Abstract: A process for the preparation of hydroxylammonium salts by catalytic reduction of nitrogen monoxide using hydrogen in the presence of a hydrogenation catalyst, comprises(a) in a first step, filtering the reaction mixture obtained after the reaction, giving a solution of essentially hydroxylammonium salt and a filter residue essentially comprising a mixture of hydrogenation catalyst and a solution of essentially hydroxylammonium salt, and(b) in a second step, subjecting the filter residue to a further separation process in order to concentrate the hydrogenation catalyst, giving a mixture having a higher concentration of hydrogenation catalyst than the filter residue and a mixture having a lower concentration of hydrogenation catalyst than the filter residue.