浆态床合成二甲醚复合催化剂失活原因探索

在反应温度260℃、压力5.0MPa的条件下，对浆态床反应器中二甲醚合成复合催化剂的失活规律进行了研究。结果表明， Cu基催化剂失活较快是导致浆态床二甲醚合成催化剂不稳定的主要原因。通过分析Cu基催化剂在浆态床反应器和固定床反应器中的活性变化规律，发现在浆态床反应器中不能及时导出反应体系的H2O对催化剂的毒副作用导致了浆态床Cu基催化剂快速失活。对失活催化剂进行的TPR、XRD和SEM EDS表征结果可以看出，Cu粒子的长大和积炭是Cu基催化剂失活的重要原因，与已有文献报道不同的是并未发现明显的Cu元素流失。

Effects of CaO-modified zeolite on one-step synthesis of dimethyl ether

Synthesis of dimethyl ether (DME) was carried out in a fixed bed reactor over a bifunctional catalyst CaO/HZSM-5+JC207, which was composed of a methanol-synthesis catalyst JC207 (Jingjing Catalyst Plant, China) and a dehydrator HZSM-5 (Si/Al = 38) modified with CaO. The effects of zeolite modification with CaO on the performance of the bifunctional catalyst in one-step synthesis of DME were investigated. XRD analysis of the modified zeolite CaO/HZSM-5 indicates that CaO is highly dispersed on the zeolite HZSM-5 without any new species formed. Pyridine-IR analysis shows that the modification of HZSM-5 with CaO not only brings on significant changes in acid type and acid amount but also turns some of Bronstead acid sites into Lewis acid sites. NH₃-temperature programming desorption analysis indicates that the number of acid sites on the zeolite surface, especially, that of the strong acid sites decreases with the increase of CaO loading. Modification of zeolite HZSM-5 with appropriate dose of CaO turns the strong acid sites into weak or less strong acid sites; such a redistribution of acid sites may be beneficial for the increase of DME selectivity.