ZrO₂ nanoparticles, ZrO₂ (P) and ZrO₂ (H), with different tetragonal phase contents, were prepared. ZrO₂ (P) possessed higher tetragonal phase content than ZrO₂ (H). Ni/ZrO₂ catalysts (10% (w/w)), using ZrO₂ (P) and ZrO₂ (H) as supports, were prepared using an impregnation method, and were characterized using XRD, Raman, H₂-TPR, XPS, and H₂-TPD techniques. Their catalytic performance in maleic anhydride hydrogenation was tested. The Ni/ZrO₂ (P) catalyst exhibited stronger metal-support interactions than the Ni/ZrO₂ (H) catalyst because of its higher number of oxygen vacancies and the low-coordinated oxygen ions on its surface. Consequently, smaller Ni crystallites and a higher C=C hydrogenation activity for maleic anhydride to succinic anhydride were obtained over a Ni/ZrO₂ (P) catalyst. However, the C=O hydrogenation activity of Ni/ZrO₂ (P) catalyst was much lower than that of the Ni/ZrO₂ (H) catalyst. A 43.5% yield of γ-butyrolacetone was obtained over the Ni/ZrO₂ (H) catalyst at 210 °C and 5 MPa of H₂ pressure, while the yield of γ-butyrolactone was only 2.8% over the Ni/ZrO₂ (P) catalyst under the same reaction conditions. In situ FT-IR characterization demonstrated that the high C=O hydrogenation activity for the Ni/ZrO₂ (H) catalyst could be attributed to the surface synergy between active metallic nickel species and relatively electron-deficient oxygen vacancies.

A Cu-based nano-catalyst has been widely used in the ethynylation of formaldehyde; however, the effects of the presence of Cu on the reaction have not yet been reported. CuO/SiO₂ catalysts with different Cu species were prepared by impregnation (IM), deposition–precipitation (DP), and ammonia evaporation (AE). The structural evolution of the Cu species in different states of the ethynylation reaction and the structure–activity relationship between the existence state of the Cu species and the catalytic properties of the ethynylation reaction were studied. The results show that the Cu species in the CuO/SiO₂ (IM), prepared using the impregnation method, are in the form of bulk CuO, with large particles and no interactions with the support. The bulk CuO species are transformed into Cu⁺ with a low exposure surface at the beginning of the reaction, which is easily lost. Thus, this approach shows the lowest initial activity and poor cycle stability. A high dispersion of CuO and copper phyllosilicate exists in CuO/SiO₂ (DP). The former makes the catalyst have the best initial activity, while the latter slows release, maintaining the stability of the catalyst. There is mainly copper phyllosilicate in CuO/SiO₂ (AE), which is slowly transformed into a highly dispersed and stable Cu⁺ center in the in situ reaction. Although the initial activity of the catalyst is not optimal, it has the optimal service stability.

Catalytic systems consisting of copper oxide and bismuth oxide are commonly employed for the industrial production of 1,4-butynediol (BD) through ethynylation. However, few studies have investigated the influence mechanism of Bi for these Cu-based catalysts. Herein, a series of nanostructured CuO-Bi₂O₃ catalysts were prepared by co-precipitation followed by calcination at different temperatures. The obtained catalysts were applied to the ethynylation reaction. The textural and crystal properties of the catalysts, their reduction behavior, and the interactions between copper and bismuth species, were found to strongly depend on temperature. When calcined at 600 °C, strong interactions between Cu and Bi in the CuO phase facilitated the formation of highly dispersed active cuprous sites and stabilized the Cu⁺ valency, resulting in the highest BD yield. Bi₂O₃ was completely absent when calcined at 700 °C, having been converted into the spinel CuBi₂O₄ phase. Spinel Cu²⁺ was released gradually to form active Cu⁺ species over eight catalytic cycles, which continuously replenished the decreasing activity resulting from the formation of metallic Cu and enhanced catalytic stability. Moreover, the positive correlation between the in-situ-formed surface Cu⁺ ions and BD yield suggests that the amount of Cu⁺ ions is the key factor for ethynylation of formaldehyde to BD on the as prepared CuO-Bi₂O₃ catalysts. Based on these results and the literature, we propose an ethynylation reaction mechanism for CuO-based catalysts and provide a simple design strategy for highly efficient catalytic CuO-Bi₂O₃ systems, which has considerable potential for industrial applications.

The highly effective catalytic synthesis of 1,4-butynediol (BD) from the Reppe process is a fascinating technology in modern chemical industry. In this work, we reported the effects of the existential states of Mg species in the CuO/silica-magnesia catalysts for the ethynylation of formaldehyde in a simulative slurry reactor. The physichemical properties of the supports and the corresponding catalysts were extensively characterized by various techniques. The experimental results indicated that the introduced Mg species in the form of MgO particles, MgO microcrystals, or Si-O-Mg structures effectively resulted in an abundance of medium-strong basic sites, which can synergize with the active Cu⁺ species, facilitate the activation of acetylene, and improve the ethynylation activity. For the CuO/MgO-SiO₂ catalyst, the existence of Si-O-Mg structures strengthened the Cu–support interaction, which were beneficial to improving the dispersion and the valence stability of the active Cu⁺ species. The highly dispersed Cu⁺ species, its stable valence state, and the abundant medium-strong basic sites enhanced the synergistic effect significantly, leading to the superior activity and stability of CuO/MgO-SiO₂. The insights into the role of the existential states of Mg species and the revelation of the synergistic effect between active Cu⁺ species and basic sites can provide theoretic guidance for future rational design of catalysts for the ethynylation reation.

Composite nanomaterials have been widely used in catalysis because of their attractive properties and various functions. Among them, the preparation of composite nanomaterials by redox has attracted much attention. In this work, pure Cu₂O was prepared by liquid phase reduction with Cu(NO₃)₂ as the copper source, NaOH as a precipitator, and sodium ascorbate as the reductant. With Fe(NO₃)₃ as the iron source and solid-state phase reaction between Fe³⁺ and Cu₂O, Cu_xO-Fe_yO_z nanocatalysts with different Fe/Cu ratios were prepared. The effects of the Fe/Cu ratio on the structure of Cu_xO-Fe_yO_z nanocatalysts were studied by means of X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), ultraviolet confocal Raman (Raman), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS, XAES), and hydrogen temperature-programmed reduction (H₂-TPR). Furthermore, the structure–activity relationship between the structure of Cu_xO-Fe_yO_z nanocatalysts and the performance of formaldehyde ethynylation was discussed. The results show that Fe³⁺ deposited preferentially on the edges and corners of the Cu₂O surface, and a redox reaction between Fe³⁺ and Cu⁺ occurred, forming Cu_xO-Fe_yO_z nanoparticles containing Cu⁺, Cu²⁺, Fe²⁺, and Fe³⁺. With the increase of the Fe/Cu ratio, the content of Cu_xO-Fe_yO_z increased. When the Fe/Cu ratio reached 0.8, a core–shell structure with Cu₂O inside and a Cu_xO-Fe_yO_z coating on the outside was formed. Because of the large physical surface area and the heterogeneous structure formed by Cu_xO-Fe_yO_z, the formation of nonactive Cu metal is inhibited, and the most active species of Cu⁺ are exposed on the surface, showing the best formaldehyde ethynylation activity.