Confinement Effect of Carbon Nanotubes: Copper Nanoparticles Filled Carbon Nanotubes for Hydrogenation of Methyl Acetate

Abstract

Copper nanoparticles filled carbon nanotubes (CNTs) with varied tube diameters were prepared via a convenient sonication-assisted impregnation approach. CNTs and Cu nanoparticles filled CNTs were thoroughly investigated using transmission electron microscopy, Raman spectroscopy, N 2 adsorption, X-ray diffraction, and H 2 temperature programmed reduction. Confinement effects of CNTs, originated from its diameter and microstructure, on the filled Cu nanoparticles were discovered. For CNTs with smaller tube diameter, a consequential strong autoreduction for the confined Cu nanoparticles was observed, which showed a downward trend with the increasing anneal temperature. Methyl acetate (MeOAc) hydrogenation forming methanol and ethanol was chosen as model reaction to further explore the influence of CNTs confinement effects on the catalytic performance. In the case of catalysts derived from CNTs with smaller inner diameter (4−10 nm), their catalytic performance were improved after the CNTs heat treatment under Ar atmosphere and the optimum treatment temperature was 973 K. On the contrary, the CNTs catalysts with larger inner diameter (20−30 nm) exhibited reduced catalytic activity after the same heat treatment. In addition, the selectivity to ethanol from MeOAc was also found dependent on CNTs tube diameter. Furthermore, the Cu nanoparticles loaded outside of CNTs catalyst were prepared and compared with the Cu nanoparticles filled inside CNTs catalyst, and the latter exhibited higher catalytic activity because of the confinement effects of CNTs. All in all, when using CNTs as support materials, the likely synergistic effects created by CNTs diameter, the pretreatment on CNTs, and the nanocatalyst loaded inside or outside CNTs are responsible for the catalytic activity of the prepared catalysts. These findings propose an in-depth insight into the confinement of CNTs to the filled metal catalysts, and thus inspire the development of novel catalyst with beneficial catalytic performance.

Structural features and catalytic performance in CO preferential oxidation of CuO–CeO2 supported on multi-walled carbon nanotubes

“…35, 48, H 2 -TPR profiles of CuO-CeO 2 (r)/CNT catalysts:The above assignment of reduction peaks is mainly from the point of view of the copper oxides dispersion and interaction between copper oxides and ceria. Nevertheless, the effect of support should also be taken into consideration in the case of supported CuO-CeO 2 system since the facilitated reduction of CuO due to the promoted electron transfer by CNT as previously reported,65,70 which is witnessed by the comparison of TPR profiles between CuOCeO 2 (5/5)/CNT and those supported on AC, Al 2 O 3 and SiO 2 (shown as supplementary data)…”

Chemical reactions confined within carbon nanotubes

“…Indeed, the calculated turnover frequency (TOF) for gold nanoparticles in the hydrogenation of cinnamaldehyde was reported to increase 90-fold upon confinement within MWCNT, despite only 40% of AuNP estimated to be encapsulated. 51 These examples of methyl acetate and cinnamaldehyde hydrogenation within narrow MWCNT and SWCNT respectively demonstrate the concept that greater confinement effects may be possible within narrower CNT, with the potential drawback of reduced diffusion relative to wider CNT. The authors appraised the influences of nanoscale confinement, the impregnation procedure and hightemperature annealing on the yields and distributions of products across a range of hydrogenation reactions.…”

“…46,47 Along with these remarkable changes to selectivity, almost all confined catalysts described showed enhanced activity as a consequence of nanoscale confinement. 51,52 Interestingly, MWCNT of internal diameter 7 (AE3) nm and 25 (AE5) nm were compared and the highest conversion values were observed within the narrower CNT. 48 Rong et al recently explored the ruthenium nanoparticlecatalysed hydrogenation of benzene, p-chloronitrobenzene and cinnamaldehyde in MWCNT.…”

The Effect of Doping and Confinement on the Adsorption of Pt on CNTs upon Be, B, N and O Doping: A Theoretical Study

“…For example, Bao et al found that encapsulation interactions of CNT could not only reduce the size of Pt nanoparticles, but also prefer the Pt species at active reduced states [14]. In addition, the metal NPs (i.e., Pd, Rh, Fe, Ru and so on) encapsulated inside the nanotube could deliver enhanced catalytic activity or higher enantioselectivity towards a wide range of reactions, such as oxygen reduction reaction (ORR) [15], Fisher-Tropsch synthesis (FTS) reaction [16][17][18] and liquid phase hydrogenation reaction [19][20][21]. As illustrated, the confining metal or metal oxide nanoparticles inside CNTs often lead to a different catalytic activity with respect to the same particles deposited on the external surfaces.…”