Mordenite coating onto cordierite monolith: Micropore accessibility.

M. A. ULLA; R. MALLADA; L. B. GUTIERREZ; L. CASADO; J. P. BORTOLOZZI; E. E. MIRÓ; J. SANTAMARÍA

Zaragoza

Congreso; International Zeolite Membrane Meeting; 2007

In a previous work pure mordenite layer onto cordierite monolith was obtained via hydrothermal synthesis without using any template molecules. The zeolite crystal shape was needle-type with an average length of 15 µm. However, the surface area of the as-synthesized mordenite layer was lower than the expected for a microporous zeolite. The aim of the present study is to analyze the effect of different post-treatments on the micropores accessibility of the mordenite layer and to understand the causes of their obstructions. The mordenite layer onto cordierite monoliths was obtained by hydrothermal synthesis. After the synthesis, different post-treatments were done: (A) calcination in air flow from 25C to 480C with a heating ramp of 1C.min-1 and them kept at this final temperature for 8h, (B) Treatment with an aqueous solution of 0.2M NaOH at 95C for 5h, (C) Treatment with an aqueous solution of 0.2M HCl at 95C for 1h (D) Treatment with an aqueous solution of CH3COOH + NaCH3COO (pH: 5.2) at 60C for 4h,. Mordenite layer on cordierite substrates was characterized by SEM, XRD and Raman Spectrocopy. The surface area was estimated by BET analysis using N2 adsorption. Besides, strong basic post treatment (Sample B) caused an important weight lost and some decrease of the crystallinity occurred. On the other hand, the surface area values remarkably increase after acidic post-treatments. Moreover, the mild one at pH: 5.2 do not cause any important weight lost and preserved the zeolite crystal size and its crystallinity as well the coating morphology. The acidic post treatment remove some extraframework cations located in the main channels of the mordenite crystals which hamper the accessibility to the micropores.