Metal traps are devices used in the petroleum and chemical industries to remove metal impurities from liquid or gas streams. These impurities can include metals such as iron, copper, arsen and nickel, which can cause corrosion and damage to equipment and pose a safety risk to workers. They can also impose a problem for catalytic processes, as these metal impurities might act as catalyst poison. Therefore, it is important to remove these impurities from the stream before it is used or transported. Metal traps work by using a bed of adsorbent material, such as activated carbon or zeolite, to selectively capture metal ions from the stream. The adsorbent material is typically contained in a vessel or tower and the stream is passed through it. As the stream passes through the bed, the metal ions are adsorbed onto the surface of the adsorbent material, effectively removing them from the stream. It is typically applied upstream of the main active catalyst bed.