Chemisorption of hydrogen on copper

Madhavan P and Whitten J L 1982 Theoretical studies of the chemisorption of hydrogen on copper J. Chem. Phys. 77 2673-83... 

Ward studied the chemisorption of hydrogen on copper powder and found the heat of adsorption to be independent of surface coverage. Equilibrium data from experiments at 25°C are as follows ... 

Data of the chemisorption of hydrogen on small copper particles were obtained by Ward (Proc Roy Soc London A133 506, 1031) in the units P, Torr, and V in cc/g STP. The plots show the Langmuir to be a better fit than the Freundlich. 

Kwan and Izu (23) investigated the chemisorption of hydrogen on carefully reduced copper, with results strikingly different from those in the earlier work discussed above. Kahlbaum s extra fine copper and other samples of an equally high grade of purity were reduced at 450°C. with hydrogen at a pressure of several centimeters of mercury. Hydrogen... 

Evidence that the surface compositions of the nickel-copper catalysts are different from the bulk compositions is provided by data on the chemisorption of hydrogen on the catalysts at room temperature. This evidence is based on the observation that strong chemisorption of hydrogen does not occur... 

Figure 2.7 Chemisorption of hydrogen on nickel-copper catalysts at room temperature as a function of composition (6,23). (Reprinted with permission from Academic Press, Inc.)...

Fast chemisorption followed by slow activated adsorption involving only small amounts of the adsorbent have been reported from studies in the gas phase. Trapnell reports that adsorption may be nonactivated in its initial stages, but becomes activated when more than about half of the surface becomes covered.Experimental evidence for mixed chemisorption (activated adsorption) and diffusion control has been reported by Ward for the adsorption of hydrogen on copper. ... 

Analogous studies of the chemisorption of 14C-labeled benzene on copper powder and on platinum powder showed no chemisorption on the former, and the establishment of a low surface coverage over a range of temperature on the latter (Fig. 1). Again the surface coverage of hydrogen on platinum appeared to be about three times that achieved by benzene. 

Whereas the heats of chemisorption of hydrogen, found on various nickel adsorbents, are higher on films than on reduced powder, copper films do not bind hydrogen by chemisorption (268,269), although copper powder does (270,271) (see Sec. X,4). 

As for the above examples, the adsorption of hydrogen on reduced copper can also be regarded as occurring almost equally over the whole available surface inasmuch as Kwan and Kujirai (32) showed the active sites of the copper specimen to be identical with lattice points in studying the adsorption rate on the basis of the absolute rate theory. Consequently, the author has reached the conclusion that the surface of a number of reduced metallic catalysts is of a homogeneous nature for chemisorption as long as they are prepared by a very careful reduction and are kept free from any poisoning materials. 

Pure copper exhibits no strong chemisorption of hydrogen. Data on strong hydrogen chemisorption on ruthenium-copper aggregates have been used as a measure of the amount of ruthenium surface not covered by copper (3,4). As the coverage by copper increases, the amount of strongly chemi-... 

Ruthenium-copper and osmium-copper clusters (21) are of particular interest because the components are immiscible in the bulk (32). Studies of the chemisorption and catalytic properties of the clusters suggested a structure in which the copper was present on the surface of the ruthenium or osmium (23,24). The clusters were dispersed on a silica carrier (21). They were prepared by wetting the silica with an aqueous solution of ruthenium and copper, or osmium and copper, salts. After a drying step, the metal salts on the silica were reduced to form the bimetallic clusters. The reduction was accomplished by heating the material in a stream of hydrogen. 

In most of the catalysts composed of copper zinc and copper-pyrochlore a correlation between the copper surface area, the amount of formates located on the copper sites after CO2 or methanol chemisorption, and the catalytic activity can be found, but in most cases the relation is not strictly linear. The promoting effect of ZnO on Cu-LaZr catalysts cannot be ascribed to an enhancement of copper coverage or formate formation. Zinc plays therefore rather a positive role in the formate hydrogenation than its formation. 

---