Occurrence and mechanism of formation of CeOCl in Pd/CeO2 catalysts

The formation of the CeOCl phase in a Pd(Cl)/CeO2 catalyst during reduction in hydrogen was studied by HRTEM, XRD, and low-temperature N-2 adsorption (BET), The results indicate that CeOCl crystallites nucleate at (110) faces of CeO2 crystals at T less than or equal to 300 degrees C and then grow by coalescence of existing nuclei and attachment of Ce-O-Cl species continuously formed at the ceria surface. Lateral growth of CeOCl results in rapid decline of the BET surface of the catalyst between 300 and 500 degrees C due to the "enwrapping" of the grains of the catalyst, The mechanism of an ordered CeOCl-CeO2 transformation in an oxidizing atmosphere is proposed. (C) 2000 Academic Press.