DEALUMINATION OF ZEOLITE-BETA VIA DICARBOXYLIC-ACID TREATMENT

It is demonstrated that zeolite beta and zeolite beta containing catal ysts can be dealuminated to very low acidity levels using a novel oxal ic acid treatment without reducing zeolite integrity. The effect of th e oxalic acid treatment has been studied over a wide range of treatmen t conditions for both silica-bound and unbound zeolite beta catalysts. Greater than 90% dealumination is observed with a concomitant reducti on in n-hexane-cracking activity as measured by the alpha (alpha) test . Removal of framework aluminum occurs via a two-step hydrolysis/chela tion mechanism, with the oxalic acid acting both as an acid and as a c helating agent. Framework aluminum removal is accompanied by the forma tion of internal silanol groups. Water soluble aluminum oxalates are p resent in the extracted solutions. Silanol groups are annealed with ex tended oxalic acid treatment. Oxalic acid treatment results in a uniqu e contraction of the zeolite beta lattice structure not observed for m ineral acid treated or steamed zeolite beta catalysts.