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An in situ spatially resolved method to probe gas phase reactions through a fixed bed catalyst

A new method to spatially probe heterogeneously catalysed reactions within a packed bed of catalyst has been developed. The spatial resolution is achieved using a stationary perforated capillary coupled to a mass spectrometer while the catalyst bed is moved. The oxidation of CO promoted by H2 over a Pd catalyst has been used to demonstrate the technique.

The benefit of this technique is that it provides information on the concentration of reactants and products through a catalyst bed as the conversion increases from zero at the inlet of the bed. Much more information can be obtained using this new equipment than is possible from a conventional inlet analysis (of the reactants) and an outlet analysis (of the final products).

The procedure whereby the catalyst reactor (catalyst bed) is moved with respect to the fixed capillary is shown below with a photograph of the reactor and a schematic showing the dimensions.

Using this equipment, we can follow the progressive reaction of CO through the catalyst bed, as shown in Figure 1. the catalyst bed is represented by the yellow box.



Figure 1. Gas profile of CO oxidation through the catalyst bed at 250 °C; CO (red), O2 (blue) and CO2 (green).


The different profiles observed at temperatures in the range 150 to 300 °C are shown in Figure 2.

Figure 2. Gas profile of CO oxidation through the catalyst bed at different temperatures: 150 °C (light blue), 200 °C (purple), 225 °C (green), 250 °C (red) and 300 °C (blue).



The technique allows us to monitor the conversion of both CO and H2 at 250 °Cwhen the CO is oxidised in the presence of H2, as shown in Figure 3.

Note the difference with Figure 1 and how the addition of H2 accelerates the oxidation of CO..

Figure 3. Conversions of CO, H2 and O2and the yield of CO2 for CO oxidation in the presence of H2: CO conversion (green), H2 conversion (red), O2 conversion (purple), CO2 yield (blue)



The results demonstrate the capacity of this manual instrument to provide additional important information regarding the mechanism of reactions over packed bed powdered catalysts and the benefits of the technique as compared with conventional end of pipe measurements.  Such spatial information has not been previously demonstrated using this probe technique. These sets of experiments have proved the concept of spatially resolved concentration profiles using such instrumentation and future work will focus on optimisation of the system and the incorporation of other spectroscopic techniques.

This work has been accepted for publication: Jamal Touitou, Kevin Morgan ,Robbie Burch, Christopher Hardacre and Alexandre Goguet*, Catalysis Science and Technology (2012), DOI:10.1039/C2CY20141K.