Palladium catalytic properties

Metals and alloys, the principal industrial metalhc catalysts, are found in periodic group TII, which are transition elements with almost-completed 3d, 4d, and 5d electronic orbits. According to theory, electrons from adsorbed molecules can fill the vacancies in the incomplete shells and thus make a chemical bond. What happens subsequently depends on the operating conditions. Platinum, palladium, and nickel form both hydrides and oxides they are effective in hydrogenation (vegetable oils) and oxidation (ammonia or sulfur dioxide). Alloys do not always have catalytic properties intermediate between those of the component metals, since the surface condition may be different from the bulk and catalysis is a function of the surface condition. Addition of some rhenium to Pt/AlgO permits the use of lower temperatures and slows the deactivation rate. The mechanism of catalysis by alloys is still controversial in many instances. 

This review aims to present an account of the catalytic properties of palladium and nickel hydrides as compared with the metals themselves (or their a-phase solid solutions with hydrogen). The palladium or nickel alloys with the group lb metals, known to form /8-phase hydrides, will be included. Any attempts at commenting on the conclusions derived from experimental work by invoking the electronic structure of the systems studied will of necessity be limited by our as yet inadequate knowledge concerning the electronic structure of the singular alloys, which the hydrides undoubtedly are. 

The effect that the presence of hydrogen in the lattice of nickel or nickel-copper alloys has on catalytic properties is much more difficult to trace in the literature than is the case with palladium and its alloys. Several factors contribute to this ... 

A novel chiral dissymmetric chelating Hgand, the non-stabiUzed phosphonium ylide of (R)-BINAP 44, allowed in presence of [Rh(cod)Cl]2 the synthesis of a new type of eight-membered metallacycle, the stable rhodium(I) complex 45, interesting for its potential catalytic properties (Scheme 19) [81]. In contrast to the reactions of stabihzed ylides with cyclooctadienyl palladium or platinum complexes (see Scheme 20), the cyclooctadiene is not attacked by the carbanionic center. Notice that the reactions of ester-stabilized phosphonium ylides of BINAP with rhodium(I) (and also with palladium(II)) complexes lead to the formation of the corresponding chelated compounds but this time with an equilibrium be-... 

Nickel(II) complexes of ligands 38 (R=H,Me R =H,Me,Et,Tr,CH30 R =H, CH3O R =H, F, CH3O) are highly active catalysts for ethylene polymerization [86,159], whereas palladium(II) complexes possess catalytic properties in the copolymerization of CO and alkenes [160] (Scheme 36). 

Preparation conditions of Pd/CNFs by wet impregnation method, such as palladium precursor, impregnation time, calcinations and reduction, are proved to have profound effect on the catalytic property. The catalyst prqjared by impregnating HzPdCLi precursor in an hour, then calcinated in air and reduced in 20%H2/Ar is believed to perform better in CTA hydropurification than the industrial Pd/C under laboratory conditions. 

Zhou WP, Lewera A, Larsen R, Masel RI, Bagus PS, Wieckowski A. 2006. Size effects in electronic and catalytic properties of unsupported palladium nanoparticles in electrooxidation of formic acid. J Phys Chem B 110 13393-13398. 

The synthesis, structure, and catalytic properties of a Pd11 complex with a partially hydrogenated ligand, shown in Figure 31, are described.393 This study provides the first asymmetric epoxidation of alkenes catalyzed by a palladium complex.393... 

Kostic et al. recently reported the use of various palladium(II) aqua complexes as catalysts for the hydration of nitriles.456 crossrefil. 34 Reactivity of coordination These complexes, some of which are shown in Figure 36, also catalyze hydrolytic cleavage of peptides, decomposition of urea to carbon dioxide and ammonia, and alcoholysis of urea to ammonia and various carbamate esters.420-424, 427,429,456,457 Qggj-jy palladium(II) aqua complexes are versatile catalysts for hydrolytic reactions. Their catalytic properties arise from the presence of labile water or other solvent ligands which can be displaced by a substrate. In many cases the coordinated substrate becomes activated toward nucleophilic additions of water/hydroxide or alcohols. New palladium(II) complexes cis-[Pd(dtod)Cl2] and c - Pd(dtod)(sol)2]2+ contain the bidentate ligand 3,6-dithiaoctane-l,8-diol (dtod) and unidentate ligands, chloride anions, or the solvent (sol) molecules. The latter complex is an efficient catalyst for the hydration and methanolysis of nitriles, reactions shown in Equation (3) 435... 

Rare, shiny, and lightest metal of the platinum group. Hardens platinum and palladium. The presence of 0.1 % of ruthenium in titanium improves its resistance to corrosion 100-fold. The spectacular catalytic properties of ruthenium are used on industrial scales (hydrogenations, sometimes enan-tioselective, and metathesis). Titanium electrodes coated with ruthenium oxide are applied in chlorine-alkaline electrolysis. Suitable for corrosion-resistant contacts and surgical instruments. 

The supported aqueous phase methodology was applied to the system Pd(OAc)2/5 TPPTS, a catalytic precursor for the Trost-Tsuji reaction. The characterization of the solid by 31P MAS NMR confirms the presence of Pd°(TPPTS)3 as the main surface species. The catalytic properties of the solid were tested for the allylic substitution of E-cinnamylethylcarbonate by different nucleophiles such as ethyl acetoacetate, dimethyl malonate, morpholine, phenol, and 2-mercapto-pyridine. The absence of palladium leaching was demonstrated, and having solved the problem of water leaching from the solid to the organic phase, the SAP-Pd catalyst was successfully recycled several times without loss in its activity. It was used in a continuous flow experiment which... 

Gold forms a continuous series of solid solutions with palladium, and there is no evidence for the existence of a miscibility gap. Also, the catalytic properties of the component metals are very different, and for these reasons the Pd-Au alloys have been popular in studies of the electronic factor in catalysis. The well-known paper by Couper and Eley (127) remains the most clearly defined example of a correlation between catalytic activity and the filling of d-band vacancies. The apparent activation energy for the ortho-parahydrogen conversion over Pd-Au wires wras constant on Pd and the Pd-rich alloys, but increased abruptly at 60% Au, at which composition d-band vacancies were considered to be just filled. Subsequently, Eley, with various collaborators, has studied a number of other reactions over the same alloy wires, e.g., formic acid decomposition 128), CO oxidation 129), and N20 decomposition ISO). These results, and the extent to which they support the d-band theory, have been reviewed by Eley (1). We shall confine our attention here to the chemisorption of oxygen and the decomposition of formic acid, winch have been studied on Pd-Au alloy films. 

Ab initio methods, 147-49 Acetate ion, decomposition, 135 Acetylene, interaction with palladium, tunneling spectroscopy, 435,437f Acid-dealuminated Y zeolites catalytical properties, 183 sorption, 175-78 Acid sites, on zeolites, 254 acidification effects, 266 Acoustic ringing, in NMR, elimination, 386 Active sites, nature, 104 Activity measurements, Co-Mo catalysts, 74 Adsorbed molecules,... 

Turkevich, J. and Kim, G., Palladium- preparation and catalytic properties of particles of uniform size, Science, 169, 873, 1970. 

Schmid, G. et al., Catalytic properties of layered gold-palladium colloids, Chem. Eur. J., 2,1099,1996. 

Bonnemann, H. Brinkmann, R., and Neiteler, P., Preparation and catalytic properties of NR4+-stabi-lized palladium colloids, Appl. Organomet. Chem., 8, 361,1994. 

A colloidal suspension prepared according to the method described in Section 13.2.3 was contacted with a porous alumina carrier to obtain a bimetallic palladium-tin catalyst. Evaluation of the catalytic properties of this system is detailed... 

Gryaznov, V. M. 1986. Surface catalytic properties and hydrogen diffusion in palladium alloy membranes. Z. Phys. Chem. Neue Folge 147 761-70. 

Two types of catalysts have been proposed for the CPOM reaction copper and palladium. The catalytic properties of these materials show significant discrepancies with respect to by-product formation and the effect of oxygen partial pressure. The Cu-based catalysts display high selectivity for the CPOM reaction whereas for the Pd-based catalysts CO formation is significant. 

The group 10 metals, such as palladium and platinum, are active for the conversion of methanol. However, they are much less selective than the copper-based catalysts, yielding primarily the decomposition products [123,124,133]. This catalytic property makes them less feasible for fuel cell applications. The only exception found is for Pd/ZnO, which showed selectivity close to that of a copper catalyst [105, 121]. 

Heterogenization of homogeneous metal complex catalysts represents one way to improve the total turnover number for expensive or toxic catalysts. Two case studies in catalyst immobilization are presented here. Immobilization of Pd(II) SCS and PCP pincer complexes for use in Heck coupling reactions does not lead to stable, recyclable catalysts, as all catalysis is shown to be associated with leached palladium species. In contrast, when immobilizing Co(II) salen complexes for kinetic resolutions of epoxides, immobilization can lead to enhanced catalytic properties, including improved reaction rates while still obtaining excellent enantioselectivity and catalyst recyclability. 

Adsorption and Catalytic Properties of Palladium Supported by Silica, Alumina, Magnesia, and Amorphous and Crystalline Silica-Aluminas... 

Since parallel variations were observed in turnover number for benzene hydrogenation and in CO vibration frequency, interaction between metal and oxidizing supports does exist. This interaction modifies the electronic state and catalytic properties of palladium. 

The most significant conclusion that may be drawn from these results is that palladium-charcoal exhibits similar catalytic properties as does Raney nickel if used under similar conditions. The same types of lignin hydrogenolysis products are obtained, and as before the major fraction under neutral conditions is the phenylpropanol derivative, dihydro-coniferyl alcohol. With a minimum temperature ca. 150°C. required for any reaction to occur and an optimum temperature ca. 195°C. for maxi-... 

Catalytic isomerization of 3,4-dichlorobutene catalyzed by Pd nanoparticles of Pd-PPX film was studied at 100°C [91], The ratio of trans- to cis-1, 4-dichlorobutene for the reaction in this system with low concentration of Pd nanoparticles is 10, and coincides with the ratio obtained for the reaction with the usual palladium catalyst. But the selectivity of the reaction decreases with increasing of Pd concentration the yield of trans-l, 4-dichlorobutene decreases while the yield of cA-1,4-dichlorobutene remains constant. This result shows that the change in the catalytic properties of the composite is determined by interactions between nanoparticles rather than by the size effects. At catalytic reaction catalyzed by Pd-PPX films, where the volume content of Pd nanoparticles is close to percolation threshold, the trans-to-cis ratio for produced isomers of 1,4-dichlorobutene is 2.9 that is close to equilibrium value of this ratio. 

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