Pre-reduction

Inorganic ar senic normally occurs in two oxidation states As(V) and As(III). Arsenic (V) gives a significantly lower response than ar senic (III). For pre-reduction As(V) to the As(III) concentrated hydrochloric acid and potassium iodide/ascorbic acid reagents were used. As organoarsenic compounds do not react with sodium tetrahydi oborate, they were decomposed with a mixture of HNO and on a hot plate. 

Vor-reaktion, /. preliminary reaction, -rech-nung, /. calculation coimting up. -recht, n. privilege, -rede, /. preface preamble, -reduktion,/. prereduction previous reduction. -reduktionsansatz, m. (Calico) pre reduction paste. 

Submerged arc smelting process Pre-reduction of ilmenite (50% Ti02) followed by smelting in arc furnace to yield pig iron and titania slag (87% Ti02) TINFOS, Norway... 

Addition of platinum-black catalyst to ethanol caused ignition. Pre-reduction with hydrogen and/or nitrogen purging of air prevented this. 

Menon and Froment (755c) studied the activity of Pt-Al203 and Pt-black pretreated in hydrogen at various temperatures. The overall activity had a very sharp minimum as a function of the pre-reduction temperature (550°C for supported, 500°C for unsupported platinum). This was due mainly to the almost complete ceasing of hydrogenolysis, whereas the amount of Cg products altered to a lesser extent. 

Speciation of a solution of mixed arsenic standards determine the limit of detection observe and explain the effects of pre-reduction. 

Why is it necessary to perform pre-reduction before hydride generation ... 

Catalysts prepared by the wash-coating method were first used to check the reproduction of the measured values. For this reason, six elementary metal salts (platinum, zirconium, molybdenum, nickel, silver, and rhodium) were dissolved and impregnated onto a titer-plate. The catalysts were pre-reduced inside the reactor with 5% hydrogen in 95% nitrogen at 250 °C. The results were recorded first before the pre-reduction and then after the pre-reduction. The repeated measurements indicated good reproducibility in both cases. The conversion of methane with the rhodium catalyst is better after the pre-reduction. Methane conversion after 18 h runtime was still stable. 

In the literature, higher values for the activation energy are also found [82, 83]. One reason for this could be the neglect of a pre-reduction of the platinum catalyst and also the low porosity of the sputtered catalyst. Another possibly important aspect is that here we actually measured intrinsic kinetic data compared with the diffusion-affected kinetic data in refs. [82] and [83]. 

With the instant McMurry reaction time can be saved. This is important, particularly since the pre-reduction doesn t take place as once believed ... 

J. L. Burguera, P. Carrero, M. Burguera, C. Rondon, M. R. Brunette, P. Gallignani, Flow injection for the determination of Se(IV) and Se(VI) by hydride generation atomic absorption spectrometry with microwave oven on-line pre-reduction of Se(VI) to Se(IV), Spectrochim. Acta, 51B (1996), 1837-1847. 

Pre-Reduction of Carbonyl Groups with Lithium Aluminum Hydride (Note I)... 

Some of the very first studies dealing with the CO interaction with ceria supported noble metal catalysts consisted of TPD-MS experiments carried out on powdered Pt/Ce02 catalysts (149,330). By combining TPD studies of isotopically labelled O2 and CO species with XPS and IR spectroscopy, the authors were able to show that, as a function of the pre-reduction conditions, CO and CO2 might be inter-converted on their catalysts. 

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