正丁烷在金属钼酸盐催化剂上的氧化脱氢

Oxidative Dehydrogenation of n-Butane over Metal Molybdates

用柠檬酸盐法合成了第一系列过渡金属 (Cr ,Mn ,Fe,Co ,Ni,Cu和Zn)及Mg的钼酸盐催化剂 ,研究了它们对正丁烷氧化脱氢反应的催化作用 .结果表明 ,这些钼酸盐催化剂的催化性能受阳离子的影响较大 .CoMoO4催化剂具有最高的催化活性和较高的选择性 ,其催化性能与文献报道的对正丁烷氧化脱氢反应催化性能最好的ZrP2 O7和Mg3 V2 O8催化剂大致相当 ;MgMoO4催化剂虽然选择性较高 ,但活性较低 ;Cr2 (MoO4) 3 上基本没有C4烯烃生成 ;其它钼酸盐催化剂对正丁烷氧化脱氢反应的催化活性和对烯烃的选择性都较低 .XRD ,NH3 TPD和H2 TPR的研究结果表明 ,催化剂为单一的钼酸盐晶相 ,催化剂的性能由其氧化还原性决定而与其表面酸量没有直接关系 .通过对产物分布的分析 ,提出了正丁烷在CoMoO4催化剂上的氧化脱氢反应途径 .在 5 5 8℃ ,正丁烷发生氧化脱氢生成正丁烯和丁二烯以及氧化燃烧生成CO2 三个平行竞争反应的竞争分率分别约为 75 % ,10 %和 15 % .在正丁烷转化率较高的条件下 ,产物中的CO2 主要来自C4烯烃的再氧化反应 ,而CO则完全来自C4烯烃的再氧化 .

Molybdates of the first-row transition metals (Cr, Mn, Fe, Co, Ni, Cu, Zn) and Mg have been prepared by the citrate method and their catalytic performance for the n-butane oxidative dehydrogenation has been studied. The properties of these catalysts strongly depend on the cations of the metal molybdates. Among the catalysts, CoMoO 4 is the most active catalyst with higher selectivity being comparable to that of ZrP 2O 7 and Mg 3V 2O 8 reported in literature. Although the MgMoO 4 catalyst is more selective for the n-butane oxidative dehydrogenation under the identical reaction conditions, it is less active than CoMoO 4. Over the Cr 2(MoO 4) 3 catalyst, the combustion reaction takes place predominantly and almost no C 4 olefins are obtained in the products. The other metal molybdates show poor catalytic activity and selectivity. The results of XRD, NH 3-TPD and H 2-TPR indicate that each catalyst prepared by the citrate method is composed of pure molybdate crystal phase. The redox properties of the catalysts play a key role in the n-butane oxidative dehydrogenation and no relationship between the catalytic performance and the acid amount on the catalyst surface is observed. According to the product distribution, the reaction network for the oxidative dehydrogenation of n-butane over the CoMoO 4 catalyst at 558 ℃ is proposed. Under the reaction conditions, three competitive parallel reactions take place, producing butene (75%), carbon dioxide (15%) and butadiene (10%), respectively. At high n-butane conversion, carbon dioxide results mainly from re-oxidation of C 4 olefins, while CO is entirely produced from the deep oxidation of C 4 olefins.