Enhanced Photocatalytic Performance toward CO₂ Hydrogenation over Nanosized TiO₂-Loaded Pd under UV Irradiation

Abstract

A series of Pd/TiO2 photocatalysts were synthesized by a simple glucose reduction method, and their photocatalysis properties were evaluated in an array of CO2 hydrogenations. The samples were characterized by XRD, SEM, TEM, EDX, EDX mapping, UV–vis DRS, Raman spectroscopy, PL spectroscopy, XPS, and N2 adsorption. In terms of product yields (in micromoles per gram of catalyst), a 1.0 wt % Pd/TiO2 catalyst (CH4, 355.62; CO, 46.35; C2H6, 39.69) was found to be superior to pristine TiO2 (CH4, 42.65; CO, 4.73; C2H6, 2.7) and other composites under UV irradiation for 3 h, possibly because of a synergistic effect between the palladium nanoparticles and the TiO2 support. The palladium nanoparticles on the surface of TiO2 substantially accelerated electron transfer and acted as active sites for the adsorption and activation of CO2 molecules, to promote CO2 hydrogenation. During the photocatalytic CO2 hydrogenation, dissociated hydrogen reacts with CO2 – activated on the Pd/TiO2 photocatalyst to form a new PdC surface species that is stable during the reaction and further transforms to generate methane. A detailed mechanism of photocatalytic CO2 hydrogenation is discussed to account for the performance of the Pd/TiO2 photocatalyst in the reaction.

Impact of Pd Loading on CO2 Reduction Performance over Pd/TiO2 with H2 and H2O

“…These molar quantities of CH 4 per unit weight of photocatalyst were obtained after 8 [21], 6 [22], and 24 [40] h of illumination, respectively. Another study [23] reported that the molar quantity of CH 4 per unit weight of photocatalyst in the case of CO 2 /H 2 with Pd/TiO 2 was 356 µmol/g which was obtained after 3 h of illumination.…”

Photocatalytic CO2 Reduction on TiO2‐Based Materials under Controlled Reaction Conditions: Systematic Insights from a Literature Study

“…In some selected publications, more than one noble‐metal‐modified TiO 2 material is studied so comparisons can be made. In reference Pd, Pt, Ru, Rh, Ir and Ni were added to anatase TiO 2 NPs and tested in CO 2 reduction. It should be noted that most of those metals are known as classical Fischer–Tropsch or methanation catalysts .…”

“…It should be noted that most of those metals are known as classical Fischer–Tropsch or methanation catalysts . In reference , the pressure and temperature were elevated (2.5 MPa and over 100 °C due to the heat produced by the lamp) and the reaction environment was H 2 :CO 2 with a ratio of 4:1. A comparison was possible for these harsh reaction conditions.…”

“…In some selected publications, more than one noble-metal-modifiedT iO 2 materiali sstudied so comparisons can be made. In reference [42] Pd, Pt, Ru, Rh, Ir and Ni were added to anatase TiO 2 NPs and tested in CO 2 reduction.I ts houldb en oted that most of those metals are known as classical Fischer-Tropsch or methanation catalysts. [2,43] In reference [42],t he pressure and temperature were elevated (2.5 MPa and over 100 8Cdue to the heat produced by the lamp) and the reaction environment was H 2 :CO 2 with ar atio of 4:1.…”

Nb‐Doped TiO2 Photocatalysts Used to Reduction of CO2 to Methanol

“…e use of Pd as a dopant in TiO 2 was evaluated on CO 2 hydrogenation under UV irradiation generating the amount of 355.62 µmol CH 4 /g-cat by the increase of recombination time of generated electrons and adsorption and activation of CO 2 molecules on surface of catalyst [17]. Cheng et al [18] used Cu 2+ -TiO 2 nanorod thin film photocatalysts reducing CO 2 into methanol and ethanol obtaining, respectively, 36.18 µmol/g-cat·h and 79.13 µmol/g-cat·h in which Cu 2+ acted as active sites of electron traps and could suppress the electron-hole recombination allied to high surface area of TiO 2 nanorods.…”