Of Pd, The Rare Earth Co. Catalyst For Gas Phase Hydrogenation Of Unsaturated Double Bonds And Carbonyl Modification

The application of rare earth as additives in catalytic research has been researched a lot recently, especially in Three-Way Catalysts (TWCS) in disposal of discharged gas from cars. In this paper, the modification of various lanthanide elements to palladium and cobalt based catalysts in hydrogenation of C=C and C=O was investigated, using gas hydrogenation of acrylonitrile and crotonic aldehyde as probe reactions.Propionitrile is a good chemical widely applied as raw material, and can be prepared by hydrogenation of acrylonitrile. Supported Ni, amorphous Ni and its alloy have ever been utilized, while their catalytic activity and stability are not satisfying. Though palladium based catalysts have very preferable activity and selectivity, but it can't be widely used due to its high price. So there is much significance for investigation into the catalytic behavior of low-loaded palladium catalysts. The experiments indicated that Pd(0.05 wt.%)/Al2O3 showed a good selectivity to propionitrile since no other product but propionitrile was identified, and a better ability resisting deactivation was also perceived compared with high-loaded palladium catalysts. But due to the limited numbers of active species, the conversion of the reactant was comparatively low; and the stability of the catalysts needs to be improved. According to the literatures during the recent years, lanthanides widely used in TWCS have the capability of improving the thermal ability to resist calcination, and the dispersing degree of active species. On the other aspect, oxides of lanthanides can be reduced by hydrogenation due to the interaction of lanthanides with palladium, and the reduced lanthanide ions also have catalytic activity. So Pd-REOx/Al2O3 showed a better catalytic activity, stability, compared with palladium only catalysts. While the content and the nature of lanthanide elements play a key role in the hydrogenation reaction. The best content of lanthanide was around 3 wt.%; and the best modification effect was observed on catalysts doped with Yb, Sm, La,Ce and etc.There are both theoretical significance and application foreground for preparationof unsaturated alcohol by hydrogenation of unsaturated aldehyde. Cobalt based catalysts were widely used in hydrogenation of unsaturated aldehyde to unsaturated alcohol, so gas hydrogenation of crotonaldehyde was carried out in fixed bed reactor over CO/Al2O3 and Co-REOx/Al2O3 in this research work. The results illuminated that both activity and selectivity of the catalysts got enhanced after the addition of some lanthanide elements such as La, Nd and etc, but not over all lanthanide doped catalysts.According to various characterizations such as X-Ray diffraction(XRD), Transmission Electronic Microscopy(TEM), X-Ray Photoelectronic Spectra(XPS), Temperature-Programmed Reduction(TPR), the interaction between transition metals and rare earth was investigated. Lanthanides interacted with transition metals, then modified the catalysts from electronic and structural aspects, but the strong metal-support interaction (SMSI) also took effect.