Abstract: Benzylamine, with its diverse applications in medicine, pesticides, dyes and spices, has garnered the attention for its industrial significance. While benzylamine can be synthesized through the reductive amination of benzaldehyde, the catalysts employed are often complex and expensive. In this work, we report a series of alkali metal cation-modulated cobalt catalysts supported on silica (Co-M/SiO2) prepared via a simple impregnation method. The catalysts were evaluated for the reductive amination of benzaldehyde. Notably, the best catalyst Co-Na/SiO2 (Co2+:Na+=1:1.5),obtained the conversion of benzaldehyde to 100% and the selectivity of benzylamine to 94.6%. The doped catalyst increased benzylamine selectivity by 24.6 percentage points and decreased benzyl alcohol byproduct formation by 17.1 percentage points. Characterization of the catalysts (XRD, XPS, TEM, Raman, NH3-TPD, CO2-TPD, H2-TPD, TGA) provided insights into the structural and morphological properties of the catalysts. Results indicated that cobalt in the Co-Na/SiO2 catalyst primarily existed in the Co0 and CoOx form, and the addition of Na+ changed the binding energy of Co0 species in the catalyst through electron transfer. Moreover, the Co-Na/SiO2 catalyst offered a balanced distribution of acid-base sites and optimal hydrogen adsorption capacities, favoring the reductive amination. The in situ DRIFTS experiments were utilized to illustrate the differences between species adsorption abilities and reaction processes over Co-Na/SiO2 and Co/SiO2 catalysts. Results revealed that the Co-Na/SiO2 catalyst had a superior ability to reduce benzaldehyde amines to benzylamine compared to the Co/SiO2 catalyst, as it could inhibit the formation of benzyl alcohol byproduct. This work provides a cost-effective and highly active cobalt-based catalyst preparation strategy for reductive amination, paving the way for future research in designing efficient catalysts for this important transformation.

Key words: benzaldehyde, benzylamine, reductive amination, alkali metal cation modulation, Co-based catalyst

摘要： 苄胺因其在医药、农药、染料和香料等领域的广泛应用而备受瞩目。苄胺可以通过苯甲醛(BzH)还原胺化反应进行制备，但受限于用于该反应的催化剂制备步骤复杂、成本高。本工作通过浸渍法制备了一系列负载在二氧化硅上的碱金属阳离子调变的钴催化剂(Co-M/SiO2)，并评价了不同催化剂对BzH还原胺化反应的影响。最佳催化剂Co-Na/SiO2 (Co2+:Na+=1:1.5)催化BzH转化率为100%，目标产物苄胺的选择性为94.6%。与未加入碱金属阳离子的Co/SiO2催化剂相比，该催化剂使苄胺选择性提高了24.6个百分点，副产物苯甲醇(BzAh)减少了17.1个百分点。通过一系列表征技术(XRD, XPS, TEM, Raman, NH3-TPD, CO2-TPD, H2-TPD, TGA)深入探究了催化剂结构和形貌特征。结果表明，在Co-Na/SiO2中，钴主要以Co0和CoOx形式存在，引入的Na+通过电子转移作用改变了催化剂中Co0物种的结合能；此外，Co-Na/SiO2催化剂提供了适量的酸碱性位点及适当的氢气吸附能力，有利于还原胺化反应发生。利用原位红外实验分析了Co-Na/SiO2催化剂和Co/SiO2催化剂的吸附能力和反应过程差异。结果表明，Co-Na/SiO2催化剂催化苯甲醛还原胺化合成苄胺的能力优于Co/SiO2催化剂的原因在于能够抑制副产物BzAh的生成。本工作为还原胺化反应提供了一种低成本且高活性的钴基催化剂制备策略，为以后用于该反应的高效催化剂的设计研究奠定了基础。

关键词: 苯甲醛, 苄胺, 还原胺化反应, 碱金属阳离子调变, 钴基催化剂