ACIDITY AND CATALYTIC ACTIVITY OF MEAPSO-44 (ME = CO, MN, CR, ZN, MG), SAPO-44, AIPO4-5, AND AIPO4-14 MOLECULAR-SIEVES IN METHANOL DEHYDRATION

SAPO-44 and the isomorphously substituted MeAPSO-44 (Me = Co, Mn, Cr, Zn, Mg) molecular sieves have been synthesized. The temperature-programmed desorption (TPD) spectra and the reaction rates of methanol dehydration have been measured on these samples in comparison with AlPO4-5 and AlPO4-14 samples. The acidity strength of samples has been determined qualitatively from the temperatures of dimethylether desorption peaks, and the following sequence has been obtained: MnAPSO-44 > CoAPSO-44 ≈ ZnAPSO-44 > MgAPSO-44 > CrAPSO-44 > SAPO-44 ≫ AlPO4-5 ≈ AlPO4-14. The following sequence of catalytic activity has been observed: AlPO4-14 > AlPO4-5 ≈ SAPO-44 > CoAPSO-44 > MnAPSO-44. The highest selectivity to ethene production among these catalysts has been found for CoAPSO-44. The selectivities to ethene of SAPO-44 and MeAPSO-44 (Me = Co, Mn, Cr) samples are about three times higher than the selectivities of SAPO-34 and MeAPSO-34 (Me = Co, Mn, Cr) samples. The selectivities of transition-metal-substituted MeAPSO-44 samples follow the Irving-Williams transition metal-ligand complex stability order. © 1993 Academic Press, Inc.