ORALS
SESSION:
PhysicalSatPM3-R10
| Vayenas International Symposium on Physical Chemistry and its applications for sustainable development |
| Sat Oct, 26 2019 / Room: Aphrodite B (100/Gr. F) | |
| Session Chairs: Dionysios Tsousis; Session Monitor: TBA |
17:50: [PhysicalSatPM313]
Characterization of WOx-ZrO2/MWCNT: An Aqueous Phase Acid Catalyst for Alcohol Dehydration Patrick
Kelleher
1 ; Cyril
Thomas
2 ; Hui
Shi
3 ;
Gary
Haller1 ;
1Yale University, New Haven, United States;
2Sorbonne Université, Paris, France;
3Department of Chemistry, Catalysis Research Center, Technische Universität München, Garching, Germany;
Paper Id: 32
[Abstract] Tungstated zirconia supported on multi-walled carbon nanotubes (WO<sub>x</sub>-ZrO<sub>2</sub>/MWCNT) has been characterized by transmission electron microscopy (TEM), X-ray diffraction (XRD), X-ray absorption spectroscopy (XAS), NO<sub>x</sub> temperature programmed desorption (NO<sub>x</sub>-TPD) and probe reaction of cyclohexanol dehydration in liquid water. TEM and XRD establish that the ZrO<sub>2</sub> grafted to MWCNT are tetragonal crystalline nanoparticles of about 2 nm [1]. XAS and thermal gravimetric analysis indicates that the tungstated zirconia nanoparticles are hydrothermally stable at 200°C and NO<sub>x</sub>-TPD [2] was used to measure the interaction of impregnated WO<sub>x</sub> with ZrO<sub>2</sub>/MWCNT; the WO<sub>x</sub> preferentially interacts with the surface of ZrO<sub>2</sub> until about a monolayer (~4 W/nm<sup>2</sup>) of coverage is reached when a WO<sub>3</sub> particulate phase develops. At a coverage of 8 W/nm<sup>2</sup>, WO<sub>3</sub> can be detected by XRD. The turnover frequencies (TOF) normalized per W atom for cyclohexanol dehydration at 215°C at W surface densities of 2, 4 and 8 W/nm<sup>2</sup> are 0.043, 0.029 and 0.027, respectively, compared to a commercial bulk WO<sub>x</sub>-ZrO<sub>2</sub> with W surface density of 5 W/nm<sup>2</sup>, where it is 0.021. Thus, the TOF of the WO<sub>x</sub>-ZrO<sub>2</sub>/MWCNT at 2 W/nm<sup>2</sup> is about twice that of unsupported WO<sub>x</sub>-ZrO<sub>2</sub> and exceeds the bulk WO<sub>x</sub>-ZrO<sub>2</sub> even when the W density is greater than that of unsupported WO<sub>x</sub>-ZrO<sub>2</sub>. Dividing the bulk 15.5 wt% WO<sub>x</sub>-ZrO<sub>2</sub> TOF (based on acid site density) by the TOF (based on a W atom normalization) indicates that on average it requires 3.3 W atoms per acid site. Because the acid site is a hydronium ion in all cases [3], a better interpretation is that fewer W atoms per acid site are required on the low W density WO<sub>x</sub>-ZrO<sub>2</sub>/MWCNT. Thus we estimate that about 1.6 W atoms per acid site are required on the 2 W/nm<sup>2</sup> WO<sub>x</sub>-ZrO<sub>2</sub>/MWCNT.
References:
\n[1] C. Lui, S. Lee, D. Su et al., J. Phys. Chem. C, 116 (2012) 21742.\n[2] H. Y. Law, J. Blanchard, X. Carrier et al., J. Phys. Chem. C, 114 (2010) 9731.\n[3] H. Shi, S. Eckstein, A. Vjunov et al., nature Commun., 8 (2017) 15442.
