非晶态Mn-Ce-O催化芳香醇选择氧化

Selective Oxidation of Aromatic Alcohols over Amorphous Mn-Ce-O Catalyst

采用氧化还原-沉淀法制备了一系列不同Mn/Ce摩尔比的Mn-Ce-O催化剂,并以分子氧为氧化剂考察了催化剂对芳香醇选择氧化反应的催化性能.当n(Mn)/n(Ce)=10时,Mn-Ce-O的催化活性最高,100oC下反应1h时苯甲醇转化率为96.6%,催化剂的质量比活性可达19.3mmol/(g·h).该催化剂可循环使用6次以上而其催化活性无明显降低.采用粉末X射线衍射、N2物理吸附、X射线吸收光谱和程序升温还原等手段对Mn-Ce-O催化剂进行了表征.结果表明,以Mn3+和Mn4+共存的非晶态MnOx是活化分子氧及氧化芳香醇的主要活性组分,高分散在非晶态MnOx表面的CeOx对催化剂性能有重要影响,添加少量的Ce能增大催化剂的比表面积,促进MnOx的还原,提高其表面氧中心的恢复能力,从而显著提高催化剂活性和循环使用性能.

A series of Mn-Ce-O catalyst samples with different Mn/Ce molar ratios were synthesized by a redox-precipitation method. The catalytic performance of Mn-Ce-O for the selective oxidation of various aromatic alcohols to corresponding aldehydes or ketones with molecular oxygen as an oxidant in liquid phase was studied. The catalytic activity of Mn-Ce-O with Mn/Ce molar ratio of 10 was the highest, and the benzyl alcohol conversion was 96.6 % with the mass specific activity of 19.3 mmol/（g.h） at 100℃ in 1 h. The catalyst could be recycled up to six runs without appreciable loss of its activity. X-ray diffraction, nitrogen physisorption, X-ray absorption spectroscopy, and hydrogen temperature-programmed reduction were used to characterize the Mn-Ce-O catalyst. The key active component for the O2 activation was the amorphous MnO, with coexistence of Mn^3＋ and Mn^4＋. The addition of highly dispersed CeOx to the amorphous MnOx played an important role in catalytic performance of the Mn-Ce-O catalyst, increasing its BET surface area, promoting the reduction of MnOx, increasing the capacity of surface oxygen reproduction of MnOx, and thus remarkably enhancing the catalytic activity and the recycling capability.