Single‐phase ZnPd with different elemental composition as well as ZnO‐supported ZnPd nanoparticles were prepared and tested concerning their catalytic properties in the formic acid decomposition with the aim to investigate a possible formate pathway in the steam reforming of methanol (MSR). Pd‐rich ZnPd showed higher catalytic activity than ZnPd with lower Pd content. All samples showed high and stable CO2 selectivity. The stability of the materials was investigated both ex situ by powder X‐ray diffraction (XRD), scanning electron microscopy (SEM), and Raman spectroscopy after formic acid decomposition as well as by in situ X‐ray photoelectron spectroscopy (in situ XPS) and operando differential thermal analysis–thermogravimetry (DTA/TG). Samples with higher Pd content exhibited higher stability against oxidation, corroborating earlier observations under MSR conditions. The supported ZnPd/ZnO material and Zn‐rich bulk ZnPd samples showed a strong modification after reaction, which is attributed to zinc formate formation during formic acid decomposition. Kinetic data give strong indications to exclude dehydrogenation of a formate intermediate as rate‐limiting step in MSR.
A combined approach of grazing incidence X-ray diffraction (GIXRD) and X-ray reflectivity (XRR) under in operando conditions on polycrystalline materials is presented. This approach allows tracking of material changes of amorphous or crystalline nature in the nearsurface region. Crystalline phases formed in operando can be identified by X-ray diffraction, while by XRR measurements information about the thickness and the density of overlayers is obtained. The setup also allows collection of data generated with higher incident angles which permit a direct comparison of the changes close to the surface and in
The intermetallic compound ZnPd has demonstrated excellent catalytic properties in methanol steam reforming. While it is known that defects and microstructures influence the catalytic properties, little is known about the defects occurring in ZnPd. Due to recent advances in synthetic methods, coarse-grained ZnPd samples are accessible. This enables the detection and investigation of twinning in ZnPd by studying the twinned regions from the macroscopic scale by polarised light and electron backscattering diffraction (EBSD) down to the atomic scale by high-resolution transmission electron microscopy (HR-TEM). Twinning occurs in {101} and is coupled with a change in the c/a ratio in the vicinity of the twin boundary. Quantum chemical calculations result in only very small energy differences between the ideal and the twinned structure, explaining the experimentally observed thermal stability of the latter. The chemical bonding was investigated by the electron localizability indicator (ELI) and compared to the one in the ideal structure. The results confirm twinning along the {101} plane and demonstrate the high stability of the twin boundaries after formation.
Comparability of information gathered by different methods is vital to enhance knowledge in heterogeneous catalysis. A new type of flow-reactor has been developed which enables the comparison between the detailed information gained by surface science methods and industrial catalysis, thus contributing to bridge the pressure and material gaps. The design allows for catalytic investigations of compact, low-surface area materials at temperatures and pressures up to 500 °C and 10 bar, respectively. Catalytic measurements on pressed pills of Pd11Bi2Se2 in the semi-hydrogenation of acetylene and oriented single-crystalline slabs of InPd in methanol steam reforming are used as test cases for the reactor design. In the former, high-conversion of acetylene is demonstrated along with ensured inert sample transfer. In the latter, higher catalytic activity for the (110) surface is observed compared to the (100) and (111) surfaces. Most importantly, both test cases prove the viability of the reactor design, which opens new possibilities for studying different materials and systems.
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