Contents 3 Temperature programming

The spent catalysts were characterized by chemical analysis (carbon content), temperature programmed oxidation coupled to a mass spectrometer (TPO/MS) and thermal analysis (DTA and TG). The samples were also submitted to extraction of soluble coke in a soxhiet apparatus with n-hexane and dichloromethane for 24h, after being treated with fluoridric acid (40%) at room temperature (2h), followed by reflux with hydrocloric acid (36%) for 2h. The extracts were analyzed by gas-chromatography-mass spectrometry (GC/MS), Fourier transformer infrared spectroscopy (FTIR), ultraviolet spectroscopy (UV) and X ray diffraction. The insoluble fraction was analyzed by X ray diffraction and FTIR. 

Temperature programmed GC (Fig. 2) separates these components as well as a cyclic formal. The mono, di and tri brominated products of 1 require higher temperatures to elute in a reasonable time more than the column can withstand. TMS derivatives do not require temperatures quite so high (Fig. 3). Using this technique for quantitation, however, is complicated by the decreasing sensitivity of the FID to increasing bromine content. 

An important prerequisite for the use of CRMs as calibrants, at least for optical methods and particularly all AAS modes, is that they should match the matrix and level of analyte contents of the materials to be analyzed as closely as possible, so that potential matrix effects will be compensated if calibrant and sample material are affected by the applied method, e.g. the temperature program for furnace techniques, in the same way. Further it is very important for all methods that the CRMs used should not show a nugget effecf, i.e. particles with extremely high analyte content that can lead to a high analyte heterogeneity (Kurfiirst 1991 Kurfiirst et al. 

The promoter role of ceria in WGS reaction is demonstrated in Figure 8.6. Temperature-programmed conversion of CO was carried out in an oxygen-deficient medium. The oxygen content was adjusted to obtain a maximum conversion of 40% by... 

The catalysts were characterized by inductively coupled plasma emission spectroscopy (ICP-ES Perkin Elmer Optima 3300RL) to determine cobalt content, x-ray diffraction (XRD Bruker A-500) with crystallite size determination using the Rietveld method, and temperature-programmed reduction (Zeton Altamira AMI-200) using 30 ml/min 10% H2/Ar and a ramp rate of 10°C/min. Surface area... 

Catalytic superactivity of electron-deficient Pd for neopentane conversion was recently verified for Pd/NaHY (157, 170). The reaction rate was positively correlated with the proton content of the catalyst. Samples that contained all the protons generated during H2 reduction of the catalysts were two orders of magnitude more active than silica-supported Pd. Samples prepared by reduction of Pd(NH3)2+NaY displayed on intermediate activity. It was suggested that Pd-proton adducts are highly active sites in neopentane conversion. With methylcyclopentane as a catalytic probe, all Pd/NaY samples deactivated rapidly and coke was deposited. Two types of coke were found (by temperature-programmed oxidation), one of... 

It was appreciated at the outset that the characterization of these materials would be an altogether more difficult problem than that of EUROPT-1, by reason of the lower metal content, and the bimetallic nature of EUROPT-4. It was hoped that study of the latter would help resolve some of the questions concerning the intimacy of mixing of the two metals in the functioning catalyst, but these queries have been only partially answered. Temperature programmed reduction (TPR) studies have confirmed the sensitivity of the reduction profile to experimental conditions and sample pretreatment but, notwithstanding reports in the liter-... 

Acyl derivatives of triazines were used by Bailey et al. [495] for their determination in potatoes, peas and tomatoes. Their preparation requires catalysis by trimethylamine or pyridine. A 15-jul volume of HFB anhydride was added to a dry residue of triazine (1—25 ftg) in a 15-ml test-tube fitted with a screw-cap, 1.0 ml of 0.5 M trimethylamine in benzene (or 1 ml of benzene plus 6 droplets of pyridine) was then added and the closed test-tube was stirred gently for 30 sec and then allowed to stand at room temperature for 30 min. Subsequently 4.0 ml of benzene were added and the contents were stirred for 1 min, then 10 ml of water were added and the contents were shaken vigorously for 1 min. The phases were separated and a suitable portion of the benzene phase was injected. Several stationary phases (OV-1, OV-101, OV-210 and a mixture of OV-101 and QF-1) were applied at temperatures of 180—200°C or with temperature programming. Exclusively mono-derivatives are said to be prepared by this procedure, with bis-deriva-tives in small amounts and for only some substrates. The sensitivity of the analysis using an ECD is from 300- to several thousand-fold higher that with free substances. 

All alkylates produced by second-step reactions in which isobutylene was the feed olefin had relatively low ROM s and contained relatively large amounts of LE s, DMH s, and HE s as compared to alkylates produced from butyl sulfate. The LE content of the alkylate generally varied between 23 to 28%, and the HE content between 30 to 40% (based on analyses with the temperature-programmed unit). The calculated RON values of the alkylate varied from about 88-91. The compositions of the TMP family were considerably different for the isobutylene runs (see Table III) as compared to those of the n-butene run (see Table II). For runs using isobutylene, 2,2,4-TMP accounted for about 60% of the TMP family. The LE s had similar compositions, however, at a given temperature for both n-butene and isobutylene runs. 

The molybdenum dispersion also depends on the phosphorus content of the catalyst. Atanasova et al. (68, 87) reported that the dispersion of molybdenum and nickel, measured by X-ray photoelectron spectroscopy (XPS), shows a steep increase due to the presence of phosphorus at low loadings. The dispersion of molybdenum in NiMoP/Al catalysts increases further as a result of calcination, whereas that of nickel decreases. In contrast, Sajkowski et al. (83) reported, on the basis of an extended X-ray absorption fine structure (EXAFS) investigation, that phosphorus does not affect the size of the polymolybdate species, Mangnus et al. (31) inferred that the stacking of molybdates does not increase as a result of the addition of phosphorus since the height of a temperature-programmed reduction (TPR) peak at 400°C due to the reduction of deposited multilayered molybdenum oxo-species was found to be independent of the phosphorus content. However, Chadwick el al. (60) concluded from XPS measurements that the dispersion of molybdenum decreases upon addition of phosphorus. 

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