Activity of Nitrogen Containing Carbon Nanotubes in Base Catalyzed Knoevenagel Condensation

Abstract

The catalytic activity of Nitrogen containing Carbon Nanotubes (NCNT), grown from acetonitrile or pyridine over supported Fe-, Co or Ni catalysts at various conditions, were tested for the base catalyzed Knoevenagel condensation of benzaldehyde and ethylcyanoacetate. All NCNT displayed activity for the reaction with initial turn over frequencies between 9 9 10 -3 and 5 9 10 -2 s -1 which is comparable with to those of activated basic carbons and a rehydrated hydrotalcite. Furthermore, the initial activity per gram of catalyst of NCNT was related to the amount of pyridinic type nitrogen in the NCNT. However, the reaction rate decreased with time on stream which was explained by competitive adsorption of reactant and product. The reaction rate can be described using LangmuirHinshelwood type kinetics including product adsorption.

One-dimensional nitrogen-containing carbon nanostructures

“…The activity was, in this case, related to the amount of pyridinic nitrogen incorporated into the structure [713], while competitive adsorption of reactant and product is responsible for the activity decay [714]. Basic nature of MWNCNTs was also pointed as crucial for their use as catalysts for wet air oxidation of oxalic acid, while catalytic activity was found to decay during the catalytic process due to the loss of the basic character [385].…”

“…Base properties of NCNTs enabled their use as a solid base catalyst for Knoevenagel condensation [713,714]. The activity was, in this case, related to the amount of pyridinic nitrogen incorporated into the structure [713], while competitive adsorption of reactant and product is responsible for the activity decay [714].…”

Carbocatalysis in Liquid‐Phase Reactions

“…Nitrogen doping or amine grafting can enhance the basic strength of carbon materials. Bitter and co‐workers showed that nitrogen‐containing CNTs are effective for the Knoevenagel condensation of ethyl α‐cyanoacetate with benzaldehyde (Scheme ): an initial activity of 14 mmol g cat −1 h −1 was obtained over NCNTs . The activity was determined by the concentration of pyridinic nitrogen atoms, but both O and N heteroatoms were needed for the reaction, since a maximum activity was obtained at a surface N/O ratio of 0.8–1.0 .…”

Nitrogen-doped carbon nanomaterials: To the mechanism of growth, electrical conductivity and application in catalysis

“…As shown in [76][77][78], an aqueous suspension of N-CNTs has pH 8-9 and there exists a correlation between the number of basic sites and nitrogen content in the pyridine-like state [78,79]. The presence of pyridine-like nitrogen on the carbon surface opens interesting routes for the development of advanced bifunctional materials with different types of surface sites.…”

“…And finally, activity of N-CNTs was investigated in the acid-base catalysis using the Knoevenagel reaction [76,77]. CNTs were shown to be inactive in this reaction, while in the case of N-CNTs a direct dependence of catalytic activity on the concentration of pyridinelike nitrogen was found, Fig.…”