Vapor-Phase Crotonaldehyde Selective Hydrogenation On Noble Metal (Ru, Ir)Catalysts

a,(3-unsaturated alcohols are widely applied in the synthesis of fine chemicals such as pharmaceutical, agrochemical, and fragrance compounds, which are mainly synthesized by α,β-unsaturated aldehydes selective hydrogenation. The hydrogenation prefers to C=C bond compared with C=O bond to obtain saturated aldehyde. Thus it is challenging to improve the selectivity to unsaturated alcohols. Crotonaldehyde is a typical representative of a, B-unsaturated aldehyde and vapor-phase crotonaldehyde selective hydrogenation on heterogeneous catalysts is an appealing green process. In this work, supportd Ir catalysts were prepared using an impregnation method to test their catalytic performance of selective hydrogenation of crotonaldehyde. A variety of methods characterization such as powder X-ray diffraction analysis(XRD), Temperature programmed technology(H2-TPR,NH3-TPD,TPO), X-ray electron spectrum(XRF、XPS), was used. It was found that the RuIr catalysts obtained better catalytic activity and selectivity to crotyl alcohol. Main work consists of the following contents:1. Characterizations the performance of Ru/ZnO catalysts for crotonaldehyde selective hydrogenationAn impregnation method was usd to prepare Ru/ZnO catalysts with different Ru contents so as to investigate the effects of Ru loading on the catalytic behaviors. Many characterization techniques such as (XRD), NH3temperature-programmed desorption (NH3-TPD), transmission electron microscopy (TEM) and temperature-programmed oxidation (TPO). It was found that with increasing Ru contents in Ru/ZnO catalysts, the activity (TOF), surface acidity amount and deactivation rate increased. The highest selectivity to crotyl alcohol (up to88.0%) obtained on the3Ru/ZnO catalyst for the hydrogenation of crotonaldehyde. Initial TOF values relies on the surface acidity of the catalyst intensity and Ru a particle size. The more Lewis acid sites made catalysts deactivate more easily. It was assumed that the deactivation was due to the formation of organic compounds deposition and poison effect of CO strongly adsorbed on the Ru atoms. 2. Promoting effect of Ir on the catalytic property of Ru/ZnO catalystsA series of ZnO supported Ru-Ir bimetal catalysts were used for crotonaldehyde hydrogenation. The addition of Ir element could effectively promote the catalytic performance, especially the catalyst stability. A Ru-0.5Ir/ZnO catalyst showed the highest activity (a conversion of63.3%) and selectivity to crotyl alcohol (94.4%) after30h reaction. The enhanced stability was attributed to the modified electronic property of Ru by the formation of RuIr alloy as the X-ray photoelectron spectroscopy results showed charge transfer from Ru to Ir, as well as the weakened surface acidity in the Ru-Ir/ZnO catalyst as evidenced by NH3temperature-programmed desorption technique. Besides, the deactivation of the catalysts was due to the CO poisoning and deposition of organic compounds on the catalyst surface, which was characterized by CO poisoning experiment.3. Effect of pretreatment temperature on Ru-Ir/ZnO catalystsWith ZnO as the carrier, the impregnation method was used for the Ru-0.5Ir/ZnO catalyst, Mainly to study the pretreatment temperature impact on the performance of Ru-0.5Ir/ZnO. Techniques as powder X-ray diffraction, NH3temperature-programmed desorption (NH3-TPD), transmission electron microscopy (TEM) was used. It was found that as the reduction temperature increases, the noble metal Ru-Ir alloy is formed, and the particle size of the metal particles is increased significantly, in addition to the amount of acid is decreased gradually. When the reduction temperature of200℃, In this case the activity of the catalyst after reaction10h the the crotonaldehyde conversion rate of93.5%, selectivity to crotyl alcohol(86.6%). It is attributed to suitable amount of acid and the noble metal species having the appropriate interaction. High temperature reduction (400℃), so that the catalytic amount of acid reduced the size of metal particles is also changed to reduce the surface active sites, thereby inhibiting the catalytic activity.