Safety and handling

Precious metal catalysts (PMCs) are supported catalysts with platinum group metals, such as Pt, Pd, Rh and Ru, as active components. The precious metal loading is in the range of 1–20 wt % and catalysts with 5 wt % metal loading are generally used. Usually the support to which the metal is bound is a highly porous activated carbon with a high surface area. However, it is also possible to use other supports, such as alumina and silica. PMCs are mainly used in liquid phase hydrogenations, but also in dehydrogenation or oxidation reactions. Generally, stirred tank reactors are used for such applications, in which case the catalysts need to be finely divided solids so they can be easily suspended in the reaction medium. Due to the potentially pyrophoric nature of the PMCs, their handling requires special care. PMCs may be used either dry or water-wet. Both types behave as free-flowing powders even if the wet catalysts contain 40–70 wt % water. Water-wet PMCs are less dangerous than dry PMCs in the presence of flammable organic vapors or liquids and oxygen. Mechanical losses due to dusting can also be avoided by using a wet catalyst. For safety reasons, the material safety data sheet (MSDS) for the chosen PMC must be read before handling the catalyst.

Activated metal catalysts (AMCs) are prepared by the caustic leaching of alloys containing aluminum and a catalytic base metal. This leaching process removes most of the aluminum, leaving behind a hydrogen-rich skeletal framework of the catalytic metal. After this activation, the catalyst is washed and stored under water. The protective layer of water over the catalyst is caustic; therefore contact of this solution with eyes, skin and clothing should be avoided. Appropriate personal protection equipment, such as goggles (preferably a face-shield or goggles with side shields), gloves, an easy-to-remove flame-retardant lab coat and flame-retardant boots, should be used by those handling AMCs. Contact lenses should not be worn.

Eye splashes must be flushed immediately with large amounts of water, while occasionally lifting the upper and lower lids. An examination must then be made by a qualified medical practitioner, such as an optician, to make sure that all particles have been removed. Skin that comes into contact with this solution must also be washed immediately with large amounts of water and any soaked clothing must be removed. It is always recommended that you then seek appropriate medical attention from a qualified medical practitioner. For safety reasons, the material safety data sheet (MSDS) for the chosen ABMC must be read before handling the catalyst.

These catalysts will, with time, desorb hydrogen and are therefore stored in drums that have devices, such as pressure-release valves, to prevent the build-up of excess hydrogen, while avoiding exposure to air. Care should be taken not to damage or block these devices. When transporting the drums, they should be fixed in an upright position so they cannot tip over. If a drum containing an ABMC is allowed to tip over, then the ventilation valve will be blocked from the inside and water loss may occur.

Although the AMCs are stored in these special drums, it is important that precautions are taken when opening them. Open them slowly, only in well-vented areas, while wearing the above-described personal protection equipment. Do not position any part of your body over the container when opening it. Open flames, spark sources and smoking must be forbidden while opening and/or venting these containers. Laboratory samples are provided in closed containers, and these should be opened using the same precautions, due to the over-pressure of hydrogen.

These catalysts are considered pyrophoric, due to the exothermal oxidation of the catalytic metal in the presence of oxidizing agents. If they are allowed to dry in air or any oxygen containing gas, they will rapidly heat up and become an ignition source for flammable materials.