Potassium acid sites, neutralization

Addition of promoters to resist deactivation. For example, greater support stability with alumina is achieved with small amounts of added silica or zirconia, sintering and coking of platinum is reduced by adding rhenium, and acid sites neutralized with potassium. 

Pure alumina catalyst prepared either by hydrolysis of aluminum isopropoxide or by precipitation of aluminum nitrate with ammonia, and calcined at 600-800°, contains intrinsic acidic and basic sites, which participate in the dehydration of alcohols. The acidic sites are not of equal strength and the relatively strong sites can be neutralized by incorporating as little as 0.1 % by weight of sodium or potassium ions or by passing ammonia or organic bases, such as pyridine or piperidine, over the alumina. 

Poisons which neutralize or destroy acid sites, as for instance sodium, potassium, nitrogen. 

From these results, it is observed that the way selected to add potassium is very important with respect to the resultant catalyst stability. When potassium is added on the monometallic Pt/y-A Os system previous to the reaction with SnBit), the reaction between platinum and SnBu4 results, apparently, non affected, however, the stability of these catalysts is relatively low, lower than the one of the systems in which potassium is added on the bimetallic catalyst at the final preparation stage. Consequently, it is more effective to prepare well defined bimetallic phases, and afterwards neutralizing with potassium the superficial acid sites. 

Small Quantities. Wear eye protection, laboratory coat, and nitrile rubber gloves. In the fume hood, add solid potassium dichromate to a container of water (about 100 mL/5 g). Acidify with 3 M sulfuric acid (35-55 mL, pH 1 with pHydrion paper). While stirring, slowly add solid sodium thiosulfate (about 13.5 g) until the solution becomes cloudy and blue colored. Neutralize the solution with sodium carbonate. After a few minutes a blue-gray flocculent precipitate is formed. Let the mixture stand for a week or filter immediately through Celite. After a week, much of the supernatant can be decanted. The remaining liquid is allowed to evaporate or the solid filtered. The liquid may be washed into the drain. The solid residue should be washed with hot water to remove sodium sulfate, and then dried, packaged, labeled, and sent to a secure landfill site.6... 

Any basic or alkaline material can react with a zeolite to effectively neutralize the acidic active sites, which generally results in irreversible loss of catalyst activity. Basic compounds found in the ethylene or benzene feedstocks can include amines, amides, nitriles, and trace metal cations such as sodium and potassium. Of particular concern are nitrogen-containing organic compormds typically present in the benzene feed. 

A part of the throughfall flux of sulfur, calcium, magnesium, and potassium is due to the deposition of sea-salt particles. Ion fluxes in bulk and stand precipitation can be corrected for the contribution of sea-salt particles, using sodium or chloride as sea-salt tracers. Sea-salt contributions between 8% (Europe) and 45% (coastal sites) of the total sulfur in stand precipitation were found. Deposited sea-salts are neutral salts, and these do not contribute to either acidic (in the case of sulfur) or alkaline (in the case of base cations) reactions in the forest soil (Biittner et al. 1986). 

Procedure. Filter paper impregnated with sodium dipicrylaminate is spotted with a drop of the neutral test solution, or several grains of the ignition residue are placed on the paper. In the latter case, the material is then moistened with a drop of water. The paper is dried in a current of heated air, and placed in 0.1 iV nitric acid. If potassium is absent, or present in quantities less than the identification limit, the original orange-red paper turns bright yellow (color of free dipicrylamine). If sufficient potassium is present to form its dipicrylaminate, a red fleck or ring remains at the site of the spot. 

Small quantities of acids and bases may also be added to the stationary phase to cover or neutralize active sites on a solid support. They usually have the same acid-base properties of the species being analyzed and are referred to as tail reducers. Phosphoric acid-modified packings are effective for analyzing fatty acids and phenols potassium hydroxide has been used with success for amines and other basic compounds. 

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