Supported Metal Sulfate Catalysts FexZny/SiO2 for Selective Dimerization of Isobutene in Mixed C4 to Isooctenes

Graphical A supported bi-sulfate catalyst Fe x Zn y /SiO 2 was prepared for isobutene selective oligomerization to obtain higher C 8 = yield. The catalytic performance of Fe x Zn y /SiO 2 were superior to the supported single-sulfate catalysts (Fe x /SiO 2 or Zn y /SiO 2 ) because of the synergetic effect of the Brönsted and Lewis acid sites and the electron-donating Fe 2+ species. Among them, the Brönsted and Lewis acid sites can trigger the oligomerization of isobutene by forming carbocation intermediate and the Fe 2+ is easy to give electron to inhibit the growth of carbon chain and thus form isooctane. Isobutene dimerization is an important route to properly utilize mixed C 4 and further produce isooctane with a high-octane number to replace MTBE in gasoline. A highly selective catalyst, which is effective for isobutene dimerization but ineffective for other olefins in the C 4 mixture, is necessary for industrial implementation. In this work, a series of supported metal sulfate catalysts Fe x Zn y /SiO 2 were prepared and characterized by XRD, SEM, N 2 physical adsorption-desorption, NH 3 -TPD, Py-FTIR, and XPS. Fe 0.2 Zn 1.8 /SiO 2 can achieve isobutene conversion up to 89 % with 0 % conversion of n -butene, and the selectivity of isooctenes (C 8 = ) product is 57 % (10 h on stream). Furthermore, isobutene conversion can sustain above 80 % after 50 h. It is found that these supported catalysts contain Zn 2+ , Zn + , Fe 3+ , and Fe 2+ species, and there is a synergetic effect between Zn 2+ and Fe 2+ . Zn 2+ is beneficial to improve the conversion of isobutene, and Fe 2+ facilitates the formation of C 8 = , resulting in a high C 8 = yield.