Assessing carbon or tungstates coverage of ZrO2 nanoparticles supported on MWCNT via NOx-TPD

Multi-walled carbon nanotubes (MWCNT) promoted by oxides, that are far from trivial to characterize, have emerged as promising candidates in several fields such as biosensors and catalysis. In this study the coverage of ZrO2 nanoparticles supported on MWCNT, by carbonaceous deposits or tungstates was investigated by NOx temperature-programmed desorption (NOx-TPD). ZrO2 coverage by carbonaceous deposits was found to be about 30 %, whereas that by tungstates varied from 40 to 77 % depending on the W loading of the sample. The size of the ZrO2 particles estimated by NOx-TPD (∼2.3 nm) was found to be in excellent agreement with that determined by TEM. Remarkably, it was found that W interacted preferentially with the ZrO2 nanoparticles for a W surface density of 1.9 W/nmZrO22 (half monolayer coverage of the ZrO2 nanoparticles by tungstates). Monolayer coverage of ZrO2 by tungstates was nearly complete when introducing a W loading twice as high as that theoretically needed. These insights into the surface coverage of ZrO2 by carbon or tungstates could not be obtained by any means other than NOx-TPD, which makes it a unique method to provide advanced characterization of the surface of oxides supported on MWCNT, in particular, and carbon supports, to a broader general interest. [Display omitted] •The coverage of ZrO2 nanoparticles supported on MWCNT by C or WO3 was assessed.•Only NOx-TPD could provide in-depth characterization of these complex nanomaterials.•The size of the ZrO2 nanoparticles estimated by TEM and NOx-TPD were consistent.•Monolayer coverage of ZrO2 by WO3 was nearly complete only when excess W was added.