Cao Wei, Xia Guang-Jie, Yao Zhen, Zeng Ke-Han, Qiao Ying, Wang Yang-Gang
Department of Chemistry and Guangdong Provincial Key Laboratory of Catalysis, Southern University of Science and Technology, Shenzhen 518055, Guangdong, China.
JACS Au. 2022 Dec 28;3(1):143-153. doi: 10.1021/jacsau.2c00560. eCollection 2023 Jan 23.
The aldehyde hydrogenation for stabilizing and upgrading biomass is typically performed in aqueous phase with supported metal catalysts. By combining density functional theory calculations and ab initio molecular dynamics simulations, the model reaction of formaldehyde hydrogenation with a Pt/TiO catalyst is investigated with explicit solvent water molecules. In aqueous phase, both the O vacancy (Ov) on support and solvent molecules could donate charges to a Pt cluster, where the Ov could dominantly reduce the Pt cluster from positive to negative. During the formaldehyde hydrogenation, the water molecules could spontaneously protonate the O in the aldehyde group by acid/base exchange, generating the OH* at the metal-support interface by long-range proton transfer. By comparing the stoichiometric and reduced TiO support, it is found that the further hydrogenation of OH* is hard on the positively charged Pt cluster over stoichiometric TiO. However, with the presence of Ov on reduced support, the OH* hydrogenation could become not only exergonic but also kinetically more facile, which prohibits the catalyst from poisoning. This mechanism suggests that both the proton transfer from solvent water molecules and the easier OH* hydrogenation from Ov could synergistically promote aldehyde hydrogenation. That means, even for such simple hydrogenation in water, the catalytic mechanism could explicitly relate to all of the metal cluster, oxide support, and solvent waters. Considering the ubiquitous Ov defects in reducible oxide supports and the common aqueous environment, this synergistic effect may not be exclusive to Pt/TiO, which can be crucial for supported metal catalysts in biomass conversion.
用于生物质稳定化和升级的醛加氢反应通常在水相中使用负载型金属催化剂进行。通过结合密度泛函理论计算和从头算分子动力学模拟，使用明确的溶剂水分子研究了Pt/TiO催化剂上甲醛加氢的模型反应。在水相中，载体上的氧空位（Ov）和溶剂分子都可以向Pt簇提供电荷，其中Ov可以主要将Pt簇从正电荷还原为负电荷。在甲醛加氢过程中，水分子可以通过酸碱交换使醛基中的氧自发质子化，通过长程质子转移在金属-载体界面处生成OH*。通过比较化学计量比的TiO载体和还原后的TiO载体，发现在化学计量比的TiO上，带正电荷的Pt簇上OH的进一步加氢很困难。然而，在还原载体上存在Ov的情况下，OH加氢不仅可以是放能的，而且在动力学上更容易，这可以防止催化剂中毒。这种机制表明，溶剂水分子的质子转移和Ov更容易进行的OH*加氢可以协同促进醛加氢。这意味着，即使对于水中如此简单的加氢反应来说，催化机制也可能与所有的金属簇、氧化物载体和溶剂水都有明确的关系。考虑到可还原氧化物载体中普遍存在的Ov缺陷和常见的水环境，这种协同效应可能并非Pt/TiO所独有，这对于生物质转化中的负载型金属催化剂可能至关重要。
