Catalysts, analysis Fluorescence

Spent Catalyst Analysis. Analysis of catalysts subjected to car and engine testing by x-ray fluorescence (XRF) revealed the expected con-... 

Polyester composition can be determined by hydrolytic depolymerization followed by gas chromatography (28) to analyze for monomers, comonomers, oligomers, and other components including side-reaction products (ie, DEG, vinyl groups, aldehydes), plasticizers, and finishes. Mass spectroscopy and infrared spectroscopy can provide valuable composition information, including end group analysis (47,101,102). X-ray fluorescence is commonly used to determine metals content of polymers, from sources including catalysts, delusterants, or tracer materials added for fiber identification purposes (28,102,103). 

The inorganic sorbents act as catalysts in all this [3,4]. Hie pH also probaUy plays a role. Reactions that do not otherwise occur are observed on add silka gd [3] or basic aluminium oxide layers. Reactions of this type have also been obsoved for amino [6-8] and RP phases [9]. The products of reaction are usually fluorescent and can normally be used for quantitative analysis since the reactions are reprodudble. 

Applications X-ray fluorescence is widely used for direct examination of polymeric materials (analysis of additives, catalyst residues, etc.) from research to recycling, through production and quality control, to troubleshooting. Many problems meet the concentration range in which conventional XRF is strong, namely from ppm upwards. Table 8.42 is merely indicative of the presence of certain additive classes corresponding to elemental analysis element combinations are obviously more specific for a given additive. It should be considered that some 60 atomic elements may be found in polymeric formulations. The XRF technique does not provide any structural information about the analytes detected the technique also has limited utility when... 

The fractions from elution chromatography were studied by a number of spectroscopic methods, n.m.r., i.r., u.v., fluorescence and phosphorescence spectroscopy. Equivalent fractions from chromatographic separation of the various oils showed no significant differences in their spectra and it appears that the composition of the fractions was independent of the catalyst concentration used to produce the oil. Though, as previously mentioned the amounts of the various fractions especially the polar fractions differ with the catalyst concentration. G.1.C. analysis of the saturate fractions also indicated no changes with different catalyst concentrations. 

Electron probe and X-ray fluorescence methods of analysis are used for rather different but complementary purposes. The ability to provide an elemental spot analysis is the important characteristic of electron probe methods, which thus find use in analytical problems where the composition of the specimen changes over short distances. The examination of the distribution of heavy metals within the cellular structure of biological specimens, the distribution of metal crystallites on the surface of heterogeneous catalysts, or the differences in composition in the region of surface irregularities and faults in alloys, are all important examples of this application. Figure 8.45 illustrates the analysis of parts of a biological cell just 1 pm apart. Combination of electron probe analysis with electron microscopy enables visual examination to be used to identify the areas of interest prior to the analytical measurement. 

The activity trend obtained with Cui xCoxFe204 catalysts is well supported by the surface metal ions composition determined from XPS analysis. Figure 8 displays the Cu/(Co+Fe) (Co/Fe for X = 1) ratio calculated from XPS results in the left panel and phenol conversion with products selectivity for all catalyst compositions in the right panel. This exercise is mainly to imderstand the distribution of metal ions and their heterogeneity on the smface, as it directly influences catalytic activity. On fresh catalysts, relative Cu-content decreases linearly with decreasing Cu-content and it is in good correlation with bulk Cu-content measmed by x-ray fluorescence. A high Cu/Fe ratio is found on spent catalysts at 0.25 < x < 0.75. It is to be... 

The characterization of fresh and used automotive catalysts, which includes the examination of poisons accumulated in the catalysts, uses a variety of modem analytical techniques. The two principal tools, besides conventional chemical methods, are atomic absorption and, most important, X-ray fluorescence (XRF). The latter technique has been refined and adapted for the analysis of automotive catalysts to permit rapid and accurate determination of all constituents, including the inadvertent contaminants. An example of a simultaneous XRF analysis of... 

X-Ray Fluorescence Analysis of 15 Components in a Catalyst Calibration Standard... 

The cerium(IV) oxidation reaction of many organic acids provides a sensitive and selective method for HPLC analysis of these compounds [116,117]. The oxidation of specific classes of organic compounds with cerium(lV), and the effects on the reaction of temperature, acidity, anion and catalyst, have been studied extensively [118-120]. The reaction produces cerium(HI) which is fluorescent and can be measured spectrofluori-metrically. The method has been applied successfully to the post-column reaction and detection of nmole amounts of organic acids by HPLC. 

To verify the success of the different deposition steps, in combination with the Split Pool methodology X-ray fluorescence was chosen as an analysis tool. Elemental analysis was performed by X-ray fluorescence analysis on an Eagle II pProbe (Roentgenanalytik) with Rh-Ka radiation. An essential feature is the small diameter of the measurement spot The X-ray beam is focused by a multi-capillary system to a 50 pm spot on the sample surface. XRF analysis of the 8x12 catalyst library selection (Fig. 2.20) was routinely accomplished automatically by an elemental mapping at a pattern of 512x400 points, equally distributed over the rectangular library field, each point (50 pm diameter) was measured for 300 ms. 

Boitiaux et al. (61) have examined the influence of palladium sulfuration on the hydrogenation and isomerization of 1-butene, 1,3-butadiene, and 1-butyne. The tested catalysts have been sulfided with thiophene to obtain an atomic ratio (sulfur per surface palladium) varying between 0 and 0.5. The thiophene in heptane solution is put in contact with the reduced palladium catalyst at 50°C, under 2 MPa hydrogen pressure. The butane evolution is followed during the sulfiding step (see above) and a control of total sulfur adsorption is performed by the analysis of the heptane after the sulfiding step and through X-ray fluorescence after the reaction step. 

The used catalysts were washed with toluene in a Soxhlet extractor, stored in purified toluene and dried before analysis. C, H, S and N elemental analysis were performed by combustion using a Carlo Erba apparatus. The coke content is therefore defined in this work as being the carbon content of a used catalyst washed by hot toluene. Metal contents were measured by X-ray fluorescence spectroscopy. The coke hydrogen content was determined by difference between the hydrogen content measured for the used catalyst and the hydrogen content measured for the fresh NiMo catalyst (0.6 wt %). 

Emission spectrography is used for rapid determination of the presence of mineral impurities, for example, in samples of catalysts taken from a unit with operating problems. A semi-quan-titative estimate of the elements identified can be used for a speedy appraisal of the possible degree to which they arc responsible for the deactivation of the catalyst. This analysis may supplement that of X-ray fluorescence (XRF) by determining the presence of light elements (Li, Na, B) where XRF cannot provide information on low concentrations, and by determining the presence of elements likely to lead to spectral interference. 

X-ray fluorescence analysis is well adapted to the analysis of catalysts because it is a direct measurement method and does not require the specimen to be put into solution. Frequent applications in the area of catalysts are as follows ... 

Monometallic catalysts on alumina supports are ideal cases for X-ray fluorescence analysis the matrix (alumina or alumina containing approximately 2% weight chlorine) remains " constant in terms of the matrix effects, and analysis can be conducted directly on finely crushed powder. Texture or grain effects must, however, be carefully avoided by using, in the preparation of standards, the same support as that of the catalysts. Any change in the nature of the support (granulometry, structural modifications, etc.) should be systematically indicated by the person requesting the analysis. 

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