Palladium nitrate

Fehlhammer, W. P. et al., Z. Naturforsck, 1983, 38B, 547 In the first stage of the preparation of bis(triphenylphosphine)palladium(II) isothiocyanate, a large deficiency of aqueous palladium nitrate must be added with rapid stirring to an excess of sodium azidodithioformate solution to avoid the precipitation of explosive palladium(II) azidodithioformate. 

The mechanism of stabilisation of the palladium and magnesium nitrates modifier was not investigated [749]. It is known, however, that palladium nitrate decomposes via the oxide to the metal at 870 °C, which melts at 1552 °C. The appearance temperature for palladium in a graphite furnace is around 1250 °C. As most of the investigated elements are stabilised to temperatures around 1200 °C, it can be assumed that the modifier acts by imbedding the analyte into the palladium matrix, or even by forming a kind of alloy with the analyte. 

The different molecular species present in a palladium nitrate solution can be easily identified by UV-visible spectroscopy (Fig. 13.2). Two absorption peaks are generally observed at A, = 285 nm and A = 378 nm, the latter being ascribed to free nitrate ions corresponding to the electronic transition from the a to the it state in the NOs ions, as observed in the case of an aqueous solution of NaNOs. The other absorption band at A = 285 nm is assigned to a d-d transition in the aquo complex Pd(H20)4 These UV-visible results show the noncomplexant behavior of nitrate ions toward palladium metallic centers. The palladium containing species in the starting solution is then the planar tetra-aquo complex Pd(H20)4 +. 

The formation of palladium oxide colloidal particles from an acidic palladium nitrate solution can be achieved by addition of an alkaline solution. The different steps, describing the chemistry involved in such a process are ... 

Figure 13.4 shows the titration curve of a palladium nitrate solution [Pd] = 5 g/L by soda [NaOH] = 0.1N. Three regions can be clearly distinguished, corresponding to a true solution (starting point until addition of about 14 mL of soda), to the formation of colloidal PdO particles (from 14 to 24 mL added), and to the flocculation of particles with segregation of liquid and solid phases (above 25 mL). 

FIGURE 13.4. Neutralization curve of a palladium nitrate solution [Pd] = 5 g/L by addition of soda [NaOH] = 0.1 N. 

The reverse operation, i.e. the addition of palladium nitrate solution to soda, can also be used to prepare colloidal suspensions. Figure 13.8 presents the corresponding titration curve of a soda ([NaOH] = 0.2 N) by a palladium nitrate solution ([Pd] = 5 g/L). 

FIGURE 13.7. PdO particle size distributions obtained by neutralization of palladium nitrate solution by soda at different pH determined by transmission electron microscopy. 

FIGURE 13.9. PdO particle size distributions for different pH by neutralization of palladium nitrate by soda (a) and soda by palladium nitrate (b) as determined by TEM. 

For direct neutralization (addition of soda into palladium nitrate) different hydrolyzed intermediate species can be formed from Pd(H20)4 + (Fig. 13.14) Pd(H20)2(0H)2, Pd(H20)3(0H)+. In the reverse method, i.e. the addition of Pd(H20)4 + in a NaOH solution at pH = 12, the only complex produced is the neutral complex Pd(H20)2(0H)2, in agreement with UV-visible measurements. In this case, the cloudy solution appears in the initial stage of the experiment with the first drops of palladium nitrate solution. 

Figures 13.23a and b show the PdO particle size distribution of PdO-supported catalysts prepared from an acidic hydrosol (neutralization of palladium nitrate solution by addition of soda) and a basic one (neutralization of soda by addition of palladium nitrate). Comparisons with the corresponding histograms of the initial suspensions (Figs. 7b and 9b), show that the distributions are not significantly modified. Only a very slight increase of the standard deviation of the dispersion values is observed...

Palladium nitrate is a catalyst in many organic synthesis. 

Palladium oxide is prepared by heating palladium sponge in oxygen at 350°C. The oxide is obtained as a black powder. The oxide also may be prepared specially for catalytic use by heating a mixture of palladium chloride and potassium nitrate at 600°C and then leaching out water-soluble residue. A hydrated form of the oxide, which is acid soluble can be prepared by precipitation from solution, for example, by hydrolysis of palladium nitrate. The brown hydrated oxide converts to black anhydrous oxide on heating. Its solu-bdity in acids decreases with lowering of water content. 

The catalyst was prepared by impregnation of the powdered activated carbon support, Norit SX Ultra, (surface area 1200 m g ) with sufficient palladium nitrate to produce a metal loading of 3 %. The resulting suspension was dried and calcined at 423 K for 3 hours. The dispersion of the catalyst was... 

In a 1985 patent by Hoffmann-La Roche, the Wittig condensation was also the crucial step in assembling isotretinoin (1, Scheme 2). Under the optimized conditions, 1.03 equivalents of phosphonium salt 8 was condensed with 1 equivalent of hydroxybutenolide 9 in the presence of 1.25 equivalents of 2 N KOH in isopropanol at -30°C for 1 to 1.5 h. The product (91.5% total yield) consisted of 75.9% of 2-cis-4-cis-vitamin A acid (10) and 16.7% of isotretinoin (1). Without separation, the mixture of 10 and 1 was subjected to palladium-catalyzed isomerization conditions the mixture was heated at 50°C for 1 h in acetonitrile in the presence of 0.10 mol% of palladium(n) nitrate, four equivalents (based on palladium nitrate) of triphenylphosphine and 2... 

A detrimental effect of excess nitric acid on the ZnO support was observed, resulting in a reduced ZnO particle size and losses of surface area. This excess was present in the palladium nitrate solution that was applied for catalyst impregnation. Additionally it was found that the PdZn alloy was not only formed during the initial reduction step but also in situ in the hydrogen-rich reaction mixture of methanol steam reforming. 

Modifier Working Solution Weigh an amount of palladium nitrate equivalent to 1 g of palladium, and dilute to 100 mL with 15% nitric acid to make a stock solution. Just before use, prepare a Modifier Working Solution by diluting the stock solution 1 10 with water. 

In alkaline solution oxidation of ferrous iron is fairly rapid,8 but certain acids retard the reaction. Ferrous sulphate, for example, in the presence of free sulphuric acid, is very stable in air. Concentrated hydrochloric acid assists the oxidation, as also do traces of certain substances, such as platinic and cupric chlorides, palladium nitrate, etc.9... 

Recently, novel nanomaterials have become a new frontier for SERS experiments, where different metals are collected together to form, for example, bimetallic particles. Thus, the same nanoparticle could be responsible for both SERS effect and catalytic activity. This is the case of the Ag/Pd colloids synthesized by chemical reduction with sodium borohydride (NaBH4) of silver nitrate (AgNOs) and palladium nitrate (Pd(N03)2), with a 96 4 Ag/Pd molar ratio [11]. The silver nanoparticles provide the SERS enhancement for the ligand molecules, while palladium may induce catalytic reactions. Also, in this case, TEM microscopy provides an important help to characterize these composite materials. In Fig. 20.6 TEM images at different magnifications are reported for bimetallic Ag/Pd particles, in comparison with those constituted by pure silver. While these latter present spheroidal shapes, bimetallic particles show more irregularities, due to palladium clusters in contact with the silver core surface. 

Supported mixed metal catalysts are also prepared by other means such as the deposition of bimetallic colloids onto a support O and the decomposition of supported bimetallic cluster compounds.208 The photocatalytic codeposition of metals onto titania was also attempted with mixed results.209 with a mixture of chloroplatinic acid and rhodium chloride, very little rhodium was deposited on the titania. With aqueous solutions of silver nitrate and rhodium chloride, more rhodium was deposited but deposition was not complete. In aqueous ammonia, though, deposition of both silver and rhodium was complete but the titania surface was covered with small rhodium crystallites and larger silver particles containing some rhodium. With a mixture of chloroplatinic acid and palladium nitrate both metals were deposited but, while most of the resulting crystallites were bimetallic, the composition varied from particle to particle.209... 

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