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Abstract: We report a systematic study of the 5 d -electron-doped system Ce ( Fe 1 − x Ir x ) 2 Al 10 ( 0 ≤ x ≤ 0.15 ) . With increasing x , the orthorhombic b axis decreases slightly while accompanying changes in a and c leave the unit cell volume almost unchanged. Inelastic neutron scattering, along with thermal and transport measurements, reveal that for the Kondo semiconductor CeFe 2 Al 10 , the low-temperature energy gap, which is proposed to be a consequence of strong c − f hybridization, is suppressed by a small amount of Ir substitution for Fe and that the system adopts a metallic ground state with an increase in the density of states at the Fermi level. The charge or transport gap collapses (at x = 0.04 ) faster than the spin gap with Ir substitution. Magnetic susceptibility, heat capacity, and muon spin relaxation measurements demonstrate that the system undergoes long-range antiferromagnetic order below a Néel temperature T N of 3.1(2) K for x = 0.15 . The ordered moment is estimated to be smaller than 0.07(1) μ B /Ce, although the trivalent state of Ce is confirmed by Ce L 3 -edge x-ray absorption near edge spectroscopy. It is suggested that the c − f hybridization gap, which plays an important role in the unusually high ordering temperatures observed in Ce T 2 Al 10 ( T = Ru and Os), may not be necessary for the onset of magnetic order with a low T N seen here in Ce ( Fe 1 − x Ir x ) 2 Al 10 .

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Abstract: Extended X-ray absorption fine structure (EXAFS) and X-ray Pair Distribution Function (XPDF) analysis are versatile complementary techniques that provide information about local structure and bonding in crystalline and non-crystalline materials. Both techniques provide information about the coordination number of neighbouring atoms, bond distances and the degree of static/thermal disorder. EXAFS is a well-established element-specific method that provides short-range order information around the X-ray absorber of interest. XPDF is not element-specific, but provides short-range order information similar to EXAFS, alongside long- range structure. Calcium methoxide (Ca(OCH3)2) is one of the prominent heterogeneous catalysts that are being used in the formation of sustainable biolubricants and biodiesel from natural/synthetic oils via transesterification. Other compounds that have been considered as viable catalysts include calcium oxide (CaO) and calcium hydroxide (Ca(OH)2). Unlike these two bases, which have been comprehensively characterised using EXAFS, the short-range crystalline structure of Ca(OCH3)2 is yet to be fully determined. Not much is known about its structure beyond the indication that it has the same hexagonal space group (P-3m1) as Ca(OH)2. This was determined over 40 years ago, using powder X-ray diffraction and mid infrared spectroscopy, and has not been investigated since. Hence, we present a comparative study on the local structure of CaO, Ca(OH)2 and Ca(OCH3)2 using EXAFS and XPDF analysis. Our results demonstrate how a new/refined model crystal Ca(OCH3)2 structure was obtained using XPDF data, crystal symmetry and unit cell dimensions. This model was subsequently used in EXAFS simulations to determine atom coordination numbers, bond distances and static disorder in Ca(OCH3)2. To the best of our knowledge, this is the first time EXAFS and XPDF data has been presented on a calcium alkoxide. The structural information obtained from this study could benefit development of more sophisticated alkoxide-based heterogenous catalysts. This multi-technique ex situ analysis of the three basic calcium catalysts could also inform operando studies of alkaline-earth metal catalysis with these techniques.

Open Access

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Abstract: P2-layered sodium-ion battery (NIB) cathodes are a promising class of Na-ion electrode materials with high Na+ mobility and relatively high capacities. In this work, we report the structural changes that take place in P2–Na0.67[Mg0.28Mn0.72]O2. Using ex situ X-ray diffraction, Mn K-edge extended X-ray absorption fine structure, and 23Na NMR spectroscopy, we identify the bulk phase changes along the first electrochemical charge–discharge cycle—including the formation of a high-voltage “Z phase”, an intergrowth of the OP4 and O2 phases. Our ab initio transition state searches reveal that reversible Mg2+ migration in the Z phase is both kinetically and thermodynamically favorable at high voltages. We propose that Mg2+ migration is a significant contributor to the observed voltage hysteresis in Na0.67[Mg0.28Mn0.72]O2 and identify qualitative changes in the Na+ ion mobility.

Open Access

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Abstract: Platinum group metals (PGM) such as palladium and rhodium based catalysts are currently being implemented in Gasoline Particulate Filter (GPF) autoexhaust aftertreatment systems. However, little is known about how the trapped particulate matter, such as the incombustible ash, interacts with the catalyst and so may affect its performance. This operando study follows the evolution of the Pd found in two different model GPF systems: one containing ash components extracted from a GPF and another from a catalyst washcoat prior to adhesion onto the GPF. We show that the catalytic activity of the two systems vary when compared with a 0 g ash containing GPF. Compared to the 0 g ash sample the 20 g ash containing sample had a higher CO light off temperature, in addition, an oscillation profile for CO, CO2 and O2 was observed, which is speculated to be a combination of CO oxidation, C deposition via a Boudouard Reaction and further partial oxidation of the deposited species to CO. During the ageing procedure the washcoat sample reduces NO at a lower temperature than the 0 g ash sample. However, post ageing the 0 g ash sample recovers and both samples reduce NO at 310 circleC. In comparison, the 20 g ash GPF sample maintains a higher NO reduction temperature of 410 circleC post ageing, implying that the combination of high temperature ageing and presence of ash has an irreversible negative effect on catalyst performance.

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Abstract: Synthesizing atomically dispersed synergistic active pairs is crucial yet challenging in developing highly active heterogeneous catalysts for various industrially important reactions. Here, a single molecular Re species is immobilized on the inner surface of a Y zeolite with Brønsted acid sites (BASs) within atomic proximity to form Re OMS–BAS active pairs for the efficient catalysis of olefin metathesis reactions (OMS: olefin metathesis site). The synergy within the active pairs is revealed by studying the coadsorption geometry of the olefin substrates over the active pairs by synchrotron X-ray and neutron powder diffraction. It is shown that the BAS not only facilitates olefin adsorption but also aligns the olefin molecule to the Re OMS for efficient intermediate formation. Consequently, for the cross-metathesis of ethene and trans-2-butene to propene, this catalyst shows high activity under mild reaction conditions without observable deactivation. The catalyst outperforms not only traditional ReOx-based catalysts but also the best industrially applicable WOx-based catalyst thus far that we discovered previously. The concept of using two isolated active sites of different functionalities within atomic proximity in a confined cavity can provide opportunities for designing synergistically catalytic materials.