Modification of the Catalytic Hydrogenation Activity of Glassy Pd81Si19. Surface Analysis by ISS and XPS

Intermetallic compounds in heterogeneous catalysis—a quickly developing field

“…The same concept of a homogeneous intermetallic compound as precursor for relevant catalysts was developed with self-supporting amorphous intermetallic compounds transformed in situ into nanocrystalline highly stable supported systems of uniform size and thus superior catalytic properties. The concept [90–95] developed for ammonia synthesis and CO oxidation was successfully transferred [96] to technical applications in selective hydrogenation using PdSi x intermetallic compounds.…”

Fused Catalysts

“…In a study of the application of Pd-Si amorphous alloys as selective hydrogenation catalysts [3], it was found that in-situ activation provides a route to active and selective catalysts, whereas ex-situ activation caused crystallization of the system into the thermodynamically stable Pd + SiO 2 system, which is in distinguishable in terms of its activity and poor selectivity from conventional catalysts of the same composition. In this study, it was possible to show conclusively that bulk amorphous alloys are not amorphous on their surfaces as they undergo, in reactive gas atmospheres, chemically induced phase segregation which starts the crystallization process according to Fig.…”

“…The detection of metastable phases by spectroscopic and local structure-sensitive methods has been described in case studies [3,48,49,57,58]. The detection of nonequilibrium mesostructures is rather difficult, and less frequently carried out due to the fact that the relevant size range is between local atomic microstructural motives and macroscopic crystal morphologies.…”

“…One material-saving development in the use of such bulk-phase metallic alloy catalysts is the application of bulk metallic glasses in the form of ribbons with macroscopic dimensions [2][3][4][5]. In this class of material, the atomic dispersion in the liquid alloy is preserved in the solid state as a single phase, although the material may be metastable from its composition.…”

“…Subsequently, Raney produced a nickel catalyst by leaching a 50 wt.% Ni − Al alloy in aqueous sodium hydroxide; this catalyst was even more active, and a patent application was filed in 1926 [3]. This class of materials is generically referred to as ''skeletal'' or ''sponge'' metal catalysts.…”