1. Walker, P.L. Jr., F. Rusinko and L.G. Austin. Advan. Catal. 11, 133 (1959).
2. Long, F.L. and K.W. Sykes. Proc. Roy. Soc. A215, 100 (1952).
3. Jüntgen, H. Carbon 6, 297 (1968).
4. Thrower, P.A., J.C. Bouquet and G.K. Matthew. Carbon 20, 457 (1982).
5. Katta, S. and D.L. Keairns. Proc. 180th Nat. Meeting Am. Chem. Soc., Div. Fuel Chem., 101, Las Vegas (1980).