TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Component: The ammonia consumption unit is the catalyst for SCR of NO x in the oxygen-containing exhaust gas, where the SCR of NO x in the exhaust gas is effected in an automobile, truck, train, ship or other motorized machine, vehicle or engine-driven generator. The second ammonia absorbing and desorbing material is magnesium-ammonia chloride (Mg(NH 3) 6Cl 2), iron-ammonia chloride (Fe(NH 3) 6Cl 2), and/or nickel-ammonia chloride (Ni(NH 3) 6Cl 2).    TECHNOLOGY FOCUS - ORGANIC CHEMISTRY - Preferred Method: The first ammonia generating material and/or its decomposition product and the second ammonia storage material are contained in different containers in fluid communication, and are at the same temperature. The fluid communication can be interrupted and re-established. The first ammonia generating material and/or its decomposition product are at a higher temperature than the second ammonia storage material. The first ammonia generating material and/or its decomposition product are used as an ammonia source in a system having an ammonia consumption unit in operation, where the ammonia consumption unit is a fuel cell or a catalytic device for splitting ammonia into nitrogen and hydrogen. The first ammonia generating material and/or its decomposition product are brought into fluid communication with the second ammonia storage material at or above the pressure threshold (preferably about ambient pressure) when the operation of the ammonia consumption unit has ended to reduce the ammonia pressure in the system; or brought into fluid communication with the second ammonia storage material at or above the pressure threshold (preferably at or higher than 5 bars) during operation of the consumption unit. The pressure threshold is assumed to be exceeded as soon as a signal from a secondary safety system signals an abnormality, e.g. a fire or a crash-like situation. The ammonia consuming unit in operation is preceded by a thermally and/or catalytically operating device for generating ammonia by decomposition of the first ammonia generating material. The second ammonia storage material is in proximity to a material that can dissipate the heat of absorption generated by the second material when adsorbing or absorbing ammonia. The second ammonia storage material can be heated to desorb ammonia when the saturation with ammonia of the second material is higher than an upper value at which the second material effectively absorbs ammonia released from the first ammonia generating material when the pressure threshold is reached or exceeded. The second ammonia storage material is used to supplement ammonia released from the decomposition of the first ammonia generating material during operation of the ammonia consumption unit to such a degree that the saturation with ammonia of the second material continuously remains below an upper value at which the second material effectively absorbs ammonia released from the first ammonia generating material when the pressure threshold is reached or exceeded. Preferred Properties: The ammonia partial pressure of the second ammonia storage material having a low ammonia pressure is below 1, preferably below 0.1 bar at 25 degrees C. The vapor pressure of the first ammonia generating material and/or its decomposition product is 0.1-1 bar at 25 degrees C. Preferred Component: The first ammonia generating material is one or more of ammonium carbamate, ammonium carbonate, urea, or their solution in a solvent as well as a solution of ammonia in a solvent. The second ammonia storage material is an ammonia absorbing and desorbing material, preferably a metal amine complex. The metal amine complex is from metal ammine complexes of the general formula: M a(NH 3) nX z.M=one or more cations from alkali metals, e.g. Li, Na, K or Cs; alkaline earth metals, e.g. Mg, Ca or Sr; transition metals, e.g. V, Cr, Mn, Fe, Co, Ni, Cu, or Zn; and/or their combinations, e.g. NaAl, KAl, K 2Zn, CsCu, or K 2Fe;X=one or more anions from fluoride, chloride, bromide, iodide, nitrate, thiocyanate, sulfate, molybdate, or phosphate ions;a=the number of cations per salt molecule;z=the number of anions per salt molecule; andn=the coordination number of 2-12.