A cost-effective synthesis was used to grow ZnxCu1−xOy nanostructures. DFT calculations show that charge transfer along with changes in Fermi level facilitate H2 gas sensing, which is further enhanced by Zn doping.

h i g h l i g h t sSr and Ba are doped into the CaMnO 3 structure for enhanced phase stability and CLOU properties. Strontium dopant helps to prevent irreversible decomposition of the perovskite structure. Sr-doped oxygen carriers have CLOU capabilities at lower temperatures while being redox stable. Computational techniques, such as DFT, can potentially be used to guide oxygen carrier selection. a b s t r a c tOperated under a cyclic redox mode with an oxygen carrier, the chemical looping with oxygen uncoupling (CLOU) process offers the potential to effectively combust solid fuels while capturing CO 2 . Development of oxygen carriers capable of reversibly exchanging their active lattice oxygen (O 2À ) with gaseous oxygen (O 2 ) under varying external oxygen partial pressure (P O2 ) is of key importance to CLOU process performance. This article investigates the effect of A-site dopants on CaMnO 3 based oxygen carriers for CLOU. Both Sr and Ba are explored as potential dopants at various concentrations. Phase segregations are observed with the addition of Ba dopant even at relatively low concentrations (5% A-site doping). In contrast, stable solid solutions are formed with Sr dopant at a wide range of doping level. While CaMnO 3 perovskite suffers from irreversible change into Ruddlesden-Popper (Ca 2 MnO 4 ) and spinel (CaMn 2 O 4 ) phases under cyclic redox conditions, Sr doping is found to effectively stabilize the perovskite structure. In-situ XRD studies indicate that the Sr doped CaMnO 3 maintains a stable orthorhombic perovskite structure under an inert environment (tested up to 1200°C). The same oxygen carrier sample exhibited high recyclability over 100 redox cycles at 850°C. Besides being highly recyclable, Sr doped CaMnO 3 is found to be capable of releasing its lattice oxygen at a temperature significantly lower than that for CaMnO 3 , rendering it a potentially effective oxygen carrier for solid fuel combustion and carbon dioxide capture.

Active and stable metal-free heterogeneous catalysts for CO2fixation are required to reduce the current high level of carbon dioxide in the atmosphere, which is driving climate change. In this work, we show that defects in nanosilica (E′ centers, oxygen vacancies, and nonbridging oxygen hole centers) convert CO2to methane with excellent productivity and selectivity. Neither metal nor complex organic ligands were required, and the defect alone acted as catalytic sites for carbon dioxide activation and hydrogen dissociation and their cooperative action converted CO2to methane. Unlike metal catalysts, which become deactivated with time, the defect-containing nanosilica showed significantly better stability. Notably, the catalyst can be regenerated by simple heating in the air without the need for hydrogen gas. Surprisingly, the catalytic activity for methane production increased significantly after every regeneration cycle, reaching more than double the methane production rate after eight regeneration cycles. This activated catalyst remained stable for more than 200 h. Detailed understanding of the role of the various defect sites in terms of their concentrations and proximities as well as their cooperativity in activating CO2and dissociating hydrogen to produce methane was achieved.

A rationalized strategy to optimize transition-metal-oxide-based redox catalysts for water splitting and syngas generation through a hybrid solar-redox process is proposed and validated. Monometallic transition metal oxides do not possess desirable properties for water splitting; however, density functional theory calculations indicate that the redox properties of perovskite-structured BaMn Fe O can be varied by changing the B-site cation compositions. Specifically, BaMn Fe O is projected to be suitable for the hybrid solar-redox process. Experimental studies confirm such predictions, demonstrating 90 % steam-to-hydrogen conversion in water splitting and over 90 % syngas yield in the methane partial-oxidation step after repeated redox cycles. Compared to state-of-the-art solar-thermal water-splitting catalysts, the rationally designed redox catalyst reported is capable of splitting water at a significantly lower temperature and with ten-fold increase in steam-to-hydrogen conversion. Process simulations indicate the potential to operate the hybrid solar-redox process at a higher efficiency than state-of-the-art hydrogen and liquid-fuel production processes with 70 % lower CO emissions for hydrogen production.

Chemical looping with oxygen uncoupling (CLOU) is a novel process for carbon dioxide capture from coal combustion. Designing a metal oxide oxygen carrier with suitable oxygen release and uptake (redox) properties represents one of the most critical aspects for CLOU. The current work aims to correlate oxygen vacancy creation energy of metal oxide oxygen carriers with their redox properties. Oxygen vacancy creation energies of CaMnO 3−δ , Ca 0.75 Sr 0.25 MnO 3−δ , CaMn 0.75 Fe 0.25 O 3−δ , and BaMnO 3−δ were determined through density functional theory (DFT) calculations. The effect of the Hubbard U correction on the ground state magnetic configurations and vacancy creation energies was investigated, along with the effect of lattice oxygen coordination environment. It was determined that Hubbard U only slightly changes the relative differences in vacancy creation energies between the Mn-containing perovskites investigated. Therefore, ranking of oxygen vacancy creation energies among the various oxides can be determined using a simplified method without using Hubbard U. Comparisons with experimental data confirmed that vacancy creation energy is an effective indicator for oxygen release properties of the perovskites investigated: oxygen carrier materials with lower vacancy creation energies can release their lattice oxygen more readily. Thermogravimetric analysis indicated increased oxygen release with decreasing oxygen vacancy creation energy at temperatures below 700 °C. Higher activities for coal char combustion were also observed. The simplified DFT strategy also satisfactorily predicted the effects of iron and strontium doping on lattice distortions as well as the crystal volume changes upon oxygen vacancy creation. These findings indicate that oxygen vacancy creation energies in Mncontaining perovskites can potentially be used as an effective design parameter for oxygen carrier development and optimizations.

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High oxygen carrying capacity, lack of loosely bound lattice oxygen, and preferential surface segregation of Ba make BaMnxB1−xO3 (B = Ni or Fe) based redox catalysts suitable for chemical looping reforming of methane with high syngas yield and coke resistance.

In this work, we were able to significantly increase the activity of boron nitride catalysts used for the oxidative dehydrogenation (ODH) of propane by designing and synthesising boron nitride (BN) supported on dendritic fibrous nanosilica (DFNS). DFNS/BN showed a markedly increased catalytic efficiency, accompanied by exceptional stability and selectivity. Textural characterisation together with solid-state NMR and X-ray photoelectron spectroscopic analyses indicate the presence of a combination of unique fibrous morphology of DFNS and various boron sites connected to silica to be the reason for this increase in the catalytic performance. Notably, DFNS/B2O3 also showed catalytic activity, although with more moderate selectivity compared to that of DFNS/BN. Solid-state NMR spectra indicates that the higher selectivity of DFNS/BN might stem from a larger amount of hydrogen-bonded hydroxyl groups attached to B atoms. This study indicates that both boron nitride and oxide are active catalysts and by using high surface area support (DFNS), conversion from propane to propene as well as productivity of olefins was significantly increased.