Most of the hydrogenation reactions are exothermic, and most of them are carried out at high temperatures. The hydrogen and most of the materials used have the danger of ignition and explosion, and some of the materials, products or intermediate products are toxic and corrosive. In case of leakage, reactor blockage and other failures, there is a great risk of fire and explosion. 

Ice-forming agents are mainly used for cold cloud catalytic operations from -6℃ to 20℃. Silver iodide (AgI) is the most commonly used and effective ice-forming agent because its crystal structure is similar to that of ice crystals, and it is highly effective in making ice crystals. Silver iodide forms extremely large and fine silver iodide particles in the air through combustion or explosion, and 1 gram of silver iodide can produce more than 1000 ice nuclei.