Structure and Basicity of Microporous Titanosilicate ETS-10 and Vanadium-Containing ETS-10

Abstract

ETS-10 has attracted considerable attention as a base catalyst. It is desirable to confirm the location of basic sites. Vanadium-substituted ETS-10 also attracts much attention for the interesting feature that the Ti can be fully replaced by V without changing its topology. It is important to characterize the local environment upon V substitution for understanding the property and reactivity of ETVS-10. The structural and acid–base properties of pure titanosilicate ETS-10 and a series of vanadium-substituted ETVS-10 with different framework V content were studied by a combination of Raman spectroscopy and FTIR of absorbed acetylene and carbon monoxide as molecular probes. The substitution of up to 70% of Ti atoms with V in the structure of ETS-10 results in ETVS-10 materials with a homogeneous distribution of Ti and V species. At higher V concentrations, a distinct phase separation between the vanadium-rich domains is observed. The intrinsic basicity of ETVS-10 as revealed by FTIR spectroscopy of adsorbed C2H2 gradually increases with the increasing V content. It is shown that the specific basicity of the ETS-10 lattice is mainly associated with the presence of highly basic oxygen centers adjacent to the lattice defects. Liquid phase Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate was used as a test reaction to investigate the catalytic reactivity of different basic sites in the synthesized materials. The reactivity of the materials considered in the base-catalyzed Knoevenagel condensation is determined not only by the strength of the basic sites but also by their density. The optimum combination of both factors is achieved for the ETVS-10 material with V/(Ti+V) ratio of 70%.