Platinum preparation

Hexahydronicotinic acid (90%) is obtained by catalytic hydrogenation of nicotinic acid at 3 atm. pressure over colloidal platinum. Preparation of the catalyst is described. The 9,10 double bond in the acridine nucleus is reduced at 10° by sodium amalgam in dilute sodium carbonate solution to give 9,10-dihydroacridine-S>-carboxylic acid in 70% yield. 2-Phenyl-cyclohexanecarboxylic acid (96%) is prepared by the selective reduction, of 2-phenylbenzoic acid by a large excess of sodium in refluxing amyl alcohol. ... 

FIGURE 27.6 Scanning electron microscope photomicrographs of representative microstructures of (a) PZT and (b) BT thin films on platinum prepared by a chelate process. 

One of the major reasons why this reaction is not more widely used is that the catalyst is usually deactivated before the oxidation is completed. This deactivation is thought to be caused by either the oxidation of the metal or the blocking of the metal surface by the strong adsorption of reaction by-products. A number of procedures have been employed to minimize this deactivation. Most of the early work in this area used a large amount of platinum, prepared by the hydrogenation of platinum oxide (Adam s catalyst), as the catalyst.52 These larger metal particles are more resistant to oxidation than the smaller particles present on supported platinum catalysts.63 In addition, the large quantity of catalyst ensures that some active species will still be available toward the end of the reaction. 

In studies of dual-functional catalysis the mixed catalyst technique has many advantages, two of which are mentioned. (1) It allows separate and independent preparation of each component for example, a platinum preparation can be made in any manner desired in order to obtain a certain platinum activity without regard to what such procedures might do to the acidic properties of the oxide base, this interdependence always being a matter of concern in conventional direct impregnation techniques. (2) A component s relative activity contribution can be flexibly varied in a perfectly known and controllable manner by simply varying its bulk amount in admixture with the other. 

Platinum, prepared by reduction of Pt02 (Adams catalyst) with H2, is pyrophoric. 

Single Crystal Platinum Prepared in Different Cooling Atmospheres.240... 

The metric standard of mass is the kilogram, a lump of platinum prepared by Borda to represent the mass of a cubic decimetre of water at the temperature of its maximum density, namely 40 C. It is called the Kilogram des Archives. 

Solubility tests in absence of Ti02 were first performed with a lO M solution of platinum prepared from an ammonium tetrachloroplatinate salt. However, upon mixing NaOH and lO M (NH4)2PtCl4 no precipitation was initially observed. At room temperature, the formation of a precipitate becomes nonetheless detectable after 24 h stirring. After 48 h precipitate was still forming. In m effort to obtain a complete precipitation in a reasonable time, an attempt was made to hydrolyze at 60°C. At this temperature, precipitate formation... 

When an essentially nonacidic platinum preparation with a platinum content and (de)hydrogenation activity typical of re-forming catalysts (about 1000 Aimoles/sec./g. by cyclohexane test) is tested in the reactor, the gas production rate is near the background rate of the test reactor, correspond-... 

Figure 13. Wettability of various monolayers on platinum prepared by retraction from aqueous solution [43]...

It was found that the photoreduction method produced platinum particles of 14 and 12 A mean sizes using NaDDS and DDACl. When chloroplatinic acid was reduced by hydrogen, mean particle sizes were 92 and 39 A in the presence of NaDDS and DDACl, respectively. It was noted that the photoreduction yields a more uniform distribution of particle sizes than from the reaction of H2PtCl4 with hydrogen. Colloidal particles of platinum prepared by photoreduction exhibited high activity during vinyl acetate hydrogenation. 

An intriguing experiment was first done with reduced platinum (prepared in the presence of Csl), which was placed in an acenaphthenoquinone (AcQ) (E° = -0.31 V versus SCE) solution. No diffusion of the anion radical was observed around the reduced Pt. On the contrary, an intense blue color stays at the platinum surface. One can expect the formation of an insoluble radical-anion-cesium salt that covers the surface. However, after rinsing the sample with acetone and water in an ultrasonic bath, it appears that the Pt surface is deeply attacked [52]. This preliminary experiment suggests that AcQ is reduced by the cesium-platinum phase and that the reduced form of the acceptor reacts with the still unreacted platinum phase. In order to simply mimic this kind of chemical route, the concomitant reduction of the acceptor at a platinum sheet was realized under superdry conditions with a salt such as Csl. One may see a noticeable increase of the mass of the electrode after a sufficient charge was passed, accompanied by a huge modification of the surface as depicted by SEM images, exemplified in Figure 2.31. 

Krupp and others [204] proposed that skeletal platinum, prepared by decomposition of an alloy between platinum and aluminum, should be used as catalyst. As shown by Petrii and Marvet [209], hydrogen adsorption isotheims for disperse platinum catalysts (platinized platinum, platinum Idack, Adams platinum, and various forms of skeletal platinum) in aqueous solutions of electrolytes exhibit relatively small differences. 

A templating approach can be important for preparing low-dimensional platinum nanostructures, as the platinum metal has a fee cubic symmetry. In template-free solution-phase synthesis, the introduction of defects can serve as a useful strategy. Some examples of nanorods, nanowires and nanotubes of platinum prepared using different methods, with and without templates, are shown in Figure 10.8. Notably, when the diameter of nanowires becomes very small, they can exhibit excellent flexibUity and form interconnected networks. 

Throughout this paper the silica-supported platinum prepared and characterised in this investigation is referred to as Pt/silica, whereas the silica-supported platinum reference catalyst is referred to as EUROPT-1. 

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