Rhodium supported

Recently we reported EXAFS results on bimetallic clusters of iridium and rhodium, supported on silica and on alumina (15). The components of this system both possess the fee structure in Efie metallic state, as do the components of the platinum-iridium system. The nearest neighbor interatomic distances in metallic iridium and rhodium are not very different (2.714A vs. 2.690A). From the results of the EXAFS measurements, we concluded that the interatomic distances corresponding to the various atomic pairs (i.e., iridium-iridium, rhodium-rhodium, and iridium-rhodium) in the clusters supported on either silica or alumina were equal within experimental error. Since the Interatomic distances of the pure metals differ by only 0.024A, the conclusion is not surprising. 

New developments in the field of ceramic foam monoliths could also potentially provide new catalytic process technology for the conversion of methane into synthesis gas. For example, workers at Minnesota University [9] have achieved high synthesis gas yields at both high temperatures and space velocities using rhodium supported on a ceramic foam. 

A few additional points have also been raised by specific surface-science work concerning the catalytic reduction of NO. For instance, it has been widely recognized that the reaction is sensitive to the structure of the catalytic surface. It was determined that rough surfaces such as (110), or even (100), planes enhance NO dissociation over flatter (111) surfaces, and also favor N2 desorption instead of N20 production. On the other hand, NO dissociation leads to poisoning by the resulting atomic species, hence the faster reaction rates seen with medium-size vs. larger particles on model rhodium supported catalyst (the opposite appears to be true on palladium). Also, at least in the case of palladium, the formation of an isocyanate (-NCO) intermediate was identified... 

Several diphosphine ligands have been applied and the corresponding complexes have been tested for the immobilization (Fig. 2.1.6.3). The activity of different free and immobilized complexes in the enantioselective hydrogenation of dimethyl itaconate and methyl a-acetamidoacrylate was investigated. In blank reactions over pure mesoporous materials no reaction took place. When rhodium supported on carriers was used as catalyst, no enantiomeric excess was observed. 

Miessner, H., Surface-chemistry in a zeolite matrix—Well-defined dinitrogen complexes of rhodium supported on dealuminated Y-zeolite. J. Am. Chem. Soc. 116,11522 (1994). 

In addition to performing acid/base catalysis, zeolite structures can serve as hosts for small metal particles. Transition metal ions, e.g., platinum, rhodium, can be ion exchanged into zeolites and then reduced to their zero valent state to yield zeolite encapsulated metal particles. Inside the zeolite structure, these particles can perform shape selective catalysis. Joh et al. (16) reported the shape selective hydrogenation of olefins by rhodium encapsulated in zeolite Y (specifically, cyclohexene and cyclododecene). Although both molecules can be hydrogenated by rhodium supported on nonmicroporous carbon, only cyclohexene can be hydrogenated by rhodium encapsulated in zeolite Y since cyclododecene is too large to adsorb into the pores of zeolite Y. 

Blackmond et al. compared the selectivities of ruthenium, platinum, and rhodium supported on NaY and KY zeolites with those supported on carbon, in the hydrogenation of cinnamaldehyde and 3-methylcrotonaldehyde in isopropyl alcohol at 100°C (for rhodium and ruthenium) or 70°C (for platinum) and 4 MPa H2.52 Good selectivities to unsaturated alcohols were obtained over zeolite-supported ruthenium and platinum with... 

Propylene Hydroformylation over Various Metal Carbonyl Clusters Impregnated on Metal Oxides Compared with That over Conventional Rhodium Supported Catalyst"... 

Resasco D, Haller GL (1982) Dispersion effects on alkane hydrogenolysis over rhodium supported on titanium oxide. Stud Surf Sci Catal 11 105... 

Logan AD, Braunschweig EJ, Datye AK, Smith DJ (1988) Direct observation of the surfaces of small metal crystallites - rhodium supported on TiO. Langmuir 4 827... 

Weber, W.A. and Gates, B.C. (1998) Rhodium supported on faujasites effects of cluster size and CO ligands on catalytic activity for toluene hydrogenation. 

Over rhodium-supported on AI2O3, the reaction takes place at temperatures above 400 K [508,509], showing that under oxygen-free conditions, gold-based catalysts easily outperform those based on the PGMs for this reaction. 

Zeolitic systems are very active at low temperatures but they also have disadvantages related to their hydrothermal stability and the possibility of inhibition or poisoning by different compounds. These drawbacks drastically limit the industrial applications of these catalysts. Rhodium-supported systems are also active at low temperatures and low N2O concentration, but at high temperatures and in the presence of O2 the noble metal is oxidized. Furthermore, the high cost of Rh may prove to be a limit for industrial applications. 

Rhodium supported on y-ALOs is an important component of 3-way automotive catalysts and has been studied by a wide variety of methods [1-5] including ESR. In the last 15 years Rh-species introduced into zeolites of different types (Y, X, L, A, SAPO) have also been examined by several techniques [6-9]. However, most of these methods were applied after the specimens were removed from actual reaction conditions and transferred into the respective characterization instruments and the state or behavior of the catalyst in-situ was arrived at indirectly by inference. Also the deactivation processes or the effect of modifiers is seldom, if ever, determined by direct in-situ observations. We have previously devised a method for high-temperature measurement of ESR-active ions under flow conditions and applied it to characterize specimens containing Cu [10] or Cr " [11]. We have extended this method now to specimens containing Rh. Here, we summarize the results of a study of the interaction of Rh/y-ALOB and Rh/ZSM-5 with different gases and gas mixtures (NO, NO2, CO, propene, O2, H2O) at 120-573 °K. The amount of Rh present in the samples is evaluated quantitatively. The effect of copper and lanthanide addition on the stabilization of by the zeolitic matrix was also investigated. 

RHODIUM - SUPPORT INTERACTIONS IN AUTOMOTIVE EXHAUST CATALYSTS... 

Rhodium-Support Interactions in Automotive Exhaust Catalysts",... 

Another classic work in the area of the solid-state NMR of dispersed metal systems is the work of Duncan and Zilm [ 100]. In this work CO was examined on samples of rhodium supported on a silica. CO adsorbs on oxide-supported transition metals in three forms linear, bridge-bonded, and multicarbonyls. As... 

A.D. Logan, E.J. Braunschweig, A.K. Datye, and D.J. Smith. Direct Observation of the Surfaces of Small Metal Crystallites Rhodium Supported on Ti02. Langmuir 4 827 (1988). 

As described above, the hydrogenation of citral by unmodified rhodium supported on silica is non-selective. It leads to numerous products whereas the addition of tin to a Rh/Si02 catalyst (atomic ratio of tin/rhodium = 1) results in a totally selective reaction for 3,7-dimethyl-2,6-octenol (geraniol + nerol). A study of the catalytic properties as a function of the amount of tin per surface rhodium has shown that... 

Dreyer et al. [33] investigated the oxidative steam reforming of diesel surrogates over wash-coated ceramic monoliths carrying 5 wt.% rhodium supported by y-alumina. The conversion of M-decane dropped with increasing S/C ratio because the reaction temperature decreased significantly. The beneficial effect of... 

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