Quantitative in situ X-ray diffraction in combination with catalytic tests in dry reforming of methane (DRM) has been performed to unveil the strong structural dynamics of LaNiO 3 catalysts during the DRM reaction. Structure−activity correlations reveal polymorphic changes of the rhombohedral LaNiO 3 structure first into cubic LaNiO 3 and further into transient oxygen-deficient triclinic LaNiO 2.7 and monoclinic LaNiO 2.5 . These changes occur up to 620 °C and already cause considerable DRM activity. Another intermediate structure, the Ruddlesden−Popper phase La 2 NiO 4 with moderate DRM activity, is formed in parallel with the decomposition of monoclinic LaNiO 2.5 . The decay of La 2 NiO 4 directly goes along with the appearance of crystalline metallic Ni and monoclinic La 2 O 2 CO 3 and a drastic enhancement of DRM activity. The formation of monoclinic La 2 O 2 CO 3 and decomposition of La 2 NiO 4 proceed exactly alike up to 670 °C with the accumulation of metallic Ni. At 670 °C and up to 750 °C, monoclinic La 2 O 2 CO 3 is directly transformed into hexagonal La 2 O 2 CO 3 , and no further Ni exsolution is observed. Only above 750 °C, hexagonal La 2 O 3 is observed and apparently formed directly from a drastically accelerated decomposition of monoclinic La 2 O 2 CO 3 alongside another small increase in metallic Ni. Our direct structure−activity correlation unambiguously shows that the active phase in DRM is a mixture of metallic Ni in contact with monoclinic La 2 O 2 CO 3 . The roles of the latter phase are twofold: acting as the CO 2 -activated species and stabilizing the metallic Ni particles. Naturally, this implies a perfect carbon removal ability of the metallic Ni/La 2 O 2 CO 3 interface, which directly relates to an enhanced coking resistance and, most probably, long term stability. Heating LaNiO 3 in hydrogen yields a similar sequence of structural transformations with the striking difference of the missing transient La 2 NiO 4 structure, corroborating its crucial role in the formation of the DRM-active Ni/monoclinic La 2 O 2 CO 3 interface. The final structural fate is a metallic Ni/hexagonal La 2 O 3 phase mixture. Exemplified for the DRM reaction and the initial LaNiO 3 structure, only the knowledge about the sheer complexity of the structural dynamics allows the unequivocal assignment of participating structures and phases to their respective catalytic performance, and therefore, allows definite conclusions about the formation and the properties of the final active phase.

A 5% Ni/MnO catalyst has been tested for the dry reforming of methane at different temperatures and reactant partial pressures. Changing the reactant ratio with time on stream results in a decrease in the deactivation rate of the catalyst. Graphitic carbon growth and metal particle sintering have been observed by applying in situ transmission XRD using synchrotron radiation under actual reaction conditions. Both methane and carbon monoxide separately result in graphitic surface carbon, which can then be oxidized by carbon dioxide. The morphology of the surface carbon has been analyzed by TEM, and the reactions of both methane and carbon monoxide result in the same graphitic multiwalled carbon nanotubes. The present combination of catalytic experiments and in situ techniques suggests that surface carbon acts as an intermediate in the formation of CO and that catalyst deactivation happens via metallic particle sintering. These results enable a more rational choice of reaction conditions to ensure high catalyst activity and long-term stability. Future catalyst advances must aim to prevent metal particle sintering.

A dependence of structural transformation and iron exsolution on chemical environment and reducing conditions is proven for the perovskite La0.6Sr0.4FeO3−δ.

C‐saturated Pd0 nanoparticles with an extended phase boundary to ZrO2 evolve from a Pd0Zr0 precatalyst under CH4 dry reforming conditions. This highly active catalyst state fosters bifunctional action: CO2 is efficiently activated at oxidic phase boundary sites and PdxC provides fast supply of C‐atoms toward the latter.