高分散CuMnMgAl-LDH催化剂的可控制备及其在苯乙烯环氧化反应中的催化性能研究

Controllable preparation of high-dispersed CuMnMgAl-LDH catalysts and their catalytic performance for epoxidation of styrene

基于水滑石(LDHs)层板元素的可调控性,采用共沉淀法制备了系列Cu、Mn双活性组分非贵金属CuMnMgAl-LDH催化剂,用于苯乙烯环氧化反应.受LDHs层板晶格定位效应的影响,活性组分高度稳定分散,与采用沉淀沉积法制备的负载型CuMnO_x/MgAl-LDH催化剂相比,苯乙烯转化率提高13.9%.且CuMnMgAl-LDH表面丰富的羟基结构,降低了催化剂的表面酸性,有效抑制了环氧苯乙烷(SO)的开环,从而提高了SO的选择性.进一步通过调变Cu/Mn摩尔比探究了双金属组分的协同作用对催化性能的影响.其中,Cu/Mn比为0.5:0.5时,Cu_(0.5)Mn_(0.5)Mg_5Al_2-LDH催化剂协同作用最强,具有最低的活化能(22.5kJ/mol)及最优的活性(97.3%)和选择性(66.3%),且催化剂经3次循环使用后,活性无明显下降.此外,发现溶剂与催化剂对氧化剂的活化存在竞争效应.

Based on the cation-tunability of the brucite-like layers in LDHs, a series of CuMnMgA1-LDH catalysts were prepared by co-precipitation method for epoxidation of styrene. Cu and Mn as active metals were highly dispersed and stably immobilized in the layers due to the lattice orientation effect, resulting in 13.8% higher conversion than that over supported DP-CuMnOJMgA1-LDH catalyst synthesized by deposition-precipitation method. Moreover, because of the rich hydroxyl groups on the surface of CuMnMgA1-LDH, the acidity was reduced, which could suppress the hydration, and thus enhanced the selectivity of styrene oxide （SO）. Furthermore, the synergistic effect of Cu and Mn was also investigated by adjustment of the molar ratio of Cu/Mn with 1：0, 0.75：0.25, 0.5：0.5, 0.25：0.75 and 0：1. Among them, Cu0.5Mn0.5Mg5Al2-LDH was in the highest activity （97.33% conversion） and selectivity （66.31%）, as well as the lowest activation energy （22.46 kJ/mol）. The as-synthesized Cu05Mn0.5MgsAl2-LDH was used in 3 successful cycles, in which the activity has no obvious decrease. Meanwhile, it is found that there is a competition effect between the solvent and the catalyst on the activation of oxidation agent, and the amount of the solvent could directly impact the selectivity.