Wang and co-workers (Catalysis Today 364 (2021) 21-34) prepared three-dimensionally ordered macroporous-mesoporous silica (3DOM-m SiO2) by combining a polymethyl methacrylate colloidal crystal template with the triblock copolymer surfactant P123, and loaded it with mixed manganese-metal oxides (MnMOx) for diesel soot combustion, finding the synthesis conditions empirically. They acknowledged that finding a facile method to synthesize materials with both highly ordered macropores and mesoporous pores is still a major challenge, that the formation mechanism remained a plausible scenario rather than a validated model, that soot-catalyst testing protocols are not standardized across the literature, and that catalyst durability under realistic exhaust was unproven. Dual-template approaches keep being reinvented and tuned per material (MgO, KIT-6 silica, MgFe2O4/MgO, zeolite-carbon templating, and dual-templated silica still under development in 2026), and no general, facile, widely reproducible route with quantified parameter windows and a mechanistic model of the coupled dual-ordering route has been reported in the literature to date (see References). The synthesis-plus-mechanism core therefore remains open, while protocol standardization and catalyst durability are adjacent application-level open issues.

Background

Diesel soot emitted by engines is trapped in a diesel particulate filter (DPF) and must be oxidized; catalysts lower the soot oxidation temperature, and the catalytic activity depends strongly on how well the solid catalyst contacts the soot particles. Porous solids are classified by pore width: mesopores are 2-50 nm and macropores are larger than 50 nm (IUPAC convention). Ordered mesoporous silicas such as MCM-41 and SBA-15 are made by surfactant templating, in which amphiphilic block copolymer molecules (here P123, a poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide) triblock copolymer) self-assemble into micellar arrays around which a silica precursor, typically tetraethyl orthosilicate (TEOS), hydrolyzes and condenses; evaporation-induced self-assembly (EISA) concentrates the surfactant so the mesophase forms during drying. Three-dimensionally ordered macroporous (3DOM, or inverse opal) materials are made by colloidal crystal templating: monodisperse polymer spheres, e.g. poly(methyl methacrylate) (PMMA), are packed into an opal-like crystal (often assisted by centrifugation), the voids are infiltrated with a precursor, and removal of the spheres by calcination leaves an ordered array of macropores connected through windows. Macropores of comparable size to soot particles improve catalyst-soot contact and mass transport, while mesopores in the walls provide high surface area; combining both scales with high ordering at each is achieved by dual templating (hard colloidal crystal + soft surfactant). Wang et al. (Catalysis Today 364 (2021) 21-34) synthesized 3DOM-m SiO2 this way, found suitable conditions only by systematically modifying reaction variables (reaction temperature 45 C, P123:TEOS mass ratio 0.533, water:ethanol volume ratio 0.5), and supported MnMOx mixed manganese-metal oxides (M = Fe, Co, Ni, Cu, Zn, La, Ce) on it; MnCeOx/3DOM-m SiO2 gave the best soot combustion (temperatures of 10%, 50% and 90% soot conversion of 285, 355 and 393 C, and 98.8% selectivity to CO2). Ordering is diagnosed by small-angle X-ray diffraction or small-angle X-ray scattering (SAXS) for the mesophase, scanning/transmission electron microscopy (SEM/TEM) for the macropore array, and N2 physisorption (BET surface area) for pore metrics; H2-TPR and O2-TPD (temperature-programmed reduction by H2 and desorption of O2) characterize redox and oxygen mobility. The difficulty of dual ordering is that two self-assembly processes at very different length scales - micrometer-scale sphere packing and nanometer-scale micelle templating - are coupled through one precursor solution: the rheology and wetting behavior that let TEOS infiltrate the PMMA crystal without disturbing micellar order, the hydrolysis kinetics of TEOS, centrifugation conditions for PMMA ordering, solvent composition, and calcination to remove both templates must all be controlled at once. The authors state that finding a facile method to synthesize materials with both highly ordered macropores and mesoporous pores is still a major challenge, that the variables governing final order are not quantitatively controlled, and that their proposed formation pathway (involving micellization thermodynamics and TEOS hydrolysis kinetics in the presence of the PMMA template) has not yet been established as a validated mechanism.

Problem Statement

Develop a facile and widely reproducible synthesis that yields materials - silica-based systems such as 3DOM-m SiO2 and, optionally, the broader class of oxide supports - in which the macropore framework and the mesopore system are simultaneously highly ordered, together with a mechanistic model of the dual-ordering route and a plan for its validation. Concretely, in the spirit of the source work: (i) replace the current empirical, trial-and-error condition search (centrifugation time and speed for polymer-sphere ordering, TEOS hydrolysis control, surfactant:TEOS and water:alcohol ratios, aging temperature, calcination) by quantified, controllable parameter windows whose effect on the 'highly ordered' status at both length scales is established, such that independent laboratories can reproduce the dual-ordered structure; (ii) demonstrate the route for at least one additional composition of the silica-based dual-templated family (a variant of the 3DOM-m SiO2 synthesis), showing which parameter transfers are material-specific, and optionally extend this to other oxide supports; and (iii) move the proposed formation pathway - coupling surfactant micellization thermodynamics with TEOS hydrolysis and condensation kinetics inside the colloidal crystal template - from a plausible process-level scenario to a mechanistic model of the coupled dual-ordering route consistent with the reported evidence for the assembly process, and design the concrete route by which that model would be validated - the decisive in situ or time-resolved measurement; the validation route is accepted as a plan and need not be executed. The problem is solved when a facile method to synthesize materials with both highly ordered macropores and mesopores can be reproducibly obtained from quantified parameter windows that also hold for at least one additional composition of the silica-based dual-templated family, together with a mechanistic model of the coupled dual-ordering route and the designed route to its validation, so that obtaining such dual ordering no longer constitutes a major challenge. Like the validation route under (iii), the synthesis deliverables (i) and (ii) may be met by a designed route with predicted parameter windows and need not be experimentally executed. Operationally, 'highly ordered' means that long-range order at each length scale is demonstrated by the diagnostics named in the Background (an ordered mesophase signature in small-angle X-ray scattering/diffraction and an ordered macropore array imaged by SEM/TEM); 'facile' means the route uses the dual-templating steps described in the Background without additional, undisclosed processing; and 'widely reproducible' means the reported parameter windows are tight enough that independent laboratories can recover those ordering signatures; 'mechanistic model' means a coupled kinetics and thermodynamics description that specifies the micellization and TEOS hydrolysis and condensation steps and reproduces a named set of reported observables. (The same source additionally calls for standardized soot-combustion testing protocols and for establishing long-term stability, sulfur tolerance and transient-exhaust performance of the supported Mn-based catalysts; these adjacent application-level questions are separate problems from the synthesis-and-mechanism objective stated above.)

References

  1. Lanyi Wang, Maozhong Chen, Xuehua Yu, Zhen Zhao, Xiaoqiang Fan, Yuechang Wei, Jian Liu, Preparation, characterization and catalytic performance of ordered macroporous-mesoporous SiO2-supported MnMOx catalysts for soot combustion, Catalysis Today 364 (2021) 21-34, DOI 10.1016/j.cattod.2020.07.047, https://doi.org/10.1016/j.cattod.2020.07.047
  2. Chunlei Zhang, Di Yu, Chao Peng, Lanyi Wang, Xuehua Yu, Yuechang Wei, Jian Liu, Zhen Zhao, Research progress on preparation of 3DOM-based oxide catalysts and their catalytic performances for the combustion of diesel soot particles, Applied Catalysis B: Environmental 319 (2022) 121946, DOI 10.1016/j.apcatb.2022.121946, https://doi.org/10.1016/j.apcatb.2022.121946
  3. Shengran Zhou, Lanyi Wang, Siyu Gao, Xinyu Chen, Chunlei Zhang, Di Yu, Xiaoqiang Fan, Xuehua Yu, Zhen Zhao, Research Progress on Preparation of Metal Oxide Catalysts with Porous Structure and Their Catalytic Purification of Diesel Engine Exhausts Gases, ACS Catalysis 14 (2024) 6062-6127, DOI 10.1021/acscatal.4c00323, https://doi.org/10.1021/acscatal.4c00323
  4. Xiaoao Du, Di Yu, Siyu Gao, Lanyi Wang, Ying Feng, Chunlei Zhang, Borui Ji, Xiaoqiang Fan, Xuehua Yu, Zhen Zhao, Research progress on rare earth-modified manganese-based oxide catalysts for diesel soot combustion, Journal of Rare Earths (2026), DOI 10.1016/j.jre.2026.05.010, https://doi.org/10.1016/j.jre.2026.05.010
  5. JiaJi Lin, Alexandre A. S. Gonçalves, Pasquale F. Fulvio, Krista S. Walton, Tailoring the particle size and hierarchical mesoporous-macroporous structure of dual-templated silica powders by a hydrothermal synthesis method, Microporous and Mesoporous Materials 407 (2026) 114090, DOI 10.1016/j.micromeso.2026.114090, https://doi.org/10.1016/j.micromeso.2026.114090
  6. Sabina Siles-Quesada, Christopher M. A. Parlett, Alexander C. Lamb, Jinesh C. Manayil, Yang Liu, Jim Mensah, Hamidreza Arandiyan, Karen Wilson, Adam F. Lee, Synthesis and catalytic advantage of a hierarchical ordered macroporous KIT-6 silica, Materials Today Chemistry 30 (2023) 101574, DOI 10.1016/j.mtchem.2023.101574, https://doi.org/10.1016/j.mtchem.2023.101574
  7. Baixiong Liu, Cong Li, Lina Zhang, Zhiping Liu, Mengjie Kuang, Xingyu He, Fabrication of three-dimensional ordered macroporous/mesoporous magnesium oxide for efficient cadmium removal, Ceramics International 47 (2021) 22830-22838, DOI 10.1016/j.ceramint.2021.04.301, https://doi.org/10.1016/j.ceramint.2021.04.301
  8. Lina Zhang, Jiarui Lu, Baixiong Liu, Hierarchically Ordered Macroporous-Mesoporous (HOM-m) MgFe2O4/MgO for Highly Efficient Adsorption of Ce(III) and La(III): Experimental Study and DFT Calculation Analysis, Separations 11 (2024) 333, DOI 10.3390/separations11120333, https://doi.org/10.3390/separations11120333
  9. Yuqing Ouyang, Ningning Du, Xiaoyun Xiong, Qingxun Hu, Hongman Sun, Tingting Li, Jie Zhong, Youhe Wang, Zifeng Yan, Preparation of hierarchical TS-1 zeolites from ordered macroporous-mesoporous carbon templates for efficient chloropropene epoxidation, Microporous and Mesoporous Materials 371 (2024) 113089, DOI 10.1016/j.micromeso.2024.113089, https://doi.org/10.1016/j.micromeso.2024.113089
  10. Anqian Hu, Qiongyi Xie, Liyu Chen, Yingwei Li, Hierarchically ordered meso-/macroporous MOF-based materials for catalysis and energy applications, EnergyChem 6 (2024) 100137, DOI 10.1016/j.enchem.2024.100137, https://doi.org/10.1016/j.enchem.2024.100137
  11. Lanyi Wang, Yanjun Chen, Shiwei Wang, Xinyu Chen, Shengran Zhou, Jiahong Li, Di Yu, Chunlei Zhang, Siyu Gao, Xuehua Yu, Chengyang Yin, Xiaoqiang Fan, Zhen Zhao, Preparation of macroporous Cu-SSZ-13-supported MOx catalysts and their catalytic performance for the simultaneous removal of soot and NOx, Chemical Engineering Journal 516 (2025) 164138, DOI 10.1016/j.cej.2025.164138, https://doi.org/10.1016/j.cej.2025.164138