Ammonia synthesis gas production having a shift reaction stage employing a
copper-based catalyst wherein the air supplied to the process is passed
through an absorber that removes sulfur and/or halide contaminants, is
described. The absorber has a support carrying an absorbent for sulfur
compounds and/or absorbent for halide compounds. The removal of the
contaminants improves the lifetime e.g. copper-zinc low temperature shift
catalysts.