Fine-tuning the catalytic activity by applying nitrogen-doped carbon nanotubes as catalyst supports for the hydrogenation of olefins

New Insights into N-Doped Porous Carbons as Both Heterogeneous Catalysts and Catalyst Supports: Opportunities for the Catalytic Synthesis of Valuable Compounds

Among the vast class of porous carbon materials, N-doped porous carbons have emerged as promising materials in catalysis due to their unique properties. The introduction of nitrogen into the carbonaceous matrix can lead to the creation of new sites on the carbon surface, often associated with pyridinic or pyrrolic nitrogen functionalities, which can facilitate various catalytic reactions with increased selectivity. Furthermore, the presence of N dopants exerts a significant influence on the properties of the supported metal or metal oxide nanoparticles, including the metal dispersion, interactions between the metal and support, and stability of the metal nanoparticles. These effects play a crucial role in enhancing the catalytic performance of the N-doped carbon-supported catalysts. Thus, N-doped carbons and metals supported on N-doped carbons have been revealed to be interesting heterogeneous catalysts for relevant synthesis processes of valuable compounds. This review presents a concise overview of various methods employed to produce N-doped porous carbons with distinct structures, starting from diverse precursors, and showcases their potential in various catalytic processes, particularly in fine chemical synthesis.

Cobalt-ferrite/Ag-fMWCNT hybrid nanocomposite catalyst for efficient degradation of synthetic organic dyes via peroxymonosulfate activation

The activation of peroxymonosulfate (PMS) by nanocatalysts has shown promise as an effective wastewater treatment protocol. Magnetic CoFe₂O₄/Ag-nanoparticles (NPs) anchored on functionalized multiwalled carbon nanotubes (fMWCNTs), a support material, were synthesized using a one-pot solvothermal method. The surface morphologies and physicochemical properties of the CoFe₂O₄/Ag-fMWCNT hybrid nanocomposite catalyst were investigated by powder X-ray diffraction analysis, field-emission scanning electron microscopy, energy-dispersive X-ray spectroscopy, high-resolution transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and nitrogen adsorption-desorption isotherms. The activity of the nanocomposite combined with PMS (serving as an activator) toward the degradation of rhodamine B, methylene blue, methyl orange, and methyl red was investigated. The obtained optimal 0.02 g CoFe₂O₄/Ag-fMWCNTs exhibited the highest PMS activation performance, with a removal percentage of 100% for 20 ppm dye concentration at pH 6.5 within 14 min. In addition, the rhodamine B degradation product was investigated by analyzing the intermediate products by liquid chromatography/mass spectrometry (LC-MS). The homogeneous distribution of CoFe₂O₄/Ag NPs on fMWCNTs accelerated PMS activation and enhanced the catalytic degradation of dyes. The effects of the reaction parameters on the dye degradation efficiency were investigated by using different nanocatalysts (fMWCNTs, CoFe₂O₄/fMWCNTs, and CoFe₂O₄/Ag-fMWCNTs) as well as by varying the pH (3-11), dye concentration (10-50 mg/l), catalyst dose (0.002-0.3 g), and PMS dose (0.02-0.1 g). Quenching experiments revealed that sulfate radicals are primarily responsible for rhodamine B degradation. A plausible mechanism for catalytic PMS activation was also proposed. Complete decolorization occurred within the first few minutes of the reaction. Furthermore, the catalytic activity of the CoFe₂O₄/Ag-fMWCNT/PMS hybrid nanocomposite remained stable after five successive cycles. This study verifies the applicability of CoFe₂O₄/Ag-fMWCNTs as an ultrafast catalyst for the complete removal of persistent organic pollutants via PMS activation, revealing their promising application in wastewater treatment.

How to Make a Cocktail of Palladium Catalysts with Cola and Alcohol: Heteroatom Doping vs. Nanoscale Morphology of Carbon Supports

Sparkling drinks such as cola can be considered an affordable and inexpensive starting material consisting of carbohydrates and sulfur- and nitrogen-containing organic substances in phosphoric acid, which makes them an excellent precursor for the production of heteroatom-doped carbon materials. In this study, heteroatom-doped carbon materials were successfully prepared in a quick and simple manner using direct carbonization of regular cola and diet cola. The low content of carbon in diet cola allowed reaching a higher level of phosphorus in the prepared carbon material, as well as obtaining additional doping with nitrogen and sulfur due to the presence of sweeteners and caffeine. Effects of carbon support doping with phosphorus, nitrogen and sulfur, as well as of changes in textural properties by ball milling, on the catalytic activity of palladium catalysts were investigated in the Suzuki–Miyaura and Mizoroki–Heck reactions. Contributions of the heteroatom doping and specific surface area of the carbon supports to the increased activity of supported catalysts were discussed. Additionally, the possibility of these reactions to proceed in 40% potable ethanol was studied. Moreover, transformation of various palladium particles (complexes and nanoparticles) in the reaction medium was detected by mass spectrometry and transmission electron microscopy, which evidenced the formation of a cocktail of catalysts in a commercial 40% ethanol/water solution.