Palladium magnetic susceptibility

The disappearance of the paramagnetism of palladium-silver alloys (rich in Pd) when the ratio (H + Ag)/Pd = 0.6 (24) illustrates that the effect of both these alloying" elements in palladium is additive and each one contributes essentially in the same way to the change of magnetic susceptibility of palladium. 

The formation and presence of both phases of the Pd-H system in the palladium catalyst samples investigated was confirmed by Brill and Watson by the values of the magnetic susceptibility of the samples investigated under the same conditions as in the kinetic studies. 

It is a matter of speculation as to whether or not the activity would pass through a significant maximum at a surface composition between 0 and 30% Rh. It is interesting to note in this connection that the magnetic susceptibility (156, 157) and the electronic specific heat coefficient (156) increase from low values at 60% Ag-Pd through pure palladium and reach a maximum at - 5% Rh-Pd, thereafter decreasing smoothly to pure rhodium. Activity maxima have also been reported for reduced mixed oxides and supported alloys of group VIII metal pairs. For example, in the... 

The nc value for palladium-hydrogen is 0.25 from magnetic susceptibility measurements (52) with Tc = 564°K (52), and from P-C-T data, de Ribaupierre and Manchester (26) estimate nc = 0.29 and Tc = 566°K. The Bragg-Williams approximation gives a reasonable WfiH value by using an average value of nc, the critical temperature, and an analytical expression for ie(n) determined... 

Another, more direct, indication is obtained from the work of Dilke, Eley, and Max ted (85), who found from the change in magnetic susceptibility of palladium on adsorption of dimethylsulfide that an electron of the sulfide had entered the d band of the metal. As we saw in Sec. V,8,b, a coordinate link is formed in this case. 

Palladium has the highest magnetic susceptibility of the platinum group, and because it is so high it has been termed an incipient ferro-magnet. The implication is that palladium could be induced to become... 

Effect of Hydrogen Adsorption on the Magnetic Susceptibility of Palladium Dispersed on Silica Gel... 

In all of this work there was little suggestion that the surface states of the palladium might behave differently from bulk states. Selwood (17) indicated that, from some sorption-magnetic susceptibility data for hydrogen sorbed on palladium which was finely dispersed on alumina gel, the ultimate sorption capacity was approximately at the ratio 2H/Pd. Trzebiatowsky and coworkers (25) deposited palladium on alumina gel in amounts ranging from 0.46 to 9.1% of gel weight. They found the palladium to be present in a normal crystal lattice structure, but its susceptibility was less than for the bulk metal. This suggested to the present authors that the first layer of palladium atoms laid down on the alumina gel underwent an interaction with the alumina, which has some of the properties of a semiconductor. Such behavior was definitely shown in this laboratory (22) in the studies on the sorption of NO by alumina gel. Much of this... 

The investigation here reported was carried out in an attempt to show that such surface states did exist and that sorption and magnetic susceptibility studies of hydrogen-palladium systems might answer some of the questions raised by previous investigators. 

Magnetic Susceptibility of Palladium Dispersed on Silica Gel. Figure 1 shows the susceptibility values obtained as increasing amounts of palladium were deposited on the gel surface. As ordinates the values of the relative susceptibility, Xs/x0, are plotted against amounts of palladium on the gel. xs is the measured susceptibility while x0 is that of the bulk metal as given in the literature (4, 5),... 

Figure 8. Magnetic susceptibility of palladium on silica gel as function of adsorbed hydrogen and NO at 0° C.

The magnetic susceptibility of palladium is also diminished by hydrogen absorption.3 and if the diminution continues uniformly— which has not as yet been experimentally demonstrated—then palladium saturated with hydrogen should actually be diamagnetic. 

Fig. 2. Temperature dependence of the magnetic susceptibility x (right scale) and of the field for Pd NMR at fixed Larmor frequency Bo (left scale) for palladium. Similar to Fig. la, the NMR field shift and the susceptibility are proportional. Both are (mainly) caused by the Pauli-type paramagnetism of the d-like conduction electrons. (The temperature dependence is not predicted by the simple free-electron description of the susceptibility in metals.) [Reproduced with permission from Seitchik et al. (16). Copyright 1964 American Physical Society.]...

For X < 0.4, the magnetic susceptibility is temperature dependent like that of pure palladium, but it has lower values. For x > 0.6, this temperature dependence disappears and the system is diamagnetic (60), like that of silver, a neighbor of Pd in the periodic table. This change is related to a change in position of the Fermi level with respect to the d-band. For low X the Fermi level crosses the d-band, as in pure Pd (cf. Fig. 9) at x 1, Ef is above the d-band (Fig. 21a) (61). When the H/Pd ratio increases, the total DOS at Ef (and therefore the susceptibility) decreases, but it is calculated that the LDOS at Ef on the hydrogen site should increase (62) (Fig. 21b). 

In his pioneering contributions Moiseev has shown that giant cationic palladium clusters , e.g. Pd56iL6o(OAc)i8o (L = phenanthroline, bipyridine), characterized by use of high-resolution TEM, SAXS, EXAFS, IR and magnetic susceptibility data, catalyze, under mild conditions (293 363 K, 1 bar), the oxidative acetoxylation of ethylene into vinyl acetate, propylene into allyl acetate, and toluene into benzyl acetate. The oxidation of primary aliphatic alcohols to esters, and the conversion of aldehydes into acetals were also studied. ... 

The toxicity of an element such as sulfur is dependent on the presence, in the valency shell of the toxic element, of free electron pairs which are evidently necessary for the formation of the link with the catalyst. The toxicity—i.e., the power of forming a relatively strong chemisorptive bond—disappears if the structure of the molecule is of a shielded type in which this element is already associated with a completely shared electron octet. Thus, it appears (Maxted, 8) that the chemical bond by means of which the poison is linked to the metallic surface resembles the ordinary dative bond in which the poison is the donor. In the case of methyl sulhde adsorbed on palladium, indications have been obtained (Dilke, Eley, and Maxted, 9) by means of magnetic susceptibility measurements that electrons from the methyl sulfide enter the d-band of the adsorbing metal to give a coordinate link, the process being probably accompanied (Maxted, 10) by a filling up of the fractional deficiencies or holes in the d-band of the metal due to d- -band overlap which seem to be responmble for the catalytic activity of the transition metals (11). 

All platinum metals are paramagnetic (x > 0). The magnetic susceptibilities of palladium and platinum decrease with increasing temperature, the magnetic susceptibilities of rhodium, iridium, ruthenium, and osmium increase with increasing temperature (Fig. 3.1-272 [1.218]). 

Rosenblum and cowoikers have described a number of routes to lace-to-lace polymetallocenes. Ruthenium- and iron-based materials were synthesized via palladium-catalyzed cross-coupling reaction of 1,8-diiodonaphthalene with metallo-cenylzinc chloride (M=Fe, Ru). The MW of the face-to-lace polyferrocenes with R=H,R = 2-octylwasintherangeof 18,000, while that of200 when R=R =2-octyl, was 139,000. The conductivity of polymer 200 (M=Fe, R=H, R =2-octyl) on doping with I2 was 6.7 X 10 S/cm. The incorporation of nickelocene and cobaltocene units into the fece-to-lace polyferrocenes resulted in materials with magnetic susceptibilities of 3.51 and 5.2 (1 for the Ni Fe and Co Fe ohgomers, respectively. ... 

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