This report discusses work on the characterization by extended x-ray absorption fine structure spectroscopy, structures formed on the surface of partially dehydroxylated magnesium oxides by adsorption of (HRe(CO)5).

Re and Ir carbonyls, and other compounds, were chosen as precursors. MgO, La2O3, zeolite NaX and KL, among others, were chosen as supports. EXAFS was used to study the metal-support interactions. Structures formed on almost fully dehydroxylated MgO by HRe(CO)5, and on MgO by Ir4(CO)12, were studied. A metal-oxygen distance of 2.15 Å holds in for the metal-support interface in oxide-supported metal clusters following reduction in H2 above 450 C; for reduction below 350 C, the distance is 2.5--2.7 Å.

With contributions from experts in supported metal catalysis, from both the industry and academia, this book presents the latest developments in characterization and application of supported metals in heterogeneous catalysis. In addition to a thorough and updated coverage of the traditional aspects of heterogeneous catalysis such as preparation, characterization and use in well-established technologies such as Naphtha reforming, the book also includes emerging areas where supported metal catalysis will make significant contributions in future developments, such as fuel cells and fine chemicals synthesis. The second edition of Supported Metals in Catalysis comes complete with new and updated chapters containing important summaries of research in a rapidly evolving field. Very few other books deal with this highly pertinent subject matter, and as such, it is a must-have for anyone working in the field of heterogeneous catalysis.

It is now IS years since the first patents in polymer supported metal complex catalysts were taken out. In the early days ion-exchange resins were used to support ionic metal complexes. Soon covalent links were developed, and after an initially slow start there was a period of explosive growth in the mid to late 1970s during which virtually every homogeneous metal complex catalyst ever reported was also studied bound to a support. Both polymers and inorganic oxides were studied as supports, although the great preponderance of workers studied polymeric supports, and of these polystyrene was by far the commonest used. This period served to show that by very careful design polymer-supported metal complex catalysts could have specific advantages over homogeneous metal complex catalysts. However the subject was a complicated one. Merely immobilising a successful metal complex catalyst to a functionalised support rarely yielded other than an inferior version of the catalyst. Amongst the many discouraging results of the 1970s, there were more than enough results that were sufficiently encouraging to demonstrate that, by careful design, supported metal complex catalysts could be prepared in which both the metal complex and the support combined together to produce an active catalyst which, due to the combination of support and complex, had advantages of activity, selectivity and specificity not found in homogeneous catalysts. Thus a new generation of catalysts was being developed.

Metals are dominant catalysts, being used in forms ranging from simple atomically dispersed (single-site) metal complexes to few-atom clusters to nanoparticles to bulk metals. Investigations of atomically dispersed metal complexes are drawing wide attention because their well-defined structures facilitate fundamental understanding of catalysis as well as offering new catalytic properties. In this work, we extend the field of atomically dispersed supported metal catalysts to dinuclear clusters to build a bridge between atomically dispersed metal complexes and few-atom clusters. Thus, the research extends the subject of atomically dispersed supported catalysts to supported metal pair-site catalysts, which have heretofore been little investigated because of their instability, lack of uniformity, and difficulty of precise synthesis. A separate, collaborative project reported on here includes characterization by in-situ X-ray absorption spectroscopy of the structures of single-site supported metals present as promoters in complex catalysts that contain metal nanoparticles for selective hydrogenation of nitroarenes. Iridium and rhodium pair-site catalysts supported on MgO were synthesized and characterized with infrared (IR) and X-ray absorption spectroscopies and high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM), supported by density functional theory (DFT) calculations done by collaborators. In-situ IR and X-ray absorption near edge structure (XANES) spectra were used to characterize the structural changes of the pair-sites under various treatment conditions, including ligand substitution reactions involving CO and hydrogen. Catalytic properties for ethylene hydrogenation and H-D exchange in the H2 + D2 reaction were tested and compared with those of single-site iridium and rhodium analogues as well as few-atom clusters of these metals supported on MgO. The pair-site catalysts on MgO activated by removal of ligands facilitate H2 dissociation much more rapidly than their single-site analogues and catalyze ethylene hydrogenation one to two orders of magnitude faster than their single-site analogues on MgO. The pair sites are active for ethylene hydrogenation even after being partially poisoned by CO, and, in contrast, the analogous single-site catalysts are fully poisoned. The results provide understanding of the roles of neighboring metal sites and the effects of ligands on pair sites catalysts, opening opportunities for synthesis of stable pairs of various metals on various supports. The benefits of such stable metal pair sites may extend to numerous reactions other than those investigated in this work. The single-site promoters investigated in this work are Sn cations on TiO2 supports that incorporate noble metal nanoparticle catalysts. These catalysts decidedly outperform the comparable unpromoted supported metals for hydrogenation of nitroarenes substituted with various reducible groups. X-ray absorption spectroscopy at the Sn K edge was used to characterize the structural changes in the single-site Sn in the catalysts as influenced by H2 and by nitrobenzene at 353 K and 1 atm. The changes in Sn–O coordination numbers and distances give evidence that the high activity and selectivity of these catalysts result from the creation of oxygen vacancies on the TiO2 surface associated with single-site Sn sites that lead to efficient, selective activation of the nitro group (in contrast to the other reducible group) coupled with reaction involving hydrogen atoms activated on the nearby metal nanoparticles.

Metal-Support and Metal-Additive Effects in Catalysis, Volume 11, documents the proceedings of an international symposium organized by the Institut de Recherches sur la Catalyse - CNRS – Villeurbanne and sponsored by the Centre National de la Recherche Scientifique, Ecully (Lyon), September 14-16, 1982. This volume contains 40 manuscripts that cover a wide range of topics. Among these are studies of metal-support interactions involving Pt/Al2O3, Pt/TiO2,Fe/TiO2, Pt/MgO, Rh /Al2O3, and Pt/CeO2 catalysts. There are also separate chapters dealing with ethane, n-butane, and cyclohexane hydrogenolysis; skeletal isomerization of methylpentanes; the catalytic activity and selectivity of noble metals; CO hydrogenation over supported on SiO2, Al2O3, Ti O2,and Zr O2 nickel catalysts; and the role of promoters in Pd catalysts for methanol synthesis. Subsequent chapters cover the poisoning of platinum and nickel by sulfur; C6H6 and CO chemisorption on Pt78Ni22 (111) single crystal alloy; the surface composition of industrial ammonia synthesis catalysts; and the role of alkalis and electronegative promoters on Fe and Ni catalysts.