Substitution of Copper by Magnesium in Malachite: Insights into the Synthesis and Structural Effects.

The phase width of the copper hydroxycarbonate malachite, CuCO(OH), upon substitution with magnesium has been studied in detail. In extension of a previous study on amorphous precursors, the introduction of a hydrothermal aging step allowed the retrieval of crystalline hydroxycarbonate samples with up to 37 atom % Mg (metal content) that are suitable candidates as precursors to Cu/MgO catalysts for CO hydrogenation. Simultaneous refinements of X-ray powder diffraction and pair distribution function (PDF) data as well as complementary spectroscopic insight (X-ray absorption and infrared spectroscopy) revealed that samples with up to 18 atom % Mg are phase-pure magnesian malachites but the magnesium content can be increased beyond this threshold when mcguinnessite (CuMgCO(OH)) is accepted as a side phase.

Hard X-ray-based techniques for structural investigations of CO methanation catalysts prepared by MOF decomposition.

Thermal decomposition of metal-organic framework (MOF) precursors is a recent method to create well-dispersed metal centers within active catalyst materials with enhanced stability, as required for dynamic operation conditions in light of challenges caused by the renewable energy supply. Here, we use a hard X-ray-based toolbox of pair distribution function (PDF) and X-ray absorption spectroscopy (XAS) analysis combined with X-ray diffraction and catalytic activity tests to investigate structure-activity correlations of methanation catalysts obtained by thermal decomposition of a Ni(BDC)(PNO) MOF precursor. Increasing the decomposition temperature from 350 to 500 °C resulted in Ni nanoparticles with increasing particle sizes, alongside a decrease in Ni species and strain-induced peak broadening.

Pushing data quality for laboratory pair distribution function experiments.

Over the last decade, some studies with laboratory pair distribution function (PDF) data emerged. Yet, limited Q or instrumental resolution impeded in-depth structural refinements. With more advanced detector technologies, the question arose how to design novel PDF equipment for laboratories that will allow decent PDF refinements over r = 1-70 Å.