High-P behaviour of zeolites in “penetrating” fluids: Recent insights and new opportunities from XPRESS, the high-P dedicated diffraction beamline at ELETTRA

The high-pressure behavior of zeolites when compressed in potentially “penetrating” fluids, i.e. those whose molecules can be intruded into the zeolitic structural micropores, has recently been a subject of growing research interest. Pressure-mediated intrusion of molecules can induce changes in the physical and chemical properties of zeolites, thus offering an excellent tool for the tailoring of the properties of these industrially relevant materials. In situ experiments on SiO2-ferrierite (FER; Lotti et al., 2015) and AlPO4-5 (AFI; Lotti et al., 2016) zeolites, conducted in diamond anvil cells (DACs) using “penetrating” pressuretransmitting fluids, showed that theP-induced intrusion of molecules can be readily recognized from the synchrotron single-crystal and powder diffraction data. In case of FER, the complex patterns of phasetransitions at increasing pressure reveal the intrusion, whereas for AFI, the drastically different compressibilities provide evidence of this process. In this scenario, recently commissioned dedicated highpressure diffraction beamline Xpress, at the Elettra synchrotron light-source (Trieste, Italy), represents a new facility for high-pressure investigations in the field of geomaterials, using X-ray diffraction. Xpress is part of a scientific partnership between Italy and India (Indian Institute of Science, Bangalore). At Xpress, a liquid nitrogen cooled silicon single crystal, cut along the [111] direction, intercepts the beam from multipole superconducting wiggler source and deflects it at a fixed energy of 25 keV. The beam is focused using a toroidal mirror of 1.4 m length and 2.9 mrad grazing angle. The mirror is Pt coated to achieve 80% reflectivity at 25 keV. Focused beam from the mirror is further optimized by collimators (ranging from 30 to 200 micrometer in diameter), in order to have intense and well defined monochromatic beam for the HP-XRD experiments. On-line pressure monitoring is achieved through a ruby fluorescence microscope. The present experimental stage is equipped to host different kinds of DACs, in order to permit room-temperature - highpressure experiments in the pressure range 0-50 GPa. An image plate MAR345 with a controllable linear movement along the beam direction is available for the collection of the diffraction pattern. The setup for hosting in-situ high-P single-crystal X-ray diffraction experiments is under development and will be available for users in the near future.