Catalytic conversion of methanol to olefins on SAPO-n (n=11, 34, and 35), CrAPSO-n, and Cr-SAPO-n molecular sieves

The catalytic conversion from methanol to olefins has been studied for SAPO-11 SAPO-34, and SAPO-35 silicoaluminophosphate molecular sieves with and without chromium incorporation. The selectivity for methanol conversion to ethene and propene has been investigated as a function of structure type, silica content, chromium location, and chromium concentration. Among protonated H-SAPO-n materials, SAPO-34 shows the highest selectivity for ethene and propene, whereas SAPO-11 shows the longest lifetime for catalytic activity. The variation of silicon content indicates that there is an optimum silicon content in SAPO-34 for the best catalytic activity. Incorporation of Cr into the framework of SAPO-n increases the lifetime and the selectivity toward ethene compared with those from Cr incorporation by ion exchange. This is interpreted as an acidity difference between synthesized CrAPSO-n and ion-exchanged Cr-SAPO-n. CrAPSO-11 also increases the lifetime, the distribution of ethene and propene, and the selectivity toward ethene compared with SAPO-11. However, SAPO-34 and CrAPSO-34 with higher Si content compared to that of SAPO-11 show similar selectivity toward ethene and propene, but CrAPSO-34 has a longer lifetime. The chromium influence is smaller in CrAPSO-34 compared to CrAPSO-11. With an increase in Cr amount, CrAPSO-11 shows higher selectivity toward ethene and propene and has a longer lifetime.