High temperature gas loading system for catalyzed gas/solid or liquid/solid reactions.

We introduce a high pressure – high temperature gas loading system for combined in-situ synchrotron powder X-Ray Diffraction and Mass Spectrometry during catalyzed gas/solid or liquid/solid reactions (Figure 1). The pressure cell consists of a cylindrical, quartz capillary connected to high pressure gas lines via mechanical tightening (Figure 2). This assembly allows the alignment of the capillary into the X-ray beam and its rotation in order to homogenise powder diffraction rings. The capillary serves both as the body and the reactor cell, and could be filled under inert atmosphere. Two configurations can be used: i) vertical configuration, one end of the capillary is closed, for example to study Liquid/Solid reactions (Figure 2.a), ii) horizontal configuration for example to study Gas/Solid reactions, a gas flow being able to be applied thought the both opened ends of the capillary (Figure 2.b). Different sizes of capillary can be used (o.d. 4 mm/w.t. 500 m or o.d. 6 mm/ w.t. 1.5 mm) according to the users’ needs. The pressure stability of the cell has been tested from 10^-2 mbar up to 115 bars (still under investigations to reach a pressure range 10^-5 mbar to 250 bars). Working temperature range of the cell is from T_amb to 900 °C (1173K) (still under investigations to reach -200 °C (77K)), currently achieved by a cylindrical ceramic furnace. Figure 3 presents a view of the gas distribution lines feeding the capillary. Typically, argon is used as inert gas and H₂ flow and/or pressure was applied to the sample. However the flexibility of the system allows the use of N₂ or He as inert gas, and the study of a wide range of gas reaction with H₂O, O₂, CO, CO₂, CH₄, C₃H₈, etc… In-situ gas detection is carried out by a home-made mass spectrometer (Figure 4) connected to a derivative line at the outing of the reactor cell. Mass spectrometer is based on a mass spectrometer head RGA-c25-cv13, arbitrary mass unity range 0-100, from MKS instruments. MS signals from the different gases are recorded on a PC (Process Eye Professional software v. 5.62.0.1) through a Microvision-IP interface. The mass spectrometer head is mounted on a CF40 five ways cross which serves as body and chamber test. Turbomolecular pump ensures a minimum chamber pressure of 5x10^-9 mbar after backout at 130 °C during two days. A leak valve (rating down to 7.5x10^-8 Torr.L.s^-1, E-MLV-22, MDC Vascuum) is connected to the reactor cell and defines a working pressure of 1x10^-7 mbar, allowing a minimum gas detection of about 100 ppm.

Using this high pressure - high temperature gas loading system, we recently performed dehydrogenation experiments on catalyzed LiBH₄/MgH₂ composite. Thus, such system allows the in-situ study of hydrogenation/dehydrogenation steps and cycling process on a wide variety of H₂ storage compounds (Metal and chemical hydrides, MOF, mesoporous materials) taking advantages of both combined techniques (SXRD/MS) and hard X rays (high volume gauge, high Q range, short acquisition time). In a more general way, this high pressure high temperature gas loading system has been designed for catalyzed gas/solid or liquid/solid reactions and could be adapted according to the users’ needs.

Figure 1. General view of the high pressure high temperature gas loading system.

Figure 2. The high pressure high temperature gas loading cell. For a) vertical and b) horizontal configurations.

Figure 3. Gas distribution lines scheme (left) and picture (right).

Figure 4. Mass spectrometer scheme (left) and picture (right).