Carbonate catalyst, recoverability

To address the recoverability of the alkali carbonate catalyst from the ash, both ambient and warm water washes were used. In the ambient temperature wash, 1 gram of ash was stirred 1 hr in 100 ml H20. Between 80-100% (87% average for 24 samples) of the initial potassium used in the gasification run could be dissolved in the aqueous solution. The range of potassium solubility reflects some of the difficulties previously referred to. No attempt was made to recrystallize potassium compounds from the ambient temperature washes. 

Our interest in silicon chemistry quite naturally led to a study of the hydrosilation reaction, the addition of the Si-H group across an olefin or an acetylene. This reaction is one of the most useful methods of making silicon-carbon bonds and is an important industrial process. Typically, homogeneous catalysts based on platinum, rhodium or ruthenium are used, and while very efficient, they are not recoverable(46). 

Fresh and recvcled liquid ethylbenzene combine and are heated from 25°C to 500°C and the heated ethylbenzene is mixed adiabaiically with steam at 700 C to produce the feed to the reactor at 600 C (The steam suppresses undesired side reactions and removes carbon deposited on the catalyst surface.) A once-through conversion of 35% is achieved in the reactor(2). and the products emerge at 560 C The product stream is cooled to 25°C , condensing essentially all of the water, ethylbenzene, and styrene and allowing hydrogen to pass out as a recoverable by-product of the process. 

The reaction was initially tested by the use of PdCliCPPhs) . Although 6 equiv of iodide 80 was required to complete the reaction, the desired product 65 was obtained in 80% yield (Table 11, Entry 1) [97]. The catalyst is, however, inadequate especially in terms of cost. Studies were undertaken to search for a better protocol. Nickel system was resorted in this connection. The use of inexpensive nickel(IT) acetylacetonate [Ni(acac)2] was tested to reduce the cost of raw material, which led to a moderate yield of 65 (78%, Table 11, Entry 2) [98]. Easily recoverable heterogeneous palladium on activated carbon (Pd/C) catalyst was then examined. While the use of the standard conditions using THF and toluene as the solvent resulted in a moderate yield (50%, Table 11, Entry 3), addition of DMF to the reaction mixture considerably improved the yield, providing 65 in 94% yield (Table 11, Entry 4) [99]. Much less pyrophoric Pearlman s catalyst [Pd(OH)2/C] was found to give 65 in an excellent yield with such a tiny catalyst loading as 0.65 mol% (Table 11, Entry 5) [100]. 

A series of supported chiral VO(salen) complexes anchored on silica, single-wall carbon nanotube, achvated carbon or ionic liquids have been prepared through the simple methods based on the addition of mercapto groups to terminal C=C double bonds (Scheme 7.17) [58]. The four recoverable catalysts and the standard VO(salen) complex 37 were tested for the enantioselechve cyanosilylation of benzaldehyde using trimethylsilyl cyanide (Table 7.9). It should be noted that the ionic liquid-supported IL-VO(salen) showed the highest catalyhc achvity, though the ee-value was considerably reduced compared to the soluble 37 in [bmim][PF6] (entries 4 and 5). 

Coke consists mainly of carbon (90-95%) and has a low mineral matter content (determined as ash residue). Coke is used as a feedstock in coke ovens for the steel industry, for heating purposes, for electrode manufacture, and for production of chemicals. The two most important categories are green coke and calcinated coke. This latter category also includes catalyst coke deposited on the catalyst during refining processes this coke is not recoverable and is usually burned as refinery fuel. 

Immobilization of such catalytically highly efficient HPA into an insoluble, readily recoverable solid acid is, therefore, an interesting and significant research target because environmentally benign solid-acid catalysts should replace problematic sulfuric acid and aluminum chloride. Several efforts have been made to immobilize HPA. Active carbon tightly entraps HPA inside its pores to form an insoluble solid acid that catalyzes liquid-phase organic reactions in polar media... 

Hydroxyapatite (CajQ(P04)g(0H)2) has also attracted considerable interest as a catalyst support. In these materials, wherein Ca sites are surrounded by P04 tetrahedra, the introduction of transition metal cations such as Pd into the apatite framework can generate stable monomeric phosphate complexes that are efficient for aerobic selox catalysis [99]. Carbon-derived supports have also been utihzed for this chemistry, and are particularly interesting because of the ease of precious metal recovery from spent catalysts simply by combustion of the support. Carbon nanotubes (CNTs) have received considerable attention in this latter regard because of their superior gas adsorption capacity. Palladium nanoparticles anchored on multiwalled carbon nanotubes (MWCNTs) and single-walled carbon nanotubes (SWCNTs) show better selectivity and activity for aerobic selox of benzyl and cinnamyl alcohols [100, 101] compared to activated carbon. Interestingly, Pd supported on MWCNTs showed higher selectivity toward benzaldehyde, whereas activated carbon was found to be a better support in cinnamyl alcohol oxidation. Functionalized polyethylene glycol (PEG) has also been employed successfully as a water-soluble, low-cost, recoverable, non-toxic, and non-volatile support with which to anchor nanoparticulate Pd for selox catalysis of benzyl/cinnamyl alcohols and 2-octanol [102-104]. 

Successively, carbon aerogels doped palladium nanoparticles as a recoverable catalyst was applied in the hydroxycarbonylation of aryl iodides by Cacchi and colleagues [144]. Using DMF as a solvent at 100 °C with acetic anhydride/lithium formate along with lithium chloride and DiPEA (MA-dusopropylethylamine) as a base, high to excellent yields can be achieved. The catalyst can be reused up to 12 times without any appreciable loss of activity in the case study of p-iodotoluene. 

Soler R, Cacchi S, Fabrizi Get al (2007) Sonogashira Cross-Coupling Using Carbon Aerogel Doped with Palladium Nanoparticles A Recoverable and Reusable Catalyst. Synthesis 19 3068-3072 Du H, Li B, Kang Fet al (2007) Carbon aerogel supported Pt-Ru catalysts for using as the anode of direct methanol fuel cells. Carbon 45 429-435... 

Interestingly, the procedure of hydroxycarbonylation by using lithium formate and acetic anhydride as internal condensed sources of carbon monoxide can be carried out in the presence of a recoverable and reusable phosphine-free palladium-carbon aerogel catalyst [61]. To support high-speed chemistry and automated organic synthesis, an operationally simple and environmentally safe hydroxycarbonylation of vinyl triflates can... 

Cacchi, S., Cotet, C.L, Fabrizi, G., Forte, G., Goggiamani, A., Martinez, S., Molins, E., Moreno-Manas, M., Petrucd, F., Roig, A. and VaDribera, A. (2007) Fffident hydroxycarbonylation of aryl iodides using recoverable and reusable carbon aerogels doped with palladium nanopartides as catalyst Tetrahedron, 63, 2519-2523. 

Scandium(III) trifluoromethanesulfonate (Sc(OTf)3) is extensively used in organic synthesis to catalyze a wide variety of carbon-carbon bond-forming reactions in aqueous media. The polymer microencapsulated triflate ME catalysts are recoverable and reusable, often reduce metal leaching, and have activity similar to that of their homogeneous counterparts [128]. 

Ruthenium s supremacy in the carbene chemistry of Group 8 elements is a direct consequence of the tremendous interest raised by NHC-Ru complexes as catalysts for olefin metathesis. Indeed, the synergy of a late transition metal tolerant of a wide variety of functional groups, together with a class of ligands whose physical and chemical properties are easily modulated to tailor the activity, selectivity, stability, water-solubility, recoverability, or latency of the resulting catalytic species, translated into an unprecedented success story of modern synthetic chemistry. Yet, the ability of ruthenium complexes to promote carbon-carbon bond formation goes well beyond... 

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