Direct amide synthesis over core–shell TiO₂@NiFe₂O₄ catalysts in a continuous flow radiofrequency-heated reactor

Abstract

A note on versions:The version presented here may differ from the published version or, version of record, if you wish to cite this item you are advised to consult the publisher's version. Please see the 'permanent WRAP url' above for details on accessing the published version and note that access may require a subscription. AbstractCore-shell composite magnetic catalysts TiO2@NiFe2O4 with a titania loading of 9-32 wt. % have been synthesised by sol-gel method for direct amide synthesis in a radiofrequency (RF)-heated continuous flow reactor. The catalyst calcination temperature was optimised in the range of 350-500 ºC and the highest activity was observed for the catalyst calcined at 500 ºC due to conversion of titania into catalytically active anatase phase. No reaction between the magnetic core and the titania shell was observed up to the calcination temperature of 1000 ºC and no sintering of titania shell was observed after calcination at 500 ºC. The comparison of direct amide synthesis in a continuous flow fixed bed reactor under conventional and RF heating demonstrated that the RF heating mode increased the apparent reaction rate by 60 % and decreased the deactivation rate due to a better temperature uniformity. The titania weight normalised reaction rate in the RF-heated reactor was constant for titania loadings above 17 wt. %, while it decreased by a factor of 3 at lower titania loadings because of interactions between the ferrite core on the thin layer of the catalyst. The catalyst deactivation study showed that the deactivation rate could be accurately described by a first order kinetics and that the main reason of deactivation was coking. The catalyst regeneration via calcination at 400 ºC resulted in the catalyst sintering, while a treatment with a hydrogen peroxide solution at 90 ºC fully recovered catalytic activity.

The enhancement of direct amide synthesis reaction rate over TiO 2 @SiO 2 @NiFe 2 O 4 magnetic catalysts in the continuous flow under radiofrequency heating

“…This study follows our previous work [20,28,31] where we developed different titaniacontaining composite catalysts for this reaction. The main problems with these catalysts were (i) the relatively fast catalyst deactivation due to product inhibition, as a result of a strong product adsorption on the titania surface and (ii) limited reaction rate.…”

“…Under RF heating, the composite magnetic catalyst should provide both high heating and reaction rates. A core-shell structure is often used because the shell layer often acts as a catalyst and protects the magnetic core from chemical erosion and aggregation [19,20].…”

“…However, the charge transfer between the core and shell elements is often detrimental for catalytic properties [20,21]. Beydoun et al [21] observed the photodissolution of the catalytic titania shell at the boundary with the magnetic core which changed the magnetic properties and reduced the catalytic activity.…”

Engineering Iron–Nickel Nanoparticles for Magnetically Induced CO2Methanation in Continuous Flow

“…The target temperature is reached within few seconds and the energy is directly transferred inside the material without the need for heating the whole reactor system. This technology appeared first as an engineer solution for fast heating catalytic reactors, making use either of the walls of the reactor or from heating elements embedded inside, such as iron balls or ferrite microparticles . We have demonstrated the possibility to magnetically induce CO 2 methanation in a continuous‐flow reactor using core–shell NPs consisting of Ni or Ru coated iron carbide cores displaying high heating properties .…”

“…This technology appeared first as an engineer solution for fast heating catalytic reactors, making use either of the walls of the reactor [10][11][12] or from heating elements embedded inside, such as iron balls or ferrite microparticles. [1,13,14] We have demonstrated the possibility to magnetically induce CO 2 methanation in a continuous-flow reactor using core-shell NPs consisting of Ni or Ru coated iron carbide cores displaying high heating properties. [2,4] However, a modest CO 2 conversion (50 %) was achieved with a CH 4 yield of 15 %.…”