The specific copper surface areas in Cu/ZnO methanol synthesis catalysts by oxygen and carbon monoxide chemisorption: Evidence for irreversible CO chemisorption induced by the interaction of the catalyst components

The chemisorption of oxygen and carbon monoxide has been employed to determine the copper metal surface areas of CuZnO methanol synthesis catalysts in the compositional range CuZnO = 0100 to 1000. The total, reversible and irreversible adsorption capacities for oxygen and carbon monoxide have been measured at 78 and 293 K, respectively. The reversible CO capacities show good linearity with the irreversible O2 capacities and lie on a line connecting the capacity for pure copper with that, at zero intercept, of pure zinc oxide. Thus, the crystalline copper surface areas in these biphase catalysts have been evaluated from the specific irreversible adsorption of O2 on pure copper having surface stoichiometry Cu:O = 2:1. The reversible CO Chemisorption also is a measure of the copper metal surface area but irreversible CO Chemisorption is associated with defect sites, attributed to nonmetallic copper species in zinc oxide. A critical comparison with another traditionally employed method, N2O decompositive Chemisorption, shows that the low temperature adsorption of O2 is the preferred, reliable technique for the determination of crystalline copper surface areas.