STRUCTURAL INVESTIGATION ON THE STOICHIOMETRY OF BETA-PDHX IN PD SIO2CATALYSTS AS A FUNCTION OF METAL DISPERSION/

Structural investigations of dispersed Pd/SiO2 catalysts were carried out with XRD and SAXS techniques, supported by TPR and CO chemisorptio n measurements. The stoichiometry of Pd hydride, beta-PdHx, was determ ined by measuring the shift of Pd 111 XRD reflection in the presence o f hydrogen. It was confirmed that x decreases when the metal dispersio n increases. This behaviour could be quantified up to about 0.45 of Pd dispersion since the angular position of XRD peaks cannot be determin ed with the necessary precision at higher dispersions. TPR data, obtai ned up to dispersions of about 0.6, confirms such behaviour. The beta- PdHx stoichiometry versus Pd dispersion relationship substantially agr ees with that found with other techniques by Boudart and Hwang.