Swelling and pillaring of the layered precursor IPC-1P: tiny details determine everything

Abstract

The influence of swelling (i.e. the size of tetraalkylammonium surfactant molecule, the presence of tetrapropylammonium hydroxide (TPAOH), pH) and pillaring (i.e. the ratio between the swollen precursor IPC-1P and tetraethyl orthosilicate) conditions on the structure and textural properties of the resulting materials was studied in detail for IPC-1P, which is the layered precursor of zeolite PCR. The swelling of IPC-1P proceeds efficiently under basic conditions both in mixed C_nH_2n+1N(CH₃)₃Cl/TPAOH systems and in C_nH_2n+1N(CH₃)₃OH (n = 8, 10, 12, 14, 16, 18) solutions at pH = 13–14. The intercalation of C_nH_2n+1N⁺(CH₃)₃ in IPC-1P resulted in the formation of expanded materials with interlayer distances growing with increasing length of the alkyl chain in C_nH_2n+1N(CH₃)₃⁺: 1.59–1.86 (n = 8) < 1.89–2.11 (10) < 2.05–2.26 (12) = 2.08–2.26 (14) < 2.37–2.43 (16) < 2.57–2.71 (18) Å. IPC-2 zeolite was formed during calcination of IPC-1P samples swollen in C_nH_2n+1N(CH₃)₃OH solution, while PCR zeolite can be obtained by calcination of IPC-1P treated with either C_nH_2n+1N(CH₃)₃Cl/TPAOH or C_nH_2n+1N(CH₃)₃Cl. The pillaring of IPC-1P samples swollen with C_nH_2n+1N(CH₃)₃OH provided mesoporous materials with narrow pore size distribution in the range 2.5–3.5 nm. Pillared materials derived from the samples swollen in the presence of TPAOH were characterized by a broader pore size distribution. The optimal TEOS/IPC-1PSW ratio being sufficient for the formation of well-ordered pillared derivatives characterized by improved textural properties (S_BET = 878 m² g⁻¹, V_total = 0.599 cm³ g⁻¹) was found to be 1 : 1.5.