Pd⁰–O_v–Ce³⁺ Interfacial Sites with Charge Redistribution for Enhanced Hydrogenation of Methyl Oleate to Methyl Stearate

Abstract

Improving the efficiency of metal/reducible metal oxide interfacial sites for hydrogenation reactions of unsaturated groups (e.g., C=C and C=O) is a promising yet challenging endeavor. In our study, we developed a Pd/CeO₂ catalyst by enhancing the oxygen vacancy (O_V) concentration in CeO₂ through high-temperature treatment. This process led to the formation of an interface structure ideal for supporting the hydrogenation of methyl oleate to methyl stearate. Specifically, metal Pd⁰ atoms bonded to the O_V in defective CeO₂ formed Pd⁰–O_V–Ce³⁺ interfacial sites, enabling strong electron transfer from CeO₂ to Pd. The interfacial sites exhibit a synergistic adsorption effect on the reaction substrate. Pd⁰ sites promote the adsorption and activation of C=C bonds, while O_V preferably adsorbs C=O bonds, mitigating competition with C=C bonds for Pd⁰ adsorption sites. This synergy ensures rapid C=C bond activation and accelerates the attack of active H* species on the semi-hydrogenated intermediate. As a result, our Pd/CeO₂-500 catalyst, enriched with Pd⁰–O_V–Ce³⁺ interfacial sites, demonstrated excellent hydrogenation activity at just 30 °C. The catalyst achieved a Cis–C18:1 conversion rate of 99.8% and a methyl stearate formation rate of 5.7 mol/(h·g_metal). This work revealed the interfacial sites for enhanced hydrogenation reactions and provided ideas for designing highly active hydrogenation catalysts.

Keywords

Hydrogenation / Interfacial sites / Oxygen vacancy / C=C bond

References

[1] Saravanan K, Tyagi B, Bajaj HC Esterification of stearic acid with methanol over mesoporous ordered sulfated ZrO₂–SiO₂ mixed oxide aerogel catalyst. J Porous Mater, 2016, 23(4): 937-946.

[2] Li H, Yang W, Zhou D, et al. Skeletal mechanism construction for heavy saturated methyl esters in real biodiesel fuels. Fuel, 2019, 239: 263-271.

[3] Savaliya ML, Dhorajiya BD, Dholakiya BZ Current trends in separation and purification of fatty acid methyl ester. Sep Purif Rev, 2015, 44(1): 28-40.

[4] Abe M, Nakamura R, Komatsu H, et al. Effect of additive structure on the performance of biodiesel fuel winterization. Fuel, 2021, 289.

[5] Lykakis IN, Ferreri C, Grabovskiy SA, et al. Separation of cis/trans geometrical fatty acid isomers by silver-exchanged zeolite Y. Tetrahedron, 2010, 66(12): 2203-2209.

[6] Iida H, Takahashi K, Yanagisawa A, et al. Reduction of trans fatty acids in hydrogenated soybean oil using Ni/TiO₂ catalysts. Food Chem, 2021, 340.

[7] Wong FH, Tiong TJ, Leong LK et al (2018) Role of ZnO in Ni/ZnO/Al₂O₃ as catalytic materials for hydrogenation of vegetable oil. In: AIP Conference Proceedings. Penang, Malaysia. Author(s) https://doi.org/10.1063/1.5066959

[8] Mamontova E, Trabbia C, Favier I, et al. Novel catalyst composites of Ni- and Co-based nanoparticles supported on inorganic oxides for fatty acid hydrogenations. Nanomaterials, 2023, 13(9): 1435.

[9] Wang HY, Jiao TT, Li ZX, et al. Study on palm oil hydrogenation for clean fuel over Ni–Mo–W/γ-Al₂O₃–ZSM-5 catalyst. Fuel Process Technol, 2015, 139: 91-99.

[10] Zhao L, Wang Y, An H, et al. Effects of acid-base properties on catalytic performance of supported nickel-based catalysts for 2-Ethyl-2-Hexenal Hydrogenation. J Chem Eng Chin Univ, 2017, 31(6): 1333-1339.

[11] Liu P, Zhao Y, Qin R, et al. Photochemical route for synthesizing atomically dispersed palladium catalysts. Science, 2016, 352(6287): 797-801.

[12] Schwartz TJ, Lyman SD, Motagamwala AH, et al. Selective hydrogenation of unsaturated carbon–carbon bonds in aromatic-containing platform molecules. ACS Catal, 2016, 6(3): 2047-2054.

[13] Rui N, Wang Z, Sun K, et al. CO₂ hydrogenation to methanol over Pd/In₂O₃: effects of Pd and oxygen vacancy. Appl Catal B Environ, 2017, 218: 488-497.

[14] Jiang F, Wang S, Liu B, et al. Insights into the influence of CeO₂ crystal facet on CO₂ hydrogenation to methanol over Pd/CeO₂ catalysts. ACS Catal, 2020, 10(19): 11493-11509.

[15] Liu K, Jiang L, Huang W, et al. Atomic overlayer of permeable microporous cuprous oxide on palladium promotes hydrogenation catalysis. Nat Commun, 2022, 13(1): 2597.

[16] Han X, Wu X, Deng Y, et al. Ultrafine Pt nanoparticle-decorated pyrite-type CoS₂ nanosheet arrays coated on carbon cloth as a bifunctional electrode for overall water splitting. Adv Energy Mater, 2018, 8(24): 1800935.

[17] Qin R, Liu K, Wu Q, et al. Surface coordination chemistry of atomically dispersed metal catalysts. Chem Rev, 2020, 120(21): 11810-11899.

[18] Zhang B, Wang J, Liu G, et al. A strongly coupled Ru–CrO _x cluster–cluster heterostructure for efficient alkaline hydrogen electrocatalysis. Nat Catal, 2024, 7: 441-451.

[19] Duan Y, Zhang XL, Gao FY, et al. Interfacial engineering of Ni/V₂O₃ heterostructure catalyst for boosting hydrogen oxidation reaction in alkaline electrolytes. Angew Chem Int Ed Engl, 2023, 62(10

[20] Dai F, Guo Z, Zhao W, et al. Interfacial engineering boosting charge extraction for efficient photocatalytic hydrogen evolution. Chem Eng J, 2022, 450.

[21] Zhang Y, Liu JX, Qian K, et al. Structure sensitivity of Au–TiO₂ strong metal-support interactions. Angew Chem Int Ed Engl, 2021, 60(21): 12074-12081.

[22] Liu Y, Ang EH, Zhong X, et al. Oxygen vacancy modulation in interfacial engineering Fe₃O₄ over carbon nanofiber boosting ambient electrocatalytic N₂ reduction. J Colloid Interface Sci, 2023, 652(Pt A): 418-428.

[23] Sun Y, Wu J, Wang Y, et al. Plasma-catalytic CO₂ hydrogenation over a Pd/ZnO catalyst: in situ probing of gas-phase and surface reactions. JACS Au, 2022, 2(8): 1800-1810.

[24] Zhang T, Yan H, Liu Z, et al. Engineering a Ni₁Fe₁–ZnO interface to boost selective hydrogenation of methyl stearate to octadecanol. ACS Catal, 2022, 12(24): 15181-15192.

[25] Li C, Kim SH, Lim HY, et al. Self-accommodation induced electronic metal-support interaction on ruthenium site for alkaline hydrogen evolution reaction. Adv Mater, 2023, 35(21

[26] Yang Y, Zhao S, Bi F, et al. Oxygen-vacancy-induced O₂ activation and electron-hole migration enhance photothermal catalytic toluene oxidation. Cell Rep Phys Sci, 2022, 3(8

[27] Zheng X, Yu P, Liu Y, et al. Efficient hydrogenation of methyl palmitate to hexadecanol over Cu/m-ZrO₂ catalysts: synergistic effect of Cu species and oxygen vacancies. ACS Catal, 2023, 13(3): 2047-2060.

[28] Fu L, Chen H, Wang K, et al. Oxygen-vacancy generation in MgFe₂O₄ by high temperature calcination and its improved photocatalytic activity for CO₂ reduction. J Alloys Compd, 2022, 891.

[29] Liao Y, Pan Y, Feng X, et al. Defective Auδ –-Ov interfacial sites boost C-H bond activation for enhanced selective oxidation of amino alcohols to amino acids. J Catal, 2024, 429.

[30] Wei Y, Li Y, Han D, et al. Facile strategy to construct porous CuO/CeO₂ nanospheres with enhanced catalytic activity toward CO catalytic oxidation at low temperature. Appl Nanosci, 2023, 13(6): 3633-3641.

[31] Zha M, Yan H, Li R, et al. Facet-dependent Pd⁰–O^2––Ce³⁺ active site for selective hydrogenation of linoleate ester to cis oleic acid ester. Mol Catal, 2023, 538.

[32] Utara S, Hunpratub S, Pinitsoontorn S, et al. Characterization and magnetic performance of pure CeO₂ nanoparticles via an ozonolysis reaction. Results Phys, 2021, 30.

[33] Liu Y, Yang C, Li H, et al. Effect of sulfate-modified CeO₂ with different morphologies on NH3-SCR. J Energy Inst, 2024, 112.

[34] Grabchenko MV, Mamontov GV, Zaikovskii VI, et al. The role of metal–support interaction in Ag/CeO₂ catalysts for CO and soot oxidation. Appl Catal B-Environ, 2020, 260.

[35] Rajendran S, Manoj D, Suresh R, et al. Electrochemical detection of hydrogen peroxide using micro and nanoporous CeO₂ catalysts. Environ Res, 2022, 214(3

[36] Yan H, Liu B, Zhou X, et al. Enhancing polyol/sugar cascade oxidation to formic acid with defect rich MnO₂ catalysts. Nat Commun, 2023, 14(1): 4509.

[37] Wang B, Weng D, Wu X, et al. Modification of Pd–CeO₂ catalyst by different treatments: effect on the structure and CO oxidation activity. Appl Surf Sci, 2011, 257(9): 3878-3883.

[38] Bai B, Arandiyan H, Li J Comparison of the performance for oxidation of formaldehyde on nano-Co₃O₄, 2D-Co₃O₄, and 3D-Co₃O₄ catalysts. Appl Catal B-Environ, 2013, 142–143: 677-683.

[39] Zhao Y, Zhang K, Li Y, et al. Enhanced electrocatalytic oxidation of formate via introducing surface reactive oxygen species to a CeO₂ substrate. ACS Appl Mater, 2021, 13(43): 51643-51651.

[40] Hu Z, Liu X, Meng D, et al. Effect of ceria crystal plane on the physicochemical and catalytic properties of Pd/ceria for CO and propane oxidation. ACS Catal, 2016, 6(4): 2265-2279.

[41] Qi X, Fu J, Jiang K, et al. Suppressing catalyst deactivation on Pd/CeO₂ for selective oxidation of glucose into gluconic acid. J Catal, 2022, 414: 44-52.

[42] Hu X, Fan Q, Tan M, et al. Investigating the impact of dynamic structural changes of Au/rutile catalysts on the catalytic activity of CO oxidation. Carbon Energy, 2024, 6(4

[43] Cao F, Song Z, Zhang Z, et al. Size-controlled synthesis of Pd nanocatalysts on defect-engineered CeO₂ for CO₂ hydrogenation. ACS Appl Mater Interfaces, 2021, 13(21): 24957-24965.

[44] Redjel A, Boudjahem AG, Bettahar M Effect of palladium precursor and preparation method on the catalytic performance of Pd/SiO₂ catalysts for benzene hydrogenation. Part Sci Technol, 2018, 36(6): 710-715.

[45] Long F, Wu S, Chen Y, et al. Hydrogenation of fatty acids to fatty alcohols over Ni₃Fe nanoparticles anchored on TiO₂ crystal catalyst: metal support interaction and mechanism investigation. Chem Eng J, 2023, 464.

[46] Zhao Y, Wang X, Cheng G, et al. Phosphorus-induced activation of ruthenium for boosting hydrogen oxidation and evolution electrocatalysis. ACS Catal, 2020, 10(20): 11751-11757.

[47] Tang X, Li J, Fang Z, et al. Single Ni-inserted Cu (111) surface: a DFT study of adsorption and reaction mechanisms of methanol steam reforming. Appl Surf Sci, 2022, 596.