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Correlation of urea precipitation temperature with phase formation, morphology, and catalytic activity for CO2 conversion of CeO2
(2025-08-01)
Seeharaj, Panpailin
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Duangtanon, Jenjira
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Sreemueang, Chanakan
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Noppharat, Phetchphalin
;
Kulthananat, Tachatad
This study proposes a simple method for tailoring the morphology and activity of cerium oxide (CeO<inf>2</inf>) catalysts in converting carbon dioxide (CO<inf>2</inf>) and methanol to green organic carbonate, dimethyl carbonate (DMC), to utilize and reduce CO<inf>2</inf> emissions. CeO<inf>2</inf> was prepared by urea precipitation at 85, 105, and 125 °C for 2 h, then calcining at 600 °C for 2 h. The phase structure and morphology of CeO<inf>2</inf> correlated with the urea hydrolysis rate. A low degree of supersaturation at 85 °C led to heterogeneous precipitation of cerium oxycarbonate (Ce<inf>2</inf>O(CO<inf>3</inf>)<inf>2</inf>.H<inf>2</inf>O) and CeO<inf>2</inf> with spherical morphology, while a higher degree of supersaturation at 105 °C and 125 °C resulted in homogeneous precipitation of single-phase Ce<inf>2</inf>O(CO<inf>3</inf>)<inf>2</inf>.H<inf>2</inf>O with spindle and elongated octahedral morphology, respectively. The spindle-shaped CeO<inf>2</inf> prepared at 105 °C with a predominant surface (111) facet showed the highest catalytic activity, with a DMC yield of 18.81 mmol.g<inf>cat</inf>−1. The enhanced catalytic efficiency of spindle-shaped CeO<inf>2</inf> was due to the high concentration of surface-active defect sites of exposed cerium cations and oxygen vacancies, which optimized the number of acid–base sites in adsorbing and activating CO<inf>2</inf> and methanol to produce DMC.
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Alkanolamine-Grafted and Copper-Doped Titanium Dioxide Nanosheets-Graphene Composite Heterostructure for CO2 Photoreduction
(2023-11-13)
Karawek, Apisit
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Kitjanukit, Nutkamol
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Neamsung, Wannisa
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Kinkaew, Chonlathon
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Phadungbut, Poomiwat
CO<inf>2</inf> photoreduction is an intriguing approach to carbon capture, utilization, and storage (CCUS). It relies on an effective photocatalyst to generate photoinduced electrons that incorporate carbon dioxide (CO<inf>2</inf>), yielding fuel products, e.g., methane, methanol, and ethanol. The heterostructure of titanium dioxide nanosheets (TNS) and graphene oxide (GO) is a sandwich-type composite consisting of two 2-dimensional nanostructures (2D-2D). It was demonstrated as an excellent candidate for CO<inf>2</inf> photoreduction due to its outstanding charge separation ability. This research studied the photoactivity of alkanolamine-grafted TNS and alkanolamine-grafted and copper-doped TNS/GO composites. In the first experiment, triethanolamine-grafted TNS (TEA-TNS) exhibited the best ability in CO<inf>2</inf> photoreduction compared to monoethanolamine- and diethanolamine-grafted TNS (MEA-TNS and DEA-TNS) due to the base-catalyzed hydration nature of CO<inf>2</inf>-TEA interactions. In the second experiment, we studied the photoactivity of four composites, including copper-doped TNS/GO (Cu-TNS/GO), TEA-[Cu-TNS/GO] (grafting TEA on Cu-TNS/GO), Cu-[TEA-TNS]/GO (doping Cu on TEA-TNS/GO), and TEA-Cu-TNS/GO (one-step hydrothermal synthesis with the Cu precursor, TEA, and GO). TEA-[Cu-TNS/GO] showed the best photoactivity since TEA was added last to the heterostructures, which benefited in avoiding side chelation reactions between TEA and Cu ions and ensuring TEA exposure to CO<inf>2</inf>
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Improvement of surface properties of metal doped-CeO2 nanospindle catalysts for direct synthesis of dimethyl carbonate from CO2 and methanol
(2023-06-01)
Seeharaj, Panpailin
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Saenman, Thanita
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Phiwhom, Thanabat
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Muangsuwan, Chutanan
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Srinives, Sira
To utilize carbon dioxide (CO<inf>2</inf>) which is the main greenhouse gas, this study developed effective metal doped-CeO<inf>2</inf> nanospindle catalysts for conversion of CO<inf>2</inf> and methanol into dimethyl carbonate (DMC). Ce<inf>0.9</inf>M<inf>0.1</inf>O<inf>2</inf> nanospindles (where M is a transition metal, i.e., Zr, Fe, Cu and Co) were prepared by a template-free hydrothermal method. The substitution of different valence and size cations, including Zr4+, Fe3+, Cu2+ and Co2+, for Ce4+ sites in the fluorite CeO<inf>2</inf> lattice induced the defect formation of surface-active sites of exposed Ce3+ and oxygen vacancies through the charge compensation and redox pair reactions. Ce<inf>0.9</inf>Fe<inf>0.1</inf>O<inf>2</inf> solid solution with well-preserved spindle shaped morphology showed the highest catalytic performance by giving DMC yield at 3.56 mmol.g<inf>cat</inf>−1 with 100% DMC selectivity. The improvement of catalytic activity was attributed to the higher proportion of surface defect sites and variation of acid-base properties caused by the integration of Fe dopants into CeO<inf>2</inf> ionic system.
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Soft template-assisted copper-doped sodium dititanate nanosheet/graphene oxide heterostructure for photoreduction of carbon dioxide to liquid fuels
(2022-08-26)
Lertthanaphol, Napat
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Prawiset, Natthanicha
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Soontornapaluk, Pornpinun
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Kitjanukit, Nutkamol
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Neamsung, Wannisa
Photoreduction of CO<inf>2</inf> to a high-value product is an interesting approach that not only captures CO<inf>2</inf> but also converts it into other products that can be sold or used in industry. The mechanism for the CO<inf>2</inf> conversion relies strongly on photo-generated electrons that further couple with CO<inf>2</inf> and form active radicals for the reaction. In this research, we synthesized a heterostructure of copper-doped sodium dititanate nanosheets and graphene oxide (CTGN) following a one-step hydrothermal process with assistance from a sodium hydroxide soft template. The role of the template here is to facilitate the formation of the nanosheets, creating the nanosheet-graphene 2D-2D heterostructure. The heterostructure yields excellent charge mobility and a low charge recombination rate, while the nanosheet-graphene interfaces house active radicals and stabilize intermediates. The CTGN exhibits an outstanding photoactivity in the photoreduction of CO<inf>2</inf>, producing liquid fuels, including acetone, methanol, ethanol and i-propanol.
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One-Step Hydrothermal Synthesis of Precious Metal-Doped Titanium Dioxide–Graphene Oxide Composites for Photocatalytic Conversion of CO2 to Ethanol
(2021-12-28)
Lertthanaphol, Napat
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Pienutsa, Natpichan
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Chusri, Kittapas
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Sornsuchat, Thirawit
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Chanthara, Prowpatchara
We utilized a one-step hydrothermal process for the synthesis of precious metal-doped titanium dioxide (TiO<inf>2</inf>)/graphene oxide (GO) composites. The metal-doped TiO<inf>2</inf>/GO composites, including silver–TiO<inf>2</inf>/GO (Ag–TiO<inf>2</inf>/GO), palladium–TiO<inf>2</inf>/GO (Pd–TiO<inf>2</inf>/GO), and copper–TiO<inf>2</inf>/GO (Cu–TiO<inf>2</inf>/GO), were synthesized by mixing a metal precursor, titanium butoxide, and graphene oxide in a water–ethanol mixture in an autoclave hydrothermal reactor. The photocatalytic performance of the composites was tested in the photoreduction of carbon dioxide (CO<inf>2</inf>) to ethanol. Ag–TiO<inf>2</inf>/GO, Pd–TiO<inf>2</inf>/GO, and Cu–TiO<inf>2</inf>/GO exhibited an ethanol production rate of 109, 125, and 233 μmol/g<inf>cat</inf> h, respectively. The outstanding performances of Cu–TiO<inf>2</inf>/GO can be attributed to a combined effect of key parameters, including optical band gap, crystallite size, and BET surface area.

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