Reduced palladium

It was found that sorbed palladium might catalyse reaction of Mn(III) reduction by Cf not only after it s removing from coal, but AC with palladium, Pd/AC, has also his own catalytic effect. On the base of dependence between characteristics of AC, chemical state of palladium on AC surface and catalytic action of Pd/AC in indicator reaction it might establish, that catalytic action concerns only to non-reduced or partly reduced palladium ions connected with chloride ions on coal surface. The presence or absence of catalytic action of Pd/AC in above-mentioned reaction may be proposed for determination of chemical state of palladium on AC surface. Catalytic effect was also used for palladium micro-amounts determination by soi ption-catalytic method. 

The hydrogenation of 5a-cholestanone (58) in methanolic hydrobromic acid over platinum gives 3j5-methoxycholestane ° (61). This compound is also obtained from the palladium oxide reduction of (58) in methanol in the absence of acid. Hydrogenation of 5 -cholestanone also gives the 3j5-methoxy product under these conditions. Reduced palladium oxides are quite effective for the conversion of ketones to ethers. The use of aqueous ethanol as the solvent reduces the yield of ether. Ketals are formed on attempted homogeneous hydrogenation of a 3-keto group in methanol. ... 

A method for the conversion of unsaturated aliphatic aldehydes to saturated aldehydes is a gentle catalytic hydrogenation. Palladium is more selective than nickel. Hydrogenation over sodium borohydride-reduced palladium in methanol at room temperature and 2 atm reduced crotonaldehyde to butyralde-hyde but did not hydrogenate butyraldehyde [57]. Nickel prepared by reduction with sodium borohydride was less selective it effected reduction of crotonaldehyde to butyraldehyde but also reduction of butyraldehyde to butyl alcohol, though at a slower rate [57]. Hydrogenation of 2,2,dimethyl-... 

Most vinyl acetate is presently produced by the palladium-catalyzed reaction of acetic acid and ethylene that involves subsequent reoxidation of reduced palladium. This report describes an alternative process for vinyl acetate utilizing syn gas as feedstock, thus avoiding the necessity for ethylene (see figure 1). Of course, at this time of plummetting oil prices, a route utilizing syn gas cannot... 

In a second part of this study, the effect of heat treatment under nitrogen of the reduced palladium catalysts A, B and C with an egg-shell type metal distribution on the metal leaching was investigated. The reduced catalysts were tested for metal leaching after they underwent a heat treatment at temperatures of 100 to 400 °C. The metal leaching of the investigated catalysts decreased after the heat treatment of... 

The crystal structure of Pd. h Y zeolite was determined before and after hydrogen reduction at different temperatures. When the zeolite is evacuated at 600°C, Pd2+ ions are mainly found to occupy SI sites within the sodalite cages. Hydrogen adsorption at 25° C results in a complete withdrawal of Pd2+from SI sites. This displacement out of cation sites is attributed to the reduction Pd2+ — Pd(0) consistent with hydrogen volumetric measurements. Reduced palladium remains atomically dispersed inside the sodalite cages up to about 200° C. Between 200 and 800° C, Pd 0) atoms migrate toward the outer surface of the zeolite where they agglomerate into 20-A diameter crystallites. 

The distribution of cations in AH 200 is very similar to that found with AH 25, and thus the amount of reduced palladium remains unchanged. This result is not surprising because water molecules subsequent to the reduction of the first five atoms are still bonded to the cation at this temperature, and prevent subsequent reduction as suggested above. Besides, very weak and broad diffraction lines observed on Guinier photographs indicate a beginning of Pd(0) migration toward the zeolite external surface. 

Nature of Palladium in Hydrogen-Reduced Samples. In the above discussion, palladium ions were assumed to be reduced from Pd2+ to Pd(0). This assumption needs further discussion. First, the pattern of our results is well explained by assuming that isolated palladium atoms may exist in the sodalite cages after reduction by H2 up to about 200° C under our experimental conditions. Moreover, this assumption is in good agreement with infrared results obtained for similar samples. Some Pd+ ions may be also formed during the reduction, but quantitative measurements show that the amount of Pd+ does not exceed 10% of the reduced palladium (11). 

Hence, it appears that upon reduction at room temperature, the reduced palladium exists in the zeolite cavities, and perhaps the atomically dispersed palladium in the zeolite framework loses its metallic properties... 

The catalytic oxycarbonylation of benzene and naphthalene to benzoic or naphthoic acid in the presence of Wacker-type catalysts has been reported in several patents,376,448 but difficulties in reoxidizing the reduced palladium have inhibited industrial use of this chemistry. 

A likely mechanism for this reaction involves the nucleophilic attack of alcohol on two molecules of coordinated CO, followed by the coupling of the two palladium-bonded alkoxycarbonyl moieties (equation 179).438,451 jn support of this mechanism, the reaction of the bis(methoxycarbonyl) complex (143) with CO and PPh3 produces dimethyl oxalate and the reduced palladium(O) complex.451... 

The mechanism is typical of palladium olefin chemistry, and water serves as the oxygen source the reduced palladium is reoxidized by Cu(II) and ultimately by atmospheric oxygen. 

Voth-Beach, L.M. and D.E. Shrader. 1987. Investigation of a reduced palladium chemical modifier for graphite furnace atomic absorption. J. Anal. At. Spectrom. 2 45-50. 

Figure 21 provides an example of the use of ESCA to define an oxidation state of a freshly reduced palladium-on-carbon hydrogenation catalyst exposed to the air. The metallic palladium peaks (Fig. 21a) are quite evident, indicating no bulk oxidation occurred. There is a strong peak for carbon, probably due to adsorbed CO2 from the air. The presence of a small amount of PdO is suggested at 337 eV in Fig. 21B. This peak is a shoulder on the palladium 3 5/2 peak and most likely represents a surface layer of oxide on the palladium. This information could not be conveniently obtained by XRD because small palladium (or PdO) crystallites cannot diffract X rays. Furthermore, XRD measures bulk properties and would not see surface oxides even if the crystallite sizes were sufficiently large to be XRD sensitive. We can therefore expect to see more frequent use of ESCA or other surface sensitive techniques to monitor the surface of catalytic materials.

Boitiaux et al. (61) have examined the influence of palladium sulfuration on the hydrogenation and isomerization of 1-butene, 1,3-butadiene, and 1-butyne. The tested catalysts have been sulfided with thiophene to obtain an atomic ratio (sulfur per surface palladium) varying between 0 and 0.5. The thiophene in heptane solution is put in contact with the reduced palladium catalyst at 50°C, under 2 MPa hydrogen pressure. The butane evolution is followed during the sulfiding step (see above) and a control of total sulfur adsorption is performed by the analysis of the heptane after the sulfiding step and through X-ray fluorescence after the reaction step. 

Reaction efficiency was improved using ethoxy acrylate (42, R = Et Scheme 11) to avoid methoxide generation. Methoxide is capable of forming bridged dimeric palladium complexes that hinder palladium catalysis, analogous to the process observed with hydroxide. The use of ethoxy acrylate reduced palladium catalyst loading from 5-10 mol% to 0.5-2.0 mol%. 

The relative amounts of Pd(0) and Pd(II) were estimated by using a linear combination fit of the spectrum of the catalyst reduced in H2 (taken as Pd(0)) and the as-prepared catalyst (taken as Pd(II)). The changes in the XANES spectrum as a function of the various reaction conditions are subtle, but there is a measurably greater amount of reduced palladium present when the alcohol is present compared to when there is only 02 present in the supercritical C02 solvent. 

A colloidal palladium obtained by reducing palladium chloride with methanol in the presence of poly (N-vinyl-2-pyrrolidone) and sodium hydroxide. Cyclooctadienes (25 mmol-dm ) were hydrogenated over the colloidal palladium (0.01 mmol dm 3 for 1,3- 0.02 mmol-dm-3 for 1,4- 0.1 mmol-dm-3 for 1,5-cyclooctadiene) in 20 ml of methanol at 30°C and atmospheric pressure. The yields were those obtained when an equimolar amount of hydrogen had been consumed. 

Mercury(I) chloride (calomel) suspension reduces palladium(II) ions to the metal... 

The oxidation of a,p-unsatuiated caibraiyl compounds under the usual conditions in DMF using PdCl2/CuCl/02 is very slow. However, regioselective oxidation of oc, -unsaturated esters to p-keto esters (equation IS), and a,p-unsaturated ketones to 1,3-diketones (equation 16) proceeds with NazPdCU in solvents such as 50% acetic acid, isopropyl alcohol, and NMP. r-Butyl hydroperoxide and hydrogen peroxide are used as the reoxidants of the reduced palladium. The reaction proceeds slowly at room temperature but smoothly between 50 and 80 C. Some typical examples of this process are shown in Table 1. 

Pd-PVA catalyst reduced with a vanadous solution is quite interesting, as shown in Figure 6. The vanadium-reduced palladium (curve 2) not only converts benzaldehyde to benzyl alcohol at five times the rate of a hydrogen-reduced Pd-PVA catalyst but is also able to carry the reduction... 

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