Rh catalyst

Rh+ catalyst is more selective than Ir+ for acyclic stereoselection, Acyclic homoallylic systems ... 

Conditions cited for Rh on alumina hydrogenation of MDA are much less severe, 117 °C and 760 kPA (110 psi) (26). With 550 kPa (80 psi) ammonia partial pressure present ia the hydrogenation of twice-distilled MDA employing 2-propanol solvent at 121°C and 1.3 MPa (190 psi) total pressure, the supported Rh catalyst could be extensively reused (27). Medium pressure (3.9 MPa = 566 psi) and temperature (80°C) hydrogenation usiag iridium yields low trans trans isomer MDCHA (28). Improved selectivity to aUcychc diamine from MDA has been claimed (29) for alumina-supported iridium and rhodium by iatroduciag the tertiary amines l,4-diazabicyclo[2.2.2]octane [280-57-9] and quiaucHdine [100-76-5]. 

Propane, 1-propanol, and heavy ends (the last are made by aldol condensation) are minor by-products of the hydroformylation step. A number of transition-metal carbonyls (qv), eg, Co, Fe, Ni, Rh, and Ir, have been used to cataly2e the oxo reaction, but cobalt and rhodium are the only economically practical choices. In the United States, Texas Eastman, Union Carbide, and Hoechst Celanese make 1-propanol by oxo technology (11). Texas Eastman, which had used conventional cobalt oxo technology with an HCo(CO)4 catalyst, switched to a phosphine-modified Rh catalyst ia 1989 (11) (see Oxo process). In Europe, 1-propanol is made by Hoechst AG and BASE AG (12). 

Reduction and Hydrodesulfurization. Reduction of thiophene to 2,3- and 2,5-dihydrothiophene and ultimately tetrahydrothiophene can be achieved by treatment with sodium metal—alcohol or ammonia. Hydrogen with Pd, Co, Mo, and Rh catalysts also reduces thiophene to tetrahydrothiophene [110-01-0] a malodorous material used as a gas odorant. 

The emission control system for LPG is the same as is used for gasoline fueled engines with the exception of the fuel metering system. No evaporative emission system is required. Both Pt—Rh and Pd—Rh catalysts are good for emission control of LPG fuel exhaust. Pt provides the lowest light off temperature for C Hg. The sulfur content of LPG is also very low so that Pd catalysts perform very well. 

Ring enlargement of benzene derivatives by carbenes generated from diazo compounds (better in the presence of a Rh catalyst) Conversion of aldehydes to ketones by diazo compounds (Schlotterbeck) see also Ptau Planer... 

HORNER - KNOWLES - KAGAN Asymmetric Hydrogenation Enantnselective hydrogenation of prochirai olefins with chiral Rh catalysts... 

N-Acetyl-(R)-phanylalanlna (6). The rhodium catalyst was obtained by adding (-) dlop 5 (from diethyl tartrate) to a benzene solution of [RhCi(cyclooctene)2]2 under Ar, and stirring for tS mn A solution of the Rh catalyst (1 mM in EtOH PhH 4 1) was introduced under Hj to a solution of a-N acetylamino- phenytacrylic acid 4 (molar ratio Rh 4 1.540) The solvent was evaporated, the residue dissolved In 0 5 N NaOH, the catalyst was filtered and the solution acidified and concentrated to dryness to give 6 (81% ee) in 90 95% yield... 

WILKINSON Cartxinylalion decarbonylation catalyst Rh catalyst lor cartxinylation, decarbonylation, oxygenation, benzyl cleavage... 

Homogeneous methanol carboxylation with I /Rh catalyst (175-195°C, 30atm), this is now a leading route to acetic acid ... 

Ammonia bums in air with difficulty, the flammable limits being 16-25 vol%. Normal combustion yields nitrogen but, in the presence of a Pt or Pt/Rh catalyst at 750-900°C, the reaction proceeds further to give the thermodynamically less-favoured products NO and NO2 ... 

While unmodified xanthene ligands (compound a in Figure 5.2-4) show highly preferential solubility in the organic phase in the biphasic l-octene/[BMIM][PFg] mixture even at room temperature, the application of the guanidinium-modified xanthene ligand (compound b in Figure 5.2-4) resulted in excellent immobilization of the Rh-catalyst in the ionic liquid. 

After ten consecutive runs the overall turnover number reaches up to 3500 mol 1-octene converted per mol Rh-catalyst. In agreement with these recycling experiments, no Rh could be detected in the product layer by AAS or ICP, indicating leaching of less then 0.07 %. In all experiments, very good selectivities for the linear aldehyde were obtained, thus proving that the attachment of the guanidinium moiety onto the xanthene backbone had not influenced its known positive effect on... 

Certain amines, when linked to TPPTS, form ionic solvents liquid at quite low temperatures. Bahrman [33] used these ionic liquids as both ligands and solvents for the Rh catalyst for the hydroformylation of alkenes. In this otherwise interesting... 

Hydrogenation of olefinic unsaturation using ruthenium (Ru) catalyst is well known. It has been widely used for NBR hydrogenation. Various complexes of Ru has been developed as a practical alternative of Rh complexes since the cost of Ru is one-thirtieth of Rh. However, they are slightly inferior in activity and selectivity when compared with Rh catalyst. 

In the preceding section, it has been shown that considerable attention has been devoted to palladium as a heterogeneous catalyst. The present section describes the homogeneous palladium catalysts developed for hydrogenation of NBR. The main drive behind the development of various catalyst systems is to find suitable substituents of the Rh catalyst. Palladium complexes are much cheaper as compared with Rh and exhibit comparable activity and selectivity to Rh and Ru complexes. 

Ethylene glycol could he produced directly from synthesis gas using an Rh catalyst at 230°C at very high pressure (3,400 atm). In theory, five moles synthesis gas mixture are needed to produce one mole ethylene glycol ... 

Figure 2.3. Catalysis (0), classical promotion ( ), electrochemical promotion ( , ) and electrochemical promotion of a classically promoted (sodium doped) ( , ) Rh catalyst deposited on YSZ during NO reduction by CO in presence of gaseous 02.14 The Figure shows the temperature dependence of the catalytic rates and turnover frequencies of C02 (a) and N2 (b) formation under open-circuit (o.c.) conditions and upon application (via a potentiostat) of catalyst potential values, UWr, of+1 and -IV. Reprinted with permission from Elsevier Science.

Can one further enhance the performance of this classically promoted Rh catalyst by using electrochemical promotion The promoted Rh catalyst, is, after all, already deposited on YSZ and one can directly examine what additional effect may have the application of an external voltage UWR ( 1 V) and the concomitant supply (+1 V) or removal (-1 V) of O2 to or from the promoted Rh surface. The result is shown in Fig. 2.3 with the curves labeled electrochemical promotion of a promoted catalyst . It is clear that positive potentials, i.e. supply of O2 to the catalyst surface, further enhances its performance. The light-off temperature is further decreased and the selectivity is further enhanced. Why This we will see in subsequent chapters when we examine the effect of catalyst potential UWR on the chemisorptive bond strength of various adsorbates, such as NO, N, CO and O. But the fact is that positive potentials (+1V) can further significantly enhance the performance of an already promoted catalyst. So one can electrochemically promote an already classically promoted catalyst. 

Why do negative potentials (UWr=-1 V) fail to further enhance to any significant extent catalyst performance of the promoted catalyst whereas the unpromoted Rh catalyst is electrochemically promoted with both positive and negative potentials (Fig. 2.3). The answer will become apparent in subsequent chapters In a broad sense negative potential application is equivalent to alkali supply on the catalyst surface. They both lead to a substantial decrease (up to 2-3 eV) in the catalyst work function, O, aquantity which as we will see, plays an important role in the description of promotion... 

This observation is directly related to the observed dramatic electrochemical promotion of NO reduction by CO and C3H6 in presence of 02 on Rh/YSZ upon electrochemical O2 supply to the Rh catalyst surface (Fig. 2.3 and Chapters 4 and 8). 

Figure 4.14 shows a similar galvanostatic transient obtained during C2H4 oxidation on Rh deposited on YSZ.50 Upon application of a positive current 1=400 pA with a concomitant rate of O2 supply to the catalyst I/2F=2.M0 9 mol O/s the catalytic rate increases from its open-circuit value r0=1.8 10 8 mol O/s to a new value r= 1.62-1 O 6 mol O/s which is 88 times larger than the initial unpromoted rate value. The rate increase Ar is 770 times larger than the rate of supply of O2 ions to the Rh catalyst surface. 

Electrochemical Promotion of a Classically Promoted Rh Catalyst for NO Reduction by CO in Presence of 02... 

This case has been already discussed in Chapter 2 (Fig. 2.3).69 The Rh film used is shown in Fig. 8.63 and exhibits inverted volcano behaviour,67 i.e. the rate of C02 and N2 formation is enhanced both with positive and with negative potentials. This is shown in Figure 8.65 and also in Figure 2.3 which depicts the rco2 and rN2 dependence on T of the unpromoted and electrochemically promoted Rh catalyst. The corresponding Tn2o vs T behaviour is shown in Figure 8.66. 

C. Pliangos, C. Raptis, T. Badas, D. Tsiplakides, and C.G. Vayenas, Electrochemical Promotion of a Classically Promoted Rh catalyst for the Reduction of NO, Electrochim. Acta 46, 331-339(2000). 

Figure 11.3. Schematic of the experimental setup used (a) to induce electrochemical promotion (via YSZ) on Ir02 and Ir02-Ti02 porous catalyst films (b) to compare the electrochemical promotion induced on Pt via YSZ and via Ti02 and (c) to compare the electrochemical promotion behaviour induced by varying UWR on a Rh porous catalyst film (left) and on a fully dispersed Rh catalyst supported on porous (80 m2/g) YSZ support.22...

Figure 11.8. Effect of po2 on the rate (TOF) of C2H4 oxidation on Rh supported on five supports of increasing d>. Catalyst loading 0.5wt%.22,27 Inset Electrochemical promotion of a Rh catalyst film deposited on YSZ Effect of potentiostatically imposed catalyst potential Uwr on the rate and TOF dependence on po2 at fixed Pc2H4-22,33 Reprinted with permission from Elsevier Science (ref. 27) and Academic Press (ref. 33).

F.A. Alexandrou, V.G. Papadakis, X.E. Verykios, and C.G. Vayenas. The promotional effect ofNa on the NO reduction by CO on supported Pt, Pd and Rh catalysts in Proc. 4thlntnl. Congress on Catalysis and Automotive Pollution Control2, 1-16 (1997). 

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