Contents 1. Background 2. Thermochemical conversion of CO 2 to fuels 3. Photon energy conversion of CO 2 to fuels with water 3.1. TiO 2 photocatalysts 3.2. Metal-loaded TiO 2 photocatalysts 3.3. Highly dispersed TiO 2 photocatalysts 3.4. Modified/doped TiO 2 photocatalysts 3.5. Historical low conversion rates and misunderstandings when using TiO 2-based photocatalysts 3.6. Semiconductor photocatalysts other than TiO 2 3.7. Carbon-based photocatalysts 4. Photon energy conversion of CO 2 to fuels using hydrogen 4.1. Photocatalytic conversion of CO 2 to methane or CO using hydrogen 4.2. Photocatalytic conversion of CO 2 to methanol using hydrogen

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X-ray absorption spectra have been measured at the S K-, Cl K-, and Mo L3- and L2-edges for the d0 dioxomolybdenum(VI) complexes LMoO2(SCH2Ph), LMoO2Cl, and LMoO2(OPh) (L = hydrotris(3,5-dimethyl-1-pyrazolyl)borate) to investigate ligand−metal covalency and its effects on oxo transfer reactivity. Two dominant peaks are observed at the S K-edge (2470.5 and 2472.5 eV) for LMoO2(SCH2Ph) and at the Cl K-edge (2821.9 and 2824.2 eV) for LMoO2Cl, demonstrating two major covalent contributions from S and Cl to the Mo d orbitals. Density functional calculations were performed on models of the three Mo complexes, and the energies and characters of the Mo 4d orbitals were interpreted in terms of the effects of two strong cis-oxo bonds and additional perturbations due to the thiolate, chloride, or alkoxide ligand. The major perturbation effects are for thiolate and Cl- π mixed with the d xz orbital and σ mixed with the d z 2 orbital. The calculated 4d orbital energy splittings for models of these two major contributions to the bonding of thiolate and Cl ligands (2.47 and 2.71 eV, respectively) correspond to the splittings observed experimentally for the two dominant ligand K-edge peaks for LMoO2(SCH2Ph) and LMoO2Cl (2.0 and 2.3 eV, respectively) after consideration of final state electronic relaxation. Quantification of the S and Cl covalencies in the d orbital manifold from the pre-edge intensity yields, ∼42% and ∼17% for LMoO2(SCH2Ph) and LMoO2Cl, respectively. The Mo L2-edge spectra provide a direct probe of metal 4d character for the three Mo complexes. The spectra contain a strong, broad peak and two additional sharp peaks at higher energy, which are assigned to 2p transitions to the overlapping t2g set and to the d z 2 and d xy levels, respectively. The total peak intensities of the Mo L2-edges for LMoO2(OPh) and LMoO2Cl are similar to and larger than those for LMoO2(SCH2Ph), which agrees with the calculated trend in ligand−metal covalency. The theoretical and experimental description of bonding developed from these studies provides insight into the relationship of electronic structure to the oxo transfer chemistry observed for the LMoO2X complexes. These results imply that anisotropic covalency of the Mo−Scys bond in sulfite oxidase may promote preferential transfer of one of the oxo groups during catalysis.

Confirmation of 13CO2 photoconversion into a 13C-product is crucial to produce solar fuel. However, the total reactant and charge flow during the reaction is complex; therefore, the role of light during this reaction needs clarification. Here, we chose Ag–ZrO2 photocatalysts because beginning from adventitious C, negligible products are formed using them. The reactants, products, and intermediates at the surface were monitored via gas chromatography–mass spectrometry and FTIR, whereas the temperature of Ag was monitored via Debye–Waller factor obtained by in situ extended X-ray absorption fine structure. With exposure to 13CO2, H2, and UV–visible light, 13CO selectively formed, while 8.6% of the 12CO mixed in the product due to the formation of 12C-bicarbonate species from air that exchanged with the 13CO2 gas-phase during a 2 h reaction. By choosing the light activation wavelength, the CO2 photoconversion contribution ratio was charge separated at the ZrO2 band gap (λ < 248 nm): 70%, localized at the Ag surface plasmon resonance (LSPR) (330 < λ < 580 nm): 28%, and characterized by a thermal energy of 295 K: 2%. LSPR at the Ag surface was converted to heat at temperatures of up to 392 K, which provided an efficient supply of activated H species to the bicarbonate species, combined with separated electrons and holes above the ZrO2, which generated CO at a rate of 0.66 μmol h–1 gcat –1 with approximately zero order kinetics. Photoconversion of 13CO2 using moisture was also possible. Water photo-oxidation step above ZrO2 was rate-limited, and the side reactions that formed H2 above the Ag were successfully suppressed instead to produce CO via the Mg2+ addition to trap CO2 at the surface.

The combination of n-type TiO2 and p-type BiOCl photooxidizing water and photoreducing the formed O2 back to water, respectively, in acidic solution enabled a sustainable photofuel cell utilizing natural light.

In this paper, we propose a new approach to sparseness-based BSS based on the EM algorithm, which iteratively estimates the DOA and the time-frequency mask for each source through the EM algorithm under the sparseness assumption. Our method has the following characteristics: 1) it enables the introduction of physical observation models such as the diffuse sound field, because the likelihood is defined in the original signal domain and not in the feature domain, 2) one does not necessarily have to know in advance the power of the background noise since they are also parameters which can be estimated from the observed signal, 3) it takes short computational time, 4) a common objective function is iteratively increased in localization and separation steps, which correspond to the E-step and M-step, respectively. Although our framework is applicable to general N channel BSS, we will concentrate on the formulation of the problem in the particular case where two sensory inputs are available, and we show some numerical simulation results.

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