Wang Fang-Fang, Guo Rou, Jian Changping, Zhang Wei, Xue Ruifang, Chen De-Li, Zhang Fumin, Zhu Weidong
Key Laboratory of the Ministry of Education for Advanced Catalysis Materials, Institute of Physical Chemistry, Zhejiang Normal University, 321004 Jinhua, China.
Inorg Chem. 2022 Jun 20;61(24):9138-9146. doi: 10.1021/acs.inorgchem.2c00670. Epub 2022 Jun 6.
Catalytic transfer hydrogenation (CTH) of α,β-unsaturated aldehydes using single metal atom catalysts supported on nitrogen-incorporated graphene sheet (M-N-Gr) materials has attracted increasing attention recently, yet the reaction mechanism remains to be explored. Compared to the Ni-N-Gr model in which the dissociation of isopropanol is highly unfavorable as a result of steric hindrance and inertness of the Ni-N site embedded in graphene, the Ni-N site in Ni-N-Gr is more active and facilitates the formation of *H with isopropanol as the H donor, where the dissociation of H from isopropanol with an energy barrier of 0.83 eV is the rate-determining step. An alternative reaction path starts from the coadsorption of isopropanol and furfural molecules at the Ni-N site, followed by a direct hydrogen transfer between the two molecules; however, the rate-determining step has a much higher energy barrier of 1.32 eV. Our calculations suggest that the hydrogenation of the aldehyde group is kinetically more favorable than the C═C hydrogenation, revealing the high chemoselectivity of furfural to furfuryl alcohol. Our investigations reveal that the CTH mechanism using the Ni-N-Gr catalyst is different from that on traditional metal oxides, where the former has only one single active site, while two active sites are required for the latter. The proposed reaction mechanism of CTH for furfural in this study should be helpful to guide the design of single metal atom catalysts with appropriate N coordination for application in chemoselective hydrogenation reactions.
最近，使用负载在含氮石墨烯片（M-N-Gr）材料上的单金属原子催化剂对α,β-不饱和醛进行催化转移氢化（CTH）引起了越来越多的关注，但反应机理仍有待探索。与Ni-N-Gr模型相比，由于嵌入石墨烯中的Ni-N位点存在空间位阻和惰性，异丙醇的解离非常不利，而Ni-N-Gr中的Ni-N位点更具活性，有利于以异丙醇为氢供体形成*H，其中异丙醇中H的解离能垒为0.83 eV是速率决定步骤。另一条反应路径始于异丙醇和糠醛分子在Ni-N位点的共吸附，随后是两个分子之间的直接氢转移；然而，速率决定步骤的能垒要高得多，为1.32 eV。我们的计算表明，醛基的氢化在动力学上比C═C氢化更有利，这揭示了糠醛对糠醇具有高化学选择性。我们的研究表明，使用Ni-N-Gr催化剂的CTH机理与传统金属氧化物上的不同，前者只有一个单一活性位点，而后者需要两个活性位点。本研究中提出的糠醛CTH反应机理应有助于指导设计具有适当N配位的单金属原子催化剂，用于化学选择性氢化反应。
