Palladium-copper 2 effects

We plan to make studies on palladium-copper, iridium-copper, and platinum-copper catalysts to extend our investigation of the effect of varying miscibility of the components on the structural features of the bimetallic clusters present. With these additional systems, the whole range from complete immiscibility to total miscibility of copper with the Group VIII metal will be encompassed. 

Morreale, B.D., M.V. Ciocco, B.H. Howard, R. Killmeyer, A.V. Cugini, and R.M. Enick, Effect of hydrogen sulfide on the hydrogen permeance of palladium-copper alloys at elevated temperatures, J. Membr. Sci., 241, 219-224, 2004. 

Another route involves a palladium-copper-catalyzed tandem carbon-carbon formation/cycloaddition sequence (Equation 12) <2005TL8531>. Notably, cycloadditions of azide to the internal alkynes failed under click chemistry reaction conditions <2003DDT1128>. Cyclization under oxidative conditions has been reported from dithioacetal 163 (Equation 13) <1996TL3925>. The formation of 164 as a single diastereoisomer has been explained by stereoelectronic effects. 

Palladium(II) effects orthometalation of acetanilides to form the corresponding palladacycles [185]. De Vries, van Leeuwen, and coworkers exploited this reactivity to achieve regioselective oxidative coupling of acetaniUdes and n-butyl acrylate that proceeds efficiently with BQ as the stoichiometric oxidant (Eq. 46) [ 186], The use of TsOH as an additive and acetic acid as a cosolvent significantly improves the results. Inferior results are observed with hydrogen peroxide or copper(II) acetate as the stoichiometric oxidant, but efforts to use molecular oxygen were not described. 

The platinum catalyst is effective in very small amounts, and can be introduced as H2PtCl6 or as elemental platinum on an inert support. A particularly active catalyst is the soluble platinum complex of divinyltetramethyldisilox-ane, CH2=CHSiMe2-0-SiMe2CH=CH2. The hydrosilyla-tion reaction operates through the Chalk-Harrod mechanism or one of its variants. bz jn these mechanisms, the first step involves the conversion of a metal alkene complex to a metal alkene silyl hydride complex. In addition to platinum, recently ruthenium, rhodium, palladium, copper, and zinc complexes are being studied as hydrosilation catalysts. " ... 

Nickel, palladium and copper catalysts can effect a variety of C — C bond-forming reactions P to the ester carbonyl via j8-zinc esters. These include 1,4-addition to a,jS-unsaturated carbonyl compounds (copper), arylation with aryl halides (palladium, nickel), allylation with allyl chloride (copper), and acylation with acyl chlorides (palladium, copper). " ... 

The Effect of Continuous H2S Exposure on the Performance of Thick Palladium-Copper Alloy Membranes... 

Keywords Ene reaction, Hetero-Diels-Alder reaction, Ene cyclization, Desymmetrization, Kinetic resolution. Non-linear effect. Asymmetric activation, Metallo-ene, Carbonyl addition reaction, Aldol-type reaction. Titanium, Aluminum, Magnesium, Palladium, Copper, Lanthanides, Binaphthol, Bisoxazoline, Diphosphine, TADDOL, Schiff base. 

Nonactivated olefins fail to react even under strenuous conditions with cyanide anion catalysis. Due to this lack of reactivity coupled with the inherent desirability of the products, much research has focused on developing catalysts for the hydrocyanation of these nonactivated olefins. This has led to nickel, palladium, copper, and cobalt-based catalysts effective at 25-125°C with or without a solvent. Most were developed for the hydrocyanation of unactivated olefins, but many are equally applicable for oAer olefins. For example, much work has been reported on butadiene hydrocyanation employing all of the catalysts mentioned above except palladium. 

Roa F, Way JD. The effect of air exposure on palladium-copper composite membranes. Appl Surf Sci. 2005 240 85-104. 

Figure 5.4 Comparison of effects on a palladium-copper alloy membrane by thermal cycling (A) a Monel membrane support, (B) a 304 stainless steel membrane support.

Impurities in cmde metal can occur as other metals or nonmetals, either dissolved or in some occluded form. Normally, impurities are detrimental, making the metal less useful and less valuable. Sometimes, as in the case of copper, extremely small impurity concentrations, eg, arsenic, can impart a harmful effect on a given physical property, eg, electrical conductivity. On the other hand, impurities may have commercial value. For example, gold, silver, platinum, and palladium, associated with copper, each has value. In the latter situation, the purity of the metal is usually improved by some refining technique, thereby achieving some value-added and by-product credit. 

Oxidation. Carbon monoxide can be oxidized without a catalyst or at a controlled rate with a catalyst (eq. 4) (26). Carbon monoxide oxidation proceeds explosively if the gases are mixed stoichiometticaHy and then ignited. Surface burning will continue at temperatures above 1173 K, but the reaction is slow below 923 K without a catalyst. HopcaUte, a mixture of manganese and copper oxides, catalyzes carbon monoxide oxidation at room temperature it was used in gas masks during World War I to destroy low levels of carbon monoxide. Catalysts prepared from platinum and palladium are particularly effective for carbon monoxide oxidation at 323 K and at space velocities of 50 to 10, 000 h . Such catalysts are used in catalytic converters on automobiles (27) (see Exhaust CONTHOL, automotive). 

Gold Casting and Wrought Alloys. Gold alloys useful ki dentistry may contaki gold, silver, platinum, palladium, iridium, kidium, copper, nickel, tin, kon, and zkic. Other metals occasionally are found ki minor amounts. The effect of each of the constituents is empirical, but some observations have been made. 

The coupling reaction proceeds better when a rigorously degassed Raney nickel catalyst is used, but a nickel catalyst prepared by a much simplifled procedure (Note 9) is also effective. The coupling may also be promoted by other elements, including copper and palladium. 

Multiphase gold or palladium-based alloys never show dissolution of Au or Pd but often exhibit progressive surface ennoblement due to selective dissolution of copper or silver from the outer 2-3 atomic layers Heat treatment often decomposes multicomponent alloys into a Pd-Cu rich compound and an Ag-rich matrix with corrosion of the latter phase in deaerated artificial saliva and S -containing media . Au-Cu-rich lamellae have similarly been observed, again with preferential attack on Ag-rich phases or matrix. These effects presumably arise from the ability of the noble alloy phases to catalyse the cathodic reduction of oxygen . 

The corrosion behaviour of amorphous alloys has received particular attention since the extraordinarily high corrosion resistance of amorphous iron-chromium-metalloid alloys was reported. The majority of amorphous ferrous alloys contain large amounts of metalloids. The corrosion rate of amorphous iron-metalloid alloys decreases with the addition of most second metallic elements such as titanium, zirconium, vanadium, niobium, tantalum, chromium, molybdenum, tungsten, cobalt, nickel, copper, ruthenium, rhodium, palladium, iridium and platinum . The addition of chromium is particularly effective. For instance amorphous Fe-8Cr-13P-7C alloy passivates spontaneously even in 2 N HCl at ambient temperature ". (The number denoting the concentration of an alloy element in the amorphous alloy formulae is the atomic percent unless otherwise stated.)... 

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