The dry reforming of methane (DRM), i.e., the reaction of methane and CO to form a synthesis gas, converts two major greenhouse gases into a useful chemical feedstock. In this work, we probe the effect and role of Fe in bimetallic NiFe dry reforming catalysts. To this end, monometallic Ni, Fe, and bimetallic Ni-Fe catalysts supported on a MgAlO matrix derived via a hydrotalcite-like precursor were synthesized. Importantly, the textural features of the catalysts, i.e., the specific surface area (172-178 m/g), pore volume (0.51-0.66 cm/g), and particle size (5.4-5.8 nm) were kept constant. Bimetallic, NiFe with Ni/(Ni + Fe) = 0.8, showed the highest activity and stability, whereas rapid deactivation and a low catalytic activity were observed for monometallic Ni and Fe catalysts, respectively. XRD, Raman, TPO, and TEM analysis confirmed that the deactivation of monometallic Ni catalysts was in large due to the formation of graphitic carbon. The promoting effect of Fe in bimetallic Ni-Fe was elucidated by combining operando XRD and XAS analyses and energy-dispersive X-ray spectroscopy complemented with density functional theory calculations. Under dry reforming conditions, Fe is oxidized partially to FeO leading to a partial dealloying and formation of a Ni-richer NiFe alloy. Fe migrates leading to the formation of FeO preferentially at the surface. Experiments in an inert helium atmosphere confirm that FeO reacts via a redox mechanism with carbon deposits forming CO, whereby the reduced Fe restores the original Ni-Fe alloy. Owing to the high activity of the material and the absence of any XRD signature of FeO, it is very likely that FeO is formed as small domains of a few atom layer thickness covering a fraction of the surface of the Ni-rich particles, ensuring a close proximity of the carbon removal (FeO) and methane activation (Ni) sites.

Calcium looping, a CO2 capture technique, may offer a mid-term if not near-term solution to mitigate climate change, triggered by the yet increasing anthropogenic CO2 emissions. A key requirement for the economic operation of calcium looping is the availability of highly effective CaO-based CO2 sorbents. Here we report a facile synthesis route that yields hollow, MgO-stabilized, CaO microspheres featuring highly porous multishelled morphologies. As a thermal stabilizer, MgO minimized the sintering-induced decay of the sorbents’ CO2 capacity and ensured a stable CO2 uptake over multiple operation cycles. Detailed electron microscopy-based analyses confirm a compositional homogeneity which is identified, together with the characteristics of its porous structure, as an essential feature to yield a high-performance sorbent. After 30 cycles of repeated CO2 capture and sorbent regeneration, the best performing material requires as little as 11 wt.% MgO for structural stabilization and exceeds the CO2 uptake of the limestone-derived reference material by ~500%.

CO2 capture and storage (CCS) is a technological solution to stabilize or even reduce the atmospheric concentration of the greenhouse gas CO2, to mitigate climate change. In this context, MgO is a promising solid CO2 sorbent, as the energy penalty sorbent regeneration is comparatively small, but it requires the addition of promoters, typically alkali metal nitrates, to yield acceptable kinetics. Under operating conditions, the promoters are in a molten state. The main objectives of this work are (i) to assess experimentally the validity of different reaction mechanisms for the CO2 uptake of promoted MgO that are currently debated in literature and (ii) to elucidate the processes that lead to sorbent deactivation. Our experimental results support the mechanism in which the dissolution of MgO in the molten nitrate promoter is the rate-limiting step for carbonation. We were able to establish a direct correlation between the solubility of MgO in the promoter and the initial rate of carbonation. In addition, a systematic study of a large number of promoter compositions (mixtures of LiNO3, NaNO3, KNO3) indicate that promoters with a lower melting point exhibit higher CO2 uptakes, presumably due to their lower viscosity and, thus, higher ion mobility at a given temperature. Concerning the cyclic stability of promoted MgO, a decay of its CO2 uptake with number of carbonation/calcination cycles is ascribed only partially to sintering. Instead, the surface migration of the promoter was identified as an at least equally relevant deactivation mechanism. Importantly, it was also found that the CO2 uptake of the deactivated sorbent can be restored to a large extent with a simple hydration step.

CO capture and storage is a promising concept to reduce anthropogenic CO emissions. The most established technology for capturing CO relies on amine scrubbing that is, however, associated with high costs. Technoeconomic studies show that using CaO as a high-temperature CO sorbent can significantly reduce the costs of CO capture. A serious disadvantage of CaO derived from earth-abundant precursors, e.g., limestone, is the rapid, sintering-induced decay of its cyclic CO uptake. Here, a template-assisted hydrothermal approach to develop CaO-based sorbents exhibiting a very high and cyclically stable CO uptake is exploited. The morphological characteristics of these sorbents, i.e., a porous shell comprised of CaO nanoparticles coated by a thin layer of Al O (<3 nm) containing a central void, ensure (i) minimal diffusion limitations, (ii) space to accompany the substantial volumetric changes during CO capture and release, and (iii) a minimal quantity of Al O for structural stabilization, thus maximizing the fraction of CO -capture-active CaO.

This study presents the design, fabrication, and testing of biodegradable magnesium/iron batteries featuring polycaprolactone (PCL) as a packaging and functional material. The use of PCL encapsulation minimized the electrochemical cell volume and supported longer discharge lifetimes and higher discharge rates than state-of-the-art biodegradable batteries. Specifically, the electrodes were separated and insulated by a 5 µm-thick PCL layer that served as both a battery packaging material and a permeable coating for physiological solution to penetrate and activate the battery. A systematic investigation of the electrode size, discharge rates, electrolyte selection, and polymeric coating revealed the critical reactions and phenomena governing the performance of the Mg-based biodegradable batteries. Comparison with previous reports on biodegradable batteries and medical-grade non-degradable lithium-ion batteries demonstrated the superior performance of PCL-coated Mg/Fe batteries at these size scales, which exhibited an energy density of 694 Wh kg−1 and a total volume of 0.02 cm3.

Operando X-ray absorption spectroscopy (XAS) associates the superior activity and stability of the In 2 O 3 /m-ZrO 2 catalyst for the direct hydrogenation of CO 2 to methanol (300 °C, 20 bar) to indium sites with an average oxidation state of +2.3 atomically dispersed in the lattice of monoclinic ZrO 2 . The active sites in this solid solution m-ZrO 2 :In catalyst are In−V o −Zr sites (V o is an oxygen vacancy) that are stabilized in the lattice of poorly reducible m-ZrO 2 against deactivation by over-reduction to In 0 . In contrast, the amorphous ZrO 2 support does not form a (crystalline) solid solution with In 2 O 3 and, as a result, In 2 O 3 /am-ZrO 2 reduces to metallic In within minutes under the reaction conditions. Furthermore, a tetragonal ZrO 2 support stabilizes dispersed india nanocrystals (In 2 O 3 /t-ZrO 2 ) against over-reduction only partially, yielding a catalyst with an average oxidation state of the In sites below +2: i.e., In 2 O 3 /t-ZrO 2 also suffers deactivation by over-reduction. Our results demonstrate that the phase of the ZrO 2 support determines whether an active solid solution with india forms, which has major implications for the reducibility of In 3+ sites and their local structure. Comparing the stability and activity of india-based catalysts, we identified the monoclinic solid solution m-ZrO 2 :In as a superior catalyst for the direct conversion of CO 2 to methanol, which contains active In−V o −Zr surface species that are significantly more stable toward reduction than In−V o −In sites in bixbyite-type In 2 O 3 .

Allosteric mechanism of proteins is essential in biomolecular signaling. An important aspect underlying this mechanism is the communication pathways connecting functional residues. Here, a Monte Carlo (MC) path generation approach is proposed and implemented to define likely allosteric pathways through generating an ensemble of maximum probability paths. The protein structure is considered as a network of amino acid residues, and inter-residue interactions are described by an atomistic potential function. PDZ domain structures are presented as case studies. The analysis for bovine rhodopsin and three myosin structures are also provided as supplementary case studies. The suggested pathways and the residues constituting the pathways are maximally probable and mostly agree with the previous studies. Overall, it is demonstrated that the communication pathways could be multiple and intrinsically disposed, and the MC path generation approach provides an effective tool for the prediction of key residues that mediate the allosteric communication in an ensemble of pathways and functionally plausible residues. The MCPath server is available at http://safir.prc.boun.edu.tr/clbet_server.

A key challenge in the catalytic conversion of CH 4 and CO 2 into a synthesis gas (CO and H 2 ) via the dry reforming of methane (DRM) is the development of stable catalysts. We demonstrate that the reductive exsolution of metallic Ru from fluorite-type solid solutions Sm 2 Ru x Ce 2−x O 7 (x = 0, 0.1, 0.2, 0.4) yields catalysts with high activity and remarkable stability for the DRM. The catalysts feature Ru(0) nanoparticles about 1−2 nm in diameter that are uniformly dispersed on the surface of the resulting oxide support. The exsolved material was investigated by synchrotron X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS at Ru, Sm, and Ce K-edges), Raman spectroscopy, and transmission electron microscopy. In situ XAS-XRD experiments revealed that the exsolution of metallic ruthenium is accompanied by a rearrangement of the oxygen vacancies within the lattice. The catalysts derived through exsolution outperform (stable over 4 days) the reference catalysts prepared by wetness impregnation and sodium borohydride reduction. The superior performance of the exsolved catalysts is explained by their high resistance to sintering-induced deactivation owing to the stabilizing metal−support interaction in this class of materials. It is also demonstrated that the Ru nanoparticles can undergo redissolution (in air at 700 °C)−exsolution cycles.