Research Institute of Photocatalysis, State Key Laboratory Breeding Base of Photocatalysis, Fuzhou University, Fuzhou 350002, PR China.
Langmuir. 2010 Jan 19;26(2):1362-71. doi: 10.1021/la902436s.
Four types of copper-containing MCM-41 mesoporous silicas were synthesized by the surface organometallic chemistry (SOMC) procedure (Cu/MCM-41-S), mechanical mixing (Cu/MCM-41-M), impregnation (Cu/MCM-41-I), and the hydrothermal technique (Cu/MCM-41-H). The resultant samples were characterized in detail by X-ray diffraction (XRD), N(2) physical adsorption, transmission electron microscopy (TEM), UV-vis diffuse reflectance spectroscopy (UV-vis DRS), temperature-programmed reduction (TPR), and infrared spectroscopy (IR) of NO adsorption. Catalytic behaviors of these samples for hydroxylation of phenol with H(2)O(2) were evaluated. The results revealed that depending on the preparation methods the samples contain different copper-oxo species and thus show different catalytic behaviors. Among these samples, the one prepared by SOMC contains a predominant amount of isolated Cu(2+) and exhibits the most excellent catalytic activity and selectivity. The amount of isolated copper species decreases in the order of Cu/MCM-41-S > Cu/MCM-41-H > Cu/MCM-41-I > Cu/MCM-41-M, while the amount of copper oxide clusters increases in a reversal order. The difference in the catalytic activity and product selectivity of these four samples could be rationally explained by the distinction of chemical states of copper species. The highly dispersed isolated Cu(2+) species are identified as the active sites in the phenol hydroxylation, while the nonisolated Cu(2+) clusters or oxide are responsible for the deep oxidation of primary product HQ and the decrease of product selectivity. The mechanism of the copper-catalyzed phenol hydroxylation was proposed.
四种铜负载的 MCM-41 介孔硅通过表面有机金属化学（SOMC）程序（Cu/MCM-41-S）、机械混合（Cu/MCM-41-M）、浸渍（Cu/MCM-41-I）和水热技术（Cu/MCM-41-H）合成。通过 X 射线衍射（XRD）、N2 物理吸附、透射电子显微镜（TEM）、紫外-可见漫反射光谱（UV-vis DRS）、程序升温还原（TPR）和红外光谱（IR）对 NO 吸附对所得样品进行了详细表征。评估了这些样品在苯酚与 H2O2 羟化反应中的催化性能。结果表明，根据制备方法的不同，样品中含有不同的铜氧物种，因此表现出不同的催化行为。在这些样品中，通过 SOMC 制备的样品含有大量的孤立 Cu2+，表现出最佳的催化活性和选择性。孤立铜物种的量按 Cu/MCM-41-S > Cu/MCM-41-H > Cu/MCM-41-I > Cu/MCM-41-M 的顺序减少，而铜氧化物簇的量则按相反的顺序增加。这四个样品的催化活性和产物选择性的差异可以通过铜物种化学状态的区别来合理解释。高分散的孤立 Cu2+物种被认为是苯酚羟化反应的活性位，而未孤立的 Cu2+簇或氧化物则负责主要产物 HQ 的深度氧化和产物选择性的降低。提出了铜催化苯酚羟化的反应机制。
