A one-step route to SAPO-46 using H 3PO 3-containing gel and its application as the catalyst for methanol dehydration

Abstract

SAPO-46 molecular sieve has been synthesized on a new one-step route by using phosphorous acid (H 3PO 3) or the mixture of H 3PO 3 and phosphoric acid (H 3PO 4) as the phosphorus source. It has been found that the pure phase of SAPO-46 could be obtained more conveniently from the H 3PO 3-containing gels at 200 °C. Meanwhile, SAPO-46 with higher crystallinity can be synthesized in a wide range of gel compositions, containing higher silica in the product. As the catalyst for the dehydration of methanol to dimethyl ether (DME), it has exhibited high selectivity for the formation of DME as well as the activity of methanol conversion. Raman and IR have been employed to characterize the initial gel and as-synthesized sample to investigate the formation of SAPO-46 and the one-template-multiple-structures phenomena in the new one-step route, where SAPO-41 or SAPO-46 can be formed according to silica concentration. The transformation of P(III) species in the initial gels to P(V) species during crystallization have been found. It may be the key role for the formation of SAPO-46 on the new route. Besides, the correlation between silica content and the structure type of crystalline products with di-n-propylamine as the template has also been obtained.