Study On Hydroformylation Of N-hexene Over Hydrotalcite-like Co-Ni Layered Catalyst

Hydroformylation of olefins is a typical atomic economy reaction,and the high added value of aldehyde makes it one of the most important homogeneous reactions.Since the discovery of hydroformylation,homogeneous catalysis with transition metal rhodium and cobalt complexes as active components has been widely used in large-scale industrial production because of the high reaction activity and high aldehyde selectivity.However,the biggest problem in homogeneous catalysis is how to separate and recycle the catalyst,especially when higher olefins are used as substrates.Therefore,it is of great significance to develop heterogeneous catalysis for hydroformylation of higher olefins.In this paper,based on the fact that hydrotalcite material(LDH)is a layered material that still retains lamellar structure after roasting at high temperature,and the lamellar metal has the characteristics of diversity,high specific surface area and good thermal stability,the influence of CoNiAl lamellar catalyst on hydroformylation of n-hexene was explored.The hydrotalcite CoNiAl-LDHs was prepared by urea hydrothermal method,and the lamellar CoNiAl confined heterogeneous catalyst was obtained by reduction.The preparation method was simple and rapid.he factors such as n(CO(NH2)2):n(Co+Ni),n(Co+Ni):n(Al)and n(Co):n(Ni)all affect the formation of lamellar structure,lamellar thickness and active sites amount.The optimal conditions are n(CO(NH2)2):n(CO+Ni)=5,n(CO+Ni):n(Al)=2 and n(Co):n(Ni)=1.The lamellar structure of CoNiAl-x-y-z heterogeneous catalyst has the limitation effect and type selection effect,which reduces metal loss and improves the positive hetero-ratio of product aldehydes.In the lamellar structure,part of cobalt element is replaced by nickel element,and the oxygen vacancy formed increases the surface active sites.The catalyst was characterized by XRD,in situ XRD,SEM,TEM,TPD,TPR,XPS,ICP-OES,etc.The synergistic effect of Co and Ni ions in CoNiAl-x-y-z was further understood,and the reaction mechanism of n-hexene hydroformylation was speculated.The synergistic effect of Co and Ni significantly improved the catalytic performance.Among the prepared catalysts,CoNiAl-1-2-5 showed good catalytic performance.Using 1-hexene as probe,the reaction temperature was 120℃,the reaction pressure was 5MPa,the reaction time was 2 h,and the H2/CO ratio was 1,the conversion of 1-hexene was up to 99.9%,the selectivity of heptanal was 81%,and the n/i ratio of heptanal was 1.7.After 5 cycles,the catalytic activity was still up to 94%.When n-hexene,n-octene,n-decene and n-dodecene were used as substrate,the conversion of each olefin was greater than 95%,indicating that the catalyst had good adaptability.The catalyst also kept the same reaction activity with the hydroformylation of the mixed four olefins as the pure feed and gave the conversion of more than 95%.