A novel MCM-41-supported bi-functional catalyst by immobilizing organoamine and Rh–P complex for one-pot synthesis of 2-ethylhexenal from propene

Abstract

We have demonstrated the synthesis of a novel MCM-41-supported bi-functional catalyst containing organoamine and Rh–P complex. We further characterized the catalysts by state-of-the-art analytical techniques including FTIR, UV–vis, 31P CP MAS NMR, TGA, XRD, BET, TEM, ICP-AES and elemental analysis. The as-synthesized catalyst was applied to the one-pot synthesis of 2-ethylhexenal using propene as raw materials. FTIR, UV–vis, 31P CP MAS NMR, and TGA results indicate that the active sites, organoamine and Rh–P complex, are successfully immobilized on the surface of catalyst support. The N and Rh content can be adjusted by adding different amounts of organoamine and Rh–P complex during the process of catalyst preparation. The mesoporous structure of the zeolite support remains intact after immobilization. However, the specific surface area and BJH pore size of the mesoporous zeolite support decrease after being grafted with organoamine and Rh–P complex. The bi-functional catalyst with primary amine has the best catalytic performances for the one-pot synthesis of 2-ethylhexenal since it has better synergistic effect with silanol groups, followed by diamine and then tertiary amine. The Rh content of the catalyst determines the hydroformylation reaction rate of propene, while the self-condensation of n-butanal is determined by the balance between organoamine and silanol groups. The results indicate the hydroformylation reaction is the control step of this tandem reaction when the content of Rh in the catalyst is below 0.19%. In contrast, this tandem reaction is controlled by the self-condensation of n-butanal with further increasing Rh content. We found that the catalyst containing 1.73% of N (primary amine) and 0.19% of Rh is a suitable choice. And we obtained the best yield of 2-ethylhexenal above 77% in the one-pot synthesis from propene.