非表示:
キーワード:
-
要旨:
The efficient conversion of CO2 into chemicals and fuels is a prospective building block for a more sustainable usage of our global resources. Among the various strategies to convert CO2 into higher-energy intermediates, heterogeneously catalyzed processes are of special interest, because they are scalable, based on a mature and flexible technology, which is already applied in chemical industries, and can be integrated into existing value chains. The dry reforming of methane (DRM) with carbon dioxide is an interesting option to convert these two greenhouse gases into CO/H2 mixtures (eq. 1). The resulting gas mixture can then be used in the well-established downstream syngas chemistry.
(1) CO2 + CH4 ⟶ 2 CO + 2 H2 DH298 = 247 kJ mol-1
It is well known that Ru, Rh or Pt catalysts are very active in this reaction. Active base metals, in particular Ni, suffer from fast deactivation by coking. However, from an economical point of view Ni-based catalysts are more suitable for commercial application than noble metal ones. Thus, a current challenge is to find a noble metal-free catalyst that is resistant against coking.
We have found that mitigation of the coking problem of noble metal-free Ni catalyst for DRM is possible by elevating the operation temperature towards 900 °C. Compared to lower reaction temperatures, the formation of fibrous carbon was substantially lowered. This favorable operational window can be exploited only if nanostructured catalysts with sufficient thermal stability are available to survive these harsh conditions. We present the synthesis, characterization, and catalytic testing of a highly active and stable Ni/MgAlOx catalyst that is characterized by small Ni particles (10 nm), which are partially embedded in an oxide matrix with a high specific Ni and total BET surface area. Despite the high Ni loading of 55 wt.-%, this catalyst shows only minor sintering at 900 °C and performs stably in DRM over 100 hours with an outstanding high rate of syngas formation. The stability of the nanostructure is ascribed to the embedding nature of the oxide matrix as a result of the uniform elemental distribution within the layered double hydroxide (LDH) catalyst precursor.
