Applications In Heterogeneous Catalysis Research Articles

Microwave-assisted Synthesis, Characterization, Photocatalytic Degradation of Antibiotics, and Fluorometric Selective Sensing Activity of g-C3N4 Supported CuO Composites.

Herein, we have designed for the fabrication of a series of g-C3N4/CuO composite by using one-step microwave-assisted synthesis for the degradation of antibiotics and detection of nano-molar range of toxic heavy metal ions. The synthesized g-C3N4/CuO composites were analyzed and characterized to know the structure, phase, surface area, absorption region, bandgap, and size of the composites. From the observation of TEM and XRD measurements, g-C3N4/CuO composites have hexagonal shape with average diameter of the particles is 25 ± 5nm. The observed band gap values from UV-vis DRS for g-C3N4 nanosheets and CuO NPs are 2.64eV and 1.72eV. The synthesized g-C3N4/CuO composite has prodigious specific surface area (32.47 m2/g), which is the evident for superior heterogeneous catalytic applications. Therefore, the synthesized g-C3N4/CuO composites were tested for the degradation of antibiotics such as tetracycline (TC) and ciprofloxacin (CIP) under UV light illumination, it shows 88.02% and 90.01% degradation was observed within 1h due to the matching optical band gap and internal charge transfer of excitons with in the heterojunction surface among g-C3N4 and CuO in the composite than the individual components (g-C3N4 and CuO) due to the high surface area and tiny particles of CuO were randomly deposited on the surface of g-C3N4 nanosheets. The catalytic reduction reaction follows as pseudo-first order equation and reused for 5 consecutive cycles without remarkable loss of catalytic activity. Moreover, the synthesized CuO NPs and g-C3N4/CuO composites were used as a prominent fluorescence sensing probe for the selective detection of Pb2+ in nano-molar range of concentration with Ksv is 1.38 × 104mol- 1dm3. It was observed as a linear relationship based on the change in intensity, the limit of detection was determined to be 0.184 nM.

First-principles study of the magnetic exchange forces between the RuO2 (110) surface and Fe tip.

Magnetic exchange force microscopy (MExFM) is an important experimental technique for mapping the magnetic structure of surfaces with atomic resolution relying on the spin-dependent short-range exchange interaction between a magnetic tip and a magnetic surface. RuO2 is a significant compound with applications in heterogeneous catalysis and electrocatalysis. It has been characterized recently as an antiferromagnetic (AFM) material, and its magnetism has been predicted somewhat surprisingly to play an important role in its catalytic properties. In the current study, we explore theoretically whether MExFM can visualize the magnetic surface structure of RuO2 . We use density functional theory (DFT) calculations to extract the exchange interactions between a ferromagnetic Fe tip interacting with an AFM RuO2 (110) surface, as a function of tip-surface distance and the position of the tip over the surface. Mimicking the MExFM experiment, these data are then used to calculate the normalized frequency shift of an oscillating cantilever tip versus the minimum tip-surface distance, and construct corrugation height line profiles. It is found that the exchange interaction between tip and surface is strongest for a parallel configuration of the spins of the tip and of the surface; it is weakest for an anti-parallel orientation. In a corrugation profile, this gives rise to a sizable height difference of 25 pm between the spin-up and spin-down Ru atoms in the RuO2 (110) surface at a normalized frequency shift =-10.12 fNm1/2 . The O atoms in the surface are not or hardly visible in the corrugation profile.

Substrate-Free Fabrication of Single-Crystal Two-Dimensional Gold Nanoplates for Catalytic Application.

Two-dimensional (2D) gold nanoplates (AuNPLs) have shown potential in catalysis, photonics, electronics, sensing, and biomedicine fields due to their high aspect ratio, fascinating surface chemistry, and quantum-size effect. Therefore, the synthesis of substrate-free, size-controlled single-crystal gold (Au) nanoplates is highly desirable for the development of catalysis and optical near-field enhancement applications. EDTA and hydroxide anions were used in this study to stimulate the formation of microscale single-crystal gold nanoplates under hydrothermal conditions. The reaction temperature, amount of EDTA, and hydroxyl anions all have a significant effect on the morphologies and size distributions of the gold nanoplates. The gold nanoplates had an average side length of between 3 and 11 μm. The application of the microscale single-crystal gold nanoplates as a nanocatalyst proved their excellent catalytic activity and recyclability for the catalysis of 4-nitrophenol to 4-aminophenol, implying that the large-size gold nanoplates were promising in heterogeneous catalysis applications.

Porous Nanoarchitectures of Nonprecious Metal Borides: From Controlled Synthesis to Heterogeneous Catalyst Applications

Porous nonprecious metal-based nanomaterials have gained considerable attention in heterogeneous catalysis owing to their low price, high specific surface area, efficient mass/electron transfer, tunable pore structure, and unique physicochemical properties. Controlling the phase and compositions of these porous nonprecious metal-based materials is critical to their applications. Porous nonprecious transition-metal borides (TMBs), typical metal–metalloid alloys, have recently received much interest because of their optimized electronic structure, adjustable crystal phase, and abundant active site. The controlled tuning of the porous structure of TMBs, exploring the relationship between the structure and performance, and understanding the function of B are essential for developing catalysts with excellent performance; however, these factors have rarely been reviewed. Herein, a detailed summary of the synthesis methods of porous TMBs is provided by precisely defining their shape, composition, and pore size/structure. Incorporating B into metals can significantly alter their performance due to the unique metalloid properties of B. Further, we focus on the key roles of B in porous TMBs for related heterogeneous catalytic applications, including phase control, regulated electronic structure, optimized adsorption of reaction intermediates, and enhanced charge transfer and stability. Finally, we outline the shortcomings, challenges, and possible development of porous TMBs, which need to be further explored to increase TMBs’ contribution to heterogeneous catalyst applications and beyond.

(Invited, Digital Presentation) Atomic Layer Deposited Templates for Constructing Functional Metal-Organic Framework Thin Films

Metal-organic frameworks (MOFs) are a class of porous crystalline materials featuring high surface area, ordered pore structures and amenability for post-synthetic modification. Integrating MOF thin films with various substrate materials could enable applications in separations, heterogeneous catalysis, chemical sensors and electronic devices. However, it is difficult to find a universal approach to deposit uniform and high-quality MOF coatings on a variety of substrate materials. Previous attempts often require surface modification methods that may not be generally applicable.In this talk, interfacial engineering using atomic layer deposited (ALD) templates will be discussed for forming MOF thin films on various substrates. We found that ALD metal oxides are effective in promoting the heterogeneous nucleation of MOFs and also readily hydrolyzed into hydroxy double salts (HDSs) for rapid transformation to MOFs. With ALD template layers, conformal and functional MOF coatings were integrated on fibers, membranes and laminated structures. Accordingly, we developed a series of MOF-functionalized fibers for adsorption and catalytic degradation of hazardous compounds. Furthermore, we obtained ultra-thin mixed-metal MOF skin layers on porous alumina supports for membrane separation, and achieved large propylene permeance (up to 4.5×10-8 mol·m-2·s-1·Pa-1) and high propylene/propane selectivity over 250. We anticipate that this platform technology will also lead to potential device structures for chemical sensing, energy storage and many other scenarios.

The calcium alginate-immobilized Co-g-C3N4 composite microspheres as an efficient mediator to activate peroxymonosulfate for degrading organic pollutants

Poor water stability and difficult separation severely limited the application of Co-based catalysts in persulfate activation. Herein, for the first time, the calcium alginate-immobilized Co-g–C3N4–2 composite microspheres were prepared by a feasible method. Notably, embedding Co ion into g-C3N4 can improve its specific surface area and electrochemical activities. More significantly, as-prepared Co-g–C3N4–2 microsphere presented excellent catalytic performance in PMS activation for the degradation of TC. For the activation mechanisms of PMS over Co-g–C3N4–2 microspheres, the calcium alginate microspheres could mediate the direct electron transfer between TC and PMS, while both radical and nonradical pathways were involved in the activation of PMS over Co-g–C3N4–2. Meanwhile, SO4•−, OH•, O2•− and 1O2 were major reactive oxygen species formed in the Co-g–C3N4–2 microsphere/PMS system. Proposed Co-g–C3N4–2 microsphere/PMS system still exhibited great degradation ability towards TC over a wide pH range, and co-existing anions had weak influence on TC degradation over Co-g–C3N4–2 microsphere/PMS system. Moreover, the construction of Co-g–C3N4–2 microspheres not only avoided the release of metal ion from catalyst, but also provided convenience for the recovery of catalyst. In short, current work shared some novel insights into the application of heterogeneous catalysis in persulfate activation for wastewater treatment.

Propargyl carbamate-functionalized Cu(II)-metal organic framework after reaction with chloroauric acid: An x-ray photoelectron spectroscopy data record

A copper-containing metal organic framework was prepared using the new organic linker 5-(2-{[(prop-2-yn-1-yloxy)carbonyl]-amino}ethoxy)isophthalic acid [1,3-H2YBDC (where Y = alkYne and BDC = Benzene DiCarboxylate)] and functionalized with gold particles by reaction with HAuCl4 under thermal treatment in methanol. The resulting system was investigated by complementary techniques to obtain information on its structure and morphology. In the present work, x-ray photoelectron spectroscopy (XPS) was employed to analyze the chemical composition of a representative specimen. Besides wide scan spectra, data obtained by the analysis of the C 1s, O 1s, N 1s, Cu 2p, and Au 4f signals are presented and critically discussed. The results highlight the reduction of Au(III) to mostly Au(I) species. Overall, the data presented herein may act as useful guidelines for the eventual tailoring of material properties and their possible implementation toward functional applications in heterogeneous catalysis.

Surface Organometallic Chemistry as a Versatile Strategy for Synthesizing Supported Bimetallic Cluster Catalysts

Bimetallic clusters anchored on thermally stable and high-surface-area supports have gained a wide range of applications in heterogeneous catalysis. Compared to monometallic clusters or large bimetallic nanoparticles, bimetallic clusters show unprecedented catalytic performances due to the modulated electronic and geometric effects arising from the high fraction of surface unsaturated–coordinated metallic atoms and the synergistic effects between two constituting metals. However, even after more than 60 years of efforts, the controlled synthesis of homogeneously distributed bimetallic clusters with well-alloyed structure between two constituting metals remains a tremendous challenge so far. Herein, we present a versatile strategy based on the surface organometallic chemistry concept for synthesizing supported bimetallic cluster catalysts, which is achieved via the hydrogenation of a so-called “double surface organometallic complex”. The cooperative decomposition of two surface organometallic fragments in the double surface organometallic complex and their strong interaction with the support enable the formation of well-alloyed bimetallic clusters uniformly dispersed at the surfaces of different supports. This approach can serve as a platform technique for producing a variety of bimetallic clusters with varied compositions on a wide range of supports, such as Al2O3, TiO2, and zeolite. The resulting bimetallic cluster catalysts exhibit remarkably enhanced catalytic performance in benzene hydrogenation as compared to their monometallic counterparts because of highly exposed surface atoms and synergistic effects between constituting metals.

Unravelling the Reactivity of Framework Lewis Acid Sites towards Methanol Activation on H-ZSM-5 Zeolite with Solid-State NMR Spectroscopy.

Understanding the acid sites on zeolites is vital for the establishment of catalyst structure-activity relationship and exploration of their potential applications in heterogeneous catalysis. Here, we report the identification of active framework Lewis acid sites on ZSM-5 zeolites. The structures of framework-associated tri-coordinated Al that is bonding with hydroxyl groups are determined by using one- dimensional (1D) 31 P and two-dimensional (2D) 31 P-{27 Al} NMR spectroscopy of trimethylphosphine oxide probe molecule. 2D 13 C-{27 Al} NMR correlation experiments allow the observation of favorable formation of methoxy species on the framework-associated Al Lewis acid sites in methanol reaction at low temperature, which is corroborated by density functional theory calculations. These methoxy species contribute to the further conversion of methanol to hydrocarbons as active C1 species. The results provide new insights into the Lewis acidity of zeolites.

Unravelling the Reactivity of Framework Lewis Acid Sites towards Methanol Activation on H‐ZSM‐5 Zeolite with Solid‐State NMR Spectroscopy

AbstractUnderstanding the acid sites on zeolites is vital for the establishment of catalyst structure–activity relationship and exploration of their potential applications in heterogeneous catalysis. Here, we report the identification of active framework Lewis acid sites on ZSM‐5 zeolites. The structures of framework‐associated tri‐coordinated Al that is bonding with hydroxyl groups are determined by using one‐ dimensional (1D) 31P and two‐dimensional (2D) 31P‐{27Al} NMR spectroscopy of trimethylphosphine oxide probe molecule. 2D 13C‐{27Al} NMR correlation experiments allow the observation of favorable formation of methoxy species on the framework‐associated Al Lewis acid sites in methanol reaction at low temperature, which is corroborated by density functional theory calculations. These methoxy species contribute to the further conversion of methanol to hydrocarbons as active C1 species. The results provide new insights into the Lewis acidity of zeolites.

Highly Stable and Versatile Conjugated Microporous Polymer for Heterogeneous Catalytic Applications

Highly Stable and Versatile Conjugated Microporous Polymer for Heterogeneous Catalytic Applications

Synthesis, Structure, and Heterogeneous Catalysis of a Series of Structurally Diverse Coordination Polymers Based on 5-Nitroisophthalate

Four new coordination polymers have been synthesized based on a mixed-ligand strategy, viz., [Cu(4-ABPT)(HNIPA)2H2O]·H2O, SSICG-1; [Cu2(4-ABPT)2(HNIPA)4]·H2O, SSICG-2; [Ni(4-ABPT)(NIPA)H2O], SSICG-3; and [Zn2(ATRZ)2(NIPA)], SSICG-4 (4-ABPT = 3,5-di(pyridine-4-yl)-4H-1,2,4-triazol-4-amine, H2NIPA = 5-nitroisophthalic acid, and ATRZ = 3-amino-1,2,4-triazole, SSICG stands for the Solid State and Inorganic Chemistry Group at IIT Patna). The copper compounds are one-dimensional, whereas the nickel and zinc compounds are two-dimensional layer compounds. SSICG-3 possesses 4,4-net topology with a Schläfli symbol 44.62, whereas SSICG-4 exhibits a 3,3-net (fes) topology with a Schläfli symbol 4.82. SSICG-1 and SSICG-3 have active metal sites due to the presence of replaceable coordinated water molecules and exhibits efficient catalytic activity for one-pot CO2 cycloadditions. The conversions of SSICG-1 and SSICG-3 for CO2 cycloaddition are 87 and 95% (turnover numbers (TON) of 174 and 190), respectively. The kinetic studies, substrate scope, recyclability, catalyst amount, and temperature dependence studies of the CO2 cycloaddition reaction are discussed. These structurally diverse coordination polymers could contribute to broadening the scope of mixed-ligand coordination polymers for their applications in heterogeneous catalysis.

Periodic Density Matrix Embedding for CO Adsorption on the MgO(001) Surface.

The adsorption of simple gas molecules to metal oxide surfaces is a primary step in many heterogeneous catalysis applications. Quantum chemical modeling of these reactions is a challenge in terms of both cost and accuracy, and quantum-embedding methods are promising, especially for localized chemical phenomena. In this work, we employ density matrix embedding theory (DMET) for periodic systems to calculate the adsorption energy of CO to the MgO(001) surface. Using coupled-cluster theory with single and double excitations and second-order Møller–Plesset perturbation theory as quantum chemical solvers, we perform calculations with embedding clusters up to 266 electrons in 306 orbitals, with the largest embedding models agreeing to within 1.2 kcal/mol of the non-embedding references. Moreover, we present a memory-efficient procedure of storing and manipulating electron repulsion integrals in the embedding space within the framework of periodic DMET.

Nucleobases-derived carbon materials: Synthesis and application in heterogeneous catalysis

Natural nitrogen-heterocycles biomolecules have been widely used in the construction of supramolecular self-assemblies due to their abundant resources and multiple interaction sites, such as hydrogen bonding, π-π stacking, van der Waals forces. Herein, we propose a quite innovative strategy to produce two-dimensional (2D) carbon materials by direct pyrolysis of various nucleobases (e.g. guanine, adenine, uracil, cytosine xanthine, and hypoxanthine). These nucleobases can pre-organize a planar network structure through hydrogen bonding interaction. The multiple hydrogen-bonding can be stable at relatively high temperature, which limits C–C or C-N cleavage and formation in a 2D space. These 2D carbons show desirable features with highly sp2-conjugation, tunable heteroatom contents, and ultrathin thickness, without the need of any template or additional purification. Meanwhile, differences in internal structure allow easy control of the morphology of 2D carbons, porosity and surface chemical functionality at the molecular level. Moreover, the as-synthesized 2D carbons display very promising electrocatalytic ORR performance and catalytic performance for selective oxidization of ethylbenzene. Given the diversity in the structure of the nucleobase moiety, they represent ideal building blocks for the catalyst-free and metal-free formation of 2D carbon architectures.

Post-Modification of Copolymers Obtained by ATRP for an Application in Heterogeneous Asymmetric Salen Catalysis.

Copolymers are valuable supports for obtaining heterogeneous catalysts that allow their recycling and therefore substantial savings, particularly in the field of asymmetric catalysis. This contribution reports the use of two comonomers: Azido-3-propylmethacrylate (AZMA) bearing a reactive azide function was associated with 2-methoxyethyl methacrylate (MEMA), used as a spacer, for the ATRP synthesis of copolymers, and then post-functionalized with a propargyl chromium salen complex. The controlled homopolymerization of MEMA by ATRP was firstly described and proved to be more controlled in molar mass than that of AZMA for conversions up to 63%. The ATRP copolymerization of both monomers made it possible to control the molar masses and the composition, with nevertheless a slight increase in the dispersity (from 1.05 to 1.3) when the incorporation ratio of AZMA increased from 10 to 50 mol%. These copolymers were post-functionalized with chromium salen units by click chemistry and their activity was evaluated in the asymmetric ring opening of cyclohexene oxide with trimethylsilyl azide. At an equal catalytic ratio, a significant increase in enantioselectivity was obtained by using the copolymer containing the largest part of salen units, probably allowing, in this case, the more favorable bimetallic activation of both the engaged nucleophile and electrophile. Moreover, the catalytic polymer was recovered by simple filtration and re-engaged in subsequent catalytic runs, up to seven times, without loss of activity or selectivity.

Synthesis, Spectro Chemical Investigation of 4-Methyl Benzylamine Schiff Base Metal Complexes and Its Biological Studies

Schiff bases and their complexes are versatile compounds synthesized from the condensation of an amino compound with carbonyl compounds and widely used for industrial purposes and also exhibit a broad range of biological activities including antifungal, antibacterial, anti-malarial, anti-proliferative, anti-inflammatory, antiviral, and antipyretic properties. Many Schiff base complexes show excellent catalytic activity in various reactions in the presence of moisture. Over the past few years, there have been many reports on their applications in homogeneous and heterogeneous catalysis. The influence of certain metals on the biological activity of these compounds and their intrinsic chemical interest as multidentate ligands has prompted a considerable increase in the study of their coordination behaviour. Development of a new chemotherapeutic Schiff bases and their metal complexes is now attracting the attention of medicinal chemists. Primary benzylamines are highly important building blocks in the pharmaceutical and polymer industry. The present paper deals with the synthesis and characterization of metal complexes of new Schiff bases derived from 4-Methyl Benzylamine. The bidentate ligand is derived from the inserted condensation of 4-Methyl Benzylamine with 2-hydroxybenzaldehyde (OHB) in a 1:1 molar ratio. Using this bidentate ligand, complexes of Zn (II), Cd (II) with general formula ML2 have been synthesized. The synthesized complexes were characterized by several techniques using IR, 1HNMR and Mass analysis. Infrared spectral data indicate the coordination between ligand and central metal ion through deprotonated phenolic oxygen and azomethine nitrogen. In addition, the authors have screened the compounds for biological activity. It was found that the compounds have shown activity against the organisms like Candida albicans, Bacillus subtilis and Salmonella typhi.

NiyCo2-yP alloy catalysts with assistance of Y for boosting Low-pressure hydrogenation transformation of Biomass-derived levulinic acid or furfural in water

Acquiring practical catalysts was crucial for promoting the application of advanced chemical transformations. Here, a series of Co-Ni-P catalysts with addition of Y were designed for hydrogenation transformation of biomass-derived levulinic acid (LA) or furfural (FAL) in water. The molar-composition-manipulated catalysts were characterized in Co-Ni phosphide alloy nanostructure with YPO4 enriched on surface and denoted as (YPO4)x/CoyNi2-yP. By comprehensive catalytic measurements, both Co:Ni ratio in phosphide alloy and amount of YPO4 were testified to be key factors to modulate intrinsic catalytic properties (hydrogen activation and acid catalysis) along Y-Co-Ni-P interface, the attractive and reproducible yield for desired product γ-valerolactone (up to 98 %) or cyclopentanone (up to 93%) could achieve under low H2 pressure of 0.1–0.5 MPa over the well modulated catalyst (YPO4)0.2/Co1.0Ni1.0P in comparison with high H2 pressure (beyond 1.0 MPa) required in most of literature systems, indicating that the efficiency and feasibility of these important biomass transformations could be greatly enhanced on the low-cost and robust (YPO4)x/CoyNi2-yP catalysts. These findings suggested that the phosphide-alloy engineering technique provided in this work could serve as a novel and practical method for innovating competitive catalysts to boost advanced heterogeneous catalysis applications as well as current aqueous hydrogenation transformations of biomass derivatives.

Immobilized iron functionalised imidazolium-based ionic liquid: Solvent-free and recoverable heterogeneous catalytic application for the synthesis of amines under green conditions

We reported solvent-free and recoverable heterogeneous iron functionalised imidazolium-based ionic liquid for the reduction of nitroarene derivatives in the presence of formic acid under greener conditions. Additionally, the experimental result shows that the iron complex could be an extremely resourceful, high rate and reusable catalyst for a different nitroarene substrate.

Addressing the quantitative conversion bottleneck in single-atom catalysis

Single-atom catalysts (SACs) offer many advantages, such as atom economy and high chemoselectivity; however, their practical application in liquid-phase heterogeneous catalysis is hampered by the productivity bottleneck as well as catalyst leaching. Flow chemistry is a well-established method to increase the conversion rate of catalytic processes, however, SAC-catalysed flow chemistry in packed-bed type flow reactor is disadvantaged by low turnover number and poor stability. In this study, we demonstrate the use of fuel cell-type flow stacks enabled exceptionally high quantitative conversion in single atom-catalyzed reactions, as exemplified by the use of Pt SAC-on-MoS2/graphite felt catalysts incorporated in flow cell. A turnover frequency of approximately 8000 h−1 that corresponds to an aniline productivity of 5.8 g h−1 is achieved with a bench-top flow module (nominal reservoir volume of 1 cm3), with a Pt1-MoS2 catalyst loading of 1.5 g (3.2 mg of Pt). X-ray absorption fine structure spectroscopy combined with density functional theory calculations provide insights into stability and reactivity of single atom Pt supported in a pyramidal fashion on MoS2. Our study highlights the quantitative conversion bottleneck in SAC-mediated fine chemicals production can be overcome using flow chemistry.

Emerging Ultrahigh‐Density Single‐Atom Catalysts for Versatile Heterogeneous Catalysis Applications: Redefinition, Recent Progress, and Challenges

In recent years, single‐atom catalysts (SACs) with high metal loading have emerged in different heterogeneous catalysis fields and shown extraordinary catalytic properties. When there are enough coordination atoms (or functional groups) on the supports, it is possible to achieve a limit monolayer atom loading on the surface of supports with ultrahigh atom density (5–15 atoms nm−2) and extremely close site distance (0.2–0.5 nm), by using appropriate synthesis methods and procedures. These high‐density metal atoms usually have no or less metal bonds, which are mostly isolated by support atoms to form 3D foam‐like atomic constructions. Herein, a new notion of metal atomic foam catalysts (AFCs) is propsed to redefine these ultrahigh‐density SACs accommodated by specific supports. This new paradigm of 3D atomic construction for SACs has potential significance for both theoretical research and industrial applications. The latest major advancements in the controllable synthesis of AFCs on various supports (e.g., polymer, carbon, and metallic compound) via different methods (bottom‐up or top‐down approaches) are summarized. The latent catalytic principles and typical application cases of AFCs are emphasized in a wide range of heterogeneous catalysis fields (e.g., thermocatalysis, photocatalysis, electrocatalysis, etc.). The challenges and prospects of this newly 3D ultrahigh‐density AFCs materials in practical industrial application are pointed out as well.