Hydrogen-carbon ratios sample preparation

Like BSIA, two sample conversion systems are required depending on the element/s of interest. For example, Thermo Fisher Scientiflc (Waltham, MA) supplies a GC Combustion III (CIII) interface system for the preparation of samples for nitrogen and carbon isotope ratio measurements. They also have a High Temperature Conversion (TC) interface system for sample preparation for hydrogen and oxygen analysis [1,36,37]. 

Ruthenium catalysts, supported on a commercial alumina (surface area 155 m have been prepared using two different precursors RUCI3 and Ru(acac)3 [172,173]. Ultrasound is used during the reduction step performed with hydrazine or formaldehyde at 70 °C. The ultrasonic power (30 W cm ) was chosen to minimise the destructive effects on the support (loss of morphological structure, change of phase). Palladium catalysts have been supported both on alumina and on active carbon [174,175]. Tab. 3.6 lists the dispersion data provided by hydrogen chemisorption measurements of a series of Pd catalysts supported on alumina. is the ratio between the surface atoms accessible to the chemisorbed probe gas (Hj) and the total number of catalytic atoms on the support. An increase in the dispersion value is observed in all the sonicated samples but the effect is more pronounced for low metal loading. 

All errors due to chemical preparation limit the overall precision of an isotope ratio measmement to usually 0.1-0.2%o, while modem mass spectrometer instrumentation enables a precision better than 0.02%c for light elements other than hydrogen. Larger uncertainties are expected, when elements present in a sample at very low concentration are extracted by chemical methods (e.g., carbon and sulfur from igneous rocks). 

Several catalyst samples of tungsten carbide and W,Mo mixed carbides with different Mo/W atom ratios, have been prepared to test their ability to remove carbon monoxide, nitric oxide and propane from a synthetic exhaust gas simulating automobile emissions. Surface characterization of the catalysts has been performed by X-ray photoelectron spectroscopy (XPS) and selective chemisorption of hydrogen and carbon monoxide. Tungsten carbide exhibits good activity for CO and NO conversion, compared to a standard three-way catalyst based on Pt and Rh. However, this W carbide is ineffective in the oxidation of propane. The Mo,W mixed carbides are markedly different having only a very low activity. 

Preparation of the H8gg carbide was started with a commercial synthetic ammonia catalyst containing 92.6% FesOi, 4.2% MgO, 0.7% SiOj, and 0.4% Cr203. Reduction and carburization were carried out in apparatus similar to that previously described (Hofer and Peebles, 49). A stream of purified hydrogen was passed over the sample held at 450° for 82 hours. The reduced sample was then treated at 240° for 539 hours with purified carbon monoxide, until the carbon/iron ratio became nearly constant, and closely corresponded to FeaC. The reaction vessel was always opened in a carbon dioxide atmosphere to prevent oxidation. 

The use of isotope ratio mass spectrometry (IRMS) to compare the ratios of light atom isotopes in samples of forensic interest is finding increased importance. A recent report by Benson et al. details the use of IRMS to differentiate between samples of TATP that were prepared under differing conditions and from different precursors [61]. A three-dimensional plot of the carbon, hydrogen, and oxygen data clearly showed four clusters corresponding to the different sample sets. 

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