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.

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.

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.

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.