In situ catalyst

WU lowest cost SO2 produced in situ catalyst requires startup time higher most every sulfonation and sulfation ... 

Polymerizations of S and MMA with in situ catalyst formation have also been carried out. Matyjaszewski et a ..355 reported on the use of FeBr2 together with various ligands such as PfQHs). , NiCiIIo. and 133 alone or in combination. The use of diearboxylic acid (iminodiacetic acid, isophthalic acid)356 and methanimine ligands " for MMA polymerization has also been reported. 

J.-P., Kuusisto, J., Kustov, L.M., and Murzin, D. (2007) Application of in-situ catalyst potential measurements for estimation of reaction performance D-lactose oxidation over Au and Pd catalysts. Chem. Eng.J., 134, 153-161. 

Preformed complexes of type 52, 53 and 59, and in situ catalyst systems based on IMesX (X = CO, MeS03H, HCl, HBr, HI) and IPrHCl, have been tested for telomerisation of butediene with primary and secondary amines. Under optimised conditions, and low catalyst loadings, excellent activities and selectivities were observed [82]. 

In situ derived systems, in general, performed similarly to preformed complexes, in telomerisation of butadiene with MeOH, Tables 4.1 and 4.2 [68,70,71,77,78], In situ systans may be generated from free NHC or from imidazolium salt in combination with an appropriate Pd(0) or Pd(ll) source. Typically, 2-4 equivalents of imidazolium salt relative to Pd have been nsed [68,70,77], In situ catalysts derived from mono- and bis-Fc-snbstituted (Fc = ferrocenyl) imidazohnm and benzimidazolium salts (64-68) (Table 4.2) showed interesting telomerisation activities ascribed to the steric bulk of the Fc substituents [70]. Unsymmetrical salts 65 and 66 bearing A -Fc and A -Me... 

The use of imidazolium salts for in situ catalyst formation was shown to be optimal for the coupling of TMS-protected alkynes even with sterically demanding aryl bromides and avoids the formation of homocoupling-derived products. For this reaction, Nolan reported that the activation of chlorobenzene by this catalytic system was possible in moderate yield [125] (Scheme 6.41). 

Platinum complexes [PtCl2(diphosphine)] and [PtCl(SnCl3)(diphosphine)] of the ferrocenyl diphosphine ligands (35a), (35b), and (36) have been synthesized. Complexes [PtCl2(35)] and [PtCl2(36)] have been structurally characterized by XRD. Both the preformed and the in situ catalysts have been used in the hydroformylation of styrene.112... 

In FBs, tars are generated, but these can be partially decomposed to gas using in situ catalysts such as dolomite70 and treated olivine sand.46 The tars can further be cracked or reformed downstream in separate beds yielding additional syngas, and thus, hydrogen (see Section 6.3.4). A new development is the combination of ceramic gas filtration and catalytic tar cracking see Heidenreich and Nacken.71... 

Scheme 8.3. Hydroformylation of styrene with the C02-philic in situ catalyst 3-H2F6-BINAPHOS/[Rh(acac)(CO)2] (2 1) using a batch-wise CESS procedure...

Butyne-l,4-diol has been hydrogenated to the 2-butene-diol (97), mesityl oxide to methylisobutylketone (98), and epoxides to alcohols (98a). The rhodium complex and a related solvated complex, RhCl(solvent)(dppb), where dppb = l,4-bis(diphenylphosphino)butane, have been used to hydrogenate the ketone group in pyruvates to give lactates (99) [Eq. (15)], and in situ catalysts formed from rhodium(I) precursors with phosphines can also catalyze the hydrogenation of the imine bond in Schiff bases (100) (see also Section III,A,3). 

Rh(diene)(P )2+ cation precursors are formed (133, 134 also /, p. 270), and indeed such complexes may be used in place of the in situ catalysts in either media (11, 244, 269-271). 

The secondary aryl amine 24 is far less basic than primary or secondary alkyl amines, and does not form the carbamic acid to any detectable extent in the presence of scC02 [31]. Therefore, 24 is extracted readily from the catalyst-containing IL phase, which can be recycled without noticeable loss of activity and selectivity [13]. In fact, it transpires that the active species is more stable towards oxygen in the IL than in organic solvents. Furthermore, the choice of anion of the IL largely controls the performance of the active cationic species, allowing even the use of an otherwise inactive iridium chloride precursor [ Ir(cod)Cl 2] to form in-situ catalysts... 

The ligands prepared by this method were sufficiently pure for use as an in situ catalyst preparation. 

At the fundamental research level, there is a need for in-situ catalyst characterization under reforming conditions in order to understand the nature of active species involved and their stabilities during the reforming reactions. In situ studies to... 

Recently Togni et al. [19] focussed on the preparation of asymmetric dendrimer catalysts derived from ferrocenyl diphosphine ligands anchored to dendritic backbones constructed from benzene-1,3,5-tricarboxylic acid trichloride and adamantane-l,3,5,7-tetracarboxylic acid tetrachloride (e.g. 11, Scheme 11). In situ catalyst preparation by treatment of the dendritic ligands with [Rh(COD)2]BF4 afforded the cationic Rh-dendrimer, which was then used as a homogeneous catalyst in the hydrogenation reaction of, for example, dimethyl itaconate in MeOH. In all cases the measured enantioselectivity (98.0-98.7%) was nearly the same as observed for the ferrocenyl diphosphine (Josiphos) model compound (see Scheme 11). 

Numerous efforts have been made to develop in situ catalyst layer fabrication methods to lower Pt loading and increase platinum utilization without sacrificing electrode performance. 

Preliminary experiments to optimize the reaction conditions with respect to selectivity and activity (in situ catalyst generation, pH value, [P] [Ru] ratio)... 

After optimization of reaction conditions with a special focus on in situ catalyst generation, the pH value of the catalyst phase and the ratio of ligand to metal in the hydrogenation of prenal, the transferabihty of the catalyst system to other Q ,/f-unsaturated aldehydes was checked. The influence of steric hindrance at the C3-atom and the water solubiUty of the substrates on the reaction rate and selectivity to the unsaturated alcohol were analysed (Table 2). The initial concentration of the aldehyde in the organic phase was always 0.5 M. Apart from acrolein, which is not mentioned in the table, generally all kinds of Q ,/f-unsaturated aldehydes can be selectively hydrogenated with... 

An alternative method to make PAEs is the acyclic diyne metathesis (ADIMET) shown in Scheme 2. It is the reaction of a dipropynylarene with Mo(CO)6 and 4-chlorophenol or a similarly acidic phenol. The reaction is performed at elevated temperatures (130-150 °C) and works well for almost any hydrocarbon monomer. The reaction mixture probably forms a Schrock-type molybdenum carbyne intermediate as the active catalyst. Table 5 shows PAEs that have been prepared utilizing ADIMET with these in situ catalysts . Functional groups (with the exception of double bonds) are not well tolerated, but dialkyl PPEs are obtained with a high degree of polymerization. The progress in this field has been documented in several reviews (Table 1, entries 2-4). Recently, a second generation of ADIMET catalyst has been developed that allows... 

In a related report, ruthenium-catalyzed enantioselective hydrogenation of 3-keto esters was utilized to prepare the crucial alcohol intermediate 36 (Scheme 14.16). The required (3-keto ester 49 was readily prepared from commercial thiophene carboxylic acid 40. Hydrogenation of 49 then led to the desired (S)-alcohol 50 in quantitative yield and 90% enantiomeric excess, catalyzed by a chiral diphosphine-ruthenium complex generated in situ. Catalyst-substrate ratios used were as low as 1/20,000, rendering this approach amenable to industrial application. Alcohol 50 was then converted to known intermediate 36 in three steps and 60% overall yield. 

These experiments have made tremendous advances of in situ catalyst reactor system analysis. A discussion of all of them is outside the scope of this chapter. However, descriptions of the techniques that have contributed significantly to the rational design and analysis of catalysts are presented in the next section. It should be recognized that it is not an exhaustive list but, rather, should be considered a starting point to help in understanding the various in situ techniques both in use currently and at the forefront of development. In addition, review papers are referenced for the reader to find more information on techniques that are and are not discussed. 

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