1. W. Held and A. Koenig, Ger. Offen. DE 3642018 (1987) to Volkswagen A.G.
2. W. Held, A. Koenig, T. Richter and L. Puppe, SAE Paper 900496 (1990).
3. M. Iwamoto, in:Proc. Meeting of Catalytic Technology for Removal of Nitrogen Monoxide, Tokyo, January 1990, p. 17.
4. M. Iwamoto, H. Yahiro, S. Shundo, Y. Yu-u and N. Mizuno, Shokubai (Catalyst) 33 (1990) 430.
5. M. Konno, T. Chikahisa, T. Murayama and M. Iwamoto, Society of Automotive Engineering, Paper No. 920091 (1992).