Olefin Metathesis in Confinement: Towards Covalent Organic Framework Scaffolds for Increased Macrocyclization Selectivity

Covalent organic frameworks (COFs) offer vast structural and chemical diversity enabling a wide and growing range of applications. While COFs are well-established as homogeneous catalysts, so far, their high and ordered porosity has scarcely been utilized to its full potential when it comes to spatially confined reactions in COF pores to alter the outcome of reactions. Here, we present a highly porous and crystalline, large-pore COF as catalytic support in diene ring-closing metathesis reactions, leading to increased macrocylization selectivity. COF pore-wall modification by immobilization of a Grubbs-Hoveyda-type catalyst via a mild silylation reaction provides a molecularly precise heterogeneous metathesis catalyst. An increased macro(mono)cyclization (MMC) selectivity over oligomerization (O) for the heterogeneous COF-catalyst (MMC:O = 1.30) of up to 44% compared to the homogeneous catalyst (MMC:O = 0.90) was observed along with a substrate-size dependency in selectivity, pointing to diffusion limitations induced by the pore confinement.

Alginate/Banana Waste Beads Supported Metal Nanoparticles for Efficient Water Remediation

Water pollution is considered a perilous issue that requires an immediate solution. This is largely because of the strong correlation between the global population increase and the amount of waste produced (most notably food waste). This project prompts the conversion of food waste into useful materials that can be used with sodium alginate as a catalytic support for metal nanoparticles. Sodium alginate/banana peel (Alg/BP) beads were prepared simply using an eco-friendly method. The prepared materials were modified using nanostructured materials to enhance their characteristics. Alg/BP beads were employed as adsorbents for metals that were then treated with sodium borohydride to produce MNPs@Alg/BP. Different MNPs@Alg/BP (MNPs = Ag, Ni, Co, Fe, and Cu) were used as catalysts for reducing 4-nitrophenol (4-NP) by NaBH4 to evaluate each catalyst performance in a model reaction. The results exhibited that Cu@Alg/BP was most efficient toward complete transformation of 4-NP. Therefore, Cu@Alg/BP was also used as a catalyst for the reduction of potassium ferricyanide, congo red, methyl orange (MO), and methylene blue. It was found that Cu@Alg/BP beads catalytically reduced up to 95–99% of above pollutants within a few minutes. Cu@Alg/BP beads were more selective in reducing MO among the pollutants. The catalytic activity of Cu@Alg/BP was examined by evaluating the impact of numerous parameters on MO reduction. The results are expected to provide a new strategy for the removal of inorganic and organic water contaminants based on efficient and low-cost catalysts.

Laminar N-Doped Carbon Materials from a Biopolymer for Use as a Catalytic Support for Hydrodechlorination Catalysts

Nitrogen-doped porous carbons were prepared using a chitosan biopolymer as both a carbon and nitrogen precursor and metallic salts (CaCl2 and ZnCl2-KCl) as a templating agent with the aim of evaluating their performance as catalyst supports. Mixtures of chitosan and templating salts were prepared by simple grinding subjected to pyrolysis and finally washed with water to remove the salts. The resulting materials were characterized, showing that homogeneous nitrogen doping of carbon was achieved (7–9% wt.) thanks to the presence of a nitrogen species in the chitosan structure. A lamellar morphology was developed with carbon sheets randomly distributed and folded on themselves, creating slit-shaped pores. Substantial porosity was observed in both the micropore and mesopore range with a higher surface area and microporosity in the case of the materials prepared by ZnCl2-KCl templating and a larger size of mesopores in the case of ZnCl2. Catalysts with well-dispersed Pd nanoparticles (around 10 nm in diameter size) were synthesized using the chitosan-based carbons obtained both by salt templating and direct chitosan pyrolysis and tested in the aqueous phase hydrodechlorination of 4-chlorophenol. The fast and total removal of 4-chlorophenol was observed in the case of catalysts based on carbons obtained by templating with CaCl2 and ZnCl2-KCl in spite of the low metal content of the catalysts (0.25% Pd, wt.).

Dry Reforming of Methane over Carbon Fibre-Supported CeZrO2, Ni-CeZrO2, Pt-CeZrO2 and Pt-Ni-CeZrO2 Catalysts

Dry reforming of methane (DRM) is one of the most important processes allowing transformation of two most potent greenhouse gases into a synthesis gas. The CH4 and CO2 are converted at high temperatures in the presence of a metal catalyst (usually Ni, also promoted with noble metals, supported over various oxides). The DRM process is not widely used in the gas processing industry because of prompt deactivation of the catalyst owing to carbon deposition and the blockage of the metal active sites. This problem can be hindered by proper design of the catalyst in terms, e.g., of its composition and by providing strong interaction between active metal and catalytic support. The properties of the latter are also crucial for the catalyst’s performance in DRM and the occurrence of parallel reactions such as reverse water gas shift, CO2 deoxidation or carbon formation. In this paper we show for the first time the DRM performance of the ceria-zirconia and metal (Ni and/or Pt) supported on carbon fibres. The obtained Ni and Ni-Pt containing catalysts showed relatively high activity in the studied reaction and high resistance towards carbon deposition.

Mesoporous Carbon: A Versatile Material for Scientific Applications

Mesoporous carbon is a promising material having multiple applications. It can act as a catalytic support and can be used in energy storage devices. Moreover, mesoporous carbon controls body’s oral drug delivery system and adsorb poisonous metal from water and various other molecules from an aqueous solution. The accuracy and improved activity of the carbon materials depend on some parameters. The recent breakthrough in the synthesis of mesoporous carbon, with high surface area, large pore-volume, and good thermostability, improves its activity manifold in performing functions. Considering the promising application of mesoporous carbon, it should be broadly illustrated in the literature. This review summarizes the potential application of mesoporous carbon in many scientific disciplines. Moreover, the outlook for further improvement of mesoporous carbon has been demonstrated in detail. Hopefully, it would act as a reference guidebook for researchers about the putative application of mesoporous carbon in multidimensional fields.

Pd NPs supported on halloysite functionalized with Schiff base as an efficient catalyst for Sonogashira reaction

A hybrid system was designed and synthesized through reacting modified halloysite (Hal-Cl) with Schiff base (DAB-PC) and applied as catalytic support for anchoring Pd NPs to afford Pd@Hal-DAB-PC catalyst. The resultant material was well identified by various analyses including Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction patterns (XRD), thermogravimetric analysis (TGA), field-emission scanning electron microscopy (FE-SEM), energy-dispersive X-ray spectroscopy (EDS), transmission electron microscopy (TEM), and inductively coupled plasma-optical emission spectrometry (ICP-OES) and revealed outstanding catalytic activity in the Sonogashira reaction in aqueous media. Also, This nanocatalyst was simply collected and recycled up to six runs with a slight drop in efficiency, indicating the durability of Pd@Hal-DAB-PC.