The X-ray photoelectron spectra of metallic iridium and the technologically important iridium compounds, IrO 2 and IrCl 3 , have been studied. The results not only improve the accuracy of published data but also expand the binding energy database of other iridium core-levels. The difference between anhydrous and hydrated materials is explored, and the effect on curve-fitting is discussed, together with the derivation of suitable line shapes for peak fitting of data acquired from a conventional monochromatic Al K α X-ray source.

The formation of PdZn bimetallic alloys on ZnO, TiO and AlO supports was investigated, together with the effect of alloy formation on the CO hydrogenation reaction. The chemical vapour impregnation (CVI) method produced PdZn nanoparticles with diameters of 3-6 nm. X-ray photoelectron spectroscopy and X-ray diffraction revealed the changes in the structure of the PdZn alloy that help stabilise formate intermediates during methanol synthesis. PdZn supported on TiO exhibits high methanol productivity of 1730 mmol kg h that is associated with the high dispersion of the supported PdZn alloy.

Eschewing the common trend toward use of catalysts composed of Cu, it is reported that PdZn alloys are active for CO 2 hydrogenation to oxygenates. It is shown that enhanced CO 2 conversion is achievable through the introduction of Brønsted acid sites, which promote dehydration of methanol to dimethyl ether. We report that deposition of PdZn alloy nanoparticles onto the solid acid ZSM-5, via chemical vapor impregnation affords catalysts for the direct hydrogenation of CO 2 to DME. This catalyst shows dual functionality; catalyzing both CO 2 hydrogenation to methanol and its dehydration to dimethyl in a single catalyst bed, at temperatures of >270°C. A physically mixed bed comprising 5% Pd 15% Zn/TiO 2 and H-ZSM-5 shows a comparably high performance, affording a dimethyl ether synthesis rate of 546 mmol kg cat −1 h −1 at a reaction temperature of 270°C . ■ INTRODUCTIONMethanol is ubiquitous within the chemical industry, with global demand exceeding 57 Mt/annum. The majority of this is met through a two-step process whereby synthesis gas is produced via methane steam reforming and then reacted over a Cu/ZnO/Al 2 O 3 catalyst to prepare methanol. The energy consumption of this process is estimated to exceed 1 exajoule (1 × 10 18 J)/annum globally, with a significant carbon footprint (ca. 88 Mt GHG eq). 1 In line with political and social pressure to decrease society's dependence on fossil fuels, there is growing interest in producing methanol through more sustainable routes. One promising route is catalytic CO 2 hydrogenation. The process, however, is restricted by thermodynamic equilibrium; with the reverse water gas shift reaction (RWGS) dominating the reaction at high temperatures. Indeed, methanol is thermodynamically favored at lower temperatures. Unfortunately, because of the relatively low reactivity of CO 2 , high reaction temperatures and/or pressures are required for its activation. To maximize yields of valueadded products, it is important that CO 2 hydrogenation be carried out near equilibrium. One approach toward circumventing RWGS at elevated reaction temperatures is removal of the product, methanol, from the catalytic system. This can be achieved through dehydration to dimethyl ether (DME), typically over a solid acid catalyst. DME is a key feedstock for production of methylating agents for organic synthesis. 2 DME has also been identified as an environmentally friendly fuel, with low associated emissions of NO x , hydrocarbons, CO and SO x . 3 Through the methanol to gasoline (MTG) process, methanol is catalytically converted to yield an equilibrium mixture containing methanol, DME and water. This is then converted to hydrocarbons. 4 Being both exothermic and reversible, methanol dehydration is subject to thermodynamic limitation, though effectively not so under methanol synthesis conditions. 4 Integrating methanol dehydration into CO 2 hydrogenation reaction systems might increase hydrogenation yields, by intercepting the methanol through dehydration to DME, therefore shifting the reactio...

Direct seawater electrolysis is proposed as a potential low-cost approach to green hydrogen production, taking advantage of the vastly available seawater and large-scale offshore renewable energy being deployed. However, developing efficient, earth-abundant electrocatalysts that can survive under harsh corrosive conditions for a long time is still a significant technical challenge. Herein, the fabrication of a self-supported nickel-iron phosphosulfide (NiFeSP) nanotube array electrode through a two-step sulfurization/phosphorization approach is reported. The as-obtained NiFeSP nanotubes comprise abundant NiFeS/NiFeP heterointerfaces and under-coordinated metal sites, exhibiting outstanding activity and durability for the hydrogen and oxygen evolution reactions (HER and OER) in simulated alkaline-seawater solution (KOH + NaCl), with an overpotential of 380 (HER) and 260 mV (OER) at 500 mA cm -2 and outstanding durability of 1000 h. Theoretical calculations support the observed outstanding performance, showing that the heterointerface and under-coordinated metal sites synergistically lower the energy barrier of the rate-determining step reactions. The NiFeSP electrode also shows good catalytic performance for the urea oxidation reaction (UOR). By coupling UOR with HER, the bifunctional NiFeSP electrode pair can efficiently catalyze the overall urea-mediated alkaline-saline water electrolysis at 500 mA cm -2 under 1.938 V for 1000 h without notable performance degradation.

The efficient electrochemical splitting of water is limited by the anodic oxygen evolution reaction (OER). IrO2 is a potential catalyst with sufficient activity and stability in acidic conditions to be applied in water electrolysers. The redox properties and structural flexibility of amorphous iridium oxo-hydroxide compared to crystalline rutile-IrO2 is associated with higher catalytic activity for OER. We prepared IrOx OER catalysts by a simple hydrothermal method varying the alkali metal base (Li2CO3, LiOH, Na2CO3, NaOH, K2CO3, KOH) employed during the synthesis. This work reveals that the surface area, particle morphology and the concentration of surface hydroxyl groups can be controlled by the base used, and thus, greatly influence the catalyst activity and stability for OER. It was found that materials prepared with bases containing lithium cations can lead to amorphous IrOx materials with a significantly lower overpotential (100 mV @ 1.5 mA•cm -2 ) and increased stability compared to materials prepared with other bases and rutile IrO2. This facile method leads to the synthesis of highly active and stable catalysts which can potentially be applied to larger scale catalyst preparations.