Cu-IM-5 as the Catalyst for Selective Catalytic Reduction of NOx with NH3: Role of Cu Species and Reaction Mechanism

The role of Cu species in Cu ion-exchanged IM-5 zeolite (Cu-IM-5) regarding the performance in selective catalytic reduction (SCR) of NOx with NH3 (NH3-SCR) and the reaction mechanism was studied. Based on H2 temperature-programmed reduction (H2-TPR) and electron paramagnetic resonance (EPR) results, Cu–O–Cu and isolated Cu species are suggested as main Cu species existing in Cu-IM-5 and are active for SCR reaction. Cu–O–Cu species show a good NH3-SCR activity at temperatures below 250 °C, whereas their NH3 oxidation activity at higher temperatures hinders the SCR performance. At low temperatures, NH4NO3 and NH4NO2 are key reaction intermediates. In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) suggests a mixed Eley–Rideal (E–R) and Langmuir–Hinshelwood (L–H) mechanism over Cu-IM-5 at low temperatures

Biomineralization at the Molecular Level: Amino Acid-Assisted Crystallization of Zeotype AlPO4·1.5H2O–H3

International audienceThree aminoacids: proline, histidine, and lysine are used as organic additives in the hydrothermal synthesis of the zeotype material AlPO 4 •1.5H 2 O-H3 (framework topology code APC). A detailed analysis of the factors controlling the formation of AlPO 4 •1.5H 2 O-H3 is performed. The role of aminoacids in the formation process of the frameworks is addressed based on comparisons of the crystal phase selection of different synthetic recipes and the insights provided by the FTIR analysis of the synthetic gels and the crystalline products. The phase transition of AlPO 4 •1.5H 2 O-H3 to AlPO 4-C (APC), and subsequently to AlPO 4-D (APD) upon heating to 1000 o C was followed by in situ XRD analysis. The present work has been the first progress to understanding the role of the bioactive molecules in the crystallization of inorganic open-framework microporous materials. An active, non-classical structuredirecting role that aminoacids play during the zeotype crystallization is proposed, i.e., positively charged aminoacids cap the growing surface of microporous AlPO 4 , and attract aluminate and phosphate anions from the solution phase for further growth

Hydrothermal crystallization of clathrasils in acidic medium: energetic aspects

International audienceA series of clathrasils, including AST, DOH, MTN, and DDR topologies, were synthesized in an acidic medium. The general composition of the initial system was 1 SiO 2 : 0.3-0.5 SDA: 0.1-0.5 HF/NH 4 F: 0-0.3 HBr: 10-50 H 2 O in the pH range of 2-6, where SDA stands for organic amines or ammonium ions as the structure-directing agents. And the hydrothermal syntheses were performed in the 150-200°C temperature range. Besides elaborating the synthesis recipes and product characterizations, the study also attempted to elucidate the origins of slow crystallization kinetics. It was found that the thermodynamic stabilities of the SDA@Framewrok-SiO 2 compounds play an overwhelming role in the crystalline phase selection. The finding of this study can be used as a guidance of silica-based porous materials synthesis under acidic conditions

The Activity of Ultrafine Cu Clusters Encapsulated in Nano-Zeolite for Selective Hydrogenation of CO₂ to Methanol

Narrowly dispersed ultrafine Cu clusters of sizes smaller than 2.0 nm have been encapsulated in nanosized silicalite-1 zeolite through direct crystallization in the presence of Cu(en)22+ complex ions as the metal precursor. The growing silicalite-1 crystals are rich in vacancy defects and connectivity defects on the grain boundaries, where the terminating silanols promote the decomposition of Cu(en)22+, thus the deposition of ultrafine Cu species. The obtained composite material as a model catalyst is active for CO2 activation and hydrogenation to methanol. The preliminary in situ FTIR study recognizes a series of surface-adsorbed carbonyl, formyl, carbonate, and formate species when the material is exposed to CO2 and H2. Among others, the adsorbed formate decays most rapidly upon cofeeding CO2 and H2, implying that the most probable pathway toward methanol formation over this material is via the formate-mediated mechanism

Acidic medium synthesis of zeolites – an avenue to control the structure-directing power of organic templates

International audienceThis paper deals with the extension of the synthesis field of microporous zeolite-type materials and types of organic structure-directing agents (OSDA) that can be used to promote their crystallization. The highly hydrophilic hexamethylenetetramine (urotropine), with its C/N ratio = 1.5, which is unusual to act as a structure-directing agent in the crystallization of open-framework silica polymorphs, is used to exemplify the novelty of the employed approach. Namely, the protonation of urotropine in an acidic fluorine-containing medium transforms it into a very efficient OSDA that yields dodecasil 3C (MTN-type). This novel synthesis also allows gaining insights into OSDA-framework interactions in the MTN-type structure. The comprehensive 29Si and 19F MAS NMR indicate a small number of point defects of the framework T sites and the multiple bonding of F− ions to Si in a disordered manner. Based on this finding, a unit cell model has been generated using Monte Carlo simulation and validated with Rietveld refinement using experimental powder X-ray diffraction data. In the model, protonated urotropine cations are located in the center of the big hexakaidecahedral [51264] cages at full occupancy with random orientations. The charge balance is provided by the disordered F− ions

The Activity of Ultrafine Cu Clusters Encapsulated in Nano-Zeolite for Selective Hydrogenation of CO2 to Methanol

Narrowly dispersed ultrafine Cu clusters of sizes smaller than 2.0 nm have been encapsulated in nanosized silicalite-1 zeolite through direct crystallization in the presence of Cu(en)22+ complex ions as the metal precursor. The growing silicalite-1 crystals are rich in vacancy defects and connectivity defects on the grain boundaries, where the terminating silanols promote the decomposition of Cu(en)22+, thus the deposition of ultrafine Cu species. The obtained composite material as a model catalyst is active for CO2 activation and hydrogenation to methanol. The preliminary in situ FTIR study recognizes a series of surface-adsorbed carbonyl, formyl, carbonate, and formate species when the material is exposed to CO2 and H2. Among others, the adsorbed formate decays most rapidly upon cofeeding CO2 and H2, implying that the most probable pathway toward methanol formation over this material is via the formate-mediated mechanism

Copper Collector Generated Cu⁺/Cu²⁺ Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

Copper Collector Generated Cu⁺/Cu²⁺ Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

Copper Collector Generated Cu⁺/Cu²⁺ Redox Pair for Enhanced Efficiency and Lifetime of Zn–Ni/Air Hybrid Battery

Although Zn–Ni/air hybrid batteries exhibit improved energy efficiency, power density, and stability compared with Zn–air batteries, they still cannot satisfy the high requirements of commercialization. Herein, the Cu+/Cu2+ redox pair generated from a copper collector has been introduced to construct the hybrid battery system by combining Zn–air and Zn–Cu/Zn–Ni, in which CuXO@NiFe-LDH and Co–N–C dodecahedrons are respectively adopted as oxygen evolution (OER) and oxygen reduction (ORR) electrodes. For fabricating CuXO@NiFe-LDH, the Cu foam collector is oxidized to in situ form 1D CuXO nanoneedle arrays, which could generate the Cu+/Cu2+ redox pair to enhance battery efficiency by providing an extra charging–discharging voltage plateau to reduce the charging voltage and increase the discharge voltage. Then, the 2D NiFe hydrotalcite nanosheets grow on the nanoneedle arrays to obtain 3D interdigital structures, facilitating the intimate contact of the ORR/OER electrode and electrolyte by providing a multichannel structure. Thus, the battery system could endow a high energy efficiency (79.6% at 10 mA cm–2), an outstanding energy density (940 Wh kg–1), and an ultralong lifetime (500 h). Significantly, it could stably operate under harsh environments, such as oxygen-free and any humidity. In situ X-ray diffraction (XRD) combined with ex situ X-ray photoelectron spectroscopy (XPS) analyses demonstrate the reversible process of Cu–O–Cu ↔ Cu–O and Ni–O ↔ Ni–O–O–H during the charging/discharging, which are responsible for the enhanced efficiency and lifetime of battery

Silicalite-1 formation in acidic medium: synthesis conditions and physicochemical properties

International audienceZeolites are the catalytic materials that are widly applied in the processing of conventional and renewable fuels and chemicals. The present study provides a comprehensive analysis of the factors controlling the acidic medium synthesis of high silica silicalite-1 zeolite. The effect of various silica sources (TEOS, fumed and colloidal silica) and alkali metal cations (Na and K) on the silicalite-1 formation is studied. The efficiency of different types of seeds (micron-sized, nanosized, and silicalite-1 amorphous colloidal precursor) on the silicalite-1 crystal growth kinetics and crystal size formed under acidic conditions is also investigated. Further, the zeolite crystallization kinetics under acidic, neutral, and basic conditions is compared. The obtained highly crystalline samples are used to compare the physicochemical properties of zeolites synthesized in acidic, neutral, and basic medium. Thus, the crystallinity, thermal stability, and local order in silicalite-1 samples synthesized in the (2-12) pH range are evaluated