Isomorphous Substitution of Iron in the Framework of Linde B Type Zeolites under Mild Conditions

Abstract

At mild conditions such as 80°C and atmospheric pressure, zeolites containing iron (III) ions in the framework were prepared from a homogeneous solution or somewhat heterogeneous mixture as a starting material. Si nce iron (III) ions can be incorporated into excess silicate ions forming a soluble complex, [FeSiO(OH)₃]²⁺, the iron (III) nitrate solution was first added to an excess of sodium metasilicate solution (Si/Fea≥50). Then various aluminium sources were added until Si/(Al+ Fe) and Fe/ (Al + Fe)become 20 and 0.00-0.40, respectively. When sodium aluminate was used as aluminium source, the solution became homogeneous (system 1), whereas aluminium nitrate lead to a partly heterogeneous mixture (system 2). The solid prod ucts obtained from both the systems were characterized by XRD, IR, SEM, ICP-AES and magnetic susceptibility methods. These analyses confirmed the formation of Linde B₁ and B₄ from the two systems and the presence of iron (III) in their zeolite lattice framwork. The extent of iron (III)substitution goes up to 40% in the products from system 1 and ca.25% in those from system 2. These values are fairly large as compared with those reported in the literatures. In conclusion, system 1 is a better starting material than system 2, because the former gives higher crystallinity and larger extent of iron substitution.