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In situ Mo K-edge X-ray absorption spectroscopy reveals different carburization pathways for unsupported and supported MoO3 yielding Mo2C and Mo2C/SiO2. Mo2C/SiO2 features higher resistance to oxidation under dry reforming of methane than Mo2C.

Molybdenum carbide (β-Mo2C) supported on carbon spheres was prepared via a carbothermal hydrogen reduction (CHR) method from delaminated nanosheets of molybdenum(vi) oxide (d-MoO3/C). The carburization process was followed by combined in situ XANES/XRD analysis revealing the formation of molybdenum oxycarbide Mo2CxOy as an intermediate phase during the transformation of d-MoO3/C to β-Mo2C/C. It was found that Mo2CxOy could not be completely carburized to β-Mo2C under a He atmosphere at 750 °C, instead a reduction in H2 is required. The β-Mo2C/C obtained showed activity and stability for the dry reforming of methane at 800 °C and 8 bar. In situ XANES/XRD evaluation of the catalyst under DRM reaction conditions combined with high resolution TEM analysis revealed the evolution of β-Mo2C/C to Mo2CxOy/C. Notably, the gradual oxidation of β-Mo2C/C to Mo2CxOy/C correlates directly with the increased activity of the competing reverse water gas shift reaction., Nanoscale, 12 (24), ISSN:2040-3364, ISSN:2040-3372

Calcium looping (CaL) is a CO2 capture technique based on the reversible carbonation/calcination of CaO that is considered promising to reduce anthropogenic CO2 emissions. However, the rapid decay of the CO2 uptake of CaO over repeated cycles of carbonation and calcination due to sintering limits its implementation at the industrial scale. Thus, the development of material design strategies to stabilize the CO2 uptake capacity of CaO is paramount. The addition of alkali metal salts to CaO has been proposed as a strategy to mitigate the rapid loss of its cyclic CO2 uptake capacity. However, there are conflicting results concerning the effect of the addition of alkali metal carbonates on the structure and CO2 capacity of CaO. In this work, we aim at understanding the effect of the addition of Na2CO3 to CaO on the sorbent's structure and its CO2 uptake capacity. We demonstrate that under industrially-relevant conditions the addition of as little as 1 wt% of Na2CO3 reduces severely the CO2 uptake of CaO. Combining TGA, XAS and FIB-SEM analysis allowed us to attribute the performance degradation to the formation of the double salt Na2Ca(CO3)2 that induces strong sintering leading to a significant loss in the sorbent's pore volume. In addition, during the carbonation step the formation of a dense layer of Na2Ca(CO3)2 that covers unreacted CaO prevents its full carbonation to CaCO3. ISSN:1463-9084 ISSN:1463-9076

Industrial & Engineering Chemistry Research, 59 (15), ISSN:1520-5045, ISSN:0888-5885

MXenes, a recently discovered family of two-dimensional (2D) materials, are promising catalysts and supports for applications in heterogeneous catalysis; however, the thermal stability of MXenes an...

Calcium looping (CaL) is a CO2 capture technique based on the reversible carbonation/calcination of CaO that is considered promising to reduce anthropogenic CO2 emissions. However, the rapid decay of the CO2 uptake of CaO over repeated cycles of carbonation and calcination due to sintering limits its implementation at the industrial scale. Thus, the development of material design strategies to stabilize the CO2 uptake capacity of CaO is paramount. The addition of alkali metal salts to CaO has been proposed as a strategy to mitigate the rapid loss of its cyclic CO2 uptake capacity. However, there are conflicting results concerning the effect of the addition of alkali metal carbonates on the structure and CO2 capacity of CaO. In this work, we aim at understanding the effect of the addition of Na2CO3 to CaO on the sorbent's structure and its CO2 uptake capacity. We demonstrate that under industrially-relevant conditions the addition of as little as 1 wt% of Na2CO3 reduces severely the CO2 uptake of CaO. Combining TGA, XAS and FIB-SEM analysis allowed us to attribute the performance degradation to the formation of the double salt Na2Ca(CO3)2 that induces strong sintering leading to a significant loss in the sorbent's pore volume. In addition, during the carbonation step the formation of a dense layer of Na2Ca(CO3)2 that covers unreacted CaO prevents its full carbonation to CaCO3.

Molybdenum carbide (β-Mo

Carbon dioxide capture and storage (CCS) is a promising approach to reduce anthropogenic CO2 emissions and mitigate climate change. However, the costs associated with the capture of CO2 using the currently available technology, that is, amine scrubbing, are considered prohibitive. In this context, the so-called calcium looping process, which relies on the reversible carbonation of CaO, is an attractive alternative. The main disadvantage of naturally occurring CaO-based CO2 sorbents, such as limestone, is their rapid deactivation caused by thermal sintering. Here, we report a scalable route based on wet mechanochemical activation to prepare MgO-stabilized, CaO-based CO2 sorbents. We optimized the synthesis conditions through a fundamental understanding of the underlying stabilization mechanism, and the quantity of MgO required to stabilize CaO could be reduced to as little as 15 wt %. This allowed the preparation of CO2 sorbents that exceed the CO2 uptake of the reference limestone by 200 %.

Chemical looping is a promising process to produce high purity H2 while simultaneously capturing CO2. The key requirement for this process is the availability of oxygen carriers that possess a high cyclic redox stability, resistance to carbon deposition, and thermal sintering. In this study, ZrO2-supported Fe2O3-based oxygen carriers were developed using a coprecipitation technique. We assess in detail the influence of the key synthesis parameter, i.e., the pH value at which the precipitation was performed, on the morphological properties, chemical composition, local structure, and cyclic redox stability. The performance of the new oxygen carriers was compared to unsupported Fe2O3 and Al2O3-supported Fe2O3. A higher degree of disorder in the local structure of oxygen carriers precipitated at low pH values was confirmed by X-ray absorption spectroscopy (XAS) measurements. Electrical conductivity measurements showed that supporting Fe2O3 on ZrO2 lowered significantly the activation energy for charge transpo...

A flow-through method for measuring dissolution rates of cement minerals is described. The quantity of dissolved material is measured after the dissolution experiment from SEM-BSE images. This makes it possible to measure dissolution rates of individual phases in multiphase cements. The SEM images also directly show if precipitation (hydration) occurred and how the surface roughness changed during dissolution. Furthermore, the method is designed for the purpose of determining if dissolution rate is reaction- or diffusion-controlled, by changing water flow rate or by calculating expected diffusion fluxes. Dissolution rates of flat-ground Portland cement clinker and synthesized alite in deionized water were measured to demonstrate the potential of the method. Initial dissolution rates at lower flow rates were transport-controlled as indicated by the flow rate dependency and predicted diffusion fluxes. The highest alite dissolution rate measured in this study was 93 μmol/m 2 /s.

Highlights: Black-Right-Pointing-Pointer Homogeneity range for LaCr{sub 1-x}Mg{sub x}O{sub 3} with orthorhombic perovskite structure is x {

Chemical looping combustion (CLC) and chemical looping with oxygen uncoupling (CLOU) are emerging thermochemical CO2 capture cycles that allow the capture of CO2 with a small energy penalty. Here, the development of suitable oxygen carrier materials is a key aspect to transfer these promising concepts to practical installations. CuO is an attractive material for CLC and CLOU because of its high oxygen-storage capacity (20 wt %), fast reaction kinetics, and high equilibrium partial pressure of oxygen at typical operating temperatures (850-1000 °C). However, despite its promising characteristics, its low Tammann temperature requires the development of new strategies to phase-stabilize CuO-based oxygen carriers. In this work, we report a strategy based on stabilization by co-precipitated ceria (CeO2-x ), which allowed us to increase the oxygen capacity, coke resistance, and redox stability of CuO-based oxygen carriers substantially. The performance of the new oxygen carriers was evaluated in detail and compared to the current state-of-the-art materials, that is, Al2 O3 -stabilized CuO with similar CuO loadings. We also demonstrate that the higher intrinsic oxygen uptake, release, and mobility in CeO2-x -stabilized CuO leads to a three times higher carbon deposition resistance compared to that of Al2 O3 -stabilized CuO. Moreover, we report a high cyclic stability without phase intermixing for CeO2-x -supported CuO. This was accompanied by a lower reduction temperature compared to state-of-the-art Al2 O3 -supported CuO. As a result of its high resistance towards carbon deposition and fast oxygen uncoupling kinetics, CeO2-x -stabilized CuO is identified as a very promising material for CLC- and CLOU-based CO2 capture architectures.

Furthermore, deposition at such low temperatures is promising for processing of thin film assemblies. The preparation of bi-layer electrolytes of yttria stabilized zirconia and gadolinia doped ceria thin films by aerosol assisted chemical vapor deposition is demonstrated. Gadolinia doped ceria films as thin as 150 nm are applied as barrier layers between yttria stabilized zirconia electrolyte and La0.6Sr0.4CoO3–δ cathode in anode supported solid oxide fuel cells. High power densities above 850 mW cm–2 at 650 °C are only obtained with these barrier layers, indicating that the GDC thin films effectively inhibit the formation of unwanted interface reactions.