Ethylene Hydroformylation with Carbon Dioxide Catalyzed by Ruthenium Supported on Titanate Nanotubes: Infrared Spectroscopic Evidence of Surface Species

摘要

Ru nanoparticles supported on titanate nanotubes (Ru/TiNT) were catalytically active in the ethylene hydroformylation using CO2 as reactant (at atmospheric pressure and moderate temperatures) to give propanal and ethane. The rate of propanal formation at 100 degrees C with a molar feed ratio of 1 : 1 : 1 : 8 (CO2 : C2H4 : H-2 : Ar) was 0.128 mol(propanal) mol(Ru)(-1) h(-1). Raman spectra and X-ray diffraction data characterizing the catalyst confirmed the presence of the crystalline structure of Na2Ti3O7 for TiNT, whereas transmission electron microscopy (TEM) images evidenced its tubular morphology and the presence of finely dispersed Ru nanoparticles with an average diameter of 0.8 nm. Infrared spectra measured under reaction conditions allowed the identification of surface species that participate in the catalysis, namely CO bonded to the Ru nanoparticles, Ru-ethyl and Ru-acyl species and adsorbed propanal. The data show that conversion of CO2 to CO was crucial for the formation of the Ru-acyl species, regarded as a key reaction intermediate to give propanal.