Copper catalysts preparation

Another copper catalyst, prepared by treating a NaY zeolite with copper nitrate, for ammonia oxidation (160—185°C) has been studied by Williamson et al. [349], The reaction is first order in NH3 and zero order in oxygen. The mechanism here is based on a Cu(II)(NH3)4+ complex formed in the large cavities of the zeolite. The rate-determining step is the reduction of Cu(II) by ammonia. 

We recently reported that a heterogeneous copper catalyst prepared with a non-conventional chemisorption-hydrolysis technique is able to promote a hydrogen transfer reduction using a donor alcohol. In this case, the role of copper is cricial, both for activity and selectivity [20]. 

Heterogeneous copper catalysts prepared with the chemisorption-hydrolysis technique are effective systems for hydrogen transfer reactions, namely carbonyl reduction, alcohol dehydrogenation and racemization, and allylic alcohol isomerization. Practical concerns argue for the use of these catalysts for synthetic purposes because of their remarkable performance in terms of selectivity and productivity, which are basic features for the application of heterogeneous catalysts to fine chemicals synthesis. Moreover, in all these reactions the use of these materials allows a simple, safe, and clean protocol. 

The earliest study of copper catalysts prepared by the skeletal method was that of Fauconnau [6] who used... 

Cyclic and acyclic enol derivatives 480 can be asymmetrically aziridinated with (A -tosylimino)iodobenzene 481 using a chiral copper catalyst prepared in situ from [Cu(MeCN)4]PF6 and the optically active ligand 479. Collapse of the aminal (i.e., 482) leads to the formation of enantiomerically enriched Q-amino carbonyl compounds 483, although ee s to date are modest <2000EJ0557>. Similarly, dienes can be selectively aziridinated using the chiral Mn-salen complex 484 to give vinyl aziridines 486 in scalemic form (Scheme 124) <2000TL7089>. 

In the preparation of substituted diaryl ethers (ArOAr ), the reaction of alkali phenoxides and aryl halides is catalyzed by copper (Ullmann). Further studies have shown that the yield varies considerably with different copper-catalyst preparations. ... 

Choksi, H. N., Silica Supported Binuclear Copper Catalysts Preparation and Characterization , MS thesis, Georgia Institute of Technology, (1994). 

A complementary, but less pronounced, increase in cis syri) selectivity is provided when diazoacetates with rather small ester groups and rhodium catalysts with bulky ligands, such as iodorhodium(IIl) porphyrins and mcso-tetrakis(2,4,6-triarylbenzoato)di-rhodium(ll) complexes, are employed. For ethyl 2-alkylcyclopropane-l-carboxylates so obtained, a cisfran.s ratio of 2-4 was typical. Notable cis selectivities have also been achieved in the synthesis of ethyl 2-phenylcyclopropane-l-carboxylate with the catalyst [(r/ -C5H5)Fe(CO)2(THF)][BFJ (cis/trans 5.25, see Section 1.2.1.2.4.2.6.3.1.) and copper catalysts prepared in situ from a copper salt [copper(I) iodide, copper(II) acetate or triflate] and sodium tetrakis(7,8,8-trimethyl-4,5,6,7-tetrahydro-2Ff-4,7-methanoindazolyl)borate (3) cis/ trans 2.1-3.2). °... 

Preparation.1 Ninety-six grams of anhydrous aluminum chloride is added to 320 ml- of pyridine containing 2.5% of water wanned to 50°. The resulting melt is heated at 70° with 2 g. of a copper catalyst (prepared from copper sulfate solution and zinc dust according to Brewster and Groening2). 

Wang Z., Liu Q., Yu J., Wu T., Wang G. Surface structure and catalytic behavior of silica-supported copper catalysts prepared by impregnation and sol-gel methods. Appl. Catal. A Gen. 2003 239 87-94... 

Although methanol synthesis catalysts have been studied intensively for several years there is still much controversy about the nature of the active components and the reaction steps that take place on them. Many aspects of the reaction mechanism are still not fully understood and are the subject of an active debate. Several investigations (refs. 10,11) have shown that over typical commercial catalysts practically all of the methanol is formed from COj under industrial conditions and that support effects are minimal for these catalysts (ref. 12). Other workers reported a marked support effect for the synthesis of methanol over copper catalysts prepared by different methods (refs. 3,7,8,13) showing that the activity of supported copper catalysts depends strongly on both the choice of the support and the nature of the feedstock. The results suggest that more than one mechanism may lead to methanol. 

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