Selective Synthesis of 1,4-Dioxane from Oxirane Dimerization over ZrO[sub.2]/TiO[sub.2] Catalyst at Low Temperature

We report a route to produce 1,4-dioxane from oxirane by using ZrO[sub.2]/TiO[sub.2] as catalyst. The composite oxide ZrO[sub.2]/TiO[sub.2] was prepared by a coprecipitation method and the catalytic performance was tested through the synthesis of 1,4-dioxane from oxirane in a pipe reactor. The X-ray diffraction (XRD) shows that ZrO[sub.2] and TiO[sub.2] are in crystal form. When the mass percentage of ZrO[sub.2] is 25%, the composite oxide ZrO[sub.2]/TiO[sub.2] presents as an amorphous form. The sample 25%ZrO[sub.2]/TiO[sub.2] exhibits a specific surface area of 269.5 m[sup.2]·g[sup.−1] and pore volume of 1.34 mL·g[sup.−1]. The catalyst has 670 µmol·g[sup.−1] of NH[sub.3]-TPD acid, and the characterization of ammonia infrared spectroscopy (NH[sub.3]-FTIR) shows that both Brønsted and Lewis acids are present on the surface of the catalyst. The reaction mechanism was analyzed according to the distribution of product. The test of catalytic performance showed 100.0% conversion of oxirane and 86.2% selectivity of 1,4-dioxane at the optimal operation conditions: atmospheric pressure, reaction temperature 75 °C and gaseous hourly space velocity of 1200.0 h[sup.−1]. The catalyst exhibits good catalytic performance stability after continuous use for 720 h.