Noether-Charge Realization of Diffeomorphism Algebra
  It is shown in the covariant phase space formalism that the Noether charges with respect to the diffeomorphism generated by vector fields and their horizontal variations in general relativity form a diffeomorphism algebra. It is also shown with the help of the null tetrad which is well defined everywhere that the central term of the reduced diffeomorphism algebra on the Killing horizon for a large class of vector fields vanishes. 
Han-Ying Guo, Chao-Guang Huang and Xiaoning Wu