通过共沉淀法制备了一系列不同镁铝比的水滑石样品,依据物相分析与热失重实验结果确认了合成的样品具有水滑石结构.以方解石型CaCO_3为内标,对水滑石样品碱性位的CO_2-程序升温脱附(TPD)定量表征进行校正,并比较了不同实验参数对方法精密度的影响.经过各测试参数的敏感性分析证实,用CaCO_3脱附峰面积校正后,水滑石碱密度测量结果的RSD分别由9.7%、12.3%下降为4.3%、7.3%,而汇总分析的RSD可从29.6%下降至6.6%.CO_2-TPD定量分析精密度明显提高,证实了内标法的优势及其应用于固体碱定量表征的可行性.将内标法所得结果与固体碱催化酯交换反应的性能关联,结果发现,水滑石催化性能受到活性相的碱强度与碱密度双重指标的调控,碱强度和碱密度越大,酯交换催化效率越高.
A series of hydrotalcite samples with varied Mg/Al ratios were synthesized by coprecipitation route. Quantitative analysis on the basic sites of hydrotalcite samples was carried out by CO_2-TPD(temperature programmed desorption) technique which was calibrated by calcium carbonate internal standard,and the effects of various experimental factors on the precision of testing results were evaluated. The relative standard deviation(RSD) of the experiments shows that the precision of test is obviously improved under the condition that the internal standard calibration is applied. Moreover,combined with the internal standard quantitative CO_2-TPD-MS technique,the investigation on the catalytic performance of hydrotalcites in transesterification demonstrates that the solid base with the stronger alkalinity and the higher density of basic sites presents the higher catalytic activity.
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