Turnover frequency unchanged with

Even better results are obtained by a post-synthesis treatment of TS-1 with both hydrogen peroxide and ammonium hydrogen fluoride, NH4HF2. Upon such a treatment (H202/F/Ti = 10 2.5 1 60 °C 4h), a substantial amount of titanium (up to 75% of the initial value) is removed. Nevertheless, the crystalline structure of the zeolite remains unchanged and the catalytic activity does not decrease. On the contrary, it actually increases since the turnover frequency of residual titanium atoms rises from 31 to 80 h . Even more importantly, at 8.6% benzene conversion the selectivities, both on benzene and on hydrogen peroxide, also increase from 83 to 94% and from 67 to 83% respectively, with formation of catechol (4%) and hydroquinone (2%) as the only by-products, without any evidence of further oxidation reactions [19]. 

Investigation of nickel catalyst samples after ten years of operation in a commercial steam reformer [453] showed an increase in nickel crystal size with temperature, whereas the turnover frequency (specific activity) was almost unchanged, i. e. comparable with that of unused catalyst. 

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