Ammonium fluoride etching of TS-1 allows for the unbiased leaching of Si and Ti and to the generation of large mesopores that efficiently allow to reduce the diffusion path length in catalysis.
The impact of the NH4F etching on the textural and catalytic properties of TS-1 was investigated. Two TS-1 with different crystal sizes, i. e. 200 and 100 nm; were achieved, with different textural properties as inferred from nitrogen physisorption isotherms at 77 K, mercury porosimetry, powder X-ray diffraction patterns and transmission electron microscopy. The generation of larger mesopores within the parent samples was observed together with a reduction of the coherent crystal size (CCS) upon NH4F etching. The generation of secondary porosity further did not result in an alteration of the Si/Ti ratio, allowing to compare the catalytic outcomes of the samples as a function of the textural properties. It was found that the methyl-phenyl sulfide (MPS) conversion kinetics importantly depend on the textural properties of the catalysts. The initial velocity was found to increase linearly with the reduction of the CCS until reaching a plateau, indicating that diffusion limitation occur up to a CCS of approximately 100 nm. Likewise, mono- and di-oxidation product selectivity was governed by diffusion issues.Zum Volltext