Time drift spectroscopy

Then, the surface species were investigated under high-pressure methanol synthesis conditions by DRIFT spectroscopy. DRIFT spectra were recorded as a fimction of time when the sulfided Ca/Pd/SiO2 (Ca/Pd=0.5) was exposed to the stream of syngas at 613 K and S.l MPa (Figure 5 (a)). 

Specifically, data was presented describing moisture desorption and intermediate temperature air oxidation of a powdered sub-bituminous coal. In comparison to its companion method, PA-IR, DRIFT spectroscopy would appear to be the technique of choice for the study of such reaction processes involving powdered samples since the temperature and environment of the sample are more conveniently controlled. Also PA-IR in general requires longer data acquisition times than DRIFT to produce a similar quality S/N ratio (34), No effort has been made in this report to treat in any way the quantitative aspects which most surely at some point must be considered. Most quantitative work involving DR spectra has utilized the Kubelka-Munk Equation to mathematically treat the data. This Equation seems to apply mainly to species in highly reflecting matrices at low dilution. Therefore, it remains to be determined what treatment may be required for DR spectral data obtained from neat materials such as coal. 

From XPS analyses, the coexistence of Mn and Mn species was evidenced in LaMnOs material, while the LaCoOs one showed the presence of Co and Co " at the same time. Additionally, these authors established a higher Oads/Oiatt molar ratio on LaCoOs perovskite than that observed for the LaMnOs one. This phenomenon, observed at the surface of the material, improved the low-temperature reducibility of LaCoOs material, where the catalyst s properties claimed to be responsible for the remarkable catalytic performance of the cobalt-based perovskite in the CO oxidation reaction. Other authors have also remarked the importance of the presence of Co " species as active sites for the adsorption of CO [37-39]. For instance, by using DRIFT spectroscopy, Natile et al. [37]... 

SSITKA. The idea behind this approach was to compare the time response of isotopically labelled surface and gas-phase species by DRIFT spectroscopy and MS analysis. This novel technique was applied for mechanistic analysis water-gas shift (WGS) and reversed WGS reactions over F t- and Au-based catalysts with the aim of identifying true surface intermediates. These authors found that both formate and carbonate species labelled with C were formed on the catalyst surface after switching from C0/H20/Ar = 2/7/91 to C0/H20/A = 2/7/91. In order to determine which surface species actively participated in CO2 formation, they compared temporal changes in the IR bands of these surface species with those of gas-phase C02. Since the rate of CO2 formation was ca. 60 times higher than the rate of the exchange of formate species it was concluded that the formates detected by DRIFT spectroscopy could not be the main surface intermediates of gas-phase CO2. However, the role of surface formates in CO2 production may change with rising temperature as demonstrated in Ref. 129 where the formate species were spectators at 160°C but became main reaction intermediates at 220 C. 

Recently, for the first time. Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopy was applied to characterize tin oxide-based thick film gas sensors under normal working conditions (between 25 and 300 C in dry and humid air) [103]. The obtained results confirm the role of surface hydroxil groups in the CO detection ... 

An easy calibration strategy is possible in ICP-MS (in analogy to optical emission spectroscopy with an inductively coupled plasma source, ICP-OES) because aqueous standard solutions with well known analyte concentrations can be measured in a short time with good precision. Normally, internal standardization is applied in this calibration procedure, where an internal standard element of the same concentration is added to the standard solutions, the samples and the blank solution. The analytical procedure can then be optimized using the internal standard element. The internal standard element is commonly applied in ICP-MS and LA-ICP-MS to account for plasma instabilities, changes in sample transport, short and long term drifts of separation fields of the mass analyzer and other aspects which would lead to errors during mass spectrometric measurements. 

Chemometric techniques have gained enormous significance in the treatment of spectral information by virtue of their ability to process the vast amount of data produced by modern instruments over short periods of time with a view to extracting the information of interest they contain and improving the quality of the results. In some cases, the operator is unacquainted with the chemometric techniques (spectral smoothing, baseline drift correction) embedded in the software used by the instrument in others, the chemometric tools involved are inherent in the application of the spectroscopic technique concerned (e.g. in NIR spectroscopy) and thus indispensable to obtaining meaningful results. 

Vibrational spectroscopy is a very versatile and, chemically, well-resolved technique for the characterization of carbon-oxygen functional groups. The immense absorption problems of earlier experiments seems to be overcome in present times with modem FT-IR, DRIFTS or photoacoustic detection instruments. 

Newton MA, Dent AJ, Fiddy SG, Jyoti B, Evans J. Combining diffuse reflectance infrared spectroscopy (DRIFTS), dispersive EXAFS, and mass spectrometry with high time resolution potential, limitations, and application to the study of NO interaction with supported Rh catalysts. Catal Today. 2007 126 64. 

Ferri D, Kumar MS, Wirz R, et al. First steps in combining modulation excitation spectroscopy with synchronous dispersive EXAFS/DRIFTS/mass spectrometry for in situ time resolved study of heterogeneous catalysts. Phys Chem Chem Phys. 2010 12 5634. 

The analyst uses ICP-OES (inductively coupled plasma, optical emission spectroscopy) to measure twenty different metal ions in solution. To fully calibrate the instrument requires the preparation and measurement of 100 individual calibration standards (five point calibration per element). It would be impracticable for an analyst to calibrate the instrument daily. The instrument is calibrated at regular intervals (say fortnightly) by the analyst. In the intervening time, the calibration for each metal ion is checked by the use of a set of drift correction standard solutions. Minor corrections can then be made to the calibration to allow for day-to-day drift. 

Ion mobility is based on the measurement of the amount of time it takes for an ion to drift through a buffer gas under the influence of a weak electric field. This drift time inherently contains information about the conformation of the ion. Differently shaped ions have various collision cross sections and hence different mobilities (and drift times) when drifting through the gas. Thus, various computational methods are then used to generate model structures of the ions and calculate their cross sections for comparison to experiment. For instance. X-ray crystallography and NMR spectroscopy are usually used to obtain structural data on POSS molecules. However, POSS-polymer systems can be difficult to examine with these methods since synthetic polymers exist as a mixture of chain lengths data can thus only be obtained for the entire polymer distribution as a collective using these methods. In this respect, detailed information about how POSS interacts with one particular... 

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