Contact of adsorbed ammonium nitrite, NH4NO2, with HCl vapor or a solid acid such as the zeolite HY, significantly lowers the temperature of its decomposition to N-2 + H2O. Protonated NH4NO2 decomposes at room temperature. The decomposition of ammonium nitrite is one of the steps in the catalytic reduction of NOx with ammonia or other reductants.