Temperature programmed carburization

Carburization was carried out in a fixed-b i stainlras strel reactor (ID = 6 mm). Typically about 0.5 g of metal sulphide was sandwiched between 2 layers of quartz wool placed centrally in a temperature-programmed furnace. iTie sample was heated at 10 Kmin" to the... 

As a result of fliese temperature - programmed runs, additiond experiments were conducted isothermally at temperatures between 723 - 873 K. Based on tbe second phase peak (peak 2), the conversion - time profiles at different temperatures exhibited a characteristic Sigmoid shape and may therefore be used to interpret the solid carburization kinetics. As detailed in Brown [5], the transient convrasion data may be d cribed by... 

Temperature-programmed reduction combined with x-ray absorption fine-structure (XAFS) spectroscopy provided clear evidence that the doping of Fischer-Tropsch synthesis catalysts with Cu and alkali (e.g., K) promotes the carburization rate relative to the undoped catalyst. Since XAFS provides information about the local atomic environment, it can be a powerful tool to aid in catalyst characterization. While XAFS should probably not be used exclusively to characterize the types of iron carbide present in catalysts, it may be, as this example shows, a useful complement to verify results from Mossbauer spectroscopy and other temperature-programmed methods. The EXAFS results suggest that either the Hagg or s-carbides were formed during the reduction process over the cementite form. There appears to be a correlation between the a-value of the product distribution and the carburization rate. 

In order to understand better these interesting systems without complications that might arise due to different preparation procedures, we compared oxygen-treated WC and Mo2C prepared by similar reduction/ carburization procedures from their respective oxides. The effects of pretreatment conditions were also studied. An attempt was made to correlate the kinetic behavior of these catalysts in n-hexane-H2 reactions with their physical properties obtained from X-ray diffraction (XRD), CO chemisorption, temperature-programed reaction (TPR) with flowing H2 or He, temperature programed desorption (TPD) of adsorbed NH3, and X-ray photoelectron spectroscopy (XPS). 

The reduced catalysts were carburized under either isothermal or temperature-programmed conditions at 1 atm. Unless otherwise stated, the carburizing gas was a mixture of H2 and CO (H2/CO = 3 by volume). 

Carburization in tubular reactor temperature programmed at 0jS2 K min i... 

Mass Increase Resulting from Carburization. The increase of mass of hydrogen-reduced catalyst B-6 during a 72-hour carburization experiment under partial nonisothermal conditions is shown in Figure 1. During the first four hours, the temperature was programmed to rise from 425 to 598 K at a constant heating rate, after which it was held constant at 598 K. 

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