PHOIBOS 100 MCD5 (inkl. PHOIBOS 100-63 MCD)

The hydrogenation of CO₂ to methanol is a viable alternative for reducing greenhouse gases net emissions as well as a route for hydrogen storage and transportation. In this context, the synthesis of active and selective catalysts is a relevant objective. In this work, we study the promotion of Pd with Ga and Zn in the hydrogenation of CO₂ to methanol at 800 kPa and 220–280 °C. Mono and intermetallic catalysts (Pd/SiO₂, PdGa/SiO₂ and Pd-Zn/SiO₂) were synthesized by incipient wetness impregnation with the aid of triethanolamine as an organic additive, obtaining similar average metal particle sizes (between 9 and 12 nm). Kinetic analysis reveals that the addition of Ga and Zn increases the turnover frequency for methanol formation by an order of magnitude without significant changes in the reaction rate of the reverse water-gas shift (r-WGS) which is a parallel undesired reaction. The selectivity to methanol (at 220 °C) thus increases from 3% for Pd/SiO₂ to 12% for Pd-Ga/SiO₂ and 30% for Pd-Zn/SiO2. XPS studies, Infrared analysis of CO adsorption, and XRD analyses show the presence of intermetallic phases Pd₂Ga and PdZn on the surface. The results suggest that Ga and Zn promote Pd, increasing its activity towards the synthesis of methanol, by creating more active sites for this reaction. These sites are likely formed by intermetallic compounds such as Pd₂Ga and PdZn.

The structure of the solid-liquid interface often defines the function and performance of materials in applications. To study this interface at the atomic scale, we extended an ultrahigh vacuum (UHV) surface-science chamber with an apparatus that allows bringing a surface in contact with ultrapure liquid water without exposure to air. In this process, a sample, typically a single crystal prepared and characterized in UHV, is transferred into a separate, small chamber. This chamber already contains a volume of ultrapure water ice. The ice is at cryogenic temperature, which reduces its vapor pressure to the UHV range. Upon warming, the ice melts and forms a liquid droplet, which is deposited on the sample. In test experiments, a rutile TiO2(110) single crystal exposed to liquid water showed unprecedented surface purity, as established by X-ray photoelectron spectroscopy and scanning tunneling microscopy. These results enabled us to separate the effect of pure water from the effect of low-level impurities present in the air. Other possible uses of the setup are discussed.

The promotion of Ga on SiO₂ supported Cu in the hydrogenation of CO₂ to methanol at 800 kPa and 200–280 °C was investigated. Cu/SiO₂ and CuGa/SiO₂ catalysts were prepared by a water-in-oil microemulsion technique resulting in Cu clusters of 4–6.5 nm. It was found that Ga addition increased the methanol formation rate by an order of magnitude without significantly changing that for reverse water gas shift (RWGS). This trend is also evidenced by the decrease in the apparent activation barrier for methanol formation from 78 (for Cu/SiO₂) to 26–39 kJ mol⁻¹ when Ga was added, but not for RWGS (107–132 kJ mol⁻¹). Kinetic and in situ DRIFTS analyses revealed that formate intermediates are adsorbed on both Cu and Ga₂O₃ and that methoxy hydrogenation could be the rate determining step of methanol synthesis. In the case of RWGS, a zero order of CO formation with respect to H₂ concentration was consistent with a redox mechanism and with the reaction occurring predominantly on Cu sites. The results suggest that Ga promotes Cu increasing methanol selectivity, likely by creating new active sites for methanol formation without modifying its oxidation state, which under reaction conditions remains mostly metallic.

Investigations on how to replace the toxic KCN etching for the removal of Cu–S phases during the preparation of CuInS2 (CIS) absorber layers by electrochemical procedures are presented. Starting from a simple anodic treatment in V2+/V3+ electrolyte, a more complex photoelectrochemical technique is developed which consists of different consecutive etching steps for the dissolution of the predominant CuS and for the removal of remaining Cu2S and a small sacrificial layer of CuInS2. This new method also offers the possibility of in situ quality control of the CIS in a photoelectrochemical solar cell (PECS) setup. Further examination of the treated films is carried out using X-ray emission spectroscopy, X-ray photoelectron spectroscopy (XPS) and by further processing of the samples to create solid state solar cells.

The band line-up at the 4H-SiC/Ni interface was determined using X-ray photoemission spectroscopy (XPS). Ni was deposited in 14 steps on an ex situ cleaned n-type 4H-SiC substrate starting with an initial deposition of 0.5 Å up to a final thickness of 110 Å. The sample surface was characterized in situ by XPS before the growth sequence, and after each Ni deposition step. Analysis of the Ni 3d and O 1s core level peaks indicates that a thin Ni oxide layer was formed at the interface due to a chemical reaction with oxidizing agents on the sample surface due to the ex situ substrate preparation before a metallic Ni film could be grown. The substrate core level spectra exhibit a significant shift to lower binding energy due to the development of an inversion condition in the semiconductor at the interface. This resulted in the formation of an electron injection barrier of 3.26 eV at the interface.