Non-Selective Catalytic Reduction (NSCR) is a process used to reduce nitrogen oxides (NOx) emissions in the exhaust gases of internal combustion engines, using a catalyst and reductant such as hydrogen, carbon monoxide, or hydrocarbons. Unlike Selective Catalytic Reduction (SCR), it does not require specific nitrogen oxide reactants and can lead to the oxidation of other exhaust components, including hydrocarbons and carbon monoxide.