Catalytically active filters

MnOj thick film, deposited on the surface of metal oxides such as SnO and WO3 with the purpose of reducing the interference of O3 for NO sensors, acts as a catalytically active filter as well (Pijolat et al. 2003 Viricelle et al. 2006 Zhang et al. 2012). Fortunately, O3 is unstable and can be transformed to O3 by catalysts, e.g., manganese dioxide (MnO ) (Dhandapani and Oyama 1997). The results obtained have shown that the sensors with thin MnO filters are able to reduce the O3 interference while keeping a good response to NO.  

Preconcentrators used in detection of complex organic vapors employ a granular, highly porous sorption material which provides a large collection area. Some preconcentrators are packed with up to three different absorbent materials to enhance the efficiency of collection and concentration of various organic compounds. Silica gel, polyurethane foam (PDF), and other sorbents can be used for these purposes. Sorbents usually used for atmospheric air monitoring are shown in Table 12.3. 

Type of sorbent area (mVg) temperature (°C) VOC analytes retained liberation technique 

Porous organic polymers Tenax TA and GR 35 350 Aromatic compounds, nonpolar Thermal desorption 

Chromosorb 102 (styrene- 750 20-250 Alcohols, ketones, aliphatic Thermal desorption 

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Catalytically active filter elements into the freeboard of the gasifier to obtain tar- and particle-ftee syngas... 

At the Department of Chemical Engineering new catalytically active materials have been produced by burning volatile metal compounds in a flame. This produces an aerosol of very small particles that can be collected on a filter. Especially if the particles are cooled very fast, it is possible to obtain a large area per gram of material. In the following, AI2O3 is produced by this method. 

Filtration of the catalytic mixture using pore membrane filters or filter aids allows the distinction between soluble and insoluble catalysts. Further catalytic activity analysis from the solution and insoluble residue can give information about the state of the real catalyst. In turn, centrifugation can be appropriated to separate metal NPs from the catalytic solutions, due to their high molecular weight and density, and thus to be separated from molecular species. 

Improved Filtration Rate Filterability is an important powder catalyst physical property. Sometimes, it can become more important than the catalyst activity depending on the chemical process. When a simple reaction requires less reaction time, a slow filtration operation can slow down the whole process. From a practical point of view, an ideal catalyst not only should have good activity, but also it should have good filtration. From catalyst development point of view, one should consider the relationship between catalyst particle size and its distribution with its catalytic activity and filterability. Smaller catalyst particle size will have better activity but will generally result in slower filtration rate. A narrower particle size distribution with proper particle size will provide a better filtration rate and maintain good activity. 

Morgan (11) derived a rate law that adequately describes the observed kinetics and was able to extract rate constants for both homogeneous and particle-catalyzed reactions. In laboratory experiments with sterile, filtered synthetic solutions, Mn2+ oxidation proceeds much more slowly than in natural waters. It may not occur at all at neutral or acidic pH, especially in the absence of catalytically active surfaces such as preformed oxidation products (12, 13). 

The initial results were interpreted as evidence of catalytic activity by dithiolenes themselves.211,212 However, Kisch et al.m were soon able to demonstrate that the Zn(mnt)2 complex dianion decomposed to ZnS under these conditions and it is now believed that the dithiolene is only the catalyst precursor and that ZnS is the actual catalyst. The sulfide must be extremely finely dispersed, approaching near homogeneous conditions, because filtration of the solution through a cellulose acetate filter of 0.2 /jm pore size did not reduce the rate of reaction. 

A few benzisoselenazol-3(2//)-oncs were covalently immobilized to the solid support, either silica [165] or polymer [246] (147-150) (Fig. 8). They exhibited appreciable catalytic activity similar to the activity of ebselen. The most interesting prospective oxygen-transfer catalyst is benzisoselenazolone covalently bound to a silica support (147) named HALICAT. It has been applied to hydrogen peroxide oxidation of the sulfides and TBHP oxidation of the aromatic aldehydes and alky-larenes. The catalyst can be easily filtered off from the mixture after the reaction and reused several times [165],... 

The catalyst was prepared as follows. Iron hydroxides (2 g) were exposed to aqueous sulfuric acid or aqueous ammonium sulfate (30 ml) on a filter paper. After drying, the materials were powered and calcined in air. The catalytic activities of various iron oxides with or without the sulfate treatment for the reaction of 2-propanol are summarized in Table VI. The Fe203 catalysts treated with 0.25-0.5 M H2S04 showed unexpectedly high activities for the reaction, though the reaction did not occur at all over the catalysts prepared by calcining Fe(OH)3. The treatment with ammonium... 

Catalytic filters should possess the following properties 1) high thermal, chemical, and mechanical stability 2) high dust separation efficiency attained by cake filtration (no penetration of particulates into the filter structure) 3) low cost 4) high catalytic activity (operation at high superficial velocities) and 5) low pressure drop. 

Many working groups have modeled the performance of diesel particulate traps during the past few decades. Concentrated parameter models (CSTR assumption) have been applied for the evaluation of formal kinetic models and model parameters. The formal kinetic parameters lump the heat and mass transfer effects with the reaction kinetics of the complicated reaction network of diesel soot combustion. Those models and model parameters were used for the characterization of the performance of different filter geometries and filter materials, as well as of the performance of a variety of catalytically active coatings and fuel additives [58],... 

In order to remove the catalytically active iron salts, a portion of the circulating electrolyte is periodically removed, after having passed through the cathode spaces to get rid of active oxygen. Iron is precipitated by potassium ferrocyanide and the Prussian blue deposit is filtered off by a suotion filter. The purified electrolyte is then returned to normal circulation. 

As an oxidant for manganous ion in acid solution, chlorate ion was found to be the most convenient. Manganous carbonate was dissolved in concentrated nitric acid, and sodium chlorate was added a few crystals at a time until complete oxidation had apparently taken place. The precipitate was allowed to settle then the entire mass was poured into a large volume of water and filtered. The residue was catalytically active at — 20°C. 

Palladium hydrosol is a brown or brownish black liquid in which the metallic particles are exceedingly small, as evidenced by the fact that a small portion will pass through a collodion filter that will retain dilute haemoglobin solutions. The colour of the filtrate is practically the same as that of the original liquid proportionately diluted, although it sometimes exhibits a slightly redder cast. Well-defined catalytic activity is manifested by dilute solutions containing only 0-0005 per... 

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