Vibrational Spectroscopy Criteria to Determine α-Pyridyl Adsorbed on Transition Metal Surfaces

Corresponding author. Email: [email protected]; Tel: +86-592-2189023[中文摘要]基于簇模型采用密度泛函理论在B3LYP/6-311+G**/LANL2DZ(metal)基组水平上计算了吡啶及α-吡啶基吸附于Pt、Pd、Rh、Ni四种金属表面的红外和拉曼光谱.通过详细地分析和比较计算结果与文献报道的实验谱图,提出了以N端吸附的吡啶分子和α-吡啶基这两种表面物种各自存在的谱学判据.计算结果表明在以上四种金属表面,α-吡啶基的拉曼活性比吡啶的小,而特征谱峰的红外强度与吡啶相当.该结果表明红外光谱是检测金属表面α-吡啶基的有效手段,也解释了采用表面增强拉曼光谱和红外光谱研究吡啶吸附在金属表面得出不同结构的原因.[英文摘要]Density functional theory calculations at the B3LYP/6-311+G**/LANL2DZ(metal) level were used to predict the infrared (IR) and Raman spectra for pyridine and α-pyridyl upon interaction with platinum (Pt), palladium (Pd), rhodium (Rh), and nickel (Ni) clusters. After carefully comparing the simulated IR and Raman spectra with the corresponding experimental spectra from literature, the characteristic frequencies for the metal surface adsorbed pyridine and α-pyridyl were determined. Our results show that on these metal surfaces α-pyridyl has a far lower Raman activity compared with pyridine, but their characteristic frequencies have comparable IR intensities. This is the reason why different adsorption configurations are proposed for the IR and the surface-enhanced Raman spectra (SERS). Our results indicate that IR spectroscopy is an effective tool to detect α-pyridyl adsorbed on metal surface.国家自然科学基金(20973143,91027009);国家重点基础研究发展规划(973)(2007CB815303,2009CB930703); 厦门大学(2010121020);国家科学人才培养基金(J1030415)资助项

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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CACO3为内标,对水滑石样品碱性位的CO2-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CACO3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%。CO2-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 CO2-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 CO2-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.厦门大学“大学生创新性实验计划”项目;教育部科学技术研究重大(307017)资助项

Vibrational Spectroscopy Criteria to Determine alpha-Pyridyl Adsorbed on Transition Metal Surfaces

Density functional theory calculations at the B3LYP/6-311 +G**/LANL2DZ(metal) level were used to predict the infrared (IR) and Raman spectra for pyridine and a-pyridyl upon interaction with platinum (Pt), palladium (Pd), rhodium (Rh), and nickel (Ni) clusters. After carefully comparing the simulated IR and Raman spectra with the corresponding experimental spectra from literature, the characteristic frequencies for the metal surface adsorbed pyridine and alpha-pyridyl were determined. Our results show that on these metal surfaces alpha-pyridyl has a far lower Raman activity compared with pyridine, but their characteristic frequencies have comparable IR intensities. This is the reason why different adsorption configurations are proposed for the IR and the surface-enhanced Raman spectra (SERS). Our results indicate that IR spectroscopy is an effective tool to detect a-pyridyl adsorbed on metal surface.National Natural Science Foundation of China[20973143, 91027009]; National Key Basic Research Program of China (973)[2007CB815303, 2009CB930703]; Xiamen University, China[2010121020]; National Found for Fostering Talents of Basic Science, China[J1030415