Di Xin, Lafaye Gwendoline, Especel Catherine, Epron Florence, Qi Ji, Li Chuang, Liang Changhai
Laboratory of Advanced Materials and Catalytic Engineering, Dalian University of Technology, No.2 Linggong Road, Dalian City, Liaoning Province, P.R. China.
Institut de Chimie des Milieux & Matériaux de Poitiers (IC2MP), Université de Poitiers, CNRS, 4 rue Michel Brunet, 86073, Poitiers, France.
ChemSusChem. 2019 Feb 21;12(4):807-823. doi: 10.1002/cssc.201802744. Epub 2019 Feb 13.
Bimetallic Co-Re/TiO catalysts were developed for efficient citral hydrogenation. Bimetallic catalysts were prepared by co-impregnation (CI), successive-impregnation (SI), and surface redox method (SR). The arrangement between the Co and Re species on these systems was fully characterized using several techniques (TEM-energy-dispersive X-ray spectroscopy, H temperature-programmed reduction, temperature-programmed desorption, XRD, CO FTIR spectroscopy, model reaction of cyclohexane dehydrogenation), and their catalytic performances were evaluated for the selective hydrogenation of citral towards unsaturated alcohols. The Re and Co species are completely isolated in the CI sample, presenting a very limited Co-Re interaction. In SI samples, the metals coexist in a Janus-type structure with a concentration of Re around Co. Decoration/core-shell structures are observed for SR samples resulting from the redox exchange between the metallic surface of the parent Co/TiO catalyst and the Re species of the modifier precursor salt. The contact degree between the two metals gradually increases as follows: Isolated structure (CI)<Janus-type structure(SI)<decoration/core-shell structure (SR). The unchanging structure of all SI samples independent of the Re loading leads to similar electron transfer, and the increase in Re content results in agglomeration of Re, thus decreasing the catalytic activity. Density-of-state (DOS) calculations prove that the high valence of Re is a disadvantage for the hydrogenation reaction. For SR samples, the increase of Re loading contributes to the electron transfer from Re to Co that is consistent with a change of structure from decoration to core-shell. The lack of directly accessible Co atoms for SR catalysts with fully coated structure decreases the efficiency of Re reduction. The presence of Co-Re interaction resulting from the close contact between metals plays a dominant role in the hydrogenation of citral. Nevertheless, an excessively high contact degree is unnecessary for citral hydrogenation once Co-Re interaction has formed.
开发了双金属Co-Re/TiO催化剂用于高效柠檬醛加氢反应。通过共浸渍（CI）、连续浸渍（SI）和表面氧化还原法（SR）制备了双金属催化剂。利用多种技术（透射电子显微镜-能量色散X射线光谱、H程序升温还原、程序升温脱附、X射线衍射、CO傅里叶变换红外光谱、环己烷脱氢模型反应）对这些体系中Co和Re物种之间的排列进行了全面表征，并评估了它们对柠檬醛选择性加氢生成不饱和醇的催化性能。在CI样品中，Re和Co物种完全隔离，Co-Re相互作用非常有限。在SI样品中，金属以Janus型结构共存，Co周围有一定浓度的Re。对于SR样品，观察到装饰/核壳结构，这是由于母体Co/TiO催化剂的金属表面与改性剂前驱体盐的Re物种之间的氧化还原交换所致。两种金属之间的接触程度逐渐增加，顺序如下：隔离结构（CI）<Janus型结构（SI）<装饰/核壳结构（SR）。所有SI样品的结构不随Re负载量变化，导致类似的电子转移，Re含量增加会导致Re团聚，从而降低催化活性。态密度（DOS）计算证明，Re的高价态不利于加氢反应。对于SR样品，Re负载量的增加有助于电子从Re转移到Co，这与结构从装饰型变为核壳型的变化一致。对于具有完全包覆结构的SR催化剂，缺乏直接可及的Co原子会降低Re还原的效率。金属之间紧密接触导致的Co-Re相互作用在柠檬醛加氢反应中起主导作用。然而，一旦形成Co-Re相互作用，过高的接触程度对于柠檬醛加氢反应并非必要。
