Alumina surface dispersion

Ruthenium catalysts, supported on a commercial alumina (surface area 155 m have been prepared using two different precursors RUCI3 and Ru(acac)3 [172,173]. Ultrasound is used during the reduction step performed with hydrazine or formaldehyde at 70 °C. The ultrasonic power (30 W cm ) was chosen to minimise the destructive effects on the support (loss of morphological structure, change of phase). Palladium catalysts have been supported both on alumina and on active carbon [174,175]. Tab. 3.6 lists the dispersion data provided by hydrogen chemisorption measurements of a series of Pd catalysts supported on alumina. is the ratio between the surface atoms accessible to the chemisorbed probe gas (Hj) and the total number of catalytic atoms on the support. An increase in the dispersion value is observed in all the sonicated samples but the effect is more pronounced for low metal loading. 

Oxone has been successfully used in aprotic solvents for oxidation reactions by dispersing it on an alumina surface. Thus, the oxidation of secondary aliphatic, alicyclic and benzylic alcohols using Oxone/wet alumina oxide in CH2CI2 or CH3CN afforded ketones in good to excellent yields (70-96%). Similarly, the conversion of cycloalkanones to lactones is also reported. 

After fixing Pd catalyst on modified nylon 12 surfaces by various methods, they were coated by electroless Ni-P alloy plating. Alumina- or silica-modified nylon 12 was well wet by electroless plating liquid, and modified nylon 12 situations in a liquid were good dispersed. Nickel metal was deposited on silica or alumina surface. Finally, it was confirmed that the formation of metal layer was depended mainly on the method of Pd catalyst fixing. 

Doering and LaFlamme [10b] were the first to report that sodium and magnesium metal are capable of converting substituted gem-dibromocyclo-propanes to allenes in varying yield. However, it was found that sodium reacts best in the form of a high surface dispersion on alumina. At a later date, Moore and Ward [11a] and then Skattebol [12] reported that methyllithium or n-butyl-lithium reacts with gem-dibromocyclopropanes to give allenes in high yield. The related dichloro compounds were found to be inert to methyllithium but reacted slowly with -butyllithium. Several examples of the preparation of allenes from gem-dibromocyclopropanes are shown in Table I. 

Figure 10.6. Surfactant demand curves of 70% (weight) dispersions of Ti02 pigments with various levels of alumina treatment. Dispersions were prepared in DIDP plasticizer on a highspeed disk mill. Survactant used was Disperbyk I. Pigment A titania surface, no alumia surface treatment. Pigment B 1.5% alumina surface treatment, minimum viscosity achieved at 2.36% surfactant based on pigment weight. Pigment C 3.0% alumina surface treatment, minimum viscosity at 3.9% surfactant.

Phosphorus oxo-species adsorbed on alumina are present in a well-dispersed state up to a surface density of 2.9 x 10 P atom/pm (or 2.9 P atom/nm ) 31). IR spectroscopy measurements allowed identification of several types of hydroxyl groups on the y-alumina surface, such as type la (tetrahedral Al —OH, 3780 cm ), type lb (octahedral Al —OH, 3795 cm ), types 11a and Ilb (bridged OH between two Al atoms, 3736... 

Han et al (61) reported that the Al2(Mo04)3 phase on alumina is easily hydrated by moisture in air and transforms into amorphous M0O3, whereas AIPO4 only shghtly reacts with water. Further addition of phosphorus decreases the formation of Al2(Mo04)3 since competitive adsorption of phosphorus and molybdenum oxo-species occurs on the alumina surface. Phosphorus inhibits the formation of Al2(Mo04)3 in the presence of nickel (62). The number of deposited polymeric phosphorus-oxo compounds decreases in the presence of molybdenum, probably through the formation of dispersed Mo—P heteropoly compounds (63). 

As with alumina, ceria has several roles to play within the catalyst formulation. It has some effect on stabilizing alumina surface area at high temperatures, and it is also capable of stabilizing the dispersion of platinum in these systems, important because the effect is particularly marked in the 600-800°C region, where many present-day catalysts operate. In addition, ceria allows two other more directly performance-related phenomena to take place oxygen storage and the water gas shift reaction shown in Eq. (9) ... 

Another ion exchange procedure involves the interaction of a metal acetylacetonate (acac) with an oxide support. Virtually all acetylacetonate complexes, except those of rhodium and ruthenium, react with the coordinatively unsaturated surface sites of 7 alumina to produce stable catalyst precursors. On thermal treatment and reduction these give alumina supported metal catalysts having relatively high dispersions. 38 Acetylacetonate complexes which are stable in the presence of acid or base such as Pd(acac)2, Pt(acac)2 and Co(acac)3, react only with the Lewis acid, Al" 3 sites, on the alumina. Complexes which decompose in base but not in acid react not only with the Al 3 sites but also with the surface hydroxy groups. Complexes that are sensitive to acid but not to base react only slightly, if at all, with the hydroxy groups on the surface. It appears that this is the reason the rhodium and ruthenium complexes fail to adsorb on an alumina surface. 38... 

We obtained initial rates for the reaction of neopentane on supported platinum and platinum powder catalysts at 300°, 1 atm total pressure, and a hydrogen-to-neopentane ratio equal to 10. As before, surface platinum atoms were titrated by selective chemisorption of hydrogen (27). Before discussing the results, it is important to stress the reproducibility of the results on samples of different origin but nearly identical dispersion and pretreatment. Thus, the same value of the selectivity to isomerization was found on two catalysts an experimental catalyst containing 2% platinum on t -alumina and a commercial sample with 0.6% platinum on y-alumina. Percentage dispersion of the metal was 64 and 73, respectively, and the selectivity was 1.5. Both samples were reduced at 500° under identical standard conditions. 

In conclusion, one may suggest that, in silica and silica-rich supported samples, the pore system permits preferential entrance of some CoPc molecules, affecting sensibly the pore dimensions. In alumina and alumina-rich supported samples, the pore system, with its dimensions less than those of CoPc molecules, does not permit free entrance of complex molecules. Here, CoPc molecules may be forced to occupy positions in the defective structure of alumina. All these findings should be reflected on the mode of surface dispersion of the supported CoPc molecules. 

In a recent study of the CUCI2-AI2O3 catalyst system, Finocchio et al. [42] discovered that at 250 °C, whereas the oxychloiination reaction occurs on copper sites, the alumina surface converts the desired product, EDC, to by-products such as vinyl chloride, trichloroethane, and dichloroethylene. The superiority of copper chloride over copper nitrate as the catalyst precursor is probably because metal chlorides are more highly dispersed than metal nitrates on impregnated alumina surfaces and, hence, expose less of the uncovered alumina surface. CuCT is also more effective than copper nitrate in poisoning the nucleophilic sites (exposed oxide anions) on alumina. 

An extensive literature exists on the characterization and structure—activity correlation of industrial copper-alumina oxychlorination catalysts [95-120]. At least two different major copper species have been identified. At low concentrations of copper (below ca 5 %), a well-dispersed copper species in intimate interaction with the alumina surface is formed. This species has a very low oxychlorination activity. At higher concentrations, a second species, probably formed by the de-position/precipitation of the copper chloro complexes, is observed. The latter gives rise to the active sites during the oxychlorination reaction. On the basis of an FTIR study of the oxychlorination reaction Finocchio et al. [42] postulated the formation of surface copper chloride-ethylene r-complex intermediates (which lead eventually to EDC) and weakly adsorbed HCl during oxychlorination. Formate species associated with copper and probable precursors for formation of the oxides of carbon by combustion were also identified. 

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