Phosphorus modified small pore molecular sieve catalysts, and their use in the production of light olefins

A process for the modification of a small pore molecular sieve catalyst to increase its selectivity to ethylene when used in the production of light olefins from oxygenated compounds which comprises

• contacting, and incorporating with said catalyst a phosphonitrilic oligomer formed of phosphazo groups having the formula ##STR4## wherein the substituent R is the same or different, and is selected from a group consisting of halogen, alkenyl, alkynyl, alkyl, cycloalkyl, aryl, aralkyl, alkaryl, and alkoxy .chi. ranges from about 3 to about 100, the oligomer formed from the phosphazo groups is either linear or cyclic, and calcining said catalyst with which the phosphonitrilic oligomer has been incorporated at temperature sufficient to decompose said phosphonitrilic oligomer, and deposit on the catalyst from about 0.001 percent to about 50 percent phosphorus, based on the total weight of the phosphorus-containing catalyst.