Rhodium, single-crystal

Figure 3.6. Example of the type of kinetic information available for the catalytic reduction of NO on rhodium single-crystal surfaces under atmospheric conditions. The data in this figure correspond to specific rates for C02, N20, and N2 formation over Rh(l 11) as a function of inverse temperature for two NO + CO mixtures PNO = 0.6 mbar and Pco — 3 mbar (A), and Pno — Pco = 4 mbar (B) [55]. The selectivity of the reaction in this case proved to be approximately constant independent of surface temperature at high NO pressures, but to change significantly below Pno 1 mbar. This highlights the dangers of extrapolating data from experiments under vacuum to more realistic pressure conditions. (Reproduced with permission from the American Chemical Society, Copyright 1995).

Figure 10.4 A comparison of the rates of CO oxidation by 02 over two different rhodium single-crystal catalysts and supported Rh/alumina catalysts. (Reprinted from Goodman, D.W., Chem. Rev., 95, 523-536, 1995. Copyright 1995. With permission from American Chemical Society.)...

The Application of High Resolution Electron Energy Loss Spectroscopy to the Characterization of Adsorbed Molecules on Rhodium Single Crystal Surfaces... 

The procedures for sample preparation, mounting and cleaning have been described previously (26). Briefly, the rhodium single crystal rod was oriented to 1/2° using X-ray back reflection and a 1 mm. thick disc was cut by spark erosion. After mechanical... 

Marsh AL, Somorjai GA (2005) Structure, reactivity, and mobility of carbonaceous overlayers during olefin hydrogenation on platinum and rhodium single crystal surfaces. Top Catal 34 121... 

B.E. Bent. Bonding and Reactivity of Unsaturated Hydrocarbons on Transition Metal Surfaces Spectroscopic and Kinetic Studies of Platinum and Rhodium Single Crystal Surfaces. PhD thesis. University of California, Berkeley, 1986. 

G. Comelli, V.R. Dhanak, M. Kiskinova, K.C. Prince, R. Rosei, Oxygen and nitrogen interaction with rhodium single crystal surfaces. Surf Sci. Rep. 32(5), 167-231 (1998)... 

G. Fisher and co-workers, "Mechanism of the Nitric Oxide—Carbon Monoxide—Oxygen Reaction Over a Single Crystal Rhodium Catalyst," in M. 

We have undertaken a series of experiments Involving thin film models of such powdered transition metal catalysts (13,14). In this paper we present a brief review of the results we have obtained to date Involving platinum and rhodium deposited on thin films of tltanla, the latter prepared by oxidation of a tltanliua single crystal. These systems are prepared and characterized under well-controlled conditions. We have used thermal desorption spectroscopy (TDS), Auger electron spectroscopy (AES) and static secondary Ion mass spectrometry (SSIMS). Our results Illustrate the power of SSIMS In understanding the processes that take place during thermal treatment of these thin films. Thermal desorption spectroscopy Is used to characterize the adsorption and desorption of small molecules, In particular, carbon monoxide. AES confirms the SSIMS results and was used to verify the surface cleanliness of the films as they were prepared. 

The above apparatus has been used to study reactions over single crystals of nickel, ruthenium, and rhodium (1-7,12-15). 

The above described experiments over atomically clean single crystal catalysts have been extended to studies of the kinetics of various catalytic reactions over chemically modified catalysts. Examples are recent studies Into the nature of poisoning by sulfur of the catalytic activity of nickel, ruthenium, and rhodium toward methana-tlon of CO (11,12) and CO2 (15). ethane (12) and cyclopropane (20) hydrogenolysls, and ethylene hydrogenation (21). 

Temperature programmed desorption (TPD) or thermal desorption spectroscopy (TDS), as it is also called, can be used on technical catalysts, but is particularly useful in surface science, where one studies the desorption of gases from single crystals and polycrystalline foils into vacuum [2]. Figure 2.9 shows a set of desorption spectra of CO from two rhodium surfaces [14]. Because TDS offers interesting opportunities to interpret desorption in terms of reaction kinetic theories, such as the transition state formalism, we will discuss TDS in somewhat more detail than would be justified from the point of view of practical catalyst characterization alone. 

We begin with the structure of a noble metal catalyst. The emphasis is on the preparation of rhodium on aluminum oxide and the nature of the metal-support interaction. Next we focus on a promoted surface in a review of potassium on noble metals. This section illustrates how single crystal techniques have been applied to investigate to what extent promoters perturb the surface of a catalyst. The third study deals with the sulfidic cobalt-molybdenum catalysts used in hydrotreating reactions. Here we are concerned with the composition and structure of the catalytically active... 

Although the vast majority of this review has been concerned with homogeneous systems, supported catalyst and single-crystal studies of rhodium are important topics that have also been considered by some researchers. This topic extends and dovetails nicely with the discussion of the interactions of acyclic and cyclic polyamine ligands and Schiff... 

G. Fisher and co-workers, "Mechanism of the Nitric Oxide—Carbon Monoxide—Oxygen Reaction Over a Single Crystal Rhodium Catalyst," in M. J. Philips and M. Teman, eds., Proceedings of the 9th International Congress on Catalysis, Vol 3, Characterisation and Metal Catalysts, Chemical Institute of Canada, Ottawa, 1988. 

CH xCH CH H x Bu ] (x = 1 or 2). Both complexes have had their structures determined by single-crystal X-ray analysis and have a trans-C=C bond coordinated to rhodium (34,36). The 31P shifts for the x = 1 compound are to very low frequency (-42.5 ppm) consequent on the strained environment around the phosphorus nuclei. In contrast we... 

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