Investigation of ZnWO4 and CaMO4 as target materials for the CRESST-II Dark Matter search

This work reports on the investigation of calcium molybdate (CaMoO4) and zinc tungstate (ZnWO4) scintillating crystals and the development of prototype phonon detectors based on these new target materials for CRESST-II (Cryogenic Rare Event Search with Superconducting Thermometers). The CRESST-II direct dark matter search experiment seeks the detection of WIMPs (Weakly Interacting Massive Particles) via their elastic scattering off nuclei. The WIMP event rate is expected to be less than 0.1 event per kg of the target and per day while the background rate is orders of magnitude higher, even after placing the detector in a well-shielded facility. Therefore, suppression of background that would hide or mimic a potential WIMP signal is of the central importance. CRESST-II detectors can actively discriminate nuclear recoils (caused by neutrons and expected from WIMPs) from radioactive alpha-, beta-, and gamma-backgrounds while simultaneously measuring phonon and light signals caused by a particle interaction in the scintillating crystal. The challenge of such a measuring technique is the small amount of scintillation light generated. Typically, only 1% of the total energy deposited into calcium tungstate (CaWO4) crystals (standard target for CRESST-II) by gamma/beta particles is detected. In order to achieve a better discrimination threshold down to lower recoil energies (below 40 keV), the amount of emitted scintillation light has to be maximized. In this work scintillation properties of CaMoO4 and ZnWO4 crystals have been investigated at room temperature and at cryogenic temperatures and compared with those ones of CaWO4. In particular, the light output and scintillation decay time constants of CaMoO4 and ZnWO4 crystals at mK temperatures have been measured for the first time. The comparison of the materials with CaWO4 showed up to a factor of two higher light output for ZnWO4 crystals while for CaMoO4 crystals a factor of two lower. Furthermore, a 10 g ZnWO4 phonon detector was scaled up to a full 400 g prototype and 200 g CaMoO4 phonon detectors were developed. The ZnWO4 detector has been integrated into the CRESST-II setup at Gran Sasso where it has been operated in a well-shielded facility for the first time. Besides allowing for performance studies of the new detector design, data taken with this detector made a detailed investigation of radioactive contaminations of the ZnWO4 crystal possible. Due to the excellent characteristics obtained with the prototype ZnWO4 phonon detector this material will be used as an additional target unit for the CRESST-II experiment

Turning a Methanation Catalyst into a Methanol Producer: In-Co Catalysts for the Direct Hydrogenation of CO2 to Methanol

The direct hydrogenation of CO2 to methanol using green hydrogen is regarded as a potential technology to reduce greenhouse gas emissions and the dependence on fossil fuels. For this technology to become feasible, highly selective and productive catalysts that can operate under a wide range of reaction conditions near thermodynamic conversion are required. Here, we demonstrate that indium in close contact with cobalt catalyses the formation of methanol from CO2 with high selectivity (>80%) and productivity (0.86 gCH3OH.gcatalyst-1.h-1) at conversion levels close to thermodynamic equilibrium, even at temperatures as high as 300 °C and at moderate pressures (50 bar). The studied In@Co system, obtained via co- precipitation, undergoes in situ transformation under the reaction conditions to form the active phase. Extensive characterization demonstrates that the active catalyst is composed of a mixed metal carbide (Co3InC0.75), indium oxide (In2O3) and metallic Co. </div

Turning a Methanation Co Catalyst into an In–Co Methanol Producer

International audienceThe direct hydrogenation of CO2 to methanol using hydrogen is regarded as a potential technology to reduce greenhouse gas emissions and the dependence on fossil fuels. For this technology to become feasible, highly selective and productive catalysts that can operate under a wide range of reaction conditions near thermodynamic conversion are required. Here we combine a CO-producing In oxide catalyst with a methane-producing Co catalyst to obtain an In/Co catalyst for CO2 reduction to methanol. Density functional (DFT) simulations demonstrate that the charge transfer between the Co support and the In oxide film leads to enrichment of the surface of indium oxide with O vacancies, which serve as active sites for selective conversion of CO2 to methanol. Moreover, our simulations suggest that CO2 reduction on Co-supported In2O3–x films will preferentially yield methanol, rather than CO and methane. As a result, the prepared In@Co catalysts produce methanol from CO2 with high selectivity (>80%) and productivity (0.86 gCH3OH gcatalyst–1 h–1) at conversion levels close to thermodynamic equilibrium, even at temperatures as high as 300 °C and at moderate pressures (50 bar)