表面改性对Cu/活性炭催化剂表面Cu物种和催化活性的影响

摘要

通过对活性炭表面改性,研究了醋酸铜溶液浸渍后热分解制备的Cu/AC无氯催化剂对甲醇氧化羰基化合成碳酸二甲酯催化性能的影响.通过低温氮吸附-脱附、FTIR等表征对改性前后活性炭的比表面积及表面官能团变化进行了分析,发现氨水改性的活性炭比表面积略有增大,表面不饱和还原性官能团(C≡N、C≡C)增加,而KMnO4改性的活性炭比表面积减小7%,表面C=O、-COOH显著增加.进一步通过XRD、H2-TPR、XPS等表征分析了催化剂表面铜物种(Cu0/Cu1/CuⅡ)的形态,发现表面铜物种的价态和配比与活性炭表面性质密切相关,影响催化剂活性.活性炭改性后,表面微观结构和表面化学性质的变化对浸渍醋酸铜的表面分布和热分解过程产生明显影响,导致催化剂表面活性Cu物种发生变化.和其它表面改性方法相比,氨水改性的活性炭更有利于催化剂活性的提高,碳酸二甲酯的时空收率及甲醇转化率分别达到了152.8 mg·g-1·h-1和7.4%.%The chloride-free catalyst Cu/AC (activated carbon) was prepared by impregnation method with copper acetate supported on AC. The performance of the catalyst was evaulated using direct vapor-phase oxidative carbonylation of methanol to dimethyl carbonate (DMC) as a model reaction. The effects of AC surface modification on catalytic activity, microstructure and valence state of copper were investigated by low temperature adsorption-desorption, FTIR, XRD, H2-TPR, XPS techniques. When AC is treated with ammonia, its specific surface area and the unsaturated reducing functional groups(C = N, C = C) increase slightly. On the contrary, when AC is modified by KMnO4, its specific surface area decreases 7%, while the C =0 and -COOH species on the surface increase significantly. The valence state and ratio of surface copper species (Cu0/CuⅠ/CuⅡ) were determined by the surface microstructure and chemical property of AC. Cu/AC catalyst treated with ammonia exhibits an excellent activity with the methanol conversion and the space time yield of DMC of 7.4% and 152.8 mg·g-1h-1, respectively.