Selectivity-Controlling Factors in Catalytic Methanol Amination Studied by Isotopically Modulated Excitation IR Spectroscopy

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• 作者：Nobutaka Maeda ; Fabian Meemken ; Konrad Hungerb眉hler ; Alfons Baiker
• 刊名：ACS Catalysis
• 出版年：2013
• 出版时间：February 1, 2013
• 年：2013
• 卷：3
• 期：2
• 页码：219-223
• 全文大小：313K
• 年卷期：v.3,no.2(February 1, 2013)
• ISSN：2155-5435

文摘

Present mechanistic models for catalytic amination of methanol by zeolites focus on shape-selectivity of monomethylamine (MMA), dimethylamine (DMA), and trimethylamine (TMA) in the micropores. However, a rational explanation of the uniquely high selectivity to MMA and DMA achieved over Na⁺-exchanged mordenite (Na⁺-MOR) requires the consideration of additional selectivity-controlling factors. We have applied modulation鈥揺xcitation diffuse reflectance IR Fourier transform spectroscopy with periodic perturbation by the isotope CD₃OD to realize a chemically steady state but isotopically transient condition during methylamines synthesis from methanol and ammonia. These studies proved that the H-bonded network of methanol agglomerates and open dimers in the micropores can readily be replaced by NH₃ at 623 K, probably leading to a decrease in the methanol concentration around catalytically active sites and, thus, suppressing the consecutive reaction of MMA to DMA and, finally, to TMA. Concentration modulation between NH₃ and MMA indicated weaker adsorption of MMA, which was largely replaced by NH₃ at the reaction temperature, thereby hindering further methylation of MMA.

Keywords:

ammonia; in situ IR spectroscopy; isotope; methanol; methylamines; mordenite