolybdate(V) was claimed to be a heterogeneous catalyst for alcohol oxidations with TBHP . However, it seems likely that molybdenum is leached from the surface and the observed catalysis may be, at least partially, homogeneous in nature. The same applies to Cr(III) and Ce(IV) catalysts supported on a perfluorinated sulfonic acid resin (Nafion K) which catalyze the oxidation of alcohols with TBHP . Similarly, vanadium-pillared montmorillonite clay (V-PILC) ° and a zeolite-encapsulated vanadium picolinate complex were shown to catalyze... 

Zirconium Pillared Montmorillonite Reduced Charge of the Clay... 

The DRX spectra of the solids calcined up to 500°C are illustrated on fig. 3. The position of the d 001 diffraction line versus the calcination temperature for the Na+ montmorillonite (EIII-01) and the Zr pillared modified clays (EIII-02, EIII-03) is reported on fig. 4. 

The diffusion of Li+ in the octahedral cavities of the Na+montmorillonite allows to control the density of the pillars of the Zr pillared montmorillonite. The solids, stable up to 300°C, have larger surface area basal distancy than the pure Zir montmorillonite. The distance between the pillars increases while the interaction strength between the pillars and the clay layer decreases. 

The sol-pillared clay was prepared following the procedures of Yamanaka et al (1). The mixing ratio of Afsi (mol)/A/T,(moI)/CEC equivalent of clay was 30/3/1. SiC -TiCh sol pillared montmorillonite, subjected to a calcination for 4h at 773 K, was labeled as sol-PILM. Portions of the wet cake prepared with bentonite were subjected to SCD or treatment with surfactants as described below. 

Al3+-exchanged synthetic hectorite is a good catalyst for these conversions, and the 13C NMR spectrum obtained in the interlamellar, proton-catalyzed addition of water to 2-methylpropene is indistinguishable (Fig. 79) from that of f-butanol. Doubtless studies of this kind, where natural-abundance, 3C NMR signals are used to probe the chemical identity and motional freedom of reactant and product species situated in the interlamellar spaces of clays or pillared clays (see below), will become increasingly popular. Using l3C NMR linewidths and spin-lattice relaxation studies, Matsumoto et al. (466) have succeeded in discriminating between the internal and external surfaces of pillared montmorillonites. 

In an effort to more fully elucidate the structure and reactivity of metal oxide pillared clays, we have been investigating the structure-reactivity properties of chromia-pillared derivatives (17). In the following sections, we provide an example of the structure-catalytic reactivity properties of chromia-pillared montmorillonites. Also, we report our initial efforts to structurally characterize the intercalated chromia aggregates by Extended X-ray Absorption Fine Structure (EXAFS) Spectroscopy. Unlike previously reported metal oxide pillared clays, chromia-pillared clay exhibits strong K-edge absorption and fine structure suitable for determination of metal-oxygen bond distances in the pillars. 

The relatively small size of the pillars and the relatively low long-range ordering of intercalated clays exclude many surface and crystallographic techniques as suitable means of characterization. The present study is the first attempt to obtain interatomic distances in these systems from EXAFS data. Our results clearly show the utility of this method for local structural analysis of these clay materials. The interatomic distances obtained for chromia-pillared montmorillonite suggest similarities between the structure of the pillars and the structure of Cr203 (22). This result is in agreement... 

A tartrate-modified solid Ti catalyst has also been prepared starting from a montmorillonite clay (31). This clay can be pillared with Ti polycations prepared by acid hydrolysis of Ti(OiPr)4. In the presence of tartrate ester, an allylic alcohol such as tram-2-buten-l-ol is epoxidized in 91% yield with 95% ee. These results are superior even to those for the homogeneous catalyst. Moreover, the reaction also proceeds in the absence of the molecular... 

In all previous cases, V was incorporated in a monomeric form. There are also methods to introduce oligomeric V into inorganic structures. Choudary et al. (48) advocated the use of a montmorillonite, pillared with V oligomers (V-PILC). V-PILC catalyzes the epoxidation of allylic alcohols with i-BuOOH. Oligomeric V is also used to pillar anionic clays such as layered double hydroxides (LDHs) with decavanadate anions (VioOjg) (49). 

Cationic clays have also been used as supports for Cu. Cu-doped alumina-pillared montmorillonites have been employed in the oxidation of toluene and of xylenes with H2C>2. The pillaring and the Cu exchange are performed under acidic conditions at pH 2 and 3.5, respectively. It is unclear whether the Cu2+ remains fully associated with the clay in the presence of H2O2, which is itself acidic. Moreover, the reactions are unselective mixtures of ring-hydroxylated and side chain-oxidized products are obtained (180). 

The intercalation of alkylammonium cations in clays, specifically tetraalkylammonium, for the first time, was carried out by Barrer and MacLeod. These researchers prepared pillared materials by exchanging the alkali and alkaline earth cations present in a montmorillonite clay with tetraalkylammonium [29], Nevertheless, the obtained material was thermally unstable and, consequently, had no viable application in catalysis. 

Recent advances in this technology include the use of 2 1 clays converted to hydrophobic forms through the introduction of surfactants in the interlayer. For example, Boyd et al. (1991) introduced cationic chain surfactants into 2 1 clay minerals. Such clays were demonstrated to have high affinity for hydrophobic organic chemicals. Additionally, polyethylene oxides (PEOs) have been intercalated into aluminum-pillared montmorillonite (Montarges et al., 1995). Because PEOs have a... 

Preparation of pillared products. The conventional pillared montmorillonite and the pillared interstratified I/M were prepared by addition of a volume of the ACH-solution calculated to give an Al/clay ratio of 5 mmoles per g to a dispersion (1 g/1) of the clay. 

Many applications of AFM to pillared clays or zeolites have not specifically addressed the porosity characteristics, but rather the occurrence of adsorbed surface Al species in, e.g., pillared montmorillonite [41], or the crystal growth processes, adsorption on porous surfaces and the surface structure of natural zeolites [42]. Sugiyama et al. [43] succeeded to reveal the ordered pore structure of the (001) surface of mordenite after removal of impurities that clogged the pores. The authors indicated that resolution in AFM imaging of zeolites is significantly affected by the magnitude of the periodical corrugation on the crystal surface, so that if the surface contains deep pores only the pore structure, but not the atomic structure, can be resolved. 

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... 

Both Lewis and Brdnsted acid sites exist on pillared clays. The acidity depends on the exchanged cations, the preparation method and the starting clay [8], It is known that surface acidity is important for SCR reaction of NO by NH3 [4, 5, 9]. Different pillared clays were synthesized and tested for their activities in the SCR NO [10, 11]. Research on titanium pillared clays was initiated by Sterte [12], who first reported the synthesis of titanium pillared montmorillonite using TiCU solution in hydrochloric acid. Bernier et al. 

Some attempts eonsisting of adding ammonium sulfate to the pillared montmorillonite suspension have been reported [4,5], These preparation methods show that adding sulfate ions decreases considerably the basal spacing without developing high acidity. Other studies attempted to prepare zirconium sulfate pillared clays by adding in situ sulfate. However, the solids obtained have a low surface area, low thermal stability [6] and low sulfate to zirconium ratios [7], Earlier, we have prepared a zirconium sulfate pillared clay by in situ... 

The catalysts used in this study were a zeolite (Zeocat HY 510, Si/Al = 10), a Montmorillonite clay pillared with Titanium species and cationic ion-exchange resins a macroporous lER Amberlyst 15 (Rohm Haas) and resins with a gel structure (K1481 -Bayer and Amberlyst 31 - Rohm Haas). 

There is considerable current interest in the design of new catalysts by interchelating clay minerals of the smectite type with redox metal ions, leading to the formation of oxidation catalysts with interesting (shape-selective) properties [38]. For example, vanadium-pillared montmorillonite (V-PILC) proved to be an... 

Selectivity in the dehydration of olefins is improved with pillared clays. Clays with aluminum oxide or mixed aluminum and iron oxide pillars converted isopropyl alcohol to propylene with more than 90% selectivity.256 A small amount of isopropyl ether was formed. When zeolite Y is used, the two products are formed in roughly equal amounts. A tantalum-pillared montmorillonite converted 1-butanol to butenes at 500°C with 100% selectivity at 41% conversion.257 The product contained a 17 20 16 mixture of 1 -butene/c/s-2-butene/fra/ s-2-butene. No butyraldehyde or butyl ether was formed. A pillared clay has been used for the alkylation of benzene with 1-dodecene without formation of dialkylated products.258 The carbonylation of styrene proceeded in 100% yield (6.50).259... 

Exploration of the pillar-clay sheet reactivity and connectivity also indicate the important role of the specific clay type. 27 1 and 29si-MASNMR experiments have shown distinctive differences between pillaring mechanisms in trioctahedral hectorite and dioctahedral montmorillonite. Whereas Plee et al. (22) concluded that chemical crosslinking may occur between the pillar and tetrahedral layer in a beidellite montmorillonite, Pinnavaia et al. (23) showed that it did not occur in a hectorite. These are the first observations of a complex process that may depend upon several structural and chemical factors, such as substitution of Al in the tetrahedral layer, or the need for vacancies in the octahedral layer to allow rotation of structural units or migration of reactant species to facilitate crosslinking. Ongoing research should further elucidate refinements on these mechanisms, and direct the technology towards more optimized catalysts - presumably those which form chemical bonds between the pillar and clay layer. 

The acylation of 2-methoxynaphthalene (yarayara) with acetic anhydride was studied systematically by using Amberlyst-15 and Indion-130, sulphated zirconia, Filtrol-24, K-10-montmorillonite clay, aluminium pillared clay(Al-PILC), HPA, HPA/KIO, H-ZSM-5, Y,... 

Chemical modification with different amounts of tween-80, a nonionic surfactant, was foimd to enhance the mesoporous area in pillared montmorillonite samples. Deactivation of the modified clays in the vapour phase catalysis of alkylation of toluene by methanol showed that the pillar density and the rate of deactivation could be controlled by the amount of surfactant used during the preparation of pillared samples. Presence of surfactant within the gallery affects the distribution of pillars perhaps during washing and dehydration. This offers a method to suppress deactivation in pillared samples to catalyze organic reactions. 

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