Evident Loss Of Activity Research Articles

Stable Pt/MgAl2O4 catalysts for efficient production of H2 from cyclohexane dehydrogenation

Cyclohexane as liquid organic hydrogen carriers has attracted considerable interest in the field of hydrogen storage technology. However, the innovation of efficient catalyst for producing H2 through cyclohexane dehydrogenation remains a substantial challenge. In this study, we have successfully developed Pt/MgAl2O4 catalysts exhibiting outstanding catalytic performance in cyclohexane dehydrogenation. Notably, the optimal catalyst Pt/MgAl2O4-700 achieves cyclohexane conversion of 89.1 % and benzene selectivity of over 99 % at 345 °C, resulting in a high hydrogen evolution rate of 933 mmol/gPt/min. Moreover, this catalyst exhibits remarkable long-term stability, with no evident loss of activity in 225-hour dehydrogenation reaction. The catalyst was characterized by XRD, N2 adsorption–desorption, STEM, XPS, NH3-TPD, CO-FTIR and H2-TPR techniques, which provides detailed structure information for elucidation of structure–activity relationship. The spinel structure and moderate acid density of the support enable highly dispersed Pt species at the surface of MgAl2O4. This results in the formation of ultra-small and sintering-resistant Pt particles that exhibit exceptional activity in cyclohexane dehydrogenation. Additionally, the presence of positively charged Ptδ+ species in Pt/MgAl2O4 facilitates the rapid desorption of benzene product. This effectively prevents the formation of coke arising from benzene dehydrogenation, which ensures to achieve high stability. These findings provide valuable knowledge for the rational design of efficient metal-based catalysts for liquid organic hydrogen carriers in hydrogen storage systems.

Synthesis of DPA-triazole structures and their application as ligand for metal catalyzed organic reactions

In this work, the use of DPA-triazole (DPA = dipicolylamine) molecules as ligands for metal catalyzed organic reactions has been investigated. A small library of ligands has been prepared by a CuAAC (click reaction) between propargyl-DPA and different azides. For a selected ligand the complexation with Zn(II) in solution has been investigated by NMR and MS. DFT calculation supported the structure of the complex as revealed by NMR data. The ligand was then used for metal-catalyzed organic transformation. The Henry reaction between nitromethane and aromatic aldehydes was efficiently catalyzed by the Zn(II)-DPA-triazole complex with only 2 mol% of catalyst. Changing the metal from Zn(II) to Cu(II), the system proved to be effective in the formation of acetals from the reaction of aldehydes and methanol or ethanol, thus revealing the versatility of the DPA-triazole ligand. Finally, a soluble polymer-supported ligand was used in the Zn(II) catalyzed Henry reaction, allowing for the recovery and reuse of the catalyst up to five times without evident loss of activity.

Hydrogenative coupling of nitriles with diamines to benzimidazoles using lignin-derived Rh2P catalyst

SummaryNitrile (C≡N bond) activation for direct organic synthesis has been less explored so far due to a high redox potential of nitrile and its low dissociation energy of C−CN bond. Herein, we demonstrate a direct reductive coupling of nitriles and 1,2-phenylenediamines to yield various benzimidazoles in excellent yields (95%–99%) by using rhodium phosphide (Rh2P) catalyst supported on lignin-derived carbon (LC) using H2 (or hydrazine hydrate) as a hydrogen source. The high catalytic performance of Rh2P/LC is attributed to enhanced charge transfer to Rh and strong P−Rh interactions. Our isotope trace experiment confirms the presence of H/D exchange between H2 and the inert –CD3 group of CD3CN via an intramolecular D-shift. Reusability of Rh2P/LC is further demonstrated by a seven-time recycling without evident loss of activity. This research thus highlights a great potential in organic transformation with nitrile as a synthetic building block.

Hydrogenative Coupling of Nitriles with Diamines to Benzimidazoles Using Lignin-Derived Rh <sub>2</sub>p Catalyst

Nitrile is frequently high-available as commodity chemicals; however, nitrile (CΞN bond) activation for direct organic synthesis has been less explored so far due to a high redox potential of nitrile and its low dissociation energy of C-CN bond. Herein, we demonstrate a direct reductive coupling of nitriles and 1,2-phenylenediamines to yield various benzimidazoles in excellent yields (95%-99%) by using lignin-derived rhodium phosphide (Rh2P) catalyst with H2 (or hydrazine hydrate) as hydrogen sources. The high catalytic performance of Rh2P/LC is attributable to enhanced charge transfer on Rh site as well as strong interactions between P and Rh. Our isotope trace experiment confirms the presence of H/D exchange between H2 and the inert –CD3 group of CD3CN via an intramolecular D-shift. Reusability of Rh2P/LC is demonstrated by seven-time recycling without evident loss of activity. This research thus highlights a vast potential in organic transformation with nitrile as a synthetic building block.

Hydroformylation of natural olefins with the [Rh(COD)(μ-OMe)]2/TPPTS complex in BMI-BF4/toluene biphasic medium: Observations on the interfacial role of CTAB in reactive systems

The complex [Rh(COD)(μ-OMe)]2 in presence of TPPTS (TPPTS = triphenylphosphinetrisulfonate) was evaluated as catalyst precursor for the in situ hydroformylation of natural olefins (eugenol, estragole and safrole) in biphasic media BMIm-BF4/toluene. Under moderate reaction conditions, the substrates showed the following reactivity order: eugenol > estragole > safrole. The rhodium system showed a high activity and selectivity towards the desired aldehydes. It was found that the use of cetyltrimethylammoniun bromide (CTAB) as phase transfer agent inhibits the hydroformylation reaction. The catalytic phase can be recycled up to four times without evident loss of activity or selectivity. In this work we report the use of an ionic liquid with hydrophilic character, without using water in the reaction medium.

Metal-Free H2 Activation for Highly Selective Hydrogenation of Nitroaromatics Using Phosphorus-Doped Carbon Nanotubes.

We reported that phosphorus-doped carbon nanotubes (P-CNTs), showing metal-like properties, can efficiently promote metal-free hydrogenation of nitrobenzene (1a) to aniline (2a) using molecular hydrogen (H2) as a reducing reagent under very mild conditions with a reaction temperature of only 50 °C. The kinetics of 1a hydrogenation over P-CNT reveals that the hydrogenation rate of 1a is a first-order dependence on the H2 pressure and the P-CNT loading level, and a zero-order dependence on 1a concentration, demonstrating the rate-determining step of H2 adsorption and activation over P-CNT. The activation energy of P-CNT-catalyzed 1a hydrogenation is 43 ± 3 kJ mol-1 with the turnover frequency around 3.60 ± 0.12 h-1 at 50 °C. In addition to 1a, the general applicability of the P-CNT-promoted metal-free hydrogenation process is further demonstrated by applying various functionalized nitroaromatics with wide industrial interest. The P-CNT shows both excellent yields and selectivities to hydrogenation with respect to reducible, labile, and strong leaving groups on the nitroaromatics molecules. The stability and reusability of the P-CNT demonstrate up to eight-time recycling without evident loss of activity and selectivity. In addition to hydrogenation, metal-free catalytic transfer hydrogenation of 1a is achieved with P-CNT using diverse hydrogen sources, including hydrazine hydrate (N2H4·H2O), carbon monoxide/water (CO/H2O), and formic acid/triethylamine (HCOOH/Et3N).

Reductive Amination of Carbonyl Compounds with Ammonia and Hydrogenation of Nitriles to Primary Amines with Heterogeneous Cobalt Catalysts

Reductive amination of aldehydes/ketones with aqueous NH3 and hydrogenation of nitriles to primary amines with Co catalysts were reported. Co@NC-700 exhibited remarkable activity and high selectivity for the reductive amination of aldehydes/ketones with aqueous NH3 and the hydrogenation of nitriles to primary amines. Several primary amines can be obtained with good to excellent yields via the reductive amination of aldehydes/ketones and the hydrogenation of nitriles. The nitrogen-doped carbon(C)-supported Co@NC-700 metal catalyst was prepared via the pyrolysis of bioMOF Co/adenine in activated C. Co@NC-700 can be reused five times without evident loss of activity.

Atmospheric hydrogenation of α, β-unsaturated ketones catalyzed by highly efficient and recyclable Pd nanocatalyst

A thermoregulated phase-transfer Pd nanocatalyst was explored firstly and shown to be highly efficient and recyclable in the atmospheric hydrogenation of α, β-unsaturated ketones. Under optimized reaction conditions, the conversion of chalcone and the selectivity of dihydrochalcone were 99% and 98%, respectively. The catalyst can be easily separated from the product and used directly for four times without evident loss in activity and selectivity. The turnover frequency (TOF) for the atmospheric hydrogenation of chalcone was 870 h−1, which to the best of our knowledge was the highest value ever reported among transition metal nanocatalysts.

Efficient Electrochemical Production of Syngas from CO2 and H2O by using a Nanostructured Ag/g‐C3N4 Catalyst

AbstractA new series of electrocatalysts consisting of Ag nanoparticles supported on graphitic carbon nitride (g‐C3N4) are presented. The combination of nanostructured silver and a carbon nitride support results in the direct generation of synthesis gas (CO+H2) during the electrocatalytic reduction of CO2 in water. By using a state‐of‐the‐art electrocatalytic setup, the influence of different operation parameters over the final product composition is shown. The H2/CO product ratio can easily be tuned from 100:1 to 2:1 with high reproducibility by controlling the applied potential and the Ag loading. More importantly, long‐term and catalyst reuse experiments demonstrate the robustness of these electrodes, which could be operated for over 20 h time on stream and reused several times without any evident loss of activity or selectivity. Our results highlight the potential of nanostructuring Ag‐based catalysts and the relevance of the selected support for the green valorization of CO2.

One-Pot Three-Component Synthesis of 2,3-Dihydroquinazolin-4(1H)-Ones in the Presence of a Molecular Sieve Supported Lanthanum Catalyst

A series of 2,3-dihydroquinazolin-4(1H)-ones have been synthesized with good to excellent yields by one-pot reaction using isatoic anhydride, aldehydes, and ammonium acetate or amines in acetonitrile in the presence of 4 A molecular sieve modified with lanthanum(III) as an efficient heterogeneous catalyst. The catalyst could be reused without evident loss of activity.

Boronic acids as efficient cross linkers for PVA: synthesis and application of tunable hollow microspheres in biocatalysis

Herein is reported an innovative and reproducible systemic approach for the fabrication of customized 3D hollow microspheres of polyvinyl alcohol (PVA) based on the use of aromatic boronic acids (ABAs) as crosslinkers. A dedicated experimental set-up was developed to enable microsphere formulation. Most of the boronic acids tested were able to produce hollow microspheres. Depending on the ABA used and the production conditions, hollow PVA/ABA microspheres with different morphologies, mass transfer characteristics and unprecedented thermal (up to 121 °C) stability were obtained. The crosslinking temperature proved to be an operational parameter to control membrane thickness. The hollow microspheres were evaluated in biocatalysis, with naringin hydrolysis as model system, using encapsulated naringinase. The results highlighted a naringinase high operational stability, namely in PVA microspheres crosslinked with 1,4-phenylenediboronic acid and with phenylboronic acid, with no evident loss of activity throughout seven consecutive runs, theoretically resulting in an infinite half-life.

Oxidation of organosilanes with nanoporous copper as a sustainable non-noble-metal catalyst.

Although many noble-metal catalysts have been used for the oxidation of organosilanes, there has been less success with non-noble-metal catalysts. Here, unsupported nanoporous copper (np-Cu) is used to catalyze the oxidation of organosilanes under mild conditions. It is the first time that this reaction has been achieved with a heterogeneous copper catalyst with high activity and selectivity. Both water and alcohols are used as oxidants and the corresponding organosilanols and organosilyl ethers are obtained in high yield. The possible mechanism was obtained by kinetic studies. The catalyst could be reused at least five times without evident loss of activity. As a novel green catalyst np-Cu should play a unique role in organic synthesis.

Thermoregulated phase-transfer Rh nanoparticle catalyst for selective hydrogenation of ortho-chloronitrobenzene

The use of a thermoregulated phase-transfer Rh nanoparticle catalyst for the selective hydrogenation of ortho-chloronitrobenzene (o-CNB) to ortho-chloroaniline (o-CAN) in an aqueous/1-pentanol biphasic system was studied. Under the optimized reaction conditions, the conversion of o-CNB and the selectivity for o-CAN were 100% and 98%, respectively. The catalyst was easily separated from the product by phase separation and reused eight times without evident loss of activity and selectivity.

Highly selective oxidation of organosilanes with a reusable nanoporous silver catalyst

Room temperature highly selective oxidation of organosilanes to organosilanols and organosilyl ethers is achieved in liquid-phase with dealloyed nanoporous silver catalysts. In both cases, aromatic and aliphatic silanes can be effectively converted into the corresponding silanols and silyl ethers by using water and alcohols as oxidant, respectively. Moreover, hydrogen gas is the only by-product and the catalyst can be recycled for several times without evident loss of activity and selectivity.

Synthesis of ∆3-2-Hydroxybakuchiol Analogues and Their Growth Inhibitory Activity against Rat UMR106 Cells

A series of ∆3-2-hydroxybakuchiol analogues have been synthesized and tested for their growth inhibitory activity against rat UMR106 cells by using the MTT method. Some of them exhibit enhanced activities compared with the natural product, and the preliminary SAR profile shows that the chain tail on the natural product could be subtly modified to enhance the activity and the aromatic moiety or the terminal olefin on the main chain can also be modified without any evident loss of activity. The stereo-configuration of the quaternary chiral center has an important influence on the activity.

ChemInform Abstract: An Approach to the Paal—Knorr Pyrroles Synthesis in the Presence of β‐Cyclodextrin in Aqueous Media.

Abstract An efficient and facile method for the synthesis of N-substituted pyrroles in moderate to good yields by the Paal–Knorr reaction of γ-diketones with amines in the presence of β-cyclodextrin in aqueous media has been developed. Moreover, this process tolerated diamines (e.g., para-, meta- or ortho-phenylenediamine) to construct bis-pyrrole or mono-pyrrole derivates. β-Cyclodextrin can be recovered easily after the reactions and reused without evident loss in activity.

Rh Nanoparticle Catalyzed Hydroaminomethylation of 1-Octene in Thermoregulated Ionic Liquid and Organic Biphasic System

Thermoregulated ionic liquid and organic biphasic system composed of ionic liquid [CH3(OCH2 CH2)22N+Et3][CH3SO3-] (abbreviated as IL(PEG1000)) containing IL(PEG1000)-stabilized Rh nanoparticles and organic solvent, which allows for not only highly efficient homogeneous reaction but also an easy biphasic separation, was applied to the hydroaminomethylation of 1-octene for the first time. Under the optimized conditions, the conversion of 1-octene and the amine selectivity were 100% and 90%, respectively. After reaction, the Rh nanoparticle catalyst could be easily separated by simple decantation and reused for four times without evident loss in activity.

An approach to the Paal–Knorr pyrroles synthesis in the presence of β-cyclodextrin in aqueous media

Abstract An efficient and facile method for the synthesis of N-substituted pyrroles in moderate to good yields by the Paal–Knorr reaction of γ-diketones with amines in the presence of β-cyclodextrin in aqueous media has been developed. Moreover, this process tolerated diamines (e.g., para-, meta- or ortho-phenylenediamine) to construct bis-pyrrole or mono-pyrrole derivates. β-Cyclodextrin can be recovered easily after the reactions and reused without evident loss in activity.

Highly efficient and recyclable ruthenium nanoparticle catalyst for semihydrogenation of alkynes

Abstract Ru nanoparticles were used as catalysts for semihydrogenation of alkynes for the first time. Poly(ethylene glycol) (PEG)-stabilized Ru nanoparticles were used as catalysts for semihydrogenation of various terminal alkynes in thermoregulated PEG biphasic system, which allows for not only an efficient homogeneous catalytic reaction, but also an easy biphasic separation and reuse of catalyst. Under the optimized conditions, various terminal alkynes were hydrogenated to the corresponding alkenes with high selectivity. After reaction, the Ru nanoparticle catalyst could be separated from products by simple phase separation and recycled for ten times without evident loss in activity and selectivity.

Thermoregulated poly(ethylene glycol) biphasic system with Pd nanoparticle catalysts for selective hydrogenation of cinnamaldehyde

Poly(ethylene glycol) (PEG)-stabilized Pd nanoparticles were prepared by simple hydrogen reduction of PdNa 2 Cl 4 · x H 2 O in the presence of PEG 4000 (PEG with an average molecular mass of 4000 g/mol). These were shown to be efficient and recyclable catalysts for the selective hydrogenation of cinnamaldehyde in a thermoregulated PEG biphasic system, which allows for an efficient homogeneous catalytic reaction, easy biphasic separation and catalyst reuse. Under optimized reaction conditions, the conversion of cinnamaldehyde and the selectivity of hydrocinnamaldehyde (HCAL) were 99% and 98%, respectively. The PEG 4000 -stabilized Pd nanoparticle catalyst could be easily separated from the product by phase separation and reused eight times without evident loss of activity and selectivity. 将具有“高温混溶、室温分相”功能的聚乙二醇4000(PEG 4000 )与甲苯-正庚烷组成的两相体系用于纳米钯催化的肉桂醛选择性加氢反应中. 在优化的反应条件下, 14;肉桂醛转化率和氢化肉桂醛选择性分别为99%和98%. 钯纳米催化剂经简单分相即可与产物分离, 14;且循环使用8次, 14;其活性和选择性基本保持不变. 14; Poly(ethylene glycol)-stabilized Pd nanoparticles were demonstrated to be efficient and recyclable catalysts for the selective hydrogenation of cinnamaldehyde in a thermoregulated PEG biphasic system.