钯/掺杂锰氧八面体分子筛催化一步合成碳酸二苯酯

采用浸渍法制备出Ce3＋, Cu2＋, Pb2＋, Ag＋, Fe3＋掺杂锰氧八面体分子筛, 负载钯后用于一步氧化羰基化合成碳酸
二苯酯(DPC)反应. Pd/Cu-OMS-2 催化活性最高, DPC 收率为12.1%. 通过X 射线衍射(XRD), 扫描电镜(SEM), 氮气吸
附(BET)和X 射线光电子能谱(XPS)对催化剂样品进行了表征. 表征结果表明, 不同金属离子掺杂后, 催化剂的晶型仍
保持隐钾锰矿结构. 从电位滴定测试数据来看, 杂质离子引入后, 锰的平均氧化态增加. 在催化反应过程中, Mn4＋/
Mn2＋和Pd2＋/Pd0 构成了氧化还原循环链, Mn3＋的存在可以补充反应过程中消耗掉的Mn4＋. XPS 分析了晶体中氧物种的
存在形式, 化学吸附氧/(晶格氧＋化学吸附氧)的比值越高, 催化活性越好.

One Step Synthesis of Diphenyl Carbonate over Palladium/MetalDoped Manganese Oxide Octahedral Molecular Sieve Catalysts

Manganese oxide octahedral molecular sieve materials (OMS-2) with different metal cation dopants (M: Ce~(3+), Cu~(2+), Pb~(2+), Ag~+, Fe~(3+)) were prepared by a wet impregnation process and characterized through X-ray diffraction (XRD), scanning electron microscopy (SEM), Brunauer-Emmer-Teller (BET) surface area measurement and X-ray photoelectron spectroscopy (XPS). The catalytic properties of palla-dium/M-OMS-2 were investigated for oxidative carbonylation of phenol to diphenyl carbonate (DPC). Pd/Cu-OMS-2 catalyst showed the best catalytic activity, and DPC yield reached 12.1%. XRD patterns of M-OMS-2 samples are similar to that of OMS-2, which has a cryptomelane type structure, indicating that the metal dopant is well dispersed. The data of potentiometric titration have illuminated that higher average oxidation number leads to higher DPC yield, which, thus, makes sure that manganese dioxide can oxidize Pd~0 and the resulting Mn~(2+) can be reoxidized by oxygen subsequently in a redox cycle. The electrons are exchanged between Mn element and active Pd species. Moreover, Mn~(3+) plays a role in renewing Mn~(4+).Oxygen species was investigated through XPS and the results suggested that catalytic activity getted better with the increase of the content of the chemisorbed oxygen on the surface of catalysts.