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The Microstructure of Selective Palladium Hydrogenation Catalysts Supported on Calcium Carbonate and Modified by Lead ( Lindlar Catalysts), Studied by Photoelectron Spectroscopy, Thermogravimetry, X‐Ray Diffraction, and Electron Microscopy
Author(s) -
Schlägl Robert,
Noack Klaus,
Zbinden Heinz,
Reller Armin
Publication year - 1987
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19870700317
Subject(s) - chemistry , catalysis , aragonite , palladium , calcium carbonate , phase (matter) , chemisorption , calcite , thermogravimetry , x ray photoelectron spectroscopy , crystallography , octahedron , inorganic chemistry , chemical engineering , mineralogy , crystal structure , organic chemistry , engineering
A detailed analysis of the system Pd + Pb on CaCO 3 is presented. This system known as Lindlar catalyst is used for selective hydrogenations of CC bonds to CC bonds. It was found to consist of seven distinct chemical phases. Essential ingredients are solid solutions of hydrogen and oxygen in Pd. The latter phase enables the metal particles to be attached to the support via an orientational relationship calcite ( 113 )∥Pd + O ( 111 ). The addition of Pb neither changes the micromorphology of the disk‐shaped Pd particles nor does it modify the electronic structure of Pd as studied by chemisorption experiments. The addition of Pb seems to block certain active sites and, thus, to enhance the selectivity. The support was found to be a multi‐domain mixture of calcite and aragonite with domain sites of several hundred Å. The free surface of the pore‐free solid is covered by a calcium‐hydroxide carbonate. This phase as well as several other Pb phases seem to represent only spectator materials. Verification of this as well as finding the correlation between structure and function of the various components requires a kinetic analysis which is outside the scope of this paper. It is demonstrated that a variety of analytical techniques is required to unravel the complex nature of such a ‘simple' catalyst’ as it is Pd on CaCO 3 .