Copper–zirconium catalysts have been extensively applied in the hydrogenation of carbon–oxygen bonds such as in CO2 and esters. However, high-performance Cu/ZrO2 catalysts with low copper loading for dimethyl oxalate (DMO) hydrogenation to ethylene glycol (EG) are seldom reported. Herein, we fabricated 5 wt% Cu/ZrO2 catalysts by a co-precipitation method and investigated the effect of calcination temperature on the catalyst structure and the corresponding catalytic performance. The crystallization and migration of zirconium and copper species are not simultaneous when increasing the calcination temperature, so the elemental composition of Cu and Zr species is different on the surface and in the bulk CuZrO2 solid solution. The crystalline morphology of ZrO2 is transformed from a-ZrO2 to t-ZrO2 and m-ZrO2 and copper dispersion is also changed. The CZ-600 catalyst has the largest copper dispersion, surface area of Cu0 and Cu+ and strongest H2 adsorption ability, which endow this catalyst with the best catalytic performance. However, TOF values are the largest for the CZ-550 catalyst with a larger ratio of Cu+, oxygen vacancies and Zr3+, which suggests the interfacial synergy between Cu and ZrO2 in DMO hydrogenation. And further increasing the calcination temperature to above 700 °C will cause the aggregation and sintering of copper nanoparticles and deteriorate the hydrogenation reactivity.
The catalytic dehydrogenation of diethanolamine to prepare iminodiacetic acid has attracted considerable research interest. However, the lack of understanding of the structure-activity relationship of the reaction can present a challenge to the control of the catalytic behavior. Concurrently, improving the catalytic performance and reducing the cost have also become urgent issues that require resolution. This work examined the catalytic mechanism of several Cu-Ni X /ZrO 2 catalysts, differing in Cu/Ni ratios, prepared by H 2 reduction, in the context of DEA dehydrogenation to elucidate the structure-activity connection and probable reaction mechanism. Subsequently, a strategy has been put out to generate metal (Ni and Co)-doped copper-zirconium catalysts using the co-precipitation-hydrazine hydrate reduction process. The synergistic effect between metals was combined with the improvement of the surface reaction of the catalyst by hydrazine hydrate through a more efficient preparation method, thereby enhancing the catalyst's overall performance. The representative catalyst Cu-Ni/ZrO 2 required a hydrazine hydrate reduction temperature and time of 40 °C and 30 min, and after 65 min of reaction, it exhibited a high conversion rate (96.3 %) and yield (93.7 %), and after five cycles, both the conversion rate and yield exceeded 85 %. Various characterization techniques have confirmed that Ni doping induced an alloying effect and a size effect. Additionally, the hydrazine hydrate reduction method was discovered to augment the specific surface area, surface hydroxyl groups, hydrophilicity, and optimize the pore size distribution of the catalyst while also regularizing its morphology, thereby significantly enhancing the activity and stability of the metal-doped copper-zirconium catalyst. This paper discussed the correlation between catalyst structure and reaction performance, as well as the catalytic conversion mechanism, which is anticipated to provide a novel reference for the preparation, performance control, and potential applications of dehydrogenation catalysts.
Zihao Zhang,Changxue Wang,Xin Gou,Hao Chen,Kequan Chen,Xiuyang Lu,Pingkai Ouyang,Jie Fu
A series of Cu-based catalysts with different supports were synthesized and studied for the in situ hydrogenation of 5-hydroxymethylfurfural (5-HMF) to dimethylfuran (DMF) using methanol as an economical hydrogen donor. The structures and properties of the four catalysts (Cu/Al 2 O 3 , Cu/ZnO, Cu/ZrO 2 , and Cu/CeO 2 ) were characterized using X-ray diffraction (XRD), temperature-programmed reduction (H 2 -TPR), and temperature-programmed desorption of ammonia (NH 3 -TPD). The experimental results showed that the use of different supports for the Cu-based catalysts significantly influenced their activity for both H 2 production from methanol and hydrogenation of 5-HMF. The catalyst Cu/Al 2 O 3 showed the best catalytic activity, which can be attributed to the highest activity for the in situ H 2 production from methanol, smallest Cu crystallite size, and strongest acidity. The effects of the substrate concentration, catalyst loading, and reaction temperature and time on the in situ hydrogenation of 5-HMF were systematically investigated to determine the optimum reaction conditions.
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