Abstract
Time resolved oxidation and reduction cycles of ZrO2-supported Ni catalysts for dry reforming of CH4 (CO2 + CH4 ↔ 2 CO + 2 H2) during feed modulations have been studied. Under reaction conditions (1073 K) Ni remains fully reduced, whereas switching the feed gas to pure CO2 results in a slow (25 sec) formation of a stable NiO phase. When switching back to reaction conditions the NiO phase is rapidly reduced (∼ 1 sec) to metallic Ni. In the context of this study, a novel capillary cell has been built, allowing the parallel treatment of 5 catalyst samples with different gas compositions and different pressures. A comparison of the capillary cell to conventional systems regarding the spectral quality and the kinetic data shows that the capillary cell can be used to obtain identical kinetic data and high quality X-ray absorption spectra.
Highlights
Dry reforming of CH4 (CO2 + CH4 ↔ 2 CO + 2 H2) produces a synthesis gas with a H2/CO ratio close to one
The periodic treatment of a Ni/ZrO2 catalyst in CO2 is applicable for DRM, but there is no study on the influence of this treatment on the structural properties of the active metal published so far
Note that Ni shows the same degree of oxidation and the same coordination number after every cycle, which indicites that this procedure can be used to regenerate spent Ni catalysts, if the metalsupport interaction is sufficiently strong to prevent agglomeration
Summary
Dry reforming of CH4 (CO2 + CH4 ↔ 2 CO + 2 H2) produces a synthesis gas with a H2/CO ratio close to one. All data were recorded in transmission mode at the Ni K-edge at 8333 eV using a QEXAFS channel-cut Si(111) monochromator operated at an oscillation frequency of 2 Hz. All in situ X-ray absorption spectra were measured in a capillary made of quartz glass (1 mm diameter, 20 μm wall thickness, Hilgenberg), were the pressed catalyst was fixed with two plugs of quartz wool.
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