Effective delamination of a layered two-dimensional MCM-22 zeolite: Quantitative insights into the role of the delaminated structure on acid catalytic reactions

A layered precursor of MCM-22 (Mobil Composition of Matter-22), a representative two-dimensional MWW type zeolite, is a flexible, reliable platform for structural transformation via inter-layer swelling and subsequent pillaring or delamination. In particular, the delaminated MWW type zeolite, which is a few nanometers thick, is desirable for overcoming diffusional limits. Despite its promise, the conventional procedure to acquire the delaminated MCM-22 is complicated; the resulting particle is known as ITQ-2 (Instituto de Tecnologia Quimica Valencia-2). Here, we propose a simple, effective method for delaminating MCM-22 precursors into nanosheets; the calcination of swollen MCM-22 precursors resulted in successful delamination. A rigorous analysis of the structural and textural properties of the resulting delaminated forms revealed that a majority of the nanosheets had a 3–4 unit cell thickness along the c-axis, which were further formed via aggregation of particles having ca. 1–2 unit cell thickness and retaining the original intra-layer zeolite structure. In addition, we applied the MCM-22 zeolite and its derivatives (i.e., the aforementioned delaminated MCM-22 zeolite and ITQ-2) to two conventional acid catalytic reactions (methanol to hydrocarbons and toluene methylation). Furthermore, we could quantitatively correlate the catalytic performance as well as the deactivation degree of the three catalysts with the corresponding structural and acidic properties. Notably, unlike an initial expectation, the delaminated MCM-22 zeolite lowered both the catalytic activity and long-term stability. These could be attributed to the decreased acid sites in the two-dimensional micropores (mainly, those used to be present in the inter-layer) and the increased non-zeolitic acid sites (other than the micropores), respectively, by the delamination, hindering the proper uses as conventional acid catalysts.