Rhodium/zeolite, hydrogenation

Table 1.4.1 Kinetic parameters for the simultaneous hydroformylation and hydrogenation of propene over a rhodium zeolite catalyst at 7" = 423 K and 1 atm total pressure [from Rode et al., J. Catal., 96 (1985) 563].

The addition of trimethylphosphine to these rhodium/zeolite catalysts destroyed all catalytic activity because the phosphine was small enough to fit into the zeolite cavity and could deactivate all of the rhodium in the catalyst. The bulky tributylphosphine, however, could not enter the cavity and, thereby, only blocked the external rhodium from further reaction. This specific blocking enhanced the selectivity in the hydrogenation of a mixture of cyclopentene and 4-methylcyclohexene over a Rh/ZSM-11 catalyst. After treatment of the catalyst with tributylphosphine to block the external catalytically active sites, only the... 

Encapsulated rhodium complexes were prepared from Rh-exchanged NaY zeolite by complexation with (S)-prolinamide or M-tert-butyl-(S)-prolinamide [73,74]. Although these catalysts showed higher specific activity than their homogeneous counterparts in non-enantioselective hydrogenations, the hydrogenation of prochiral substrates, such as methyl (Z)-acetamidocinnamate [73] or ( )-2-methyl-2-pentenoic acid [74], led to low... 

Sanchez, F., Iglesias, M., Corma, A. and Delpino, C. New rhodium complexes anchored on silica and modified Y-zeolite as efficient catalysts for hydrogenation of olefins, J. Mol. Catal., 1991, 70, 369-379. 

Fig. 1. Model of rhodium dicarbonyl complex on dealuminated Y zeolite, as determined by IR and EXAFS spectroscopies and density functional theory. The Rh atom, near the upper center of the figure, has two CO ligands bonded to it, pointing upward, and two oxygen atoms of the zeolite lattice below. An Al atom is located between these two oxygen atoms. The dangling atoms of the cluster model of the zeolite are capped by hydrogen atoms for the calculation (Goellner, Gates, etal., 2000).

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... 

By selecting (he proper reaction conditions, ccdialt and rhodium catalysts prove active for the direct hydrogenation of the intermediate di dehyde (0 ethylene glycol [44). Glycolaldehyde is also formed with a zeolite/NaOH catalyst [451, Monsanto has patented a route to ethylene ycol, which starts with methanol (Equation (21)) [46]. 

Discrimination between surface and intrazeolite sites is often difficult. The chemical reactivity of zeolite-bound complexes to reagents of different sizes is helpful in determining the location of an irmnobilized complex. For example, in rhodium faujasites prepared from Rh(aUyl)3 and H-Na-X (i.e. the faujasite Na X in which a fraction of the sodium ions have been replaced with protons), catalytic activity for hydrogenation can be limited to the intrazeolite sites only when P(n-Bu)3 is used to poison the surface rhodium sites. Tri-n-butylphosphine is too large to penetrate the zeolite pores, thus the rhodium complexes within the zeolite remain catalytically active. 

A novel method for the preparation of metal containing small pore zeolites is described. The metal is introduced at elevated temperatures by solid state ion exchange. The zeolites obtained by the new method are highly shape selective. As an example, the competitive hydrogenation of an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l) over various platinum, palladium and rhodium containing 8-membered ring zeolites was studied. 

Palladium, rhodium and ruthenium complexes of the Schiff base salen are synthesized in the supercages of zeolite Y. The existence of intracrystalline transition metal-salen complexes is verified by a detailed physicochemical characterization. The catalytic properties of the prepared host/guest inclusion compounds are explored in the hydrogenation of hexene-(l) or an equimolar mixture of hexene-(l) and 2,4,4-trimethylpentene-(l). 

Rhodium-tin bimetallic particles have been deposited in a NaY zeolite. They were obtained by chemical vapor deposition with subsequent H2 reduction of SnR4 (R = C2H5 or CeHs) onto reduced Rh/NaY samples prepared by ion exchange (IE) or by chemical vapor deposition (CVD). The resultant product was used in the selective hydrogenation of a, (3-unsaturated aldehydes. 

Example 1 Chiral rhodium complexes anchored on modified USY zeolites.[70] For the asymmetric catalytic hydrogenation reaction of iV-acylphenylaniline, the product not only has high translation yield and ee% value (>95%), but also has a long reaction life. The assembly process of rhodium complex catalyser is as follows ... 

A. Corma, M. Iglesias, C. Pino, and F. Sanchez, New Rhodium Complexes Anchored on Modihed USY Zeolites. A Remarkable Effect of the Support on the Enantioselectiveity of Catalytic Hydrogenation of Prochiral Alkenes. J. Chem. Soc., Chem. Commun., 1991, 1253— 1255. 

Corbin, D.R., Seidel, W.C., Abrams, L., Herron, N., Stucky, G.D., and Tohnan, C.A. 1985. Shape selectivity in olefin hydrogenation using rhodium-containing zeolites. Inorganic Chemistry 24, 1800-1803. 

Rhodium catalysts were prepared by hydrogen reduction at atmospheric pressure of a cationic organometallic rhodium complex and anchored onto lamellar and zeolitic products. The effect of the structure and characteristics of the support on metal load and dispersion was studied in the heterogeneous catalysts prepared. The new rhodium catalysts were applied in the hydrogenation of acetone. The reaction was carried out under milder conditions. 

Activity, selectivity and durability of the new heterogeneous rhodium catalysts depend on the nature of the support used in the preparation of the catalyst. The lamellar structures mainly yield methyl isobutyl ketone (MIBK), whereas the zeolitic structures, in general, yield isopropanol (IPA). The activity remains steady throughout the period tested (7h), except when the support is the BENPIL indeed, the deactivation of Rh/BENPIL is relatively rapid particularly during the first hour of reaction. The turnover numbers frequencies (TOP) obtained with these catalysts might be attributed to the structure of the metal no sensitive reaction the hydrogenation acetone. 

Hydrogenation is selective for size and shape.200 Cyclohexene, but not cyclododecene, was reduced by hydrogen with a rhodium in NaY zeolite. The Beckmann rearrangement of cyclohexanone oxime to caprolactam (6.37) (for... 

The conversion of 2-phenylbutene to 2-phenylbutane and acetophenone to 1-phenylethanol over HZSM-5 modified by Pt and a chiral ligand has been reported. An asymmetric hydrogenation of N-acyldehydrophenylalanine derivatives with enantioselectivities 95% over zeolite-suported chiral rhodium complexes has been reported. 

Investigations into these topics are presented in this volume. Iron, nickel, copper, cobalt, and rhodium are among the metals studied as Fischer-Tropsch catalysts results are reported over several alloys as well as single-crystal and doped metals. Ruthenium zeolites and even meteo-ritic iron have been used to catalyze carbon monoxide hydrogenation, and these findings are also included. One chapter discusses the prediction of product distribution using a computer to simulate Fischer-Tropsch chain growth. 

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