Platform For Heterogeneous Catalysis Research Articles

Porous Salts as Platforms for Heterogeneous Catalysis (Small 30/2023)

Porous Salts as Platforms for Heterogeneous Catalysis (Small 30/2023)

Porous Salts as Platforms for Heterogeneous Catalysis.

The preparation of a new class of reactive porous solids, prepared via straightforward salt metathesis reactions, is described here. Reaction of the dimethylammonium salt of a magnesium-based porous coordination cage with the chloride salt of [CrII Cl(Me4 cyclam)]+ affords a porous solid with concomitant removal of dimethylammonium chloride. The salt consists of the ions combined in the expected ratio based on their charge as confirmed by UV-vis and X-ray photoelectron spectroscopies, ion chromatography (IC), and inductively coupled plasma mass spectrometry (ICP-MS). The porous salt boasts a Brunauer-Emmett-Teller (BET) surface area of 213m2 g-1 . Single crystal X-ray diffraction reveals the chromium(II) cations in the structure reside in the interstitial space between porous cages. Importantly, the chromium(II) centers, previously shown to react with O2 to afford reactive chromium(III)-superoxide adducts, are still accessible in the solid state as confirmed by UV-vis spectroscopy. The site-isolated reactive centers have competence toward hydrogen atom abstraction chemistry and display significantly increased stability and reactivity as compared to dissolved ions.

Few-atom-layer metallene quantum dots toward CO2 electroreduction at ampere-level current density and Zn-CO2 battery

Electrocatalytic CO 2 reduction reaction (CO 2 RR) toward commodity chemicals and fuels presents an enticing prospect wherein the emerging metallenes as catalysts have aroused great interest. Here, we report the synthesis of a kind of tiny metallene quantum dot (QD) called the stanene QD (Sn-ene QD), which features a few atom layers and rich edge centers and provides superior CO 2 RR activity by delivering ampere-level current densities with near-unity selectivity for formate production. Operando attenuated total reflection-infrared (ATR-IR) spectroscopy and theoretical calculations deciphered that the rich edge centers of Sn-ene QDs hold high reactivity, and the residual cyano ligands with electron-withdrawing nature favor the stabilization of the CO 2 RR intermediate. Furthermore, the Zn-CO 2 battery assembled with Sn-ene QDs catalyst affords a high power density of 1.25 mW cm −2 and an outstanding stability of ∼100 h. This work highlights the great potential of metallene QDs as a new platform for heterogeneous catalysis and energy conversion. • Few-atom-layer stanene quantum dots (Sn-ene QDs) with rich edge centers were prepared • Sn-ene QDs afford a superior activity toward CO 2 electroreduction to formate • The rich edge centers of Sn-ene QDs were deciphered to hold a high reactivity • Sn-ene QDs show excellent Zn-CO 2 battery performance Metallenes, the newly emerging two-dimensional metallic materials of atomic thickness, have been regarded as ascendant CO 2 RR electrocatalysts because of their plentiful accessible atoms and unique catalytic properties. When the lateral size of metallenes reduces to less than 10 nm, producing metallene quantum dots (QDs), the edge atoms with lower coordination numbers will occupy a large portion of the total atoms, which could exhibit a higher catalytic performance. Here, we delicately fabricated the few-atom-layer stanene QDs with rich edge centers via an in situ electrochemical reduction strategy. Such a unique metallene QD catalyst affords an excellent performance for CO 2 electroreduction to formate and Zn-CO 2 batteries. Few-atom-layer stanene quantum dots with rich edge centers are pioneeringly fabricated by a fast electrochemical self-reconstruction strategy and are shown to afford an excellent electrocatalytic performance for CO 2 electroreduction to formate and Zn-CO 2 batteries.

Sonosynthesis of pyranochromenes and biscoumarins catalyzed by Co3O4/NiO@GQDs@SO3H nanocomposite

Co3O4/NiO@GQDs@SO3H nanocatalyst has been used as an effective catalyst for the preparation of dihydropyrano[3,2-c]chromenes and biscoumarins under ultrasonic irradiations in ethanol. The catalyst has been characterized by FT-IR, XRD, SEM, EDS, BET, TGA, XPS and VSM. Atom economy, reusable catalyst, low catalyst loading, applicability to a wide range of substrates, high yields of products, and applying the sonochemical methodology as an efficient method and innocuous means of activation in synthetic chemistry for the preparation of medicinally privileged heterocyclic molecules are some of the substantial features of this method. The present catalytic procedure is extensible to a wide diversity of substrates for the synthesis of a variety-oriented library of pyranochromene and biscoumarins. The ultrasound approach decreases times, increases yields of products by creating the activation energy in micro surroundings. Meanwhile, this recoverable catalyst will provide a regular platform for heterogeneous catalysis, green chemistry, and environmentally benign protocols in the near future.

Hierarchical quasi waxberry-like Ba5Si8O21 microspheres: Facile green rotating hydrothermal synthesis, formation mechanism and high adsorption performance for Congo red

Towards the imperative water contamination by organic dyes, uniform hierarchical quasi waxberry-like Ba5Si8O21 microspheres (diameter: 0.65–1.30 µm) consisted of nanorods have been successfully synthesized via a facile eco-friendly and cost-effective rotating hydrothermal process (120 °C, 6.0 h) without any organic additives, templates or surfactants, using abundant BaCl2·2H2O and Na2SiO3·9H2O as the raw materials. Based on the impacts of the process parameters, a probable heat and mass transport enhanced rotating hydrothermal formation mechanism is proposed. The rotating homogeneous hydrothermal reactor provides vigorous macro- and micro-mixing of the solid and solution phase, thus favors the early stage dissolution-recrystallization, formation of the product nuclei at lower temperature, and final self-assembly for uniform waxberry-like microspheres with miniaturization of size. When employed as the adsorbents for the elimination of Congo red (CR) from simulated waste water, the adsorption data are well fitted with Langmuir isothermal model (qm: 1238.7 mg g−1). Meanwhile, the adsorption of CR is well described by the pseudo-second-order kinetic and intra-particle diffusion models, indicating the final diffusion at equilibrium stage within the mesopores of the real rate-limiting step in the whole adsorption process. The recycling test further confirms the Ba5Si8O21 microspheres as highly efficient adsorbents with satisfactory stability and reusability. As a noteworthy methodology, the heat and mass transport enhanced rotating hydrothermal synthesis presents new insights into the hierarchical porous silicate microspheres as a competitive candidate adsorbent for organic dyes removal, and also a potential new platform for heterogeneous catalysis.

Catalytic nanoliths

The nanoporous anodic aluminum oxide (AAO) structure is shown to be a useful platform for heterogeneous catalysis. By appropriately masking the perimeter during anodization and etching, the AAO can be formed at the center of an aluminum disc. The remaining aluminum ring connects seamlessly to the AAO and provides mechanical support for convenient handling. The supported AAO can be sealed in a standard fitting so that the nanopores in the structure function as an array of tubular reactors, i.e. a nanolith. Coating the walls with catalytically active materials turns the nanolith into a novel catalytic system. For the oxidative dehydrogenation (ODH) of cyclohexane, the nanolith catalytic system is superior to a conventional powdered catalyst in terms of both efficiency and in reducing over oxidation. A simple analysis of the flow through the nanolith combined with experimental data indicates that mass transfer through the nanopores follows a mixed flow model.

Entrapment of an Organometallic Complex within a Metal: A Concept for Heterogeneous Catalysis

A novel family of composite materials, organically doped metals, has been recently introduced. Here, we demonstrate their use as a new platform for heterogeneous catalysis, namely the doping of a metal with a catalytic organometallic complex. Specifically, a rhodium(I) catalyst, (RhCl(COD)(Ph2P(C6H4SO3Na))), ([Rh]), was physically entrapped within silver, thus creating a new type of catalytic material: [Rh]@Ag. Several aspects were demonstrated with the development of this heterogeneous catalyst: a metal can be used as a support for heterogenizing a homogeneous catalyst; the homogeneous catalyst is stabilized by the entrapment within the metal; the products of the composite catalyst are different compared to those obtained from the homogeneous one; and the adsorption of [Rh] on the surface of Ag and its entrapment are very different processes only the latter provided appreciable catalytic activity. Thus, while homogeneous [Rh] was entirely destroyed after converting styrene to ethylbenzne at 50%, [Rh]@Ag remained active after effecting the same reaction to a yield of 85% (compared to only 7% for [Rh] adsorbed on Ag), and while homogeneous [Rh] hydrogenated diphenylacetylene to bibenzyl (and was completely deactivated after one cycle) with no trace of cis-stilbene, [Rh]@Ag afforded that compound as the main product and could be reused.