By comparison with the current use of liquid urea, which is converted to ammonia and used as a reducing agent in SCR- und SCRT^® catalytic converters, the use of solid reducing agents has marked advantages in terms of high ammonia density. The obvious choice of substance here is solid urea or ammonium carbamate (AC). Compared with solid urea, using ammonium carbamate at virtually the same density of ammonia has the advantage that only a very low energy requirement is needed to convert the ammonium carbamate to ammonia. At a sublimation temperature of only 60°C, (solid) ammonium carbamate can be directly and reversibly converted to ammonia (gaseous). This eliminates the usual low-temperature problems that occur with liquid urea. The AC reactor developed by HJS, which ensures that ammonia is channelled directly to the catalytic converter and cannot be released even in adverse operating conditions, makes it possible to meet the requirements of small package space in combination with high range reducing agents.