Quantitative determination of the content of palladium deposited on kieselguhr using hydrogen isotherms

The isotherms of hydrogen isotope, absorbed or desorbed by palladium particles of various sizes were investigated at similar to 100 kPa of various absorption-desorption cycles at room temperature (25 degrees C). The maximum hydrogen (D) content of these samples, the hydrogen (D) absorption capactiy, was determined using the Langmuir monolayer coverage equation from the isotherms after several cycles. A ratio of the hydrogen absorption capactiy of palladium/kieselguhr (Pd/K) to that of pure palladium was calculated to determine the palladium content of Pd/K. The results showed that the particle size and cycle numbers affected the isotherms of the isotopes. Only 78 % of the maximum absorption capacity at 100 kPa was obtained at the first cycle of H absorption when the particle size was 10-30 mesh, and the absorption capacity approached 100 % after the first hydrogenation when the particle size was reduced to 100-150 mesh. At 10 -100 kPa, where the Pd-H system existed in the hydride beta-phase, the relationship between pressure and the content absorbed strictly followed the Langmuir equation (correlation coefficient was > 0.9999), which confirmed that the hydrogen atoms in the octahedral interstices follow a monolayer coverage model. According to the linear plot, the monolayer absorption capacity of H or D in the hydride beta-phase, Q(m) was calculated from the slope of the curve. The calculated Q(m) (Pd-H) and Q(m) (Pd-D) were 3.31 and 3.16 mmol/g, respectively, while Q(m) (Pd/K-H) and Q(m) (Pd/KD) were 1.231 and 1.182 mmol/g, respectively. The Pd content of Pd/K, investigated from the H and D isotherms, were 37.2 and 37.4 wt%, respectively, which correlated with the result from inductively coupled plasma atomic emission spectroscopy (ICP-AES) (37.7 wt%).