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The interaction of CaO and Ca(OH) 2 with solvated or gaseous SO 2 plays a crucial role in the corrosion of urban infrastructure by acid rain or in the removal of SO 2 from flue gas. We carried out a combined spectroscopic and theoretical investigation on the interaction of SO 2 with a CaO(001) single crystal. First, the surface chemistry of SO 2 was investigated at different temperatures using polarization-resolved IR reflection absorption spectroscopy. Three species were identified, and an in-depth density functional theory study was carried out, which allowed deriving a consistent picture. Unexpectedly, low temperature exposure to SO 2 solely yields a physisorbed species. Only above 100 K, the transformation of this weakly bound adsorbate first to a chemisorbed sulfite and then to a sulfate occurs, effectively passivatating the surface. Our results provide the basis for more efficient strategies in corrosion protection of urban infrastructure and in lime-based desulfurization of flue gas., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Multiply bonded lanthanide oxo groups are rare in coordination compounds and have not previously been reported for a surface termination of a lanthanide oxide. Here we report the observation of a Ce=O terminated ceria surface in a CeO 2 (111)-( 3 × 3 )R30° reconstruction of ≈3 nm thick ceria islands prepared on Pt(111). This is evidenced by scanning tunnelling microscopy (STM), low energy electron diffraction (LEED) and high-resolution electron energy loss spectroscopy (HREELS) measurements in conjunction with density functional theory (DFT) calculations. A Ce=O stretching frequency of 775 cm -1 is observed in HREELS, compared with 766 cm -1 calculated by DFT. The calculations also predict that the Ce=O bond is weak, with an oxygen vacancy formation energy of 0.85 eV. This could play an important role in the facile removal of lattice oxygen from CeO 2 , accompanied by the reduction of Ce IV to Ce III , which is a key attribute of ceria-based systems in connection with their unique catalytic properties., (© 2021 The Authors. Angewandte Chemie International Edition published by Wiley-VCH GmbH.)

The major challenge in solar water splitting to H 2 and O 2 is in making a stable and affordable system for large-scale applications. We have designed, fabricated, and tested a photoelectrochemical reactor characterized as follows: 1) it comprises an integrated device to reduce the balance of the system cost, 2) it utilizes concentrated sunlight to reduce the photoabsorber cost, and 3) it employs and alkaline electrolyte to reduce catalyst cost and eliminate external thermal management needs. The system consists of an III-V-based photovoltaic cell integrated with Ni foil as an O 2 evolution catalyst that also protects the cell from corrosion. At low light concentration, without the use of optical lenses, the solar-to-hydrogen (STH) efficiency was 18.3 %, while at high light concentration (up to 207 suns) with the use of optical lenses, the STH efficiency was 13 %. Catalytic tests conducted for over 100 hours at 100-200 suns showed no sign of degradation nor deviation from product stoichiometry (H 2 /O 2 =2). Further tests projected a system stability of years., (© 2020 The Authors. Published by Wiley-VCH Verlag GmbH & Co. KGaA.)

The remote hydrogen plasma is able to create abundant S-vacancies on amorphous molybdenum sulfide (a-MoS x ) as active sites for hydrogen evolution. The results demonstrate that the plasma-treated a-MoS x exhibits superior performance and higher stability than Pt in a proton exchange membrane based electrolyzers measurement as a proof-of-concept of industrial application., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A composite of the metal-organic framework (MOF) NH 2 -MIL-125(Ti) and molecular and ionic nickel(II) species, catalyzed hydrogen evolution from water under UV light. In 95 v/v % aqueous conditions the composite produced hydrogen in quantities two orders of magnitude higher than that of the virgin framework and an order of magnitude greater than that of the molecular catalyst. In a 2 v/v % water and acetonitrile mixture, the composite demonstrated a TOF of 28 mol H 2  g(Ni) -1  h -1 and remained active for up to 50 h, sustaining catalysis for three times longer and yielding 20-fold the amount of hydrogen. Appraisal of physical mixtures of the MOF and each of the nickel species under identical photocatalytic conditions suggest that similar surface localized light sensitization and proton reduction processes operate in the composite catalyst. Both nickel species contribute to catalytic conversion, although different activation behaviors are observed., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

An efficient heterogenized water oxidation catalyst (2_TiO2 ) has been synthesized by immobilizing the Kläui-type organometallic precursor [Cp*Ir{P(O)(OH)2 }3 ]Na (2, Cp*=1,2,3,4,5-pentamethylcyclopentadienyl ligand) onto rutile TiO2 . Iridium is homogeneously distributed at the molecular and atomic/small cluster level in 2_TiO2 and 2'_TiO2 (solid catalyst recovered after the first catalytic run), respectively, as indicated by STEM-HAADF (scanning transmission electron microscopy - high angle annular dark field) studies. 2'_TiO2 exhibits TOF values up to 23.7 min(-1) in the oxidation of water to O2 driven by NaIO4 at nearly neutral pH, and a TON only limited by the amount of NaIO4 used, as indicated by multiple run experiments. Furthermore, while roughly 40 % leaching is observed during the first catalytic run, 2'_TiO2 does not undergo any further leaching even when in contact with strongly basic solutions and completely maintains its activity for thousands of cycles. NMR studies, in combination with ICP-OES (inductively coupled plasma optical emission spectrometry), indicate that the activation of 2_TiO2 occurs through the initial oxidative dissociation of PO4 (3-) , ultimately leading to active centers in which a 1:1 P/Ir ratio is present (derived from the removal of two PO4 (3-) units) likely missing the Cp* ligand., (© 2016 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The mixed-phase nature of P25 TiO2 (85 % anatase/15 % rutile) plays a key role in the high H2 production rates shown by Au/P25 TiO2 photocatalysts in alcohol/water systems. However, a full understanding of the synergistic charge transfer mechanisms between the TiO2 polymorphs that drive the high rates is yet to be realised. Here, we deconstruct P25 TiO2 into its component phases, functionalise the phases with Au nanoparticles and explore charge transfer in Au/TiO2 systems using EPR spectroscopy. EPR spectroscopy and photocatalytic data provide direct evidence that electrons excited across the rutile band gap move to anatase lattice traps through interfacial surface sites, which decreases electron-hole pair recombination and increases charge carrier availability for photoreactions. In particular, three-phase interfacial sites between Au, anatase and rutile appear to be H2 evolution "hot spots". The results isolate the origin of high photocatalytic H2 production rates seen in Au/P25 TiO2 systems., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

A stable noble-metal-free hydrogen evolution photocatalyst based on graphite carbon nitride (g-C3 N4 ) was developed by a molecular-level design strategy. Surface functionalization was successfully conducted to introduce a single nickel active site onto the surface of the semiconducting g-C3 N4 . This catalyst family (with less than 0.1 wt % of Ni) has been found to produce hydrogen with a rate near to the value obtained by using 3 wt % platinum as co-catalyst. This new catalyst also exhibits very good stability under hydrogen evolution conditions, without any evidence of deactivation after 24 h., (© 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)