Palladium industrial applications

In view of its susceptibility to sulphide tarnishing, silver may itself require some measure of protection in many decorative and industrial applications. Chromate passivation processes are commonly employed, but as an alternative, thin coatings of gold, rhodium or palladium may be used. 

Amidocarbonylation converts aldehydes into amido-substituted amino acids, which have many important industrial applications ranging from pharmaceuticals to detergents and metal-chelating agents.588 Two catalyst systems have been developed, a cobalt-based system and, more recently a palladium-based system. In the cobalt system, alkenes can be used as the starting material, thus conducting alkene-hydroformylation, formation of hemi-amidal and carbonylation in one pot as... 

The almost quantitative oxidation/complexation of palladium(O) in powder or foils by Me2dazdt 2I2 in THF, acetone, acetonitrile, and methylethylketone (MEK) to afford [Pd(Me2dazdt)2](I3)2 makes this synthetic route appealing for practical industrial applications. A selective process for Pd-recovery from model three-way car converters was simulated obtaining a Pd-extraction yield > 90%, and was proposed as an alternative to hydrometallurgical processes.62... 

The cost of the catalysts represents a major hurdle on the road to the industrial application of homogeneous catalysis, and in particular for the production of fine chemicals [1, 2], This is particularly true for chiral catalysts that are based on expensive metals, such as rhodium, iridium, ruthenium and palladium, and on chiral ligands that are prepared by lengthy total syntheses, which often makes them more expensive than the metals. In spite of this, the number of large-scale applications for these catalysts is growing. Clearly, these can only be economic if the substrate catalyst ratio (SCR) can be very high, often between 103 and 105. 

Several important industrial applications of the Heck reactions are known. The world s largest producer of Naproxen is Albemarle and they make Naproxen using two homogeneously catalysed steps, a Heck reaction and a palladium catalysed hydroxycarbonylation. The last step is carried out using palladium without chiral ligand and the enantiomers obtained are separated, see Figure 13.18. 

The transformation of alcohols to the corresponding carbonyl compounds or carboxylic acids is one of the few examples in which a heterogeneous (solid) catalyst is used in a selective, liquid phase oxidation (7,2). The process, which is usually carried out in an aqueous slurry, with supported platinum or palladium catalysts and with dioxygen as oxidant, has limited industrial application due to deactivation problems. 

Tables 9—16 show PGM consumption by the Western world and Japan. The figures are broken down by industrial application and, for platinum and palladium, by the region in which they are used. In each case, net demand is shown, ie, total purchases of the metals by customers, minus any sales back to the market.

The most common oxidation state of palladium is H-2 which corresponds toa electronic configuration. Compounds have square planar geometry. Other important oxidation states and electronic configurations include 0 ( °), which can have coordination numbers ranging from two to four and is important in catalytic chemistry, and +4 (eft), which is octahedral and much more strongly oxidizing than platinum (IV). The chemistry of palladium is similar to that of platinum, but palladium is between 103 to 5 x 10s more labile (192). A primary industrial application is palladium-catalyzed oxidation of ethylene (see Olefin polymers) to acetaldehyde (qv). Palladium-catalyzed carbon—carbon bond formation is an important organic reaction. 

Palladium has been extensively used in organic syntheses and in homogeneous catalysis (ref. 1-3), but industrial applications have remained relatively rare so far (ref. 4). The main reason lies in the de-activation of the catalyst by precipitation of metallic palladium under catalytic conditions. Such a process is actually observed in the carbonylation reactions under CO pressure. 

The cycle approach for oxidation has been adopted at an industrial level for the Wacker-Chemie process for acetaldehyde production, in which ethylene is first put in contact with the oxidized catalyst solution, containing palladium chloride, and in the second step the solution containing the reduced catalyst is sent to a regeneration reactor containing cupric chloride and inside which also air is fed. The regenerated catalyst solution is returned to the first oxidation stage. Another industrial application is the Lummus process for the anaerobic ammoxidation of o-xylene to o-phthaloni-trile [68]. Du Pont has developed the oxidation of n-butane to maleic anhydride catalyzed by V/P/O, in a CFBR reactor, and built a demonstration unit in Spain [69] however, a few years ago the plant was shut down, due to the bad economics. 

Clement ND, Routaboul L, Grotevendt A, Jackstell R, Beller M (2008) Development of palladium-carbene catalysts for telomerization and dimerization of 1,3-dienes from basic research to industrial applications. Chem Eur J 14 7408-7420... 

Palladium is employed in a number of industrial applications and fundamental studies because of its high catalytic activity for many chemical reactions, e.g. its ability to absorb hydrogen [41], On the other hand, due to hydrogen absorption, only brittle Pd deposits can be obtained in aqueous solutions. The advantage of performing electrodeposition of Pd in ionic liquids is that hydrogen evolution does not occur. Sun et al. demonstrated that Pd and some of its alloys, namely Pd-Ag [42], Pd-Au [43] and Pd-In [44], can be obtained from the basic l-ethyl-3-methylimidazolium chloride/tetrafluoroborate ionic liquid. Compact alloy deposits were obtained and the Pd content in the deposits increased with the increase in Pd mole fraction in the plating bath. 

These sources were prepared by a modified chemical plating technique similar to that used to prepare palladium-californium oxide cermet for industrial applications (6). Design of the... 

Palladium chemistry dominates this area and the main problems are related to the way of reoxidizing Pd° efficiently. In general the reaction could be made catalytic in palladium by the use of an additional oxidant capable of reoxidizing the Pd to Pd . Typically, stoichiometric copper chloride, or catalytic amounts of copper chloride in the presence of air, have been used [28]. Other catalyst systems which have been described for bisalkoxycarbonylation of olefins to succinate derivatives are PdCl2 and butyl nitrite [29], Pd(OAc>2, O2 and benzoqui-none [30], and Pd(acac)2 and di-t-butyl peroxide [31]. So far, low TONs have delayed industrial applications. Because the reoxidation process is generating water, which causes side reactions, it is also necessary to add a water scavenger such as triethyl orthoformate in order to obtain good conversions and selectivities. 

In recent years, attention has been focused on alkyne carbonylation catalysts based on the metals nickel, palladium, and platinum, modified with a variety of tertiary (bi)phosphines [5]. TTie main goal has been to develop chemo- and regio-selective carbonylation catalysts for application to higher alkyne substrates for the synthesis of certain fine chemicals. Many of these catalysts do allow the carbonylation to proceed under milder conditions than those applied in the catalytic Reppe process, and some of these catalysts do provide the branched regioisomer product from higher alkynes with good selectivity. However, in all cases reaction rates are very low, i.e., below 100 (and in most cases even below 10) mol/mol metal per h, as are the product yields in mol/mol metal (< 100). These catalyst productivities are far too low for large-scale industrial application in the production of commodity-type products, such as (meth)acrylates. 

Increased presentation of industrial applications, including hydroform-ylation Grubbs and Schrock metal carbene catalysts SHOP palladium-catalyzed cross-couplings and more. 

In several cases, the in situ formation of hydrogen peroxide is the first step of the process. Thus, phenol can be obtained from benzene, carbon monoxide (5 atm) and oxygen (65 atm) at 70 °C in a benzene-water-methyl isobutyl ketone mixture, with TS-1 and a palladium complex as catalysts [26]. Despite a 91% selectivity to phenol, benzene conversion (3.2%) and productivity are still too low for industrial application. The palladium complex is required to promote hydrogen peroxide formation upon reaction of oxygen, carbon monoxide and water [27[. 

Palladium hydrogenates arenes at elevated T (>90 C) and P (>20 X 10 kPa), but still finds industrial applications such as the preparation of cyclohexanecarboxylic acid, a caprolactam intermediate, by hydrogenation of benzoic acid in quantitative yield . Water increases the reduction rate over Pd catalysts, and strained rings can be hydrogenated over palladium-on-carbon in alcohol at Rt and P [equation (a)] . Compound 1 is readily hydrogenated the less strained compound 2 is inert. 

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