An efficient method to optimize the synthesis of titanosilicates is discussed, along with strategies to unveil critical structure-function relationships. Titanosilicates are industrially relevant, versatile heterogeneous catalysts used in alkene epoxidation, ammoximation and aromatic diol production.1 Therefore, synthesis of new types of titanosilicates, targeting specialized applications, is a highly active field of research. However, their synthesis is challenging, due to requirement of expensive, specialized conditions and extreme sensitivity to changes in the synthesis environment. This, in turn, results in low catalytic performance.2
Therefore, a systematic, statistical approach to probe optimal synthesis conditions is most desirable. The Doehlert matrix (DM) statistical model is introduced as an effective tool for optimizing the synthesis of titanosilicates. The DM is a second-order statistical model, widely used in analytical sciences, to quickly determine optimal experimental conditions when many parameters play a role simultaneously.3 However, it has not yet gained prominence in the field of catalysis. Often, one condition is changed at a time, missing out on synergistic effects.
The DM approach was used to investigate the optimal synthesis conditions of a novel, hierarchically ordered, micro-mesoporous titanosilicate material (MMTS) with the aim of achieving superior catalytic performance. Catalytic characterization of MMTS was conducted via epoxidation of cyclohexene with tert-butylhydroperoxide (TBHP). The results reveal that the catalytic performance of MMTS is significantly enhanced by the optimization experiments, with unprecedented catalytic activity, measured as turn over frequency (TOF) in mols of cyclohexene converted per mol Ti and per unit of time. The relationship between catalytic performance and properties of the material, such as the amount of framework Ti, and the nature of the pore network, is thoroughly discussed. The enhanced catalytic performance, together with critical structure-function insights, demonstrates the potential of using a DM approach in catalysis.
1. Perera, A. S.; Coppens, M.-O., Titano-silicates: highlights on development, evolution and application in oxidative catalysis. In Catalysis, Spivey, J. J., Ed. RSC Publishing: 2016; Vol. 28, pp 119-143
2. Corma, A., From microporous to mesoporous molecular sieve materials and their use in catalysis. Chem. Rev. 1997, 97, 2373-2419.
3. Doehlert, D. H., Uniform shell designs. Applied Statistics 1970, 19, 231–239.