Adsorption of Oxygen by a Silver Catalyst

Abstract

An apparatus is described to measure volumetrically the amount of gas adsorbed by a catalyst a t constant pressure and at exposure times as short as 0.1 min. The volumes of oxygen adsorbed by a technical silver catalyst a t pressures of 200, 400, and 700 mm. and in the temperature range of 180" to 300" C. have been measured. Surface area determinations of 0.33 t o 0.38 sq. meter per gm. of catalyst by physical adsorption and chemisorption methods show that each silver atom of the surface is associated with approximately one osygen adatom a t a monolayer coverage. The initial rate of adsorption of oxygen is directly proportional to its pressure. Observed transitions in the oxygen adsorption rates indicate that more than one type of oxygen comples occurs on the catalyst surface. The Elovich equatioli provides the best approximation of the adsorption rate data but is of limited applicability in interpretation of the ~iiechanism of adsorptio~i. 1:alues of 22-29 Iccal./~ilole and 17-25 lical./mole have been calculated for the apparent activation energy and isosteric heat of adsorption respectively.

Catalytic Consequences of Reactive Intermediates during CO Oxidation on Ag Clusters

“…The K O 2 K O value is 26 kPa –1 , which corresponds to an average heat of O* adsorption ( Q ads,O ) of 55 ± 1 kJ (mol of O) −1 for Ag clusters with O* coverages ranging from 0.16 to 0.99 ML, assuming that O 2 loses all translational and rotational degrees of freedom during its dissociative adsorption, which is equivalent to an adsorption entropy loss (Δ S ads,2O* , per two O* adatoms) of −181 J (mol of O 2 K) −1 . This average heat of O* adsorption is similar to those measured on polycrystalline Ag {33–52 kJ (mol of O) −1 at 0.68–0.82 ML O*}. , …”

Deep oxidation of methane over zirconia supported Ag catalysts

“…Typically, 0.1 g of catalyst was reduced at 1708C in a¯ow of 10% H 2 /He for 1 h and degased at 3008C for 1.5 h. Oxygen uptake was then measured at 1708C by injecting pulses of 20% O 2 /He. The Ag dispersion was calculated based on 1:1 Ag:O stoichiometry [30,41,42]. The particle size based on the chemisorption measurements was calculated from the expression d p (nm)117.7/D, where d p is the particle diameter (assuming hemispherical particles) and D the %dispersion [43].…”

Comparative Study of Growth Morphologies of Ga2O3 Nanowires on Different Substrates

“…There are other processes, which can occur simultaneously or independent of each other, which could explain the oxygen interaction at the O and Ag interface and the enhancement of the nanowires’ density, shape, and size. First, the silver catalyst could increase the rate of oxygen adsorption as the oxidation temperature increased [ 27 ]. Second, at high temperatures, above 626 °C, the annealing of the Ag catalyst could result in high concentrations of adsorbed O 2 [ 28 ].…”