Hydrogen chemisorption measurements

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. 

The high degree of dispersion of platinum on alumina has also been confirmed by the hydrogen chemisorption measurements of Keavney and Adler (Kl), and by the chemisorption studies of Gruber (G2). In addition, high dispersion of platinum on silica-alumina has been observed by Hughes and associates, using a carbon monoxide chemisorption technique (H10). 

Nitrogen and krypton physisorption measurements at 77 K and hydrogen chemisorption measurements at 293 K were carried out with a Belsorp 28SA automatic adsorption apparatus in order to obtain BET surface area and the number of surface nickel atoms, respectively. The structure of catalysts was determined by X-ray diffraction using Cu radiation. 

To determine nickel surface areas of fresh catalysts, hydrogen chemisorption measurements were performed with the atmospheric TPH apparatus described above. Nickel surface areas of the catalysts were also measured by static volumetric hydrogen chemisorption (Coulter Omnisorp 100 cx). Before these measurements, samples were reduced in situ in a pure hydrogen atmosphere by raising the temperature up to 900°C (20°C/min). The samples were then cooled in a helium flow and the measurements were performed at 30°C. The catalyst materials and the analytical methods are described in [4,6,7]. 

Treatment and Characterization of Catalysts. A dynamic pulse adsorption apparatus (16) was used to carry out in situ pretreatments, reductions, degassing and hydrogen chemisorption measurements. 

The use of H2-O2 titration is a method of enhancing the sensitivity relative to a standard hydrogen chemisorption measurement which involves the use of hydrogen to titrate a chemisorbed layer of oxygen.63 The enhanced sensitivity results from an increased hydrogen consumption as the stoichiometry is raised to 3 H 1 Pt... 

Certainly one of the most studied systems has been Rh/Al20, which has long been a point of discussion due to apparently contradictory evidence from different experiments. In one study hydrogen chemisorption measurements indicated that the rhodium... 

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