Low Ag Loading Research Articles

Ag/CNT Catalyst Synthesized by Plasma-Enhanced Atomic Layer Deposition for Anion Exchange Membrane Fuel Cells

Anion exchange membrane fuel cells (AEMFCs) have recently gained attention as a viable alternative to proton exchange membrane fuel cells (PEMFC), offering the potential for high output without relying on expensive platinum (Pt) catalysts. PEMFCs operate in an acidic environment characterized by a high concentration of H+, necessitating the use of platinum-based catalysts to ensure both performance and stability in such conditions. In contrast, AEMFCs operate in an alkaline environment (OH-), affording the use of high-performance catalysts like silver (Ag), which is sensitive to acidity. Moreover, the cost of Ag is approximately 1/50 of Pt, offering significant cost advantages for fuel cell commercialization. Atomic layer deposition (ALD) has garnered substantial attention as a valuable technique for crafting high-performance nano-catalysts. ALD's self-limiting nature, based on the sequential exposure of vaporized precursors and reactants, enables precise control over catalyst size and composition. In this study, we employed plasma-enhanced ALD (PEALD) to fabricate cutting-edge AEMFC cathodes comprised of carbon nanotubes (CNTs) adorned with Ag. This approach yielded impressive results, achieving an AEMFC output exceeding 300 mW cm-2 or more than 2 W mgAg -1 at 65 °C with a CNT cathode featuring an exceedingly low Ag loading of less than 0.15 mg cm-2. Notably, this represents the world's highest reported Ag-AEMFC performance to date. The Ag-decorated cathode created through ALD played a pivotal role in significantly reducing resistance in the polarization region, a major contributor to overall energy losses in AEMFCs. Additionally, when evaluating the durability of the Ag-decorated CNT anode in an alkaline environment, we observed excellent long-term stability. In this presentation, we will discuss a more detailed exploration of the relationship between AEMFC performance, featuring ALD-fabricated Ag-CNT catalysts, and the intricate catalyst structure.

Photocatalytic Activity of Ag Nanoparticles Deposited on Thermoexfoliated g-C3N4.

The limited access to fresh water and the increased presence of emergent pollutants (EPs) in wastewater has increased the interest in developing strategies for wastewater remediation, including photocatalysis. Graphitic carbon nitride (g-C3N4) is a 2D non-metal material with outstanding properties, such as a 2.7 eV bandgap and physicochemical stability, making it a promising photocatalyst. This work reports the process of obtaining high-surface-area (SA) g-C3N4 using the thermal-exfoliation process and the posterior effect of Ag-nanoparticle loading over the exfoliated g-C3N4 surface. The photocatalytic activity of samples was evaluated through methylene blue (MB) degradation under visible-light radiation and correlated to its physical properties obtained by XRD, TEM, BET, and UV-Vis analyses. Moreover, 74% MB degradation was achieved by exfoliated g-C3N4 compared to its bulk counterpart (55%) in 180 min. Moreover, better photocatalytic performances (94% MB remotion) were registered at low Ag loading, with 5 wt.% as the optimal value. Such an improvement is attributed to the synergetic effect produced by a higher SA and the role of Ag nanoparticles in preventing charge-recombination processes. Based on the results, this work provides a simple and efficient methodology to obtain Ag/g-C3N4 photocatalysts with enhanced photocatalytic performance that is adequate for water remediation under sunlight conditions.

Catalytic oxidation of ammonia: A pre-occupied-anchoring-site strategy for enlarging Ag nanoparticles at low Ag loading and achieving enhanced activity and selectivity on Ag-CuOx/Al2O3 catalyst

The Ag nanoparticles (AgNPs) in Ag/Al2O3 catalysts play a crucial role in the selective catalytic oxidation of NH3 (NH3-SCO). To enhance NH3-SCO activity, Cu, which has stronger anchoring ability than Ag, is introduced onto Al2O3, reducing available anchoring sites for Ag. As Ag cannot displace anchored Cu species, Ag species agglomerate into larger AgNPs even with low Ag loading. Consequently, these enlarged AgNPs become more active centers for NH3-SCO. The optimal Ag:Cu molar ratio is confirmed as 2:3. This 'pre-occupied-anchoring-site’ strategy decreases Ag loading to 1/5 of the original, reducing catalyst costs while maintaining activity. In situ diffuse reflectance infrared Fourier-transform spectroscopy (DRIFTS) studies reveal that NH3-SCO on 2Ag1.8Cu/Al (weight ratio) catalyst follows the hydrazine mechanism below 200 °C, coexisting with the imide mechanism from 200–250 °C, and solely the imide mechanism beyond 250 °C. This strategy is applicable to various transition metals, including Mn, Co, Ni, and Fe, promoting cost-effective AgNPs formation.

Deciphering H2-induced low-temperature NOx adsorption on Ag/Al2O3: Expanding the operating temperature range of ethanol-SCR system for effective NOx abatement

Despite the advantages of the catalytic reduction of NOx by hydrocarbons, typical Ag/Al2O3 suffers from limited low-temperature activity in response to cold-start periods. In this study, the promotional effect of H2 on NOx adsorption on Ag/Al2O3 was investigated to address the low-temperature NOx emissions. H2 significantly enhanced NOx accumulation on Ag/Al2O3 below 200 °C, with desorption occurring at high temperatures. The H2-temperature-programmed reduction (H2-TPR) results showed the formation of silver oxide on metallic Ag species by H2+O2, serving as the primary site for H2-induced NOx adsorption, while the single-atom Ag species (Ag+) remained nearly unchanged. Ag/Al2O3 with low Ag loading (1–2 wt%) exhibited lower NOx adsorption capacities compared to the case with high Ag loading (4 wt%) owing to the low metallic Ag content. Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) studies identified diverse surface-adsorbed species related to H2-induced NOx adsorption. Nitrite, bridging nitrate, and bidentate nitrate contributed to low-temperature NOx desorption, whereas monodentate nitrate contributed to high-temperature desorption. Finally, we demonstrated exceptionally-high NOx reduction activity by synergistically combining the NOx trapping ability of Ag/Al2O3 with its deNOx capability through ethanol with H2, covering a wide temperature range of 100–350 °C under transient conditions at a high space velocity of 100,000 h−1.

Protein-polymer Bioconjugate Nanoparticles To Investigate Innate and Antigen-Specific CD4 T Cell Responses

Abstract Nanoparticles (NP) comprised of poly(lactic-co-glycolic acid) (PLGA) and poly(lactic acid) (PLA) have been shown to be effective delivery systems for peptide and protein antigens (Ags) capable of modulating Ag-specific T cell responses. Encapsulation and surface conjugation are common Ag association methods using NPs. However, these methods are associated with caveats such as imprecise Ag loading, high Ag burst release, and immune recognition. To improve the efficiency of Ag delivery and address these limitations, we prepared ovalbumin (OVA)-PLGA conjugates that were systematically combined with unmodified PLGA to produce NPs (acNP-OVA) with three precise Ag loadings, negligible immune recognition, and a reduced burst release. acNP-OVA was used to elucidate how NP formulation parameters, such as Ag content, influence innate and Ag-specific CD4 +T cell responses. We observed Ag loading-dependent innate immune cell activation (MHCII, CD80/86) and Ag-specific CD4 +T cell proliferation, cytokine secretions, and regulatory T cell induction in vitro. Ag-encapsulated NPs were employed as a control. CD25 expression and T cell expansion were achieved using both Ag delivery methods and observed at low Ag loading. However, high Ag loading was required to induce IFNg and IL-2 cytokine secretions. Notably, nanostring analysis identified inflammation-associated genes, such as S100a9, was significantly downregulated in dendritic cells due to NP treatment. We anticipate this study will aid in designing NP-based immunotherapies for Ag-specific immunomodulation.

“Reduction-aggregation” strategy to construct a low-cost and high-efficiency Ag/Al2O3 catalyst for NH3-SCO

Ammonia (NH3) is the main alkaline gas in the atmosphere and neutralizes acidic gases to form haze. Ag-based catalysts are widely used in the field of ammonia selective catalytic oxidation (NH3-SCO) due to their low cost and high efficiency. However, Ag-based catalysts with high activity at low temperatures are usually loaded with large amounts of Ag. To further reduce the cost of Ag-based catalysts, we used a “reduction-aggregation” strategy to aggregate isolated Ag atoms that were highly dispersed into Ag nanoparticles (AgNPs) so that more active centers could be exposed under low Ag loading conditions. Significant AgNPs size effects in the NH3-SCO reaction were found, including the effect of AgNPs size on catalyst activity and stability. Finally, novel Ag/Al2O3 catalysts with high efficiency and stability were developed at a low Ag loading of 1 wt % and achieved better NH3-SCO performance than 10% Ag/Al2O3, which significantly reduced the catalyst cost.

Surface Hydroxyl-Determined Migration and Anchoring of Silver on Alumina in Oxidative Redispersion

Hydroxyl (OH) groups are widely present on an oxide surface, which have been recognized as a key factor affecting surface properties of the oxide and interaction of the metal overlayer with the oxide. Here, γ-alumina (γ-Al2O3) supports with different OH contents are prepared by calcinating pseudo-boehmite (AlOOH) at different temperatures. The surface OH effect on oxidative redispersion of supported Ag nanoparticles including surface migration and anchoring of Ag species has been explored using in situ X-ray diffraction and UV–visible spectroscopy, as well as ex situ X-ray photoelectron spectroscopy and transmission electron microscopy. We reveal that the dispersion capacity, i.e., the amount of anchored Ag species associated with the steady dispersion state is thermodynamically determined by the surface OH contents, while the dispersion rate related to the surface migration process is kinetically limited by surface OH densities at low Ag loading. The higher dispersion ability is observed on the support with higher OH contents, and the quicker dispersion occurs on the support with higher OH densities. The results reveal that both OH contents and OH densities are critical in the redispersion of metal particles on oxide surfaces, which can be used to manipulate the Ag-catalyzed CO oxidation reaction.

Micelle-mediated assembly of metals in Ag@MnOx/m-SiO2 for reinforced antimicrobial activity and photothermal water evaporation

The increasing complexity of environmental pollution posed a higher requirement for the development of environment-governed functional materials. Herein, to achieve desired synergy and multiple functionalities of eco-friendly nanomaterials, a micelle-mediated metal assembly strategy was proposed to integrate plasmonic Ag nanoparticles into MnOx modified mesoporous silica hosts by metal-modified neutral dodecyl amine surfactant, correspondingly, a multifunctional mesoporous Ag@MnOx/m-SiO2 (AMSs) nanocomposite was obtained. The characterization results revealed that the introduction of Mn and alteration in the amount of Ag mediated the formation of a special mesostructure and nanometric morphology of the silica host. Bearing a low Ag loading (r.t. of Ag/Mn = 1/2), ultrafine Ag nanoparticles were embedded in the inner core of mesoporous silica nanospheres. While assembly with a higher Ag concentration affected the morphology of the obtained AMSs and resulted in rich Ag nanoparticles on the exterior surface of mesoporous silica. By this strategy, ultrafine Ag nanoparticles and well-dispersed amorphous MnOx species were coupled into the mesoporous silica to reach a special configuration and integrated functionality. The obtained AMSs-3 can effectively inactivate bacteria (E. coli, S. aureus, and P. aeruginosa) with a prolonged inhibitory effect, rapidly reduce harmful nitrophenol, as well as photothermally assist water evaporation (evaporation rate of 1.51 kg m−2 h−1, receiver efficiency of 87%). This work provides versatile environment-governing functional nanomaterials for both highly effective antimicrobial and environmental remediation.

Fabrication of Low Loading Ag Electrodes for CO2 Reduction Reaction in Zero-Gap Electrolyzer

In recent years, there has been intense effort directed towards catalyst development and electrode design for electrochemical carbon dioxide reduction reaction (CO2RR) with an objective of achieving high production rate (current density) of desirable products including CO, CH3OH, CH4 and C2+ hydrocarbons. Silver electrocatalyst is reported to exhibit remarkable CO selectivity and high current density, both of which are requisite parameters for CO2RR electrolyzer scale up. Silver is still moderately priced and reduction of Ag loading in CO2RR electrode is one of the technological goals for electrolyzer development.Most of the prior studies on Ag electrodes for CO2RR have utilized Ag nanoparticles, which are typically spray coated on a substrate from Ag or Ag-ionomer suspension resulting in high-Ag loading (> 1 mg/cm2 loading) and hence low mass specific activity (MSA) < 150 mA.mg-1 Ag. In this work, we developed a combined approach for Ag deposition using pulse electrodeposition (PE) and spray coating (SC) with an aim of decreasing Ag loading and increasing MSA. Such electrodes were found to exhibit high current densities and CO selectivity even with low Ag loading (< 0.5 mg/cm2).Specifically, several different gas diffusion electrodes (GDE) prepared by pulse electrodeposition of silver, spray coating of Ag nanoparticles, and combination of the two were prepared by coating of Sigracet gas diffusion layer (GDL). Commercial IrO2 electrode and the fabricated silver electrode were utilized as the anode and cathode, respectively. The anode and the cathode were separated by a polymer electrolyte membrane, which was Sustainion® X37-50 Grade 60- an anion exchange membrane. 10 mM KHCO3 electrolyte was re-circulated at the anode using a pump while humidified CO2 gas was flowed through the cathode. CO2RR tests are performed in a zero-gap electrolyzer setup, at a temperature of 25 °C.The main findings are summarized in the Figure below. The electrode prepared by pulse electrodeposition (PE) exhibits a low areal current density (~30 mA/cm2) but high mass-specific activity of 302 mA.mg-1 Ag. However, the selectivity for CO is low. On the other hand, spray coated (SC) electrodes yield higher CO selectivity and higher areal current density but mass specific activity is lower. By depositing silver sequentially, either pulse electrodeposition (PE) followed by spray coating (SC), i.e. the SC+PE electrode, or SC followed by PE (PE+SC electrode), both the mass-specific and areal current density increased drastically while CO selectivity remained high (99%). In particular, the current densities of the PE and SC electrodes are improved by 2 and 4.5 times, respectively, from 31 and 70 mA.cm-2 up to 136 mA.cm-2 on the SP+PE electrode, at the cell voltage of -3 V. Also, the CO selectivity of the electrodes is improved from 25 % (PE sample) and 81 % (SC sample) up to 99 % on the SC+PE electrode. The optimized electrode provided a catalyst layer with high surface coverage of silver on the GDL substrate at low Ag loadings (<0.5 mg/cm2). Further optimization of electrode is underway including modification of silver deposition and incorporation of ionomer to increase current density while maintaining the CO selectivity and durability of GDE. Details of the electrode fabrication and characterization as well as performance evaluation will be presented at the meeting. Figure 1

Co-assembly of microfibrous-structured Ag@SiO2-Co3O4/Al-fiber catalysts assisted with water-soluble silane coupling agent for catalytic combustion of trace ethylene

Microfibrous structured Ag@SiO2-Co3O4/Al-fiber catalyst, used for catalytic combustion of trace ethylene, is tailored with water-soluble silane coupling agent that has functionally specified multi-groups as bidirectional bridging reactant. Hydrothermally synthesized Co(OH)2/Al-fiber nanoarrays can be readily functionalized by amine groups via the silanisation reaction to form Co-O-Si bonds, followed by the assembly of Ag nanoparticles onto this microfibrous-structured substrates by coordination interaction. The as-prepared Ag@SiO2-Co3O4/Al-fiber catalyst uses very low Ag loading of only 0.2 wt% but exhibits high activity/stability at high-throughput operation. Ethylene conversion higher than 99 % was achieved at 200 °C under dry atmosphere, which shows no signs of deactivation with C2H4 conversion retained at ~94 % within 120 h running. Experimental and theoretical studies unanimously revealed that the Ag@SiO2-Co3O4 core-shell structures with strong metal-support interaction favor to bind and dissociate intermediate species during C2H4 oxidation, contributing to high activity of C2H4 oxidation.

Vapor phase polymerization of Ag QD-embedded PEDOT film with enhanced thermoelectric and antibacterial properties

Nonferric oxidant precursors have the unique advantage of directly polymerizing poly(3,4-ethylenedioxythiophene) (PEDOT)-inorganic composites. However, due to limited solubility and unmatched oxidation potentials, most oxidants only produce powders or porous materials. To obtain high-quality films with improved homogeneity and controllable particle sizes, the oxidants should be adaptable to high-standard PEDOT film fabrication techniques such as vapor phase polymerization (VPP). In this work, we discovered for the first time a nonferric metal salt suitable for the VPP process. With the addition of an Fe(III) salt to stabilize the reaction and adjust the oxidant ratio, micron-thick antibacterial S-PEDOT-Ag quantum dot (QD) composite films with tunable Ag wt% can be synthesized in one facile step. With a low Ag loading of ~0.2 wt%, the film exhibited an optimized power factor of 63.1 μW/mK2, which is among the highest values thus far reported for PEDOT-metal composites. Increase of the Ag(I) concentration in the precursor to a certain level may lead to minor decomposition of the polymer followed by the formation of Ag2S particles.

HC-SCR system combining Ag/Al2O3 and Pd/Al2O3 catalysts with resistance to hydrothermal aging for simultaneous removal of NO, HC, and CO

A combined Ag/Al2O3 and Pd/Al2O3 catalyst was investigated for the selective catalytic reduction (SCR) of NOx by H2-assisted C3H6 in the presence of excessive O2. The coexistent H2 significantly lowered the active temperature window of the de-NOx reaction because of the enhanced partial oxidation of C3H6 and NO oxidation to NO2. A low Ag loading of 1 wt% exhibited better de-NOx performance than that attained using 2 wt% Ag. Although Ag/Al2O3 exhibited a high resistance to hydrothermal aging, a high reaction temperature (>500 °C) was required to oxidize CO and C3H6 completely. In contrast to Ag/Al2O3, Pd/Al2O3 suppressed C3H6 and CO slip at relatively low temperatures, and a complete oxidation of C3H6 and CO was achieved at 195–275 °C and 240–275 °C, respectively, under varying SCR conditions and Pd contents (0.5–1.5 wt%); however, 30% de-NOx performance in a narrow temperature window of 210–240 °C was attained. The best configuration was found to be a sequential arrangement of 1Ag/Al2O3 followed by 1Pd/Al2O3, which enabled the reduction of NOx, C3H6, CO, and H2 over wide reaction temperatures, unlike the stand-alone configuration. In this configuration, the reacted NOx was reduced to N2 with negligible formation of by-products, even after hydrothermal aging.

De-NOx characteristics of HC-SCR system employing combined Ag/Al2O3 and CuSn/ZSM-5 catalyst

The combination of Ag/Al2O3 and CuSn/ZSM-5 on catalytic performance was investigated for selective catalytic reduction of NOx by H2-assisted C3H6. The Ag loading significantly affected the de-NOx performance and C3H6 conversion; a low Ag loading in the catalyst (less than 2wt% Ag) afforded superior de-NOx performance compared to that obtained with more than 4wt% Ag, owing to the lack of agglomeration of Ag particles on the support (Ag/Al2O3) in the former. Considering the C3H6 slip, a very high reaction temperature (above 525℃) was required for complete C3H6 oxidation. A combination of Ag/Al2O3 and CuSn/ZSM-5 allowed complete C3H6 oxidation below 350℃ owing to the superior C3H6 oxidation ability of CuSn/ZSM-5, which is the merit of the combined system compared with Ag/Al2O3 or CuSn/ZSM-5 used individually. The best catalytic configuration is the sequential arrangement of 1Ag/Al2O3 + 2Cu1Sn/ZSM-5, which could simultaneously reduce NOx, C3H6, and H2 over a wider temperature window ranging from 300‒600℃. Notably, the reduced NOx was almost entirely reduced to N2 with negligible generation of N2O, NH3, and HCNO.

Morphology-controllable fabrication of Ag@MoS2 composites with improved antioxidant activities at low Ag loading

Silver (Ag) has been regarded as a significant antioxidant widely used in biosystem. Nevertheless, the loading level of Ag nanospecies needs to be controlled to prevent their potential risk to human health. Herein, nanocomposite consisting of Ag and molybdenum disulfide (MoS2) has been readily synthesized via a template solvothermal method. Characterized by SEM, TEM and EDX, the Ag@MoS2 composite morphology including nanoflower, hollow sphere and solid sphere could be well controlled by adjusting solvent type and precursor-template ratio during the synthesis process. The composite structure of all three morphologies was further confirmed by XRD, Raman and N2 adsorption-desorption measurements. Ag@MoS2nanoflower and hollow sphere, in which nanosized Ag was anchored (or encapsulated) within MoS2 nanosheets, obviously boosted the radical (1,1-diphenyl-2-picyrl, DPPH and nitride oxide, NO) scavenging efficiency (minimum IC50,DPPH = 26 μg/mL while IC50,NO = 46 μg/mL) with an Ag dosage much lowered to merely 7∼20 μg/mL. As a contrast, weaker activity of radical scavenging could be observed for Ag@MoS2solid sphere. Our work will shed new lights on the cost-effective strategy to obtain a biosafe antioxidant.

Photoelectrocatalytic Degradation of C.I. Basic Blue 9 under UV Light Using Silver-Doped Titanium Dioxide Nanotubes

Titanium dioxide is a widely-investigated semiconductor photocatalyst due to its wide availability and low cost. Although it has been successfully used in the photocatalytic treatment of various organics in wastewater, it remains a challenge to modify its structure to achieve enhanced catalytic properties at a wider light spectrum. Doping with transition metals was seen to narrow its optical band gap yet synthesis routes have been largely limited to the use of high-end equipment. Herein we demonstrate the use of a simpler one-pot approach to synthesize nanoporous arrays of silver-doped titanium dioxide nanotubes (Ag-TiNTs) by double anodization of titanium sheets. The synthesized Ag-TiNTs have an average inner diameter of 58.68 nm and a wall thickness of 16.46 nm. ATR-FTIR spectroscopy revealed its characteristic peaks attributed to O-Ti-O bonds. Silver doping increased the lattice volume and crystallite size of anatase with a corresponding decrease in the degree of crystallinity due to the introduction of impurity Ag atoms in its tetragonal structure. Silver was homogeneously distributed across the nanotube surface at an average loading of 1.41 at. %. The synthesized Ag-TiNTs were shown to have a superior photoelectrocatalytic activity in degrading C.I. Basic Blue 9 under UV illumination with a pseudo-first-order kinetic rate of 1.0253 x 10-2 min-1. Most importantly, the Ag-TiNTs are photoelectrocatalytically-active even at a low Ag loading.

Synthesis of Silver-Doped Titanium Dioxide Nanotubes by Single-Step Anodization for Enhanced Photodegradation of Acid Orange 52

Silver-doped TiO2 nanotubes (Ag-TiNTs) were synthesized in a top-down approach by single-step anodization of titanium sheets. The highly-ordered array of Ag-TiNTs was confirmed by scanning electron microscopy with an average inner diameter of 41.28 nm and a wall thickness of 35.38 nm. Infrared spectroscopy confirmed the presence of O-Ti-O bonds. Analysis of the X-ray powder diffraction profiles showed the characteristic peaks for anatase and titanium for both pristine TiNTs and Ag-TiNTs. Ag-doping caused no observed changes in the crystalline structure of pristine TiNTs. High-definition X-ray fluorescence spectroscopy revealed that the synthesized Ag-TiNTs have 0.05 wt% Ag-loading. Even at low Ag-loading, the Ag-TiNTs were shown to be photo-active, achieving 10.13% degradation of Acid Orange 52 under UV illumination after 120 min.

Core-shell metal-organic frameworks and metal functionalization to access highest efficiency in catalytic carboxylation

A core-shell metal-organic frameworks (MOF@MOF) based on the Zr-MOFs assembly from core-structure UiO-66 combined with shell-structure UiO-67-BPY were explored. The synthesized materials were characterized via XRD, FTIR, SEM, TEM, and surface area analysis, etc. indicating the presence of a core-shell structure of UiO-66@UiO-67-BPY. Furthermore, incorporation of the bipyridinic (BPY) group in the linker used to construct the shell layer (UiO-67-BPY) could coordinate with active metal species and thus create an advantage for site-selective metal incorporation in the core-shell structure. Silver (Ag) was selected for the selective metal incorporation and an excellent Ag-dispersion via coordination with the bipyridinic groups in the UiO-67-BPY layer of the core-shell material was obtained. The synthesized material (UiO-66@UiO-67-BPY-Ag) was successfully applied as a heterogeneous catalyst for the CO2 fixation via carboxylation of terminal alkynes. The catalytic material showed excellent yields using at a low Ag-loading under mild reaction condition (50 °C, 1 bar). Moreover, the catalyst can be recycled for at least 5 times maintaining a stable catalytic performance. Interestingly, the high catalytic activity of the synthesized material demonstrated clearly the beneficial advantage of the metalated core-shell structure over the reported routes to synthesize silver catalysts such as encapsulated Ag nanoparticles (AgNP@MOF) or Ag-bidentately coordinated on traditional MOFs applying the same reaction model.

Carboxylation of Terminal Alkynes with Carbon Dioxide Catalyzed by an In Situ Ag2O/N‐Heterocyclic Carbene Precursor System

AbstractA carboxylation of terminal alkynes with carbon dioxide (CO2) at ambient conditions was developed in situ using a series of N‐heterocyclic carbene (NHC) precursors and Ag2O. The unique structure of NHCs largely increases the solubility of active Ag species and meanwhile activates CO2 by forming the NHC–CO2 adduct. This novel catalytic system demonstrated quite low Ag loading, very high activities, wide substrate generality and excellent tolerance for a variety of functionalities. In addition, avoiding cumbersome synthesis procedures, processing, and reserving of the photosensitive Ag complex, this system could be stored and operated as straightforward as the inorganic Ag salt catalysts.

Application of nitrogen-doped graphene nanosheets in electrically conductive adhesives

Nitrogen-doped graphene nanosheets (N-GNSs) were used as a conductive filler for a polymer resin adhesive and as a performance improver for a silver-filled electrically conductive adhesive (ECA). The N-GNS samples were prepared by the chemical-intercalation/thermal-exfoliation of graphite followed by a thermal treatment in NH3. Only 1wt.% of N-GNSs was required for the adhesive to reach a percolation threshold, and the performance using N-GNSs was much better than that obtained using carbon black or multi-walled carbon nanotubes (MWCNTs). The effect of N-GNS or MWCNT additives on reducing the electrical resistivity of Ag-particle filled ECAs at low Ag loading ratios was also investigated. With 30wt.% of Ag filler, the polymer resin was still non-conducting, while a resistivity of 4.4×10−2Ω-cm was obtained using an Ag/N-GNS hybrid filler fortified with only 1wt.% of N-GNSs due to large specific surface area, high aspect ratio, and good electrical conductivity of the doped graphene.

Effects of pretreatment atmosphere and silver loading on the structure and catalytic activity of Ag/SBA-15 catalysts

The structural properties of Ag/SBA-15 catalysts with various Ag loading after pretreatment under different atmosphere, i.e., O2, Ar and H2, in relation to their activities on CO oxidation were investigated. N2 adsorption–desorption results showed that the pretreatment atmosphere had a negligible effect on the physical structure of all catalysts. Interestingly, it was found that different pretreatment atmosphere (Ar, O2) and Ag loading exhibited a large difference on the structure of silver catalyst and their catalytic activity. For Ag/SBA-15 catalyst with low silver loading (≤6wt%), Ar pretreatment resulted in the highest activity for CO oxidation. However, the highest catalytic performance was observed after oxygen pretreatment over the silver catalyst with high loading (>6wt%). UV–vis and H2-TPR results showed Ar pretreatment and Ag loading strongly affected the states of Ag species for the silver catalysts, which were changed from metal Ag (≤4wt%) to a mixture of Ag and Ag2O (≥6wt%). Moreover Ar pretreatment was favorable for the formation of small Ag particles for Ag/SBA-15 catalyst with low Ag loading. When the silver loading is increased, the heavy aggregation of silver particles occurred after Ar pretreatment, resulting in the decrease of TOF for CO oxidation. O2 pretreatment was conductive to the formation of subsurface oxygen species on the larger silver particles for Ag/SBA-15 catalyst with high Ag loading, which resulted in the increase of TOF for CO oxidation. It was evident that small metal Ag particles was key factor of the higher catalytic activity for Ag/SBA-15 catalyst with low Ag loading, while a large number of subsurface oxygen species played an important effect on the higher catalytic activity for Ag/SBA-15 catalyst with high Ag loading.