过渡金属纳米催化剂的原位析出及催化有机酸/酯选择性加氢的研究

The selective hydrogenation of acids/esters is one of the most crucial reactions for highly efficient and clean utilization of carbon containing resource. Traditional metal based catalysts show good performance but suffer from inevitable deactivation due to the aggregation of active sites. Perovskite oxide catalysts (ABO3) show much better structural and chemical stability, but the improvement of activity is still demanded. Our previous studies have found that the artificial introduction of A-site deficiency to form non-stoichiometry can help the in-situ exsolution of B-sites metallic nanoparticles. Besides, we also found that the crystal reconstruction of selected perovskite parent can also significantly facilitate the B-site exsolution. Compared to catalysts prepared by traditional impregnation, the exsolved nanoparticles implanted on functional perovskite parents show stronger metal-support interaction, which present promoted thermal stability and desirable performance for activation of hydrogen. .Accordingly, in this project, the selective hydrogenation of typical compounds with C-O/C=O bonds including aliphatic acid (e.g., acetic acid, lactic acid) and esters (e.g.,dimethyl oxalate, ethylene carbonate) is chosen as model reactions, and the highly stable in-situ exsolved metallic particles decorated perovskite oxides are employed as a novel hydrogenation catalysts. We focus on three fundamental but significant questions including mechanism of in-situ exsolution, the role of active site for target reactions, and synergistic effect between exsolved nanoparticles and perovskite matrix. The structure-performance correlation and the the understanding of reaction mechanism on the atomic scale will be figured out through the systematic investigation on the diverse influencing effects (e.g., morphology, chemical state, and composition of exsolved particles) on hydrogenation performance.

有机酸/酯的选择性加氢是碳资源优化利用的重要反应之一，传统金属基催化剂易团聚失活，热稳定性有待提高。ABO3型钙钛矿稳定性高，此前研究表明，在其A位引入缺陷可促进大量B位金属纳米粒子均匀析出(缺陷助析出)。此外近期我们还发现一类析出新途径，即某些钙钛矿可通过高温自发相变为析出提供更强驱动力(相变助析出)。析出金属与钙钛矿本体的相互作用较传统浸渍法更强，活化氢能力及热稳定性更优。综上，本项目拟以含C-O/C=O键的典型有机酸/酯(以醋酸/乳酸、草酸二甲酯/碳酸乙烯酯为代表)的选择性加氢为目标反应，利用原位析出技术制备过渡金属纳米催化剂，围绕原位析出机理、析出金属在有机酸/酯选择性加氢中的催化作用本质、析出金属与钙钛矿本体的协同催化作用这3个关键科学问题，研究本体和析出金属的形貌、组成、电子结构等因素对C-O/C=O键加氢性能的影响，探明其构效关联，以研制出一类新颖的高稳定性加氢催化剂。

钙钛矿氧化物ABO3结构元素的可调节性高，经还原处理可原位析出大量均匀分散的金属纳米粒子，该金属/氧化物异质结构可表现出高催化性能及高热稳定性。本项目以碳资源优化利用过程中含C-O/C=O键的典型有机酸/酯的选择性加氢为目标反应，将原位析出技术运用于钙钛矿加氢催化剂的制备中，围绕原位析出的过程和机理、析出金属的催化作用本质、析出金属与本体的协同催化作用等关键科学问题，研究析出后形貌、分布、组成、电子结构等因素对C-O/C=O键加氢催化性能的影响，并进行催化构效关联研究。.在原位析出新过程方面，本项目开发了一种光催化助室温原位析出的新颖方法，即在三烷基胺作为空穴受体的辅助下，光照以直接驱动钙钛矿的得电子过程，促进过渡金属在室温下发生析出。该方法成功实现了一种温和条件下的纳米粒子原位析出新途径，所得粒子具有成分可调、形貌可控、抗焦化和粗化性能优越等优点。提出了一个质子耦合的电子转移催化循环来解释这种不寻常的电子转移途径。此外，我们发展了一种新的“后生长”原位析出方法，通过B 位阳离子连续原位析出和后硫化的两步操作过程，构建CoS2-LaFe0.8Co0.2O3或WS2- SrTiO3等高活性催化剂，为具更广泛功能的钙钛矿材料的制备开辟了一个新维度。.在有机酸/酯加氢反应方面，我们系统研究了钙钛矿催化剂在乙酰丙酸及CO2加氢反应中的催化性能及其作用机理。在2.0 MPa H2压力、453 K的反应温度下反应2.0 h，铜基催化剂能将乙酰丙酸完全转化为γ-戊内酯，但循环使用性能明显下降，即钙钛矿结构被酸性条件破坏；进一步制备了镍基钙钛矿催化剂，可改善循环寿命。将不同比例A/B的ABO3应用于CO2加氢制甲酸，发现表面碱性和Pd含量是极其重要的特征参数，A位过剩的1:0.85样品碱性密度较高，可得到较高的甲酸产量，而碱性位密度中等和较低Pd分散度的1:1钙钛矿催化剂上对CO2的TON值高至4697。