Regulation Of Heterogeneous Rhodium Catalysts For The Hydroformylation Of Olefins

The hydroformylation of olefins is one of the large-scale industrial processes for producing valuable aldehydes.Currently,most hydroformylation systems are based on homogeneous Rh catalysts,but it is difficult to separate homogeneous catalysts from the reaction system.Therefore,the development of heterogeneous Rh catalysts for industrial production is of great significance.This thesis focuses on the enhancement of the catalytic activity of heterogeneous Rh catalysts,developing strategies of valence state regulation and constructing zeolite-encapsulated alloy catalysts to improve the performance of heterogeneous Rh catalysts.The main research contents are summarized as follows:（1）Supported Rh catalysts were synthesized using a impregnation method,and then subjected to either reduction or oxidation pretreatment before being used in the hydroformylation of styrene.The catalytic results showed that the performance of the Rh/HAP,Rh/CeO₂,Rh/ZrO₂,Rh/Al₂O₃,Rh/TiO₂,and Rh/SiO₂ catalysts after oxidation pretreatment was superior to those of the pre-reduced catalysts.The average conversion rates of styrene were increased by1.3,3.1,2.0,1.5,1.6,and 9.4 times for the above catalysts,respectively.The Rh/HAP catalyst after oxidation pretreatment showed the highest activity,with an average conversion rate of 12940 mol·mol_Rh^-1·h^-1,which was comparable to that over the homogeneous Wilkinson catalyst.Characterizations of the Rh/HAP catalyst by STEM,XPS,XAFS indicated that different pretreatment methods only changed the valence state of the Rh species:the Rh/HAP catalyst after reduction pretreatment mainly contained Rh⁰,while the Rh/HAP catalyst after oxidation pretreatment mainly contained positively charged RhO_x,and the state of the HAP carrier was not affected by the pretreatments.By combining kinetic studies with FT-IR and TPD-MS characterizations,the reasons for the improved activity were elucidated:the Rh/HAP catalyst after reduction pretreatment had strong hydrogen activation ability,which inhibited the CO-adsorption on the catalyst,while the adsorptive activation of CO was a key step in olefin hydroformylation;the Rh/HAP catalyst after oxidation pretreatment suppressed this disadvantage by enhancing CO adsorption,thereby improving the catalytic performance.（2）Rhodium-cobalt nanoparticles were encapsulated in a pure siliceous zeolite（Silicalite-1）to prepare Rh₂Co₈@S-1 and Rh₁Co₉@S-1 alloy catalysts with different Rh/Co molar ratios.Rh₂Co₈@S-1 and Rh₁Co₉@S-1 had smaller particle sizes,indicating that the formation of RhCo alloy metal particles in the catalyst might expose more catalytic active sites.In the hydroformylation of styrene to produce aldehydes,the average rate of aldehyde production of Rh₂Co₈@S-1 and Rh₁Co₉@S-1 was 720 and 1050 mol·mol_Rh^-1·h^-1,which was 1.3and 1.9 times than that of Rh@S-1,respectively,indicating that constructing RhCo alloy improved the activity of the precious Rh catalysts.The Rh₁Co₉@S-1 catalyst is stable,remaining activity during several successive runs.Additionally,the RhCo@S-1 catalysts exhibited similar activity enhancement when applied to the hydroformylation of other olefins.