Increasing Metal Loading Research Articles

Multilayer-coating process for the synthesis of nickel-silicate composite with high Ni loading as high-rate performance lithium-ion anode material

BackgroundMetal silicates possess several important advantages as electrode materials for lithium-ion batteries (LIBs), including straightforward synthesis, low cost, and high thermal stability. A green synthesis routes that are capable of increasing metal loading and reducing the impact on the environment are required. MethodsA Ni-silicate with a multilayer structure and a Ni/Si molar ratio of 0.25 is first prepared using the co-precipitation method. The as-synthesized product is then repeatedly immersed in a Ni2+ solution to obtain Ni-silicate with the desired Ni contents (Ni/Si molar ratio: 0.50–2.00). Finally, the resulting Ni-silicate is reconstructed by hydrothermal treatment under various temperatures (70 °C, 100 °C, 150 °C) and durations (3 h and 24 h) to obtain Ni-phyllosilicate. The effects of the hydrothermal treatment temperature, hydrothermal time, and Ni/Si ratio on the structure, morphology, and surface area of the Ni-silicate composites are examined. Significant FindingsThe Ni-silicate with a Ni/Si ratio of 1.5 has a reversible capacity of 729 mAhg-1, which exceeds traditional graphite anodes (372 mAhg-1). Furthermore, the material exhibits a capacity retention of up to 80 % as the current density is increased from 0.025 Ag-1 to 0.5 Ag-1. Thus, the synthesized Ni-silicate composite is a promising candidate material for LIB anode.

Transition-Metal-Doped CeO2 for the Reverse Water-Gas Shift Reaction: An Experimental and Theoretical Study on CO2 Adsorption and Surface Vacancy Effects.

Transition metal-doped ceria (M-CeO2) catalysts (M = Fe, Co, Ni and Cu) with multiple loadings were experimentally investigated for reverse water gas shift (RWGS) reaction. Density functional theory (DFT) calculations were performed to benchmark the properties that impact catalytic activity of CO2 reduction. Temperature-programmed desorption (TPD) was conducted to study the CO2 binding strength on doped CeO2 surfaces; the trend of the energy along increasing metal loading agrees with the DFT calculations. Notably, CO2 dissociative adsorption energy and oxygen vacancy (OV) formation energy are key descriptors obtained from both DFT and experiments, which can be used to evaluate catalytic performance. Results show the effectiveness of transition metal doping in enhancing CO2 adsorption and reducibility of the surfaces, with Fe showing particularly promising results, i.e., CO2 conversion higher than 56% at 600 °C and 100% selectivity to CO. Cu exhibits 100% selectivity to CO but low CO2 conversion, while Co and Ni showed notable ability of methanation, particularly at high loadings. This study finds that an effective CeO2 based RWGS catalyst corresponds to OV sites that have low OV formation energies for surface reduction, and moderate CO2 adsorption energies for strong interaction with the surface to promote C-O bond scission.

Trimetallic-doped carbon nitride achieves chondroitin sulfate degradation via a free radical degradation strategy

Traditional Fenton principles for degrading polysaccharides, including chondroitin sulfate (CS), are fraught with limitations, such as strict pH-dependence, higher temperature requirements, desulfurization, and environmentally perilous. In this study, an effective Fenton-like system comprising trimetallic-doped carbon nitride material (tri-CN) with hydrogen-bonded melamine-cyanuric acid (MCA) supramolecular aggregates as its basic skeleton was engineered to overcome the challenges of traditional methods. Detailed material characterizations revealed that, compared to monometallic-doped or bimetallic-doped counterparts, tri-CN offered a larger surface area, higher porosity, and increased metal loading, thereby enhancing reactant accessibility and polysaccharide degradation efficiency. The characterization and activity assessment of the degraded polysaccharide revealed structurally intact products without significant desulfurization, indicating the effectiveness of the designed approach. Moreover, the degraded chondroitin sulfate CS3 catalyzed by tri-CN, exhibited promising antioxidant activity and anti-CRISPR potential. The results elucidated that the high-valent iron species in the material served as primary active sites, catalyzing the cleavage of hydrogen peroxide to generate hydroxyl radicals that subsequently attacked CS chains, leading to their fragmentation. Hence, the designed material can be efficiently applied to polysaccharide degradation, but not limited to photocatalysis, electrocatalysis, sensor, energy storage materials, and wastewater treatment.

General negative pressure annealing approach for creating ultra-high-loading single atom catalyst libraries

Catalyst systems populated by high-density single atoms are crucial for improving catalytic activity and selectivity, which can potentially maximize the industrial prospects of heterogeneous single-atom catalysts (SACs). However, achieving high-loading SACs with metal contents above 10 wt% remains challenging. Here we describe a general negative pressure annealing strategy to fabricate ultrahigh-loading SACs with metal contents up to 27.3–44.8 wt% for 13 different metals on a typical carbon nitride matrix. Furthermore, our approach enables the synthesis of high-entropy single-atom catalysts (HESACs) that exhibit the coexistence of multiple metal single atoms with high metal contents. In-situ aberration-corrected HAADF-STEM (AC-STEM) combined with ex-situ X-ray absorption fine structure (XAFS) demonstrate that the negative pressure annealing treatment accelerates the removal of anionic ligand in metal precursors and boosts the bonding of metal species with N defective sites, enabling the formation of dense N-coordinated metal sites. Increasing metal loading on a platinum (Pt) SAC to 41.8 wt% significantly enhances the activity of propane oxidation towards liquid products, including acetone, methanol, and acetic acid et al. This work presents a straightforward and universal approach for achieving many low-cost and high-density SACs for efficient catalytic transformations.

Iron–palladium nanoparticle biocomposites with increased metal loading

Biocomposites containing magnetic nanoparticles have the potential to combine the unique, tunable properties of nanoparticles with the strong mechanical and environmentally sustainable properties of natural fibers like cotton. Recently, a method to synthesize Fe–Pd nanoparticles on cellulose has been developed. This study presents a detailed investigation on how the structural and magnetic properties of these nanoparticle biocomposite materials are affected by increasing metal loading with respect to the cellulose while maintaining a fixed 1:1 Fe:Pd atomic ratio. Infrared spectroscopy and electron microscopy (SEM and TEM) indicate that spherical Fe–Pd nanoparticles (approximately 3–8 nm in diameter) are distributed heterogeneously throughout the fiber matrix along with amorphous iron oxide, while XRD suggests the dominant crystalline phase within the nanoparticles is likely FePd3 under significant strain. The magnetic response of the biocomposites in static and dynamic magnetic fields (as a function of frequency and temperature) reveals a polydisperse ensemble of Fe–Pd nanoparticles with up to four distributions of blocking temperatures. The lower temperature distributions are prevalent at low metal loading. As the metal loading increases, the higher temperature distributions emerge, while the lower temperature distributions are suppressed. This result points towards enhanced nanoparticle heterogeneity and agglomeration as the metal loading increases.

Ink Formulation, Binder, Catalyst & Metal Loading - How Can the Properties of Gas Diffusion Electrodes be Influenced to Control CO2 Reduction?

Exceptionally hot summers, floods and other extreme weather events of recent years underline the importance of combating climate change. Electrochemical CO2 reduction (CO2RR), which can be applied directly at CO2 point sources such as cement plants is a promising way to convert the harmful greenhouse gas into valuable compounds (e.g., alcohols). The integration of a selective catalyst into a gas diffusion electrode (GDE) allows CO2 reduction at industrially relevant current densities above 200 mA cm-2.[1] Combinations of copper and zinc, or copper and silver, are especially suitable for CO2 reduction to multi-carbon products. Whilst copper is the only metal capable of catalyzing C-C bond formation, zinc and silver are known for their CO selectivity in CO2RR. The selectivity of the reaction is shifted towards the formation of multi-carbon products such as ethylene or alcohols by the enrichment of the important intermediate CO at the catalyst surface due to the activity of Zn or Ag.[2] Here we present the preparation of bimetallic catalysts by impregnating carbon black with copper and zinc, followed by the incorporation of the catalysts into GDEs and testing of their electrocatalytic activity in CO2RR. The ink formulation for preparing a catalyst layer by spray-coating was optimized using, among other compounds, the pore-forming agent methylcellulose, the non-ionic surfactant Triton, and PTFE as binding material, to provide a stable CO2RR with the highest possible yield of C2+ products. In addition, the impact of the post-treatment steps pressing and sintering on the CO2RR performance of the electrodes was assessed.[3] Using the optimized formulation and post-treatment to produce the GDE, the influence on the product distribution was evaluated by varying (1) the PTFE powder (2) the metal loading of the catalyst (Cu and Zn in relation to the carbon black content), (3) the catalyst loading of the GDE, and (4) the current densities during CO2RR.PTFE acts as both a binder and a hydrophobizing agent of the electrode to ensure stable electrolysis on the produced GDE in a flow cell. The variation of PTFE powders shows that mechanical and electrochemical stability of the electrodes as well as the product distribution during CO2RR depend on the PTFE powder used. Although hydrophobicity and surface morphology are similar prior to CO2RR, shifts within the product distributions and differences in stability are evident during electrolysis depending on the PTFE powder chosen. Catalyst loading affects the supply and removal of reactants and products and therefore significantly influences the product distribution, which also showed a strong dependence on metal loading. In general, a trend toward increased formic acid formation was observed with increasing metal loading and film thickness. An optimum for C2+ product formation was found at 17.5% metal loading with Faraday efficiencies of 17% for ethanol and 31% for ethylene at current densities of 200 mA cm-2. SEM-EDX images show increased carbonate formation within the electrode with increasing metal loading as well as with increasing current densities. The increase in metal loading was found to be accompanied by metal agglomeration in the catalyst and is further enhanced by the GDE fabrication process.The work provides insight into the interaction of catalyst, electrode composition, and CO2RR parameters and reveals key tuning screws for a selective and stable reaction in liquid electrolysis cells. [1] Gawel, A.; Jaster, T.; Siegmund, D.; Holzmann, J.; Lohmann, H.; Klemm, E.; Apfel, U.-P. Electrochemical CO2 reduction - The macroscopic world of electrode design, reactor concepts & economic aspects. iScience 2022, 25, 104011. [2] Jaster, T.; Gawel, A.; Siegmund, D.; Holzmann, J.; Lohmann, H.; Klemm, E.; Apfel, U.-P. Electrochemical CO2 reduction toward multicarbon alcohols - The microscopic world of catalysts & process conditions. iScience 2022, 25, 104010. [3] Jaster, T.; Albers, S.; Leonhard, A.; Kräenbring, M.-A.; Lohmann, H.; Zeidler-Fandrich, B.; Özcan, F.; Segets, D.; Apfel, U.-P. Enhancement of CO2RR product formation on Cu-ZnO-based electrodes by varying ink formulation and post treatment methods. J. Phys. Energy. 2023, 5.

Fabrication of Naturally Derived Chitosan and Ilmenite Sand-Based TiO2/Fe2O3/Fe-N-Doped Graphitic Carbon Composite for Photocatalytic Degradation of Methylene Blue under Sunlight

Fabrication of chitosan and ilmenite sand-based novel photocatalysts through the catalytic graphitization of chitosan is reported. Nanocomposites consisted of TiO2, Fe2O3 and Fe nanoparticles dispersed on a nitrogen-doped graphitic carbon framework. The surface area, pore volume and macropore structure of the carbon matrix is disturbed by the heterogeneously distributed nanoparticles. The extent of graphitization expanded with increasing metal loading as indicated by variation in the ID/IG ratio. The nanomaterial's surface consists of Fe3+ and Ti4+, and graphitic, pyridinic and pyrrolic nitrogen were found in the carbon matrix. The band gap values of the composites varied in the 2.06-2.26 eV range. The photocatalytic activity of the synthesized nanomaterials was determined, and the highest rate constant for the photodegradation of methylene blue under sunlight was 4.4 × 10-3 min-1, which resulted with 10 mg/L MB and 25 mg of the best-performing catalyst. The rate constant rose with increasing concentrations of persulfate added to the medium. The rate constant greatly diminished with the addition of isopropyl alcohol as it scavenged hydroxyl radicals. The presence of co-pollutants including Pb2+, rhodamine B, PO43- and Cl- curtailed the rate of reaction. The activity reduced with an increasing number of uses of the catalyst.

Interfacial assembly of binary atomic metal-Nx sites for high-performance energy devices

Anion-exchange membrane fuel cells and Zn–air batteries based on non-Pt group metal catalysts typically suffer from sluggish cathodic oxygen reduction. Designing advanced catalyst architectures to improve the catalyst’s oxygen reduction activity and boosting the accessible site density by increasing metal loading and site utilization are potential ways to achieve high device performances. Herein, we report an interfacial assembly strategy to achieve binary single-atomic Fe/Co-Nx with high mass loadings through constructing a nanocage structure and concentrating high-density accessible binary single-atomic Fe/Co–Nx sites in a porous shell. The prepared FeCo-NCH features metal loading with a single-atomic distribution as high as 7.9 wt% and an accessible site density of around 7.6 × 1019 sites g−1, surpassing most reported M–Nx catalysts. In anion exchange membrane fuel cells and zinc–air batteries, the FeCo-NCH material delivers peak power densities of 569.0 or 414.5 mW cm−2, 3.4 or 2.8 times higher than control devices assembled with FeCo-NC. These results suggest that the present strategy for promoting catalytic site utilization offers new possibilities for exploring efficient low-cost electrocatalysts to boost the performance of various energy devices.

Synergistic Effect of Pd Co-Catalyst and rGO–TiO2 Hybrid Support for Enhanced Photoreforming of Oxygenates

Photoreforming biomass-derived waste such as glycerol into hydrogen fuel is a renewable hydrogen generation technology that has the potential to become important due to unavoidable CO2 production during methane steam reforming. Despite tremendous efforts, the challenge of developing highly active photocatalysts at a low cost still remains elusive. Here, we developed a novel photocatalyst with a hybrid support comprising reduced graphene oxide (rGO) and TiO2 nanorods (TNR). rGO in the hybrid support not only performed as an excellent scavenger of electrons from the semiconductor conduction band due to its suitable electrochemical potential, but also acted as an electron transport highway to the metal co-catalyst, which otherwise is not possible by simply increasing metal loading due to the shadowing effect. A series of hybrid supports with different TNR and rGO ratios were prepared by the deposition method. Pd nanoparticles were deposited over hybrid support through the chemical reduction method. Pd/rGO-TNRs photocatalyst containing 4 wt.% rGO contents in the support and 1 wt.% nominal Pd loading demonstrated hydrogen production activity ~41 mmols h−1g−1, which is 4 and 40 times greater than benchmark Au/TiO2 and pristine P25. The findings of this works provide a new strategy in optimizing charge extraction from TiO2, which otherwise has remained impossible due to a fixed tradeoff between metal loading and the detrimental shadowing effect.

Boosting Ferroptosis Therapy with Iridium Single-Atom Nanocatalyst in Ultralow Metal Content.

Nanocatalysts are promising tumor therapeutics due to their ability to induce reactive oxygen species in the tumor microenvironment. Although increasing metal loading can improve catalytic activity, the quandary of high metal content versus potential systemic biotoxicity remains challenging. Here, a fully exposed active site strategy by site-specific anchoring of single iridium (Ir) atoms on the outer surface of a nitrogen-doped carbon composite (Ir single-atom catalyst (SAC)) is reported to achieve remarkable catalytic performance at ultralow metal content (≈0.11%). The Ir SAC exhibits prominent dual enzymatic activities to mimic peroxidase and glutathione peroxidase, which catalyzes the conversion of endogenous H2 O2 into •OH in the acidic TME and depletes glutathione (GSH) simultaneously. With an advanced support of GSH-trapping platinum(IV) and encapsulation with a red-blood-cell membrane, this nanocatalytic agent (Pt@IrSAC/RBC) causes intense lipid peroxidation that boosts tumor cell ferroptosis. The Pt@IrSAC/RBC demonstrates superior therapeutic efficacy in a mouse triple-negative mammary carcinoma model, resulting in complete tumor ablation in a single treatment session with negligible side effects. These outcomes may provide valuable insights into the design of nanocatalysts with high performance and biosafety for biomedical applications.

Synthesis, characterization and catalytic evaluation of supported catalysts (PdNPs/TiO2, PdNPs/Al2O3, PdNPs/SiO2) for esterification of levulinic acid to levulinate esters

• The manuscript describes the synthesis of supported (Silica, titania, and alumina) Pd nanoparticles via wet-impregnation method. • The size of supported Pd nanoparticles determines their catalytic activity. • Indicators such as induction period and kinetics of de/activation were used to determine the possibility of Pd surface atom rearrangement during catalytic reaction. • The alumina-supported Pd nanoparticles proved to be more robust and activate at later reaction cycles. • The manuscript contributes towards the development of sustainable and environmentally friendly biobased value-added chemicals. In this work, we report on the synthesis of supported-palladium nanoparticles (Pd NPS /TiO 2 , Pd NPS /SiO 2 , Pd NPS /Al 2 O 3 ) and their catalytic performance in the esterification of levulinic acid (LA). The N 2 physisorption technique (BET) was used to determine the surface properties of Pd NPS and gave surface areas ranging between 69.53 – 596.5 m 2 g -1 for the set of catalysts, and the high-resolution transmission electron microscopy (HRTEM) whose images were used to measure the average nanoparticle sizes (2.2 ± 0.2 – 8.0 ± 2.0 nm) of all supported Pd NPS . Metal loading ranged from 0.5 to 5 Pd wt.% as determined by the inductively coupled plasma-optical emission spectroscopy (ICP-OES). The highest LA conversion, 96% was achieved with Pd/Al 2 O 3 . An interesting observation for 0.5 – 5% Pd NPS /TiO 2 catalytic systems is that LA's turnover frequency (TOF) decreases with increasing metal loading and/or size of the Pd NPS on TiO 2 . The Pd NPS supported on TiO 2 exhibit an induction period during the first hour of the reaction and later reported 83% LA conversion with 98% selectivity towards isopropyl levulinate (IL). Therefore, we postulate a TiO 2 support-induced surface atom rearrangement of Pd NPS prior to the catalytic reaction that is responsible for the induction period observed.

Thermal transformation of copper incorporated hydrotalcite-derived oxides and their catalytic activity for ethanol dehydrogenation

Thermal transformation of copper incorporated hydrotalcite-derived oxides is investigated in ethanol dehydrogenation. Among the copper supported catalyst c-10Cu/HT600 prepared by impregnation of thermally treated hydrotalcite at 600 °C with Cu(NO3)2 solution followed by a calcination provides a high catalytic activity, selectivity and stability. XRD, DR-UV, TGA, H2-TPR, CO2-TPD, TEM and XPS techniques reveal that the nature of the copper species depended on the thermal treatment process and support. Such treatment at high temperatures yields a homogeneous dispersion mixed metal oxide. After copper incorporation generated CuAl2O4 spinel structure linked to the copper oxide species can suppress copper agglomeration leading to the catalytic stability. Moreover, the c-10Cu/HT600 catalyst can provide a high activity and high selectivity to acetaldehyde even at low reaction temperatures (200 °C). However, the copper species may agglomerate to form relatively larger clusters upon increasing metal loading leading to the deactivation.

Mesostructured Zn/ZSM‐5 Zeolite as Catalyst for Furan Deoxygenation,

AbstractThe furan conversion into aromatics over zinc promoted ZSM‐5 zeolites was studied in a continuous‐flow fixed‐bed reactor. Two series of microporous and mesoporous catalysts were prepared at different zinc loadings of 2 and 5 wt.%. It was intended to optimize the overall aromatics production and control coke accumulation over novel synthesized mesoporous ZSM‐5 catalyst, in a continuous flow reactor. The catalysts were characterized using X‐ray diffraction (XRD), nitrogen adsorption/desorption, ammonia temperature programmed desorption (TPD) and X‐ray photoelectron spectroscopy (XPS). The zinc loaded mesoporous materials exhibit an XRD pattern that matches with the ZSM‐5 XRD reference pattern. No extra peaks were observed in the XRD results indicating the high dispersion of zinc species. The initial furan conversion rate was higher over the microporous catalysts, and increased upon increasing metal loading, however contrary to the mesoporous samples, the microporous ones deactivated rapidly over 2 hours of time on‐stream. The results indicated that around 40 % of carbon in the fed furan, was recovered in aromatics when the new mesostructured zeolite catalyst was used, whereas this could be further increased to 50 % by the addition of zinc in the catalyst, benzene being the major product.

Superiority of Dual‐Atom Catalysts in Electrocatalysis: One Step Further Than Single‐Atom Catalysts

AbstractIn recent years, dual‐atom catalysts (DACs) have attracted extensive attention, as an extension of single‐atom catalysts (SACs). Compared with SACs, DACs have higher metal loading and more complex and flexible active sites, thus achieving better catalytic performance and providing more opportunities for electrocatalysis. This review introduces the research progress in recent years on how to design new DACs to enhance the performance of electrocatalysis. Firstly, the advantages of DACs in increasing metal loading are introduced. Then, the role of DACs in changing the adsorption condition of reactant molecules on metal atoms is discussed. Moreover, the ways in which DACs can reduce the reaction energy barrier of key steps and change the reaction path are explored. Catalytic applications in different electrocatalytic reactions, including the carbon dioxide reduction reaction, oxygen reduction reaction, oxygen evolution reaction, hydrogen evolution reaction, and nitrogen reduction reaction are followed. Finally, a brief summary is made and the key challenges and prospects of DACs are introduced.

Using Transient XAS to Detect Minute Levels of Reversible S-O Exchange at the Active Sites of MoS2-Based Hydrotreating Catalysts: Effect of Metal Loading, Promotion, Temperature, and Oxygenate Reactant

Modulation excitation spectroscopy (MES) coupled with time-resolved X-ray absorption spectroscopy (XAS) was applied to unpromoted and Co-promoted Mo-based hydrotreating catalysts (i.e., Mo and CoMo catalysts) for investigating the minute as well as instantaneous differences in active site composition under the influence of H2S and H2O. Transient experiments during alternating sulfur- and water-rich conditions were performed at temperatures between 400 and 500 °C using catalysts with varying Co/Mo metal loadings to study the correlative effect of these factors on the stability of the active sites. For both types of catalysts, the features of the demodulated Mo K-edge spectrum matching the difference spectra of the MoS2 and MoO3 references indicate a reversible oxidation–sulfidation process during H2O/H2S cycling. In the case of CoMo catalysts with increasing metal loadings, transient XAS at the Mo K- as well as Co K-edge revealed minute levels of S-O exchange at both sulfided Mo and Co sites, although 26 to 47% of the Co was bound as stable CoAl2O4, which does not form a bulk sulfide. Thus, even in the presence of multiple Co phases (oxide and sulfide) and a low number of active sites relative to the total number of Mo atoms, transient XAS can successfully detect the changes occurring over both the active Co and Mo sites. Furthermore, the comparison of the amplitude of the demodulated spectra showed that Mo atoms are more prone to S-O exchange with increasing temperature, while Co promotion stabilized the molybdenum sulfide. MES-coupled XAS experiments with 1-propanol performed to evaluate the degree of S-O exchange in the presence of another oxygenate reactant revealed the higher affinity of water toward these sulfided Mo sites as compared to 1-propanol.

2D-to-3D zeolite transformation for the preparation of Pd@MWW catalysts with tuneable acidity

2D-to-3D transformation of layered zeolite precursors (e.g., MCM-22 P, IPC-1 P, pre-FER) into three-dimensional frameworks in combination with metal encapsulation has been recently shown as efficient synthetic strategy to stabilize metal clusters in a zeolite matrix. Even though, tailoring the number of acid sites in a zeolite support and its effect on the properties of thus prepared metal@zeolite materials (e.g., metal dispersion and catalytic activity) remained unrevealed. Herein, we report on the synthesis of Pd@MCM-22 catalysts via modified 2D-to-3D transformation method, which allows to achieve close to nominal loading of noble metal (e.g., 0.1, 0.3, 0.8 wt%) by time-separation of swelling of MCM-22 P layered zeolite precursor and subsequent incorporation with metal. In turn, alternating Si/Al ratio of MCM-22 P (e.g., SiAl = 15, 20, 30) enabled the preparation of Pd@MCM-22 catalysts with variable concentration of acid sites (0.28 – 0.55 mmol/g), while not affecting the Pd dispersion. Decrease in Pd dispersion with increasing metal loading was accompanied with declining catalytic activity in a model reaction of selective hydrogenation of nitro-group in 3-nitrotoluene: 0.1 wt% Pd (dispersion = 52.6%, reaction rate = 21.2 mol·g−1Pd·h−1) > 0.3 wt% Pd (9.6 mol·g−1Pd·h−1) > 0.8 wt% Pd (23.2%, 3.7 mol·g−1Pd·h−1). The results of this study reveal that the reported synthesis strategy can be successfully used to confine small metal nanoparticles in a zeolite matrix while tuning its acidic characteristics for designing bifunctional metal-acidic catalysts.

Grafting of Alkali Metals on Fumed Silica for the Catalytic Dehydrogenation of Methanol to Formaldehyde

AbstractWater free, non‐oxidative catalytic dehydrogenation of methanol to formaldehyde is an important process for the formation of anhydrous, molecular formaldehyde (FA). Sodium or sodium‐containing salts were shown to catalyze the reaction, but their reaction mechanism remains unclear. In this work, we thus investigated the performance of a series of catalysts prepared by grafting of alkali metals on amorphous silica for methanol catalytic dehydrogenation. The resulting catalysts displayed an increased activity for the catalytic dehydrogenation of methanol. Variation of the electron density of the supported alkali metal cations severely affected the FA selectivity, which followed the trend: Li>Na>K>Rb>Cs. A large gap in selectivity towards FA between ions with a high (i. e., Li, Na) and low charge density (i. e., K, Rb, Cs) was observed. Also, increased metal loading adversely affected FA selectivity and resulted in a larger production of carbon monoxide. Sodium grafted on silica yielded the best combination of moderate conversion and high selectivity.

Oxidation of Benzyl Alcohol Using Cobalt Oxide Supported Inside and Outside Hollow Carbon Spheres.

Cobalt oxide nanoparticles (6 nm) supported both inside and outside of hollow carbon spheres (HCSs) were synthesized by using two different polymer templates. The oxidation of benzyl alcohol was used as a model reaction to evaluate the catalysts. PXRD studies indicated that the Co oxidation state varied for the different catalysts due to reduction of the Co by the carbon, and a metal oxidation step prior to the benzyl alcohol oxidation enhanced the catalytic activity. The metal loading influenced the catalytic efficiency, and the activity decreased with increasing metal loading, possibly due to pore filling effects. The catalysts showed similar activity and selectivity (to benzaldehyde) whether placed inside or outside the HCS (63 % selectivity at 50 % conversion). No poisoning was observed due to product build up in the HCS.

Comparative investigation of characteristics and phosphate removal by engineered biochars with different loadings of magnesium, aluminum, or iron

Engineered biochars (EBCs) loaded with metal oxides/hydroxides have been used as sorbents to remove and recycle phosphate (P) from wastewater. However, P removal by EBCs made with different types and loading of metals have rarely been compared in a single study. Thus, in this study, EBCs were synthesized through pyrolysis of bamboo or hickory wood chips (25 g) pretreated with four amounts (25, 50, 75, and 100 mmol) of magnesium (Mg), aluminum (Al), or iron (Fe) salt solutions (Mg-EBC, Al-EBC, and Fe-EBC, respectively). The resulting EBCs were loaded with metal oxides/hydroxides that served as P adsorption sites. Al-EBCs showed the highest aqueous stability with little metal dissolution, which can be attributed to the low level of residual (unconverted) metal salt as well as the extremely low solubility of loaded Al metal oxyhydroxide. After the leaching/washing, the metal loading efficiencies of the Al- and Mg-EBCs were similar (50–60%) and stable metal loadings increased with pretreatment salt amounts, indicating that the amount of the two metal oxides/hydroxides in the EBCs can be controlled during pretreatment. However, stable iron oxide on the Fe-EBCs remained almost the same for all the four levels of pretreatment, reflecting saturation of the biochar surface. All the EBCs showed increasing P adsorption with increasing metal loading. At low initial P concentrations of 31 mg/L, Fe- and Al-EBCs removed up to 68% and 94% of P, likely through an electrostatic interaction mechanism. At high P concentrations, Mg-EBC had the largest P adsorption capacity (119.6 mg P/g), mainly through the combination of surface precipitation and electrostatic interaction mechanisms. This study demonstrates that metal oxide/hydroxide-loaded EBCs are promising sorbents that can be designed to meet specific needs for the removal of aqueous P in various applications.

Hierarchical Structure of NiMo Hydrodesulfurization Catalysts Determined by Ptychographic X-Ray Computed Tomography.

Hydrodesulphurization, the removal of sulphur from crude oils, is an essential catalytic process in the petroleum industry safeguarding the production of clean hydrocarbons. Sulphur removal is critical for the functionality of downstream processes and vital to the elimination of environmental pollutants. The effectiveness of such an endeavour is among other factors determined by the structural arrangement of the heterogeneous catalyst. Namely, the accessibility of the catalytically active molybdenum disulphide (MoS2 ) slabs located on the surfaces of a porous alumina carrier. Here, we examined a series of pristine sulfided Mo and NiMo hydrodesulphurization catalysts of increasing metal loading prepared on commercial alumina carriers using ptychographic X-ray computed nanotomography. Structural analysis revealed a build consisting of two interwoven support matrix elements differing in nanoporosity. With increasing metal loading, approaching that of industrial catalysts, these matrix elements exhibit a progressively dissimilar MoS2 surface coverage as well as MoS2 cluster formation at the matrix element boundaries. This is suggestive of metal deposition limitations and/ or catalyst activation and following prohibitive of optimal catalytic utilization. These results will allow for diffusivity calculations, a better rationale of current generation catalyst performance as well as a better distribution of the active phase in next-generation hydrodesulphurization catalysts.