Synthesis and characterization of cobalt substituted aluminophosphate molecular sieve: Co-SSZ-51 under microwave-hydrothermal conditions

Abstract

Isomorphic substitution of cobalt ions in the crystalline microporous framework of aluminophosphate molecular sieve SSZ-51 has been investigated using a gel composition of 2.5SDA:(1− x)Al 2O 3:1.0P 2O 5: xCo 2O 3:0.5HF:50H 2O ( x = 0, 0.01, 0.05, 0.08, 0.1, 0.15, 0.2) under microwave-hydrothermal conditions at 453 K. The crystallization was performed by employing cobalt nitrate, pseudoboehmite, ortho-phosphoric acid as cobalt, alumina and phosphorous precursors respectively and 4-dimethyl aminopyridine (4-DMAP) as structure directing agent (SDA) at 453 K. The effect of crystallization temperature was investigated at 423, 438, and 453 K under microwave and conventional hydrothermal conditions. Likewise, the effect of crystallization time was studied at 453 K. The crystallized samples were characterized by means of powder X-ray diffraction (PXRD), UV–visible diffuse reflectance spectroscopy (UV–DRS), and nitrogen adsorption–desorption measurements at 77 K. The obtained results demonstrated that the successful crystallization of Co-SSZ-51 framework, up to a gel having Co/Al ratio of 0.1, could be achieved at 453 K with in 20 h under microwave-hydrothermal conditions. The further increase in cobalt concentration led to the crystallization of non-microporous framework.