Acharyya Shankha S, Ghosh Shilpi, Yoshida Yusuke, Kaneko Takuma, Sasaki Takehiko, Iwasawa Yasuhiro
Innovation Research Center for Fuel Cells, The University of Electro-Communications, Chofu, Tokyo, 182 8585, Japan.
Graduate School of Informatics and Engineering, The University of Electro-Communications, Chofu, Tokyo, 182 8585, Japan.
Chem Rec. 2019 Sep;19(9):2069-2081. doi: 10.1002/tcr.201900023. Epub 2019 Jul 3.
Catalytic benzene C-H activation toward selective phenol synthesis with O remains a stimulating challenge to be tackled. Phenol is currently produced industrially by the three-steps cumene process in liquid phase, which is energy-intensive and not environmentally friendly. Hence, there is a strong demand for an alternative gas-phase single-path reaction process. This account documents the pivotal confined single metal ion site platform with a sufficiently large coordination sphere in β zeolite pores, which promotes the unprecedented catalysis for the selective benzene hydroxylation with O under coexisting NH by the new inter-ligand concerted mechanism. Among alkali and alkaline-earth metal ions and transition and precious metal ions, single Cs and Rb sites with ion diameters >0.300 nm in the β pores exhibited good performances for the direct phenol synthesis in a gas-phase single-path reaction process. The single Cs and Rb sites that possess neither significant Lewis acidic-basic property nor redox property, cannot activate benzene, O , and NH , respectively, whereas when they coadsorbed together, the reaction of the inter-coadsorbates on the single alkali-metal ion site proceeds concertedly (the inter-ligand concerted mechanism), bringing about the benzene C-H activation toward phenol synthesis. The NH -driven benzene C-H activation with O was compared to the switchover of the reaction pathways from the deep oxidation to selective oxidation of benzene by coexisting NH on Pt metallic cluster/β and Ni O oxide cluster/β. The NH -driven selective oxidation mechanism observed with the Cs /β and Rb /β differs from the traditional redox catalysis (Mars-van Krevelen) mechanism, simple Langmuir-Hinshelwood mechanism, and acid-base catalysis mechanism involving clearly defined interaction modes. The present catalysis concept opens a new way for catalytic selective oxidation processes involving direct phenol synthesis.
利用氧气将苯催化C-H活化以选择性合成苯酚仍然是一个亟待解决的具有挑战性的问题。目前，苯酚在工业上通过三步异丙苯液相法生产，该方法能源密集且不环保。因此，迫切需要一种替代的气相单路径反应工艺。本文报道了在β沸石孔道中具有足够大配位球的关键受限单金属离子位点平台，该平台通过新的配体间协同机制促进了在NH共存下用氧气选择性苯羟基化的前所未有的催化作用。在碱金属、碱土金属离子以及过渡金属和贵金属离子中，β孔道中离子直径>0.300 nm的单个Cs和Rb位点在气相单路径反应过程中对直接苯酚合成表现出良好的性能。单个Cs和Rb位点既不具有显著的路易斯酸碱性质，也不具有氧化还原性质，它们分别不能活化苯、氧气和NH，然而当它们共同吸附时，单碱金属离子位点上的共吸附物之间的反应协同进行（配体间协同机制），从而实现苯C-H活化以合成苯酚。将NH驱动的用氧气进行的苯C-H活化与在Pt金属簇/β和NiO氧化物簇/β上通过共存NH使苯的反应途径从深度氧化转变为选择性氧化进行了比较。在Cs⁺/β和Rb⁺/β上观察到的NH驱动的选择性氧化机制不同于传统的氧化还原催化（Mars-van Krevelen）机制、简单的Langmuir-Hinshelwood机制以及涉及明确相互作用模式的酸碱催化机制。目前的催化概念为涉及直接苯酚合成的催化选择性氧化过程开辟了一条新途径。
