YCoxFe1-xO3钙钛矿氧化物负载铂催化剂上肉桂醛液相选择加氢性能研究

The catalytic selective hydrogenation of alpha, beta-unsaturated aldehyde to alpha, beta-unsaturated alcohol is an important reaction in the production of various fine chemicals. Extensive investigations on selective hydrogenation of cinnamaldehyde over bi-metallic catalysts revealed that Fe (or FeOx) and Co could distinctly improve the catalytic performance of supported Pt catalysts. However, systematic investigation on the roles of such improvement on the adsorption, activation and reaction behaviors of cinnamaldehyde is still very limited, which makes it challenging to the further optimization of the adsorption/activation of cinnamaldehyde and improvement of the catalytic performance. During our preliminary research, we found that Fe/Pt molar ratio and Pt-Fe contact interfaces would influence the catalytic performance of the Pt-Fe catalysts towards the liquid-phase selective hydrogenation of cinnamaldehyde. Therefore, in this project, controllable syntheses of a series of Pt catalysts supported on YCoxFe1-xO3 perovskite-type oxide and their behaviors in liquid-phase selective hydrogenation of cinnamaldehyde as a model reaction will be investigated in detail. By changing the Fe/Co molar ratios in YCoxFe1-xO3, the differences in the structural and electronic properties of these YCoxFe1-xO3 supported Pt catalysts will be illustrated. The investigation will be focused on the effects of Pt-Fe interface on: 1, the charge transfer process; 2, the adsorption behaviors of cinnamaldehyde and the related catalytic performance; 3, reaction intermediates, reaction pathways and selective hydrogenation mechanism. The findings of this research are helpful to establish a reliable structure-performance correlation, which is important for the design of highly efficient catalysts and may provide deep understanding on the nature of the selective hydrogenation of alpha, beta-unsaturated aldehydes.

alpha,beta-不饱和醛选择加氢制alpha,beta-不饱和醇是精细化学品合成中的重要反应。研究发现在肉桂醛选择加氢中Fe对Pt催化剂有显著促进作用，但目前关于这种促进作用还缺乏清晰且统一的认识，使得在进一步提高Pt-Fe催化剂性能和优化肉桂醛吸附活化方面缺乏依据。在前期研究中，我们发现Pt/Fe摩尔比和Pt-Fe接触形式均对Pt-Fe催化剂的性能产生较大影响。为此本项目将以肉桂醛液相选择加氢为模型反应，以YCoxFe1-xO3钙钛矿氧化物为载体负载铂粒子，研究Fe/Co比例对铂粒子表面电子性质的影响；研究Pt-Fe接触形式和电子传递机制对肉桂醛吸附活化行为的影响；结合反应中间体和反应历程等问题的研究，建立清晰的构效关系；探究影响反应行为的关键因素和反应机理，为进一步提高催化性能提供实验和理论支撑。本项目的实施对深入理解alpha,beta-不饱和醛选择加氢科学本质有重要学术价值。

该项目制备了YCoxFe1-xO3钙钛矿复合氧化物和CoxFe1-xAl2O4尖晶石复合氧化物负载的铂催化剂。由于在YCoxFe1-xO3或CoxFe1-xAl2O4中可以实现CoOx和FeOx物种在空间上的隔离和分散，CoOx和FeOx物种跟其表面负载的铂纳米粒子接触界面较大，相互作用较强，因此负载量为5%的铂粒子可以在< 20 m2/g比表面积的这些复合氧化物表面高度分散，铂粒子平均尺寸为2.5-3.5 nm。另外，CoOx或FeOx物种与铂粒子之间的电子相互作用可以调节铂粒子表面的电子状态，有利于肉桂醛分子通过C=O官能团吸附到铂催化剂表面，从而使C=O被优先吸附和活化后加氢生成肉桂醇。因此，Pt/YCo0.3Fe0.7O3和Pt/Co0.5Fe0.5Al2O4催化剂上肉桂醇的选择性均可达95%，TOF可达15000 h-1左右。该项目还对FeOx或CoOx助剂与铂组分的接触方式对肉桂醛选择加氢催化性能的影响进行了研究，发现共浸渍法制备的Pt-Fe/YCoO3或Pt-Co0.25/FeAl2O4或Pt-Fe0.25/CoAl2O4催化剂由于Pt粒子与FeOx或CoOx之间接触界面较小，导致其催化性能显著低于Pt/YCo0.3Fe0.7O3或Pt/Co0.5Fe0.5Al2O4催化剂。该项目还通过理论计算对肉桂醛分子在PtFex(111)上的吸附模式进行了研究，结果表明Fe掺杂后有利于肉桂醛以一定角度直立吸附于PtFex(111)表面，有利于C=O优先吸附和活化，与实验结果非常吻合。该项目还对不同铂负载量的Pt/Co0.5Fe0.5Al2O4催化剂的铂粒子尺寸效应进行了研究，铂粒子越大，越有利于C=O官能团的选择加氢。另外，该项目还制备了NixFe1-xAl2O4尖晶石复合氧化物负载的Pt/NixFe1-xAl2O4催化剂，发现通过调变NixFe1-xAl2O4尖晶石型复合氧化物载体中Ni/Fe比例，可以实现肉桂醛中C=C和C=O选择加氢的自由切换。当Ni含量较高时，主要对C=C优先加氢生成苯丙醛；而当Fe含量较高时，优先对C=O进行优先加氢生成肉桂醇。该项目还研究了经过LaNiO3钙钛矿前驱体、再还原制得的Ni/La2O3催化剂在肉桂醛选择加氢反应中的催化性能，发现La2O3载体的碱性有利于对肉桂醛的C=C双键进行吸附和活化，从而获得90.2%的苯丙醛选择性。