Iron modifiers selective hydrogenation

Although cyclohexane oxidation dominates the market, because of cheaper raw materials, the hydrogenation of phenol remains competitive, offering better selectivity with fewer environmental and safety problems. In addition, this process allows efficient valorization of phenol-rich wastes from coal industries. Recently built plants make use of this technology, as reported by the engineering group Aker-Kvaerner (www.kvaerner.com, 2004). The availability of low-price phenol is the most important element for profitability. Besides the well-known cumene process, a promising route is the selective oxidation of benzene with N20 on iron-modified ZSM-5 catalyst [12]. In this way, the price of phenol may become independent of the market of acetone. 

Iron-modified zeolite L nanocrystals were applied for the oxidation of phenol in the presence of acetic acid with the 93.4% conversion in 30min with selective formation of 77.5% of catechol and 22.5% of hydroquinone [144]. Acetic acid was oxidized by hydrogen peroxide to form peracetic acid, which served as a better oxidizing agent (Fig. 16). 

Tests have been done further on the separation of a Cu-Pb mixed concentration of ethyl xanthate flotation of copper-lead-iron sulphide ore by E- control modifying with H2O2. Test results are presented in Table 10.3. It indicates the possibility of selective flotation separations of copper-lead flotation concentration by control. The feed of copper-lead mixed concentrated assayed Cu 6.53% and Pb 62.38%. Using hydrogen peroxide as a potential modifier, a copper concentration with 24.19% Cu and recovery with 89% can be obtained after separation. 

The emerging picture from the activity of covalently modified MPs is that to have an efficient catalyst the distal site must contain positively charged residues, which can approach the iron center their presence increases the reactivity toward both hydrogen peroxide and the substrate. The selectivity for different substrates can take advantage of the addition of other charged or polar residues that do not necessarily have to approach the iron closely, since the ET occurs through the... 

This potential, adjusted as a function of the pH of the solution and of the hydrogen pressure, is easily fixed between +0 1 V and — 0.9V/NHE (Normal Hydrogen Electrode). The H2/H+ couple was used to prepare supported catalysts with platinum, palladium, ruthenium, and rhodium modified with deposits of tin, lead, iron, germanium, and bismuth [50-54]. These catalysts were proposed for their good selectivities for different reactions in specialize organic chemistry. 

In 1975 Johnson and Nowack reported that benzene was hydrogenated to cyclohexene in 20.3% yield at 58% conversion over a cobalt ion (0.05%) modified 0.5% Ru-Ca(OH)2 in the presence of water at 180°C and 6.8 MPa H2.33 The yield of cyclohexene was definitely higher than those ever reported for the cyclohexene intermediate in the hydrogenation of benzene.34-36 Similar nickel- and iron-ion-modified 0.5% Ru-Ca(OH)2 or nickel-modified 0.5% Ru-A1203 also gave good selectivities to cyclohexene although in somewhat lower yields than over the cobalt-modified catalyst. It appears that the presence of water and small amounts of transition metal... 

In further studies it has been demonstrated that a supported platinum catalyst can also be modified either by addition of cobalt, germanium, iron or tin halides. In the hydrogenation of cinnamaldehyde the modification resulted in much higher activities and selectivities for the hydrogenation of the aldehyde group than on the parent platinum catalysts as shown in Table... 

The additive elements used to enhance the performance of the Fe-Sb-0 catalyst either enter the iron antimonate rutile phase to form a solid solution (49,50) or they form separate rutile phases (44). The promoter elements that produce the best performing iron antimonate-based ammoxidation catalysts are copper, molybdenum, tungsten, vanadium, and tellurium. Copper serves as a structural stabilizer for the antimonate phase by forming a rutile-related solid solution (23). Molybdenum, tungsten, and vanadium promote the redox properties of iron antimonate catalysts (51). They provide redox stability and prevent reductive deactivation of the catalyst, especially under conditions of low oxygen partial pressure (see above). The tellurium additive produces a marked enhancement of the selectivity of iron antimonate catalyst. How the tellurium additive functions to increase selectivity is not clear, but the presumption is that it must directly modify the active site. In fact, it is likely that it can actually serve as the site of selective oxidation because in its two prevalent oxidation states Te + and Te +, tellurium possesses the requirements for the selective (amm)oxidation site, a-hydrogen abstraction, and 0/N insertion (see below). 

The particular features of phosphonium salts were exploited for a number of synthetic applications in 2014. Phosphonium chloride salts found applications as chlorine source and as modifiers for homogeneous catalyst systems. As an example, Muller, Rosenthal and co-workers reported the study of a chromium-based catalyst for the selective tri-merization of ethylene. A phosphonium precursor of the type i cyclo-(PR2CH2CH(OH) )2][Br]2) was used for the preparation of iron(n) complexes containing unsymmetrical P-N-P pincer ligands (Scheme 5). The group of Prof. Morris tested these compounds as catalysts for the asymmetric hydrogenation of ketones and imines. ... 

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