Titanates catalytic activities

Lehn, J.-M., Sauvage, J.-R, Ziessel, R., and Hilaire, L., Water photolysis by UV irradiation of rhodium loaded strontium titanate catalysts. Relation between catalytic activity and nature of the deposit from combined photolysis and ESCA studies, Isreal ]. Chem., 22,168,1982. 

Water generation during PBT polymerization is undesirable in that it can hydrolyze ester groups in the polymer backbone as well as irreversibly hydrolyze the titanate catalyst. Partially hydrolyzed titanates will have lower catalytic activity than the pure catalyst. 

Wang Q, Gao Q, Shi J (2004) Enhanced catalytic activity of hemoglobin in organic solvents by layered titanate immobilization. J Am Chem Soc 126 14346—14347... 

Water Photolysis by UV Irradiation of Rhodium Loaded Strontium Titanate Catalysts. Relation Between Catalytic Activity and Nature of the Deposit from Combined Photolysis and ESCA Studies. Powdered catalysts used and the water photolysis efficiency is found to have a strong pH dependence. 399... 

Catalytic Activity of Nickel-Loaded Titanates. A good test of the dispersion of the active metal is the activity and selectivity for the hydrogenolysis of n-butane. For example, it is well known (6) that the hydrogenolysis of saturated hydrocarbons, or the rupture of carbon-carbon bonds by hydrogen, are structure sensitive that is, their rates per surface metal atom (TOF s) vary with the percentage of metal exposed on the catalyst (i.e.. the dispersion). Typically,... 

Table 8. Catalytic activities of some layered titanates 64],...

Titanium is an element of considerable interest in materials science because of its role in technical electroceramics such as barium titanate and lead zirconium titanate, and in engineering ceramics (TiN, TiC) and glasses. Titanium compounds also play a role in establishing catalytic activity in microporous materials. Despite the practical interest in Ti compounds, there have been relatively few NMR studies of this nucleus because of experimental difficulties, some of which are associated with the properties of its two NMR-active nuclei, which both have moderately large quadrupole moments Q in the... 

FIGURE 13.7 Representation of titanium-on-silica catalyst in SMPO as a range of silica-supported—and therefore stabilized—ultrafine titania particles containing catalytically active, coordinatively unsaturated titanate sites. 

Scheme 15. Si02 Bound Ti-TADDOLates Tested in Two Reactions [85]. The conlroUed-pore glass (CPG, supplied hy the Grace Company) has an enormously large surface/g. Up to 0.3 mmol/g of TADDOL have been loaded by first attaching Si-(CH2)3S-Trityl and then the TADDOL moiety (through S-alkylation with the corresponding benzyhc bromide) unreacted SiOH groups on the surface are trimethylsilylated. The rates and stereoselectivities of the EtjZn-to-PhCHO addition and of the diphenylnitrone 1,3-dipolar addition shown are comparable to those observed under homogeneous conditions. The material can be washed with aqueous HCl to restore, after reloading with titanate, whatever activity of the solid-state-bound catalyst had been lost after several catalytic cycles [85].

Inclusion of these cations does impart new catalytic activities, but in many cases the active site results from a metal ion that has left the framework and entered the pore space upon heating, especially in the presence of water vapour. This is thought to be the case for zinc- and gallium-containing solids used in the dehydrocyclisation of butane and propane to aromatics in the Cyclar process (Chapter 9). Boron, iron, chromium and vanadium all appear to leave the framework under harsh conditions. The incorporation of titanium and more recently tin into framework sites within silicates have become very important substitutions, because both titanosilicates and stannosilicates have been shown to contain stable Lewis acid sites of importance in selective oxidation catalysis. The metal atom can coordinate additional water molecules in the as-prepared material, but these can be removed by heating. In the synthesis of titanosilicates, titanium is usually added to the gel as the alkoxide, and synthesis performed in the absence of sodium hydroxide to avoid precipitation of sodium titanate or nanoparticulate titanium oxides. 

Only a few examples exist in the literature that positively identify isolated species as the key to catalytic activity, two of which are TiO /SiOj [30] and ZrO /SiOj [31] for methanol oxidation (x indicates the surface oxide exists in noncrystalline form). In these cases, the highest turnover frequencies (TOFs) for methanol consumption were observed at the lowest tested concentrations of supported titanate and zirconate, where isolated Ti04 and Zr04 structures were shown to dominate. It was concluded that the number of Ti-O-Si and Zr-O-Si bonds were maximized in monomeric Ti and Zr sites, respectively. Significant TOF decreases concomitant with increasing surface oxide polymerization were rationalized to occur because the number of M-O-S bonds per active M site was reduced. 

M. Kitano, E. Wada, K. Nakajima, S. Hayashi, S. Miyazaki, H. Kobayashi, M. Hara, Protonated titanate nanotubes with Lewis and Br0nsted acidity relationship between nanotube structure and catalytic activity, Chem. Mater. 25 (2013) 385-393. 

Titanium. In recent years, titanium-modified open-framework materials have been extensively stndied. Tetrahedral titanium has been incorporated into several zeolites silicalite-1 (169), silicalite-2 (170), MCM-41 (171), zeolite-Beta (172), and ZSM-5 (173). These titan-modified materials show remarkable reactivity in the oxidation reactions using diluted aqueous hydrogen peroxide nn-der mild conditions. The catalytic activity is mostly related to the tetrahedrally coordinated titanium incorporated in the framework (174-179). It is worth noticing that the titanium-incorporated silicalite-1 (TS-1) has been one of the most relevant industrial catalysts in the past two decades. These facts have directed research to investigate the possibility of the incorporation of titanium into the aluminophosphate framework. 

Layered crystalline titanates (CT) [Anthony and Dosch, U.S. Patent 5 177 045 (1993)] are pillared with tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane, and aluminum(III) acetylacetonate to prepare porous and high surface area supports for sulfided NiMo catalyst. Tetraethyl orthosilicate or aluminum(III) acetylacetonate intercalated CT are prepared by stepwise intercalation. First, the basal distance is increased by n-alkylammonium ions prior to intercalation with inorganic compounds. However, an aqueous solution of 3-aminopropyltrimethoxysilane can directly pillar CT without first swelling the titanate with n-alkylamine. The catalytic activities for hydrogenation of pyrene of sulfided NiMo supported silica or alumina pillared CT are higher than those of commercial catalysts (Shell324 and AmocatlC). The silicon and aluminum contents of the pillared CT, used as supports, have considerable effects on the catalytic activities and physical properties of the supports. 

Anthony and Dosch [1, 2] prepared a series of new crystalline titanates (CT) by modifying the procedure used to prepare hydrous titanium oxide. CT with basal spacings of 1.0, 1.17, and 1.6 nm were prepared. The catalytic activities of Pd supported catalysts were varied depending on the type of CT. One labelled as type 2 titanate, when used as a precursor in the preparation of a supported Pd catalyst, had the highest activity for hydrogenation of pyrene and 1-hexene among these Pd supported CT. However, CT were not thermally stable as... 

The major drawback of the nickel catalyst is poisoning of Ni surface by the interaction with CO to form nickel carbonyl at low temperature. Noble metal based catalysts are more active and stable catalyst in comparison with Ni based catalysts [100]. Among Ru nanoparticle dispersed on various supports (Al Oj, MgAljO, MgO, C, etc ), Ru/Al Oj showed highest catalytic activity (turnover frequency, TOF = 16.5 x 10 s" ) [101,102]. Yttrium addition to the Ru-based catalyst enhances the activity and stability for methanation reaction [103], Pd/Mg-SiO and platinum titanate nanotubes were also foimd... 

A series of new crystalline titanates (CT) are shown to have considerable potential as catalysts supports. For Pd supported catalysts, the catalytic activity for pyrene hydrogenation was substaniatially different depending on the type of CT, and one was substantially more active than Pd on hydrous titanium oxide (HTO). For 1-hexene hydrogenation the activities of the new CTs were approximately the same as for the hydrous metal oxide siqtports. Stereochemical effects, such as shape selective catalysis, ars to be occurring when pyrene is hydrogenated. 

After several attempts in which anatase titania was synthesized, new crystalline titanates with d-spacings of 1.0, 1.17, and 1.6 run were synthesized. This paper reports on the chemicals used in the synthesis, prqperties of the titanates and catalytic activities of the titanates when used as supports for Pd for the hydrogenation of pyrene and of 1-hexene. 

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