What are the advantages of catalytic hydrogenation intermediates as catalysts?

2023-01-03 18:14

　What are the advantages of 　using catalytic hydrogenation intermediates as catalysts?

　　As a catalyst, catalytic hydrogenation intermediates have the characteristics of large specific surface area, high activity and low cost, and are often used in olefin hydrogenation. In the hydrogenation reaction, the order of hydrogenation activity is: Pt≈ palladium>nickel>iron≈cobalt>catalytic hydrogenation intermediates. The activity of catalytic hydrogenation intermediates is close to that of poisoned nickel catalysts. Catalytic hydrogenation intermediate catalysts have special catalytic activity for the reduction of benzaldehyde to benzyl alcohol to aniline.

　　Catalytic hydrogenation intermediate catalysts are mainly used for hydrogenation, dehydrogenation and oxidation reactions. The catalytic hydrogenation intermediate catalyst used alone is easy to sinter. In order to improve heat resistance and toxicity resistance, cocatalysts and carriers are usually used. When studying the liquid phase furfural hydrogenation catalyst, the carrier Al2O3, activated carbon, TM grade silica and SiO2 were screened. It was found that under the same preparation conditions, SiO2 had better activity. At the same time, the influence of impregnation conditions on catalyst activity was studied, and the catalyst preparation conditions and reaction conditions were determined. Thermal analysis was performed on Cu/SiO2. The results show that CuO supported on SiO2 is easier to reduce than CuO without support. SiO2 improves the dispersion of active components, increases the reducibility of CuO, reduces the thermal effect during the reduction process of the unit catalyst, and avoids the rapid growth of Cu grains and catalyst deactivation during the reduction process. In addition, Li Guoan and others found that adding alkaline earth metals can significantly improve the performance of the catalyst. They believe that adding alkaline earth metals can make the surface active components of the catalyst better dispersed. If there is a catalytic hydrogenation intermediate catalyst in the methanol synthesis reaction of CO and H2, it shows activity, but the pure catalytic hydrogenation intermediate is not as good as ZnO (60-80%)-CuO, CuCr2O4 and ZnO-CrO-CrO ternary catalyst. They are highly heat-resistant and toxic, making them practical catalysts. The catalyst has high activity and selectivity at 100-160°C. Zhou Yaming et al. [17] tested the activity of the Cu-Zn catalyst system and found that at 160°C, the ratio of hydrogenaldehyde to 5~7, the liquid space velocity was 0.5~0.6h-1. Under normal pressure, the selectivity of furfural alcohol and yields both exceeded 98%. At the same time, they also studied the active components of the catalyst and found that CuO and ZnO already existed before the catalyst was reduced. After reduction, CuO is reduced to Cu, and ZnO changes. However, the electron kinetic energy of Zn increases and partial reduction occurs, forming oxygen-deficient ZnOx (x≤1). Bulko et al. showed that after the reduction of the Cu-Zn-O series catalyst, part of the catalytic hydrogenation intermediate enters the ZnO lattice to form a solid Melt. Zhou Yaming et al., ΔG is negative, which can compensate for the positive ΔG of ZnO reduction. The oxygen-deficient structure in Cu-ZnO solid melt plays a stabilizing role in oxygen-containing intermediates. Supported catalytic hydrogenation intermediate-based bimetallic catalysts have also been widely studied. For example, Wang Yaquan [1] used Ni-Cu/ZnO as a model catalyst and TPR, XPS and CO hydrogenation reactions, revealing that bimetallic interactions can strongly affect metal-support interactions. The synthesis of lower alcohols was studied compared with CO hydrogenation using nickel-modified Cu-Mn/ZrO2 catalyst. They found that the Cu-Mn/ZrO2 catalyst is a highly active methanol synthesis catalyst. After adding nickel, it effectively promotes the synthesis of lower alcohols and significantly increases the CO conversion rate.

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