Enhanced Visible Light Photocatalytic Hydrogenation of CO₂ into Methane over a Pd/Ce-TiO₂ Nanocomposition

Abstract

A series of Ce-doped TiO 2 nanoparticles were prepared by a sol−gel process and characterized by XRD, SEM, TEM, EDX mapping, UV−vis DRS, Raman spectroscopy, N 2 adsorption−desorption, PL spectra, CO 2 -TPD, and XPS. It is found that Ce ions can enter the lattice matrix of TiO 2 and occupy of Ti sites. This atom replacement leads to the formation of impurity energy levels in the band gap of TiO 2 , extending light absorption into the visible light region. Because Ce has a more flexible valence state, both Ce 3+ and Ce 4+ could be formed in the composites. The preference facilitates the photoinduced charge separation inside of the crystals. Moreover, Pd nanoparticles were then loaded as a co-catalyst on the surface of doped composites. As the trapping center of electrons, it can efficiently adsorb and activate CO 2 molecules, promoting their transformation into CH 4 . These composites were then evaluated as photocatalysts for CO 2 hydrogenation. While all of them could efficiently catalyze the reaction, 1.0% Pd/ 0.5% Ce-TiO 2 catalysts show the best photocatalytic performance, with CH 4 and CO yields up to 220.61 and 27.36 μmol/g, respectively, under visible light irradiation of 3 h. The improved photocatalytic behavior could be possibly induced by the synergistic effect between Ce and Pd. A probable mechanism was thus proposed based on above characterizations and experimental results.

Recent Advances in Plasmonic Photocatalysis Based on TiO2 and Noble Metal Nanoparticles for Energy Conversion, Environmental Remediation, and Organic Synthesis

“…Li et al synthesized Pd-loaded Ce-doped TiO 2 NPs for the photocatalytic CO 2 hydrogenation of methane. [401] They observed that Ce ions can enter the matrix of TiO 2 and replace the lattice sites of Ti. This atom replacement results in the generation of impurity energy levels in the TiO 2 band gap, which in turn extends the light absorption into the VIS-light region.…”

“…(2017) [401] Ag-TiO 2 Suzuki-coupling of bromoaryl 20 W LED (λ > 420 nm) Toluene, 24 h, room temperature 95% conversion, 92% selectivity (2020) [413] Pd-TiO 2 Suzuki cross coupling reactions VIS light (15 W LED lamps) NaOC(CH 3 ) 3 , air atmosphere, 28 °C, H 2 O-PEG (1:1) 93% conversion, 98% selectivity (2020) [403] HUY@S-TOH@AuPd C-C coupling reactions VIS light K 2 CO 3 , ethanol-water (2:1) mixture, room temperature >99% yield (2019) [404] Pd-TiO 2 Suzuki-Miyaura cross-coupling and Ullmann homocoupling reactions VIS light (40 W CFL bulb) Base, 70 °C, 6 h 95% conversion (2016) [405] Au/Pd-TiO (2017) [406] Pd-TiO 2 /CNFs Suzuki coupling reactions VIS light (Xe lamp) Water-ethanol mixture, 50 °C, 5 h 93.6% conversion, 94.8% conversion (2017) [407] Core-Shell Ag@TiO 2 Ullmann coupling reactions Blue laser (220 mW) H 2 O/DMF/DMSO, 5 h 65% conversion (2019) [408] www.advancedsciencenews.com www.small-journal.com 2101638 (39 of 47)…”

Titanium Dioxide: From Engineering to Applications

“…The characterization results showed that Ce ions entered the TiO2 matrix at Ti sites, leading to the formation of impurity states, as shown in Figure 5. In addition, enhanced separation of the photogenerated charge carriers was also realized due to the coexistence of Ce 3+ and Ce 4+ dopant ions [34]. Anandan et al studied the photodegradation of monocrotophos under visible light irradiation with La-doped TiO2.…”

Enhanced photocatalytic NO removal and toxic NO2 production inhibition over ZIF-8-derived ZnO nanoparticles with controllable amount of oxygen vacancies

“…The band gap energies of the photocatalysts in this study were calculated using the Kubelka-Munk formula: αhν = A(hν  Eg) η/2 , where α, h, ν, A, and Eg are the absorption coefficient, the Planck constant, the frequency of light, a constant, and the absorption band gap energy, respectively [43][44][45]. The value of η depends on the optical transition type of the semiconductor photocatalyst, and η = 1 for the systems in our study because ZnO is a direct band gap semiconductor [46].…”