Zhengting Xiao,Dongcai Shen,Kai Guo,Guangci Li,Wentai Wang,Xuebing Li,Song Chen,Chunhu Li
Cu-based catalysts were synthesized utilizing the ZnAl 2 O 4 spinel as supports for the selective hydrogenation of methyl stearate to stearyl alcohol. The presence of Zn atoms inhibited the agglomeration of the particles of Cu species in the reduction process, promoting the distribution of Cu species on the catalyst surface, which will enhance hydrogen activation and selective hydrogenation activity. DFT calculations show that the bond energies of the C-O bonds on both sides of the ester group decrease with the adsorption of the ester molecule onto Cu + species, and the C-O bond energy on the methyl side is lower than that on the carbonyl side. However, because the carbonyl carbon is more susceptible to nucleophilic attack, the C-O bond on the carbonyl side is more easily broken. In addition, the oxygen vacancies of the supports promote hydrogen spillover and the adsorption and activation of ester groups, which further enhance the selective hydrogenation activity of the catalyst on methyl stearate.
Gengrui Zhang,Yan Li,Yong Chen,Xinning Hao,Xianhua Zhang,Shuai Wang,Jingdong Lin,Yong Wang,Shaolong Wan
The development of Ni-based syngas methanation catalysts with superior thermal stability remains a formidable challenge, which typically requires the use of a high Ni loading and a recipe containing very complex components. Herein, a novel Ni catalyst using a ZnAl2O4 spinel support was designed and prepared by an isopropanol-mediated controlled hydrolysis method, which demonstrated excellent reactivity and stability toward the syngas methanation reaction. Moreover, the 35% Ni/ZnAl2O4 catalyst still maintained a high reactivity after steam treatment at 750 °C, while the 35% Ni/Al2O3 counterpart suffered a nearly complete loss of reactivity during such an accelerated test. The detailed characterization reveals that the drastic deactivation of Ni/Al2O3 after steam treatment is attributed to the favored formation of NiAl2O4 under the severe reaction atmosphere, resulting in the loss of active Ni. In contrast, the employment of the highly stable ZnAl2O4 support can not only inhibit the sintering of supported Ni particles due to their strong interaction but also avoid the loss of the active Ni component by preventing the formation of NiAl2O4. This work sheds light on the critical role and the intrinsic mechanism of the spinel support for the construction of the desired methanation catalysts. The mechanistic scenario revealed in this work provides an important and novel solution to overcome the deactivation problem not only useful for methanation catalysts but also valid for most other supported metal catalysts commonly used in the reaction processes that require severe reaction conditions.
Hierarchically porous ZnAl 2 O 4 spinel monolith derived from ionic precursors has been successfully prepared via the sol-gel route accompanied by phase separation in the presence of poly (ethylene oxide) (PEO) and propylene oxide (PO). Appropriate amounts of PEO as a phase-separation inducer and PO as a gelation mediator allow the formation of the xerogel with bicontinuous macrostructure and a monolithic shape. The macropore size of the resultant dried gel is mainly distributed in the range of 0.2–1 μm, and the whole porosity is about 65%. The dried gel is constructed by crystalline Zn Al hydrotalcite, becoming amorphous after heat-treated at 300–500 °C in air, and is further transformed into single phase ZnAl 2 O 4 spinel with plate-like shape at 600 °C. The macroporous structure is well maintained while the porosity increases to 75% and the surface area rises to 109 m 2 g −1 after heat-treatment.
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