1. V. Haensel, U.S. 2,479,109 and 2,479,110(1949); Oil and Gas J. 48, 82(1950).
2. J. R. Bernard, Proc. Fifth Intern. Conf. Zeolites, Heyden, London, 1980, p. 686.
3. W. C. Buss and T. R. Hughes, U.S. 4,435,283(1984).
4. W. C. Buss and T. R. Hughes, Belgian Patent 895,778(1983).