Which catalyst is used for Reimer-Tiemann Reaction?

CHCl3 +aq. NaOH CHCl3 +aq.KOH CH3Cl +aq. NaOH CH3Cl +aq. KOH

CHCl3 +aq. NaOH

On treating phenol (C6H5OH) with chloroform (CHCl3) in the presence of sodium hydroxide (NaOH), a –CHO group is introduced at ortho position of benzene ring.  This reaction is known as Reimer - Tiemann reaction.