Properties of Iron-Modified-by-Silver Supported on Mordenite as Catalysts for NOx Reduction

Solid Handmade Ternary Coinage Metal Mentors for Organic Bond-Making and Bond-Breaking Applications

A comparative approach is employed for the novel synthesis of a magnetically recoverable ternary nanocomposite consisting of g-C3N4-supported Fe3O4 decorated with coinage metals (Au, Ag, and Cu). This synthesis is achieved through a straightforward and convenient one-step grinding protocol. In situ, the nanoparticles were grown on the g-C3N4-assist Fe3O4 matrix (GCFM), and the agglomeration of these nanoparticles on the matrix creates a pathway for the formation of the nanocomposite (NC). The as-formed CNC was confirmed with the help of characterization analyses, namely XRD, FT-IR, HR-TEM, FE-SEM, XPS, VSM, UV-vis, and NMR studies. Together with NPs and GCFM, with the quantum consequence, the activity of the NC shows better electron transfer via transfer of electrons, which grabs tremendous attention toward it, resulting in enhanced plausible photocatalytic degradation toward pharmaceutical compounds, dyes, and anthropogenic pollutants. The activity of the C-NC hikes at 88% for ciprofloxacin (CX) and 90% for paracetamol (PM); furthermore, the activity of the C-NC hikes at 88% and 87% for xylene Cyanol FF (XCF) and malachite green (MLG), respectively. Interestingly, an added advantage is the formation of a C-C bond (homocoupling reaction) in phenylboronic acid (PA) via a greener solvent under ambient conditions. The yield percentage of the conversion product shows satisfactory results, and its reproducibility was good for the prepared ternary NC. The conversion treatment of anthropogenic pollutants, namely 4-nitrophenol, grasps a high percentage (98%). In addition, the NC shows good activity toward both types of bacteria. The reproducibility of the composite also shows virtuous activity against pharmaceutical as well as toxic contaminants. The as-prepared CNC was specifically engineered to perform both bond formation and bond cleavage of organic molecules under ambient conditions for multiple cycles.

Formation of Ag-Fe Bimetallic Nano-Species on Mordenite Depending on the Initial Ratio of Components

The formation and properties of silver and iron nanoscale components in the Ag-Fe bimetallic system deposited on mordenite depend on several parameters during their preparation. Previously, it was shown that an important condition for optimizing nano-center properties in a bimetallic catalyst is to change the order of sequential deposition of components; the order "first Ag⁺, then Fe²⁺" was chosen as optimal. In this work, the influence of exact Ag/Fe atomic proportion on the system's physicochemical properties was studied. This ratio has been confirmed to affect the stoichiometry of the reduction-oxidation processes involving Ag⁺ and Fe²⁺, as shown by XRD, DR UV-Vis, XPS, and XAFS data, while HRTEM, S_BET and TPD-NH₃ show little change. However, it was found the correlation between the occurrence and amount of the Fe³⁺ ions incorporated into the zeolite's framework and the experimentally determined catalytic activities towards the model de-NOx reaction along the series of nanomaterials elucidated in this present paper.

Active Sites in H-Mordenite Catalysts Probed by NMR and FTIR

Mordenites are widely used in catalysis and environmental protection. The catalytic properties of mordenite are largely determined by the composition of its crystal framework, i.e., the SiO2/Al2O3 molar ratio (MR), and the cationic form. In H-mordenites, the most important characteristic becomes the structure and distribution of acid sites, which depends on the number and distribution of Al tetrahedra in the framework. In the present work, the local structure of these centers in H-mordenite catalysts with a nominal MR varied from 9.9 to 19.8 was studied in detail using a combination of magic angle spinning nuclear magnetic resonance (MAS NMR) and Fourier transform infrared spectroscopy (FTIR). 27Al MAS NMR indicates the presence of extra-framework Al in most of the studied samples that results in a higher real MR of the zeolitic framework compared to the nominal value. Concentrations of Lewis and Brønsted acid sites, as well as of silanol groups were estimated by elemental analysis, NMR, and FTIR spectroscopy. The values of site concentrations obtained from band intensities of adsorbed CO and those of OH groups are compared with the amount of framework and extra-framework aluminum. The advantages and restrictions of different methods of active site characterization are discussed.

Influence of Components Deposition Order on Silver Species Formation in Bimetallic Ag-Fe System Supported on Mordenite

In the present work, various experimental and theoretical methods were combined to study in detail the modifying effect of differences in the order of deposition of components on the state of silver in bimetallic iron–silver samples based on mordenite. In each of the silver-containing samples, the formation of large (≥2 nm in diameter) varieties of silver was observed, which differed from the varieties in the other samples, and in varying degrees. The formation of large Ag NPs on the outer surface of mordenite is explained by the redox interaction of Ag+-Fe2+ and the selectivity of ion exchange. The local surrounding of Ag in the studied samples is different: for AgMOR—monatomic species dominate, FeAgMOR—silver dimers and AgFeMOR—metal particles. In all investigated samples, the partially charged intra-channel Agnδ+ clusters (~0.7 nm in size) were formed due to partial Ag+ reduction and subsequent Ag0 agglomeration into the mordenite channel. Most of the silver in the bulk of the zeolite is represented in the cationic state attached to the mordenite framework by differently coordinated electrostatic forces, which can be Ag-O, Ag-Si or Ag-Al, with variations in interatomic distances and do not depend on the order of metal deposition. In addition, the arrangement of the cations in the side pockets means that the transport channels of mordenite are free, which is favorable for the application of the materials under study in catalysis and adsorption.

Recent Advances in Catalysis Based on Transition Metals Supported on Zeolites

This article reviews the current state and development of thermal catalytic processes using transition metals (TM) supported on zeolites (TM/Z), as well as the contribution of theoretical studies to understand the details of the catalytic processes. Structural features inherent to zeolites, and their corresponding properties such as ion exchange capacity, stable and very regular microporosity, the ability to create additional mesoporosity, as well as the potential chemical modification of their properties by isomorphic substitution of tetrahedral atoms in the crystal framework, make them unique catalyst carriers. New methods that modify zeolites, including sequential ion exchange, multiple isomorphic substitution, and the creation of hierarchically porous structures both during synthesis and in subsequent stages of post-synthetic processing, continue to be discovered. TM/Z catalysts can be applied to new processes such as CO₂ capture/conversion, methane activation/conversion, selective catalytic NO_x reduction (SCR-deNO_x), catalytic depolymerization, biomass conversion and H₂ production/storage.

Cu- and Fe-speciation in a composite zeolite catalyst for selective catalytic reduction of NOx: insights from operando XAS

Cu-SAPO-34 (Cu-CZC) and Fe-mordenite (Fe-MOR) and their mechanical mixture (50 : 50) have been exhaustively investigated by means of operando X-ray absorption spectroscopy under NH₃-SCR conditions.