Dispersion Of Active Species Research Articles

Construction of CuCoCe ternary catalyst via a porous organic polymer template approach for efficient CO-PROX with wide operating temperature window

Preferential CO oxidation (CO-PROX) is a promising approach for removing trace CO from hydrogen-rich streams, effectively preventing Pt anode poisoning in proton-exchange membrane fuel cells (PEMFCs). To effectively eliminate CO within the PEMFC operating temperature range, catalysts must exhibit high CO conversion and O2 selectivity. Expanding the operating temperature window of these catalysts is crucial. This study presents the synthesis of a CuCoCe ternary catalyst (CuCo/Ce-P) using an imidazole-functionalized porous organic polymer as a sacrificial template. Compared to the CuCoCe ternary catalyst prepared without a template (CuCo/Ce), CuCo/Ce-P exhibits significantly enhanced catalytic activity, with a T50 reduction from 85 °C to 55 °C and an expanded operating temperature window of approximately 40 ℃. Characterization results indicate that the imidazole-functionalized porous organic polymer facilitates improved dispersion of active species by anchoring metal ions through electron-rich groups, enhances intermetallic interactions, promotes electron transfer, and significantly improves the oxygen-deficient capacity of the CuCoCe ternary catalyst. Consequently, the catalyst exhibits a greater number of active interfaces, leading to enhanced catalytic activity and a wider operating temperature window.

NiMo-MMO catalyst derived from LDHs precursors toward the deep hydrogenation of pyrene

A series of Ni-based catalysts were prepared via structural topological transformation from the Ni@Al2O3 layered double hydroxides (LDHs) precursors, and applied for the deep catalytic hydrogenation saturation of pyrene in a high-pressure reactor. The pore structures, active species dispersion, surface morphology, amount and type of acid of the prepared catalysts were characterized by BET, XRD, SEM, TEM, XPS, SEM, NH3-TPD and Py-IR. We studied the influence of physicochemical properties of Ni-based catalysts on the regularity and mechanism of deep hydrogenation of pyrene. Meanwhile, the synergy between Ni and Mo, and the interaction between active metals and support were discussed to further reveal the constitutive relationship during the hydrogenation reaction of pyrene. The results of the evaluation of the catalytic hydrogenation of pyrene show that the as-prepared NiMo mixed metal oxide (MMO) catalyst showed excellent catalytic activity: ∼95% pyrene conversion, 90.12% for the selectivity of deep hydrogenation products (hexahydropyrene, decahydropyrene and hexadecahydropyrene). It was expected that the successfully preparation and utilization of NiMo-MMO catalyst could provide a theoretical basis for the design of this kind of catalysts for deep catalytic hydrogenation of polycyclic aromatic hydrocarbons (PAHs).

Shaping Phenolic Resin-Coated ZIF-67 to Millimeter-Scale Co/N Carbon Beads for Efficient Peroxymonosulfate Activation.

Catalytic performance decline is a general issue when shaping fine powder into macroscale catalysts (e.g., beads, fiber, pellets). To address this challenge, a phenolic resin-assisted strategy was proposed to prepare porous Co/N carbon beads (ZACBs) at millimeter scale via the phase inversion method followed by confined pyrolysis. Specially, p-aminophenol-formaldehyde (AF) resin-coated zeolitic imidazolate framework (ZIF-67) nanoparticles were introduced to polyacrylonitrile (PAN) solution before pyrolysis. The thermosetting of the coated AF improved the interface compatibility between the ZIF-67 and PAN matrix, inhibiting the shrinkage of ZIF-67 particles, thus significantly improving the void structure of ZIF-67 and the dispersion of active species. The obtained ZACBs exhibited a 99.9% removal rate of tetracycline (TC) within 120 min, with a rate constant of 0.069 min-1 (2.3 times of ZIF-67/PAN carbon beads). The quenching experiments and electron paramagnetic resonance (EPR) tests showed that radicals dominated the reaction. This work provides new insight into the fabrication of high-performance MOF catalysts with outstanding recycling properties, which may promote the use of MOF powder in more practical applications.

MOFs-derived CuCeOx supported on H-zeolite socony mobile-5 for catalytic oxidation of 1,2-dichlorobenzene

The catalytic elimination of chlorinated aromatic hydrocarbons is the frontier of catalytic oxidation of organic pollutants, and the screen of efficient catalysts (low cost, high activity, durability and selectivity) remains challenging. In this work, the CuCeOx derived from metal-organic frameworks supported on H-zeolite socony mobile-5 (HZSM-5) complex catalyst (CuCeOx-H-C) was prepared through impregnation combined with pyrolysis and applied in the catalytic oxidation of 1,2-dichlorobenzene. The results indicate that the introduction of carboxyl groups on the surface of HZSM-5 is crucial for the formation of Ce-MOF/HZSM-COOH core–shell structure. This introduction facilitates the uniform deposition of CuCeOx on HZSM-5 and significantly enhances the overall acidity. Furthermore, the synergistic effect of Cu-Ce significantly enhanced the catalyst’s activity at low temperatures. Therefore, CuCeOx-H-C exhibited the highest activity, with a T90 of 236 °C. Additionally, the CuCeOx-H-C catalyst showed high selectivity for HCl and suppressed the generation of chlorinated by-products. The differences in catalyst activity among various catalysts arise from multiple factors, including specific surface area, dispersion of active species, oxygen mobility, oxygen storage capacity, redox properties, and others. Under the synergetic effects of above-mentioned factors, the activity of CuCeOx-H-C is remarkably enhanced and would be promising for potential industrial application.

Flower-like hierarchical TS-1/Al2O3 composite supported NiMo catalysts for efficient hydrodesulfurization of dibenzothiophenes

Flower-like Al2O3 materials were successfully incorporated by TS-1 nanocrystals to synthesize Flower-like TS-1-Al2O3 (FTA) micro-mesoporous composite by a facile nano self-assembly method. FTA supported NiMo bimetallic catalysts (NiMo/FTA) were further constructed and applied to the hydrodesulfurization (HDS) reactions for dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT). FTA composites were constructed from flower-like pore structures stacked with nanosheets, which are conducive to the even load and dispersion of active species and the diffusion of macromolecular sulfur-containing compounds with relatively low resistance. The fabrication of TS-1 nanocrystals effectively enhanced the acidic sites, regulated the metal-support interaction, which could increase the stacking layer of MoS2 slabs, and producing more NiMoS-II type active phase. NiMo/FTA-10 presented the excellent HDS conversion of DBT (99.3 %) and 4,6-DMDBT (93.2 %) at 10 h−1, the highest reaction rate constant (2.6 × 10-7 mol g−1 s−1) and turnover frequency values (6.7 × 10-4 s−1) for 4,6-DMDBT HDS reaction. Compared to the direct desulfurization route (DDS), hydrogenation route (HYD) and isomerization route (ISO) can effectively eliminate the steric hindrance of 4,6-DMDBT, which is more conducive to the HDS reaction.

Tailored Metal-Organic Frameworks for Water Purification: Perfluorinated Fe-MOFs for Enhanced Heterogeneous Catalytic Ozonation.

An industrially viable catalyst for heterogeneous catalytic ozonation (HCO) in water purification requires the characteristics of good dispersion of active species on its surface, efficient electron transfer for ozone decay, and maximum active species utilization. While metal-organic frameworks (MOFs) represent an attractive platform for HCO, the metal nodes in the unmodified MOFs exhibit low catalytic activity. Herein, we present a perfluorinated Fe-MOF catalyst by substituting H atoms on the metalated ligands with F atoms (termed 4F-MIL-88B) to induce structure evolution. The Lewis acidity of 4F-MIL-88B was enhanced via the formation of Fe nodes, tailoring the electron distribution on the catalyst surface. As a result of catalyst modification, the rate constant for degradation of the target compounds examined increased by ∼700% compared with that observed for the unmodified catalyst. Experimental evidence and theoretical calculations showed that the modulated polarity and the enhanced electron transfer between the catalyst and ozone molecules contributed to the adsorption and transformation of O3 to •OH on the catalyst surface. Overall, the results of this study highlight the significance of tailoring the metalated ligands to develop highly efficient and stable MOF catalysts for HCO and provide an in-depth mechanistic understanding of their structure-function evolution, which is expected to facilitate the applications of nanomaterial-based processes in water purification.

Promotional effect and mechanism of SiO2 on Cr-Al2O3 catalysts for N2O-assisted oxidative dehydrogenation of ethylbenzene

A series of Cr-SiO2-Al2O3 (abbreviated as Cr-Si-Al) catalysts were synthesized using an evaporation induced self-assembled (EISA) method and applied to the N2O-assisted dehydrogenation of ethylbenzene (EB), offering a versatile solution for greenhouse gas recycling and a novel pathway for styrene (ST) production. Notably, the Cr-5Si-Al catalyst calcinated at 850 °C exhibited remarkable performance with a high EB conversion of 71% and a good ST selectivity of 62%, resulting in an optimal ST yield of nearly 44%. To elucidate the impact of calcination temperature and reveal the underlying promoting mechanism, numerous types of characterization particularly in-situ DRIFTS were used. Results indicated that the Cr-5Si-Al-850 catalyst possessed a distinctively ordered mesoporous structure, which improved the specific surface area and facilitated the dispersion of active species. The interaction among the multiple species in the catalyst was enhanced under the high calcination temperatures, leading to an increased ratio of Cr6+ and Oα, and thus promoting the dehydrogenation of EB. Furthermore, in situ DRIFTS revealed two favorable reaction pathways: one involving the reaction between adsorbed N2O and EB, and the other involving the reaction between adsorbed EB and N2O. These pathways led to the formation of a similar intermediate, observed at a wavenumber of 1285 cm−1. The improved adsorption of EB played a pivotal role in the excellent catalytic performance of the Cr-5Si-Al-850 catalyst.

Mg enhanced the performance of Cu/ZnO/ZrO2 for CO2 hydrogenation to methanol and the mechanism investigation

Optimizing the microstructure of copper-based catalysts for CO2 hydrogenation to methanol is an attractive and widely reported strategy, but there are still certain barriers to improving both carbon dioxide conversion rate and methanol product selectivity. Herein, Cu/ZnO/ZrO2/MgO (CZZ1-xMx) catalysts were synthesized by co-precipitation method for CO2 hydrogenation to methanol. Furthermore, the structural features and reaction processes were systematically characterized by XRD, TEM, nitrogen adsorption/desorption, H2-TPR, CO2-TPD and in-situ DRIFT. The results showed that Mg species optimized the microstructure of the catalyst, increased the dispersion of active species and constructed appropriate basic sites. This further enhanced the capture of reactive species and improved the CO2 hydrotreating to methanol reaction performance, which was accompanied by a simultaneous increase in CO2 conversion and methanol yield. It could be convinced that the highest space time yield (STY) of methanol (305.3 gMeOH kgcat−1 h−1) was obtained at 220 °C, WHSV = 18,000 mL gcat−1 h−1 and 3 MPa (XCO2 = 7.28%, SMeOH = 71.8%) for the optimized CZZ0.8M0.2 catalyst, which exhibited twice the CO2 conversion than Cu/ZnO/ZrO2. This work elaborated a scheme for the preparation of efficient methanol catalysts. providing reference for the research of CO2 hydrogenation to methanol process.

Reasonable design of Sm-modified Cu-based catalyst for NH3-SCO: Role of the amide intermediates

The selective catalytic oxidation of ammonia (NH3-SCO) is currently the most effective method used to eliminate NH3. However, one of the major challenges for NH3-SCO is the development of catalyst capable of completely converting NH3 into harmless N2 and water vapor. In this paper, a high N2 selective catalyst prepared by the sol-gel method using TiO2 as the support, Cu as the active species, and Sm as the auxiliary agent is presented. Compared to traditional Cu/TiO2 catalyst, the 4SmCu/TiO2 catalyst has higher catalytic activity and N2 selectivity at low temperatures. The NH3 conversion can reach 100%, and the selectivity of N2 can be maintained at 100% at 275 °C. The excellent catalytic activity is attributed to the highly dispersed active species, abundant Lewis acid sites (LASs), and the generation of large amounts of surface-adsorbed oxygen. In addition, doping Sm species will cause TiO2 lattice distortion, and at the same time load the distorted TiO2 with more active material. Moreover, in-situ DRIFTS analysis suggests that both the 4SmCu/TiO2 and Cu/TiO2 catalysts follow the "internal" selective catalytic reduction (iSCR) mechanism during NH3-SCO reactions. The 4SmCu/TiO2 catalyst generates more amides (-NH2), which reduces the non-selective oxidation of the catalysts and promotes the formation of N2. This provides a new idea and method for the selective catalytic oxidation of NH3 to N2 and water vapor using Cu-based catalysts.

Influence of water in catalyst deactivation and lifetime of methane Bi-Reforming reaction over Ni-Co-Ru tri-metallic catalyst system

Recently, the bi-reforming of methane has been an emerging area of interest against conventional synthesis gas generation processes due to the achievable H2/CO ratio of around 2.0 and the possible utilization of feedstock like Biogas substitute to the limited fossil fuel resources. However, commercial implementation still needs to be improved due to the rapid deactivation of catalysts through metal particle sintering and coke formation on active sites. Consequently, developing promising catalysts that can show prolonged stability, high activity, and selectivity during the reaction is worthwhile. A facile synthesis method has been adopted to develop a ceria, magnesia, and zirconia-modified gamma-alumina support. Furthermore, Ni, Co, & Ru metals with varying weight percentages were deposited over the modified support by using a precipitation-deposition approach. The prepared catalysts were well characterized by XRD, XPS, SEM, HRTEM, Physisorption, and Chemisorption studies to elucidate the structure-activity relationship. Ascribed to small particle size, strong metal support interaction, employment of basic promoter MgO and oxygen storage capacitors like ceria and zirconia, and high dispersion of active species, all the catalysts exhibit a higher methane dissociation and carbon dioxide adsorption rate with extended stability. Further, a study has been made to understand how deactivation and catalyst lifetime can be manipulated through the amount of water in the feed composition. It was observed that using 1.8 moles of H2O in the feed can provide a syngas ratio of around 2. Under optimized reaction conditions of temperature 850 °C and weight hourly space velocity 10 Lg−1h−1, the best-selected catalyst exhibits a stable 92% CH4 and 89% CO2 conversion with a studied catalyst lifetime of up to 50 h. After the reaction, the spent catalyst was exposed to Thermogravimetric analysis, Temperature programmed oxidation, and Raman spectroscopy studies, and it was observed that there was a negligible amount of amorphous coke deposited over the catalyst used for 50 h of reaction couldn't have any substantial impact on catalyst activity.

Enhanced activity and stability for combined steam and CO2 reforming of methane over NiLa/MgAl2O4 catalyst

Ni-based catalysts were widely studied for methane reforming system in the past decades, while catalytic deactivation by carbon deposition and metal sintering limited its industrial application life. In this work, La-promoted Ni/MgAl2O4 catalysts were investigated over methane bi-reforming reaction, and significantly improved the activity and stability of catalysts. Multiple characterizations showed that the introduction of La increased the content and dispersion of active species (Ni0), providing sufficient sites for methane adsorption and dissociation. Besides, smaller particle size of active metal (12.6 nm) was proved to inhibiting carbon accumulation on catalyst surface. Ni10La5/MgAl2O4 catalyst was found to exhibit the highest catalytic performance (93% of CH4 conversion, 71% of CO2 conversion and less than 3% activity loss) under long-term reaction conditions (800 °C, 10 h). This work will provide important guiding significance for the design of high-efficiency methane reforming catalysts.

A facile strategy to prepare FeNx decorated PtFe intermetallic with excellent acidic oxygen reduction reaction activity and stability

The construction of low-Pt-content intermetallic on carbon supports has been verified as a promising method to promote the activity of the oxygen reduction reaction (ORR). In this study, we have developed a simple and effective strategy to obtain a well-designed CNT-PtFe-PPy precursor. This precursor contains modulated Pt- and Fe-based content dispersed in polypyrrole (PPy) chain segments, which are in-situ generated on the templates of carbon nanotubes (CNTs). Subsequent pyrolysis of the CNT-PtFe-PPy precursor produces a CNT-PtFe@FeNC catalyst, which contains both Fe-Nx and PtFe intermetallic active sites. Due to the highly efficient dispersion of active species, the CNT-PtFe@FeNC electrocatalyst displays a 9.5 times higher specific activity (SA) and 8.5 times higher mass activity (MA) than those of a commercial Pt/C catalyst in a 0.1 M HClO4 solution. Additionally, these results, combined with excellent durability (the SA and MA maintained 94 % and 91 % of initial activity after a 10-k cycle accelerated durability test), represent among the best performance achieved so far for Pt-based ORR electrocatalysts. Furthermore, density functional theory (DFT) calculations revealed that the presence of Fe-N4 species reduces the adsorption energy between the PtFe intermetallic compound and OH*, accelerating the ORR process.

Defect structure and species allocation of Mn-Ce/NbOPO4 surface by pH regulation

The support plays significant role in oxide-supported noble metal catalysts, which could provide the stability and dispersion of active species. NbOPO4 with strong surface acidity is a potential replacement for traditional supports, which could enhance the water and sulfur resistance obviously. In this study, the surface defects and species assignment of the support was altered by adjusting pH value. It was found that neutrality contributes the formation of porous structure. The surface defects of the support could assist the active components to trap oxygen and are beneficial for catalytic reactions. The abundant [NbO6] groups on the surface can improve the water and sulfur resistance of the catalyst. The electron transfer reaction between Nb5+ and Mn3+ on the support surface produces a large number of oxygen defects, which helps to improve the oxidation-reduction capacity of the catalyst.

Beneficial Effect of β‐Cyclodextrin Assisted Synthesis of CuO/Hydroxyapatite Catalyst in Toluene Oxidation

AbstractTwo hydroxyapatite supported CuO (10 wt% Cu) catalysts were prepared using the wet impregnation method via the conventional process and with the addition of native β‐cyclodextrin using Cu(NO3)2.3H2O as copper precursor and adopting a ratio of β‐cyclodextrin to copper of 0.1. After the impregnation step, the materials were dried at 80 °C and calcined in flowing dry air at 400 °C. The copper supported materials were characterized in the dried state and after calcination by means of conventional methods including X‐ray diffraction, TG‐MS, H2‐TPR‐MS, Raman spectroscopy, UV‐vis‐DR, ToF‐SIMS and XPS. It was found that β‐cyclodextrin hasd a profound impact on the final properties of the catalysts, both in terms of reducibility and dispersion of active species. It is suggested that at the early stages of the calcination, some hydroxyl groups of the β‐CD units in close contact with Ca2+ of hydroxyapatite could play the role of spacers between the copper‐based entities thus minimizing the aggregation process of the CuO nanoparticles. Finally, these copper oxide catalysts prepared from β‐cyclodextrin were able to oxidize toluene more efficiently than the conventional catalyst. The copper oxide particles generated by the thermal decomposition of Cu2(OH)3(NO3) were smaller than those formed with copper nitrate alone and exhibited a higher reducibility, two key determinants for VOC total oxidation on transition metal oxides.

Hybridization of porous vanadium nitride nanosheets with cobalt-encapsulated nitrogen-doped carbon nanotubes on carbon cloth as an advanced monolithic negative electrode for boosting asymmetric supercapacitors

The low energy density of asymmetric supercapacitors (ASCs) is mainly attributable to the low capacitance of the negative electrode; consequently, developing negative electrodes with high capacitance is crucial to boosting the energy density of ASCs. Vanadium nitride (VN), with excellent theoretical capacitance, is an ideal negative electrode material, but its low conductivity and poor electrochemical stability limit its application in energy storage. Herein, we design a high-performance monolithic negative electrode of ASCs that consists of well-defined porous VN nanosheets stacked with small nanoparticles decorated on a conductive substrate of ultrafine cobalt-encapsulated nitrogen-doped carbon nanotubes on carbon cloth (VN NS/Co@NCNTs/CC). Because the Co@NCNTs/CC substrate can enhance conductivity and facilitate the dispersion of active species and the exposure of more reaction sites, the newly developed porous VN NS/Co@NCNTs/CC negative electrode exhibits a high capacitance of 1016 mF cm−2 (782.3 F g−1) at 2 mA cm−2 and a superior cycle stability (110% capacitance retention after 11,000 cycles). To construct the ASC, a positive electrode of manganese dioxide (MnO2) nanoneedles grown on Co@NCNTs/CC (MnO2 NN/Co@NCNTs/CC) was also built using a similar preparation method. Benefiting from the wide operating voltage and high capacitance of the negative and positive electrodes, the assembled ASC can operate stably at a high voltage of 2 V. More importantly, the ASC can reach an energy density of 29.9 μWh cm−2 (23.9 Wh kg−1) and a capacitance retention of 94.3 % after 20,000 cycles, outperforming most of the reported aqueous ASC devices. This study provides a feasible way to reasonably design ASC electrodes with superior electrochemical performance.

Enhanced catalytic activity of Fe–Ce catalysts determined by synergistic effect of different precursors in selective catalytic reduction of NOx with NH3

AbstractBackgroundDeveloping environmentally benign and non‐vanadium SCR catalysts remains a challenging task for NOx abatement. In this article, Fe–Ce catalysts including Fe–Ce(S) and Fe(S)–Ce catalysts with different molar ratios of Fe/Ce were synthesized by different precursors of active species expecting to gain high catalytic activity for the selective catalytic reduction (SCR) of NOx with NH3 in a wide temperature range.ResultsThe Fe–Ce(S) catalyst exhibited better catalytic activity than the Fe(S)–Ce catalyst. The characterization results indicated the Fe–Ce(S)catalyst possessed better dispersion of active species, which would favor the contact of active sites and reactant molecules and thus enhance the catalytic performance. Moreover, higher ratios of Fe3+ and Ce3+ and more surface chemisorbed oxygen were observed over the Fe–Ce(S) catalyst. In addition, the Fe–Ce(S) catalyst held better low‐temperature redox properties and more weak acid sites.ConclusionsThe precursor effect was closely related to the catalytic activity of catalysts. All of the mentioned above might be the main reasons for the superior catalytic performance of the Fe–Ce(S) catalyst, especially at low temperatures. These findings indicate that Fe–Ce(S) catalyst is a promising catalyst for the SCR reaction to replace V‐W‐Ti catalysts and can provide guidance for the development of environmentally benign and non‐vanadium SCR catalysts. © 2022 Society of Chemical Industry (SCI).

MOFs-assisted synthesis of robust and efficient cobalt-based Fischer–Tropsch catalysts

The supported catalyst featuring highly dispersed active species is a challenge for industrial catalyst even with high loadings. The traditional impregnation method generally results in large particles due to the particle migration and coalescence or Ostwald ripening process. Herein, a Metal-Organic Frameworks (MOFs) strategy was proposed to assist the manufacture of supported CoOx/SiO2 catalyst. The classic organic ligand (e.g., 2-methylimidazoles) was coordinated with cobalt ions dispersed in advance on silica support, which was post-treated as a sacrificial and protective agent in different atmosphere. These operations can effectively restrain the growth of cobalt particles, yielding the high dispersion of Co metal active sites. The prepared catalyst (CoOx/SiO2-A#) exhibits superior activity, C5+ selectivity and stability in Fischer–Tropsch synthesis. It reveals that the high dispersion as well as the increased number of surface-exposed Co sites contribute to superior activity. As demonstrated by TG-MS and Raman characterizations, a large amounts of carbon species in CoOx/SiO2-N catalyst impeded the accessible active sites. The existence of Co2SiO4 verified by TPR and XPS characterizations means the strong metal-support interaction, that contributes robust performance in long-term stability test. This sacrificial MOFs strategy paves the way for the design of highly dispersed and robust FTS catalysts.

Microwave pyrolysis-engineered MOFs derivatives for efficient preferential CO oxidation in H2-rich stream

Microwave pyrolysis inherited the molecular-level engineering design of the CuCe-MOF: The tandem microwave pyrolysis firstly carbonized them to CuCe/C with topological structure, and improved the microwave absorption of MOFs in nitrogen atmosphere. Subsequently, CuCeO x catalyst was synthesized by its self-heating source of microwave in air, which endowed with molecular-level dispersed active sites to enhance preferential CO oxidation in H 2 -rich stream. • MOFs derivatives are achieved via tandem microwave pyrolysis. • Microwave pyrolysis inhibits the agglomeration of metal nanoclusters. • The tandem strategy solves the problem of poor microwave adsorption of MOFs. • Ligand carbonization provides dispersed heating sources by enhancing microwave absorption. • Microwave pyrolysis-engineered CuCeO x exhibits an outstanding performance of preferential CO oxidation. The versatile metal–organic framework (MOF) derivatives are achieved via microwave pyrolysis. The dipole vibration thermogenesis of molecules by microwave pyrolysis overcomes the issues of high energy consumption, slow heating rate, unregulated at the molecular-level, metal nanoclusters particles migration and coalescence caused by traditional thermal pyrolysis. For solving the poor microwave absorption of MOFs, a tandem microwave pyrolysis strategy is employed herein. Ligand carbonization enhances the conduction loss of microwaves and becomes a highly dispersed microwave heating source, which effectively inhibits the agglomeration. The CuCeO x catalysts obtained through this strategy retain the merits of bimetallic CuCe-MOFs with highly dispersed active species, and exhibit outstanding catalytic activities with the 100% conversion of CO being achieved at 75 °C for the preferential CO oxidation in H 2 -rich stream. These results demonstrate that the microwave pyrolysis-engineered MOFs uniformity has established catalyst with highly dispersed active species.

Investigating the effects of synthesis procedures on textural and catalytic properties of nickel/magnesium silicate catalyst in glycerol dry reforming

• The synthesis method affects the structural properties of the Ni/MgO.SiO 2 catalyst. • The structural features of the Ni catalyst affect catalytic performance significantly. • The Ni/MgO.SiO 2 catalyst prepared by one-pot method showed better performance. • The one-pot method has resulted in the highest textural properties of the Ni/MgO.SiO 2. Ni-based catalysts supported on magnesium silicate were synthesized using various synthesis procedures and were then investigated for the first time in the glycerol-DR (dry reforming) process. In general, synthesis procedures for catalyst supports included co-precipitation and hydrothermal, and nickel as active metal was attached to the support simultaneously with support preparing and impregnation technique. The results of characterizations of Brunauer-Emmett-Teller (BET), X-ray diffraction (XRD), hydrogen temperature-programmed reduction (TPR-H 2 ), temperature-programmed oxidation (TPO), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) element mapping, Fourier transform infrared (FTIR), thermogravimetric analysis (TGA-DTA), and the catalytic glycerol-DR reaction tests illustrated that the preparation route of Ni/MgO.SiO 2 catalyst is effective in the structural and physicochemical features of the sample. It was observed that the catalysts with various synthesis methods exhibited different activity and stability during the glycerol-DR reaction. However, the highest glycerol conversion (31–50%) and the yield of both H 2 and CO were achieved over the Ni/MgO.SiO 2 (I) catalyst at all reaction temperature ranges (600–750 °C). The high catalytic performance of the Ni/MgO.SiO 2 (I) sample in the glycerol-DR reaction was related to its textural properties such as surface area (411 m 2 g −1 ), the crystallite size (8.5 nm), and active species dispersion, which were superior for this catalyst in comparison with other samples. This sample also exhibited better catalytic stability during the reaction. Furthermore, synthesis gas (syngas) was produced for all catalysts with an H 2 /CO ratio of less than 1.6. These results clearly show a significant impact of the sample synthesis procedure on the catalyst's final physical and chemical properties. The Ni/MgO.SiO 2 catalyst prepared with a one-step method showed high potential as a glycerol-DR catalyst for syngas production.

Insights into Fe Species Structure‐Performance Relationship for Direct Methane Conversion toward Oxygenates over Fe‐MOR Catalysts

AbstractDirect oxidation of methane to value‐added products under mild conditions remains a grand challenge due to the problem of selective CH4 activation. Here we report a Fe‐MOR‐F catalyst prepared via freeze‐drying method, indicating excellent catalytic performance for the direct partial oxidation of methane using H2O2 under mild conditions. Various characterizations including XRD, NH3‐TPD, H2‐TPR, UV‐Vis, XPS, and EPR studies revealed that Fe‐MOR‐F catalyst possesses more highly dispersed monomeric and dimeric iron species, which is strongly correlated to its high catalytic activity for direct methane oxidation. The DFT calculations indicate the highly dispersed monomeric and dimeric iron species can effectively homogenize H2O2 into active hydroxyl groups, while iron clusters can decompose H2O2 into inactive O2. The EPR experiments show more ⋅OH was generated on Fe‐MOR‐F catalyst, which is in line with DFT calculation results. These structural characteristics endow Fe‐MOR‐F catalyst with superior catalytic performance for direct methane oxidation in terms of oxygenates yield (9.8 mol kgcat−1 h−1) and selectivity (91.8 %) at 80 °C. This work not only highlights the excellent catalytic performance of methane activation on the highly dispersed monomeric and dimeric iron species, but also promotes the potential application by freeze‐drying method for the preparation of the highly dispersed active species.