Rh-doped Ceria: Solar Organics From H2O, CO2 and Sunlight?

AbstractThe depleting supply of fossil fuels and rapidly increasing emissions of anthropogenic greenhouse gases demand sustainable solutions to the unfolding energy and environmental crises. One solution is to store concentrated solar energy in the form of chemical fuels via thermochemical cycles, which produce synthesis gas, a gas mixture of H2 and CO that is the precursor of liquid fuels in the Fischer-Tropsch (FT) processes. To date, research efforts in this field have been devoted exclusively to the improvement of synthesis gas production, and no reports are available in direct generation of organic fuels such as methane and ethanol from H2O and CO2 by solar thermochemical cycles. With the aim to generate higher grade fuels directly from H2O and CO2 via thermochemical processes, we incorporate FT catalysts into the ceria lattice. In this study, we have synthesized rhodium doped ceria by coprecipitation. X-ray powder diffraction (XRD) indicates that the as-synthesized Rh-doped ceria is single-phased. High temperature XRD reveals that the Rh-doped ceria sustains its fluorite structure even at elevated temperatures up to 1400˚C, indicating excellent structural stability highly desired for thermochemical cycles. The formation of oxygen vacancies in ceria due to the substitution of cerium by the lower valent rhodium cations is evidenced by Raman spectra. Rh-doped ceria exhibits an enhanced oxygen storage capacity (OSC) and superior activities in the conversion of H2 and CO2 into methane. These demonstrate great potential of Rh-doped ceria for the production of methane and other chemicals during the reoxidation in a thermochemical cycle, when H2O, instead of H2, is co-fed with CO2. In fact, evidence strongly indicates that the H2 produced from the splitting of H2O is partly consumed when both H2O and CO2 are used for the reoxidation of thermally reduced Rh-doped ceria. Therefore the formation of higher grade fuels seems highly likely

Pd-LaFeO3 catalysts in aqueous ethanol: Pd reduction, leaching, and structural transformations in the presence of a base

The reactive behavior of three catalysts based on Pd-loaded LaFeO3 was investigated in terms of the reducibility of Pd and its propensity to leaching into the liquid phase in flowing solutions prototypical of C–C coupling catalysis in a continuous flow reactor cell. In situ quick extended X-ray absorption fine structure spectroscopy showed that Pd remains stable and nonreducible in the flowing ethanol/water solvent mixture under heating to 353 K. However, ex situ transmission electron microscopy, high-energy X-ray diffraction, and fluorescence yield Fe K-edge X-ray absorption near-edge structure show that the addition of a significant amount of base (K2CO3, 0.1 M) results in the structural degradation of the perovskite support as well as the mobilization of Pd along the sample bed that is dependent on the structure and crystallite size of the perovskite. The results are discussed in terms of the use of perovskite-type oxides in various areas of research where they are placed in contact with liquid phases of variable temperature and elevated pH

Influence of photoadsorbed O2 on the photoreduction of CO2 with H2O at the surface of TiO2

The stoichiometry of the CO2 photoreduction using TiO2 (Degussa P25) as photocatalyst in the presence of water vapor was investigated in detail. It was observed that oxygen is missing in significant amounts on the product side and that the efficiency of the reaction decreases with time. Photoadsorption of O2 at TiO2 was investigated as a possible explanation of these facts. It was found that the photoactivity is strongly hindered by photoadsorbed oxygen and ceases completely at a surface coverage of Θ = 0.05. This low value does not allow to attribute all the missing oxygen in the reaction to oxygen photoadsorbed on the photocatalyst. Photoadsorption can therefore not be invoked to explain the fate of the missing oxygen in the reaction products

Catalytic Reduction of CO2 into Solar Fuels via Ferrite Based Thermochemical Redox Reactions

In this study, Ni based ferrite nanomaterials were synthesized using sol-gel method for solar thermochemical splitting of CO2 using a thermogravimetric analyzer. To synthesize the ferrite materials, the corresponding metal precursors were dissolved in ethanol (with required molar ratios). After achieving the dissolution, propylene oxide (PO) was added to achieve the gel formation. Freshly synthesized gels were aged, dried, and calcined by heating up to 600 C in air. Powder x-ray diffractometer (XRD), BET surface area, as well as scanning (SEM) and transmission (TEM) electron microscopy characterized the calcined powders. The sol-gel derived ferrites were further tested towards their thermal reduction and CO2 splitting ability using a high temperature thermogravimetric analyzer (TGA).Qatar Foundation;Qatar National Research FundScopu

CuO/La0.5Sr0.5CoO3: Precursor of efficient NO reduction catalyst studied by: Operando high energy X-ray diffraction under three-way catalytic conditions

Substitution of critical raw materials such as platinum group metals in automotive catalysts is challenging. In this work we prepared a nanocomposite in which CuO nanoparticles are highly dispersed on a La0.5Sr0.5CoO3 perovskite-type oxide. The behaviour and reactivity under three way catalyst conditions was monitored by operando time-resolved high-energy X-ray diffraction under oscillating rich/lean feed. The reducing environment converted CuO into Cu(0) in a two step process: Cu(ii) to Cu(i) and to Cu(0), while the perovskite evolved to an oxygen deficient brownmillerite phase. These structural transformations are shown to be crucial for catalytic activity. The in situ generated Cu(0)/Cu(i)/brownmillerite nanocomposite is active for NO reduction above 300 \ub0C, reaching 90% NO conversion at 450 \ub0C. The effect of feed composition on the diffraction patterns was studied by Rietveld refinement in order to rationalize the experimental observations under TWC conditions

Sustained solar fuel production in multiple thermochemical cycles using sol-gel derived ferrite nanopowders

In this paper, the sol-gel synthesis of Mg-doped Niferrite i.e. Ni-Mg-ferrite was attempted by using propylene oxide (PO) as a proton scvanger. Effects of two important synthesis paramaters such as amount of PO added during synthesis and aging time on phyico-chemical properties such as phase composition, specific surface area (SSA), crystallite size, and particle morphology were studied by using different analytical methods such as powder X-ray diffractometer (PXRD), BET specific surface area analyzer, and scannning electron microscope (SEM).This publication was made possible by the NPRP grant (NPRP8-370-2-154) and UREP grant (UREP 18-146-2-060) from the Qatar National Research Fund (a member of Qatar Foundation). The statements made herein are solely the responsibility of author(s). The authors also gratefully acknowledge the financial support provided by the Qatar University Internal Grant QUUG-CENG-CHE-14\15-10.Scopu

In situ study of metal leaching from Pd/Al2O3 induced by K2CO3

In situ time- and spatially-resolved Quick Extended X-ray Absorption Fine Structure Spectroscopy (QEXAFS) was deployed to study the leaching of Pd from a heterogeneous catalyst caused by K2CO3 temporally and spatially