Temperature-programmed reduction characteristics

In temperature-programmed reduction (TPR), a flow of inert gas (N2 or Ar) containing approximately 5 vol% H2 is passed through the catalyst bed of a flow reactor containing a reducible solid catalyst (66). By monitoring continuously the H2 concentration in the gas flow and its eventual consumption with a thermal conductivity detector when heating the sample with a linear temperature ramp of ca. 10 K/min, the rates of reduction are obtained as a function of time (or temperature). The total amount of H2 consumed determines the reduction equivalents present in the catalyst, and detailed analysis of the experiment permits the kinetic parameters of the reduction process to be determined and provides information on the reduction mechanisms. The characteristic numbers, which depend on the experimental parameters (amount of reducible species present, H2 concentration, flow rate, and temperature ramp), have been defined (66,67). These numbers must be kept in certain ranges for optimal performance of the experiment. 

Another method of analysis makes use of a subtraction procedure and has been applied to investigate the oxidation state of a series of Ce-Zr mixed oxides during a temperature programmed process [195]. A difference spectrum between the sample at a defined state and the calcined, fully oxidized material displays a positive peak at the position of feature Bo, characteristic of Ce, and a negative peak at the position of feature C, characteristic of Ce. The overall peak-to-peak amplitude is then proportional to the average reduction degree of Ce in the sample. 

In this work the hydrogenolysis of ethyl laurate (EL) to dodecanol (ROH) and ethanol has been studied on different Ru-Sn/ALOs catalysts. Systematic studies have been made to investigate the influence of precursor compounds, sequence of impregnation, metal loading, Sn Ru atomic ratio, catalyst pretreatment (calcination, reduction) and reaction conditions (temperature, H2 pressure). The calcined catalysts were characterized by Ten erature Programmed Reduction (TPR). Correlation between the activity and TPR characteristics of Ru-Sn/Al203 catalysts was also demonstrated. 

The three different data sets produce extreme differences In the temperature factors (Table VIII). This difference Is not characteristic of just the SRRC program, as a similar range for cellulose Is In the literature. The temperature factor (B) Is Important because It Indicates systematic error In the Lp correction or other aspect of data gathering and reduction, for at least two of the data sets. Negative temperature factors, as found In the WS data, typically Indicate either that additional atoms, such as water molecules, are needed In the structure, or, when that Is known to be Incorrect, that there Is a flaw In some overall aspect of Intensity measurement, such as background correction. 

According to the characteristic performances of ZA-5 catalyst, the reduction process should introduce the following conditions High space velocity, high content of H2, low temperature, low water vapor concentration, and the appropriate pressure. Recommended reducing program is shown in Table 5.13. 

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