The effects of high concentrations of CO and CO2 upon the H permeation behavior of a Pd membrane were investigated by using pure H2, H2-10%CO, H2-50%CO and H2-50%CO2 at temperatures ranging from 423 to 723K and pressures ranging from 0.9 to 250kPa. A deterioration of the H permeability and diffusivity was observed in the presence of H2 with 10 or 50% of CO, at temperatures below 523K (figures 27 and 28). Only a slight deterioration was observed when using H2-50%CO2 gas at temperatures below 473K. The results were explained in terms of the difference in the adsorption energies of CO and CO2 at the Pd surface. The deterioration in H permeability, due to the presence of the gases, was attributed to a decrease in the effective area for H2 dissociation via the weak adsorption of CO.

M.Amano, C.Nishimura, M.Komaki: Materials Transactions, 1990, 31[5], 404-8

Figure 28

Diffusivity of H in Pd

(a: 50%CO2, b: 10%CO, c: 50%CO)