Active impregnating

In 1942, to meet the need for a lighter respirator more suited to a war of movement, the Light-Type respirator was introduced. This had a canister, filled with activated, impregnated charcoal and a wool-resin mixture, directly attached to the left cheek of the facepiece, and, for the first time, a speech transmitter was incorporated. 

Kieselguhr G, activated, impregnated with paraffin oil-petrol ether (40—60°)... 

Still, it is not easy to find clues for the observed difference in catalytic activities from only these structmal aspects. The XPS analysis in Fig. 3.9 shows that the impregnated and annealed Pt nanoparticles have inactive bulk oxide states, while the APD Pt nanoparticles are purely metallic. This oxide formation during annealing is considered the main reason for the difference in the catalytic activities. In order to improve catalytic activity, impregnated and annealed Pt nanoparticles on T1O2 films were reduced under 100 Torr of hydrogen at 250 °C for 1 h to decrease the oxidation state. However, the catalytic activity after reduction was stiU lower than that of the... 

Promoters are sometimes added to the vanadium phosphoms oxide (VPO) catalyst during synthesis (129,130) to increase its overall activity and/or selectivity. Promoters may be added during formation of the catalyst precursor (VOHPO O.5H2O), or impregnated onto the surface of the precursor before transformation into its activated phase. They ate thought to play a twofold stmctural role in the catalyst (130). First, promoters facilitate transformation of the catalyst precursor into the desired vanadium phosphoms oxide active phase, while decreasing the amount of nonselective VPO phases in the catalyst. The second role of promoters is to participate in formation of a soHd solution which controls the activity of the catalyst. 

Uses. Nickel nitrate is an intermediate in the manufacture of nickel catalysts, especially those that are sensitive to sulfur and therefore preclude the use of the less expensive nickel sulfate. Nickel nitrate also is an intermediate in loading active mass in nickel—alkaline batteries of the sintered plate type (see Batteries, SECONDARY cells). Typically, hot nickel nitrate symp is impregnated in the porous sintered nickel positive plates. Subsequendy, the plates are soaked in potassium hydroxide solution, whereupon nickel hydroxide [12054-48-7] precipitates within the pores of the plate. 

Diphenylamine can also be produced by passing the vapors of aniline over a catalyst such as alumina, or alumina impregnated with ammonium fluoride (17). The reaction is carried out at 480°C and about 700 kPa (7 atm). Conversion per pass, expressed as parts diphenylamine per 100 parts of reactor effluent, is low (18—22%), and the unconverted aniline must be recycled. Other catalysts disclosed for the vapor-phase process are alumina modified with boron trifluoride (18), and alumina activated with boric acid or boric anhydride (19). 

Some natural gases have also been found to contain mercury, which is a reformer catalyst poison when present in sufftciendy large amounts. Activated carbon beds impregnated with sulfur have been found to be effective in removing this metal. 

Dehydration or Chemical Stabilization. The removal of surface silanol (Si—OH) bonds from the pore network results in a chemically stable ultraporous soHd (step F, Fig. 1). Porous gel—siHca made in this manner by method 3 is optically transparent, having both interconnected porosity and sufficient strength to be used as unique optical components when impregnated with optically active polymers, such as fiuors, wavelength shifters, dyes, or nonlinear polymers (3,23). 

The process by which porous sintered plaques are filled with active material is called impregnation. The plaques are submerged in an aqueous solution, which is sometimes a hot melt in a compound s own water of hydration, consisting of a suitable nickel or cadmium salt and subjected to a chemical, electrochemical, or thermal process to precipitate nickel hydroxide or cadmium hydroxide. The electrochemical (46) and general (47) methods of impregnating nickel plaques have been reviewed. 

Eor the negative electrolyte, cadmium nitrate solution (density 1.8 g/mL) is used in the procedure described above. Because a small (3 —4 g/L) amount of free nitric acid is desirable in the impregnation solution, the addition of a corrosion inhibitor prevents excessive contamination of the solution with nickel from the sintered mass (see Corrosion and corrosion inhibitorsCorrosion and corrosion control). In most appHcations for sintered nickel electrodes the optimum positive electrode performance is achieved when one-third to one-half of the pore volume is filled with active material. The negative electrode optimum has one-half of its pore volume filled with active material. 

In most cases, the impregnation process is followed by an electrochemical formation where the plaques are assembled into large temporary cells filled with 20—30% sodium hydroxide solution, subjected to 1—3 charge—discharge cycles, and subsequentiy washed and dried. This eliminates nitrates and poorly adherent particles. It also increases the effective surface area of the active materials. 

Impregnated Activated Carbon Used to Remove Gaseous Radio-Iodines from Gas Streams... 

The catalysts are prepared by impregnating the support with aqueous salts of molybdenum and the promoter. In acidic solutions, molybdate ions are present largely in the form of heptamers, [Mo2024] , and the resulting surface species are beHeved to be present in islands, perhaps containing only seven Mo ions (100). Before use, the catalyst is treated with H2 and some sulfur-containing compounds, and the surface oxides are converted into the sulfides that are the catalyticaHy active species. 

Porosity and Pore Size. The support porosity is the volume of the support occupied by void space and usually is described in units of cm /g. This value represents the maximum amount of Hquid that may be absorbed into the pore stmcture, which is an especially important consideration for deposition of metal salts or other active materials on the support surface by Hquid impregnation techniques. The concentration of active material to be used in the impregnating solution is deterrnined by the support porosity and the desired level of active material loading on the catalyst. If the porosity is too low, inefficient use of the support material and reactor volume may result. If the porosity is too high, the support body may not contain sufficient soHd material to provide the strength necessary to survive catalyst manufacture and handling. 

To add surface area, the supports are uniformly coated with a slurry of gamma-alumina and recalcined under moderate conditions. The wash coat acts to accept the active metals, typically low levels of platinum and palladium, in a conventional impregnation process. In the United States in passenger car apphcations the spherical catalyst is used almost exclusively, and methods have been developed to replace the catalyst without removing the converter shell when vehicle inspection reveals that emission standards are not met. 

Polyethylene. Low pressure polymerization of ethylene produced in the Phillips process utilizes a catalyst comprised of 0.5—1.0 wt % chromium (VI) on siUca or siUca-alumina with pore diameter in the range 5—20 nanometers. In a typical catalyst preparation, the support in powder form is impregnated with an aqueous solution of a chromium salt and dried, after which it is heated at 500—600°C in fluid-bed-type operation driven with dry air. The activated catalyst is moisture sensitive and usually is stored under dry nitrogen (85). 

In the fibrous acetylation process, part or all of the acetic acid solvent is replaced with an inert dilutent, such as toluene, benzene, or hexane, to maintain the fibrous stmcture of cellulose throughout the reaction. Perchloric acid is often the catalyst of choice because of its high activity and because it does not react with cellulose to form acid esters. Fibrous acetylation also occurs upon treatment with acetic anhydride vapors after impregnation with a suitable catalyst such as zinc chloride (67). 

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