Vol 64, No 1 (2023)

This paper presents a review of the results obtained in studying the room temperature interaction of NO₂ with model systems prepared by vacuum deposition of platinum group metals on the surface of highly oriented pyrolytic graphite (M/HOPG, M = Pt, Pd, Rh) at pressure of 10^–6–10^–4 mbar. Particular attention was focused on establishing the chemical state of the supported metal particles and carbon support using X-ray photoelectron spectroscopy (XPS). Before treatment in NO₂, M/HOPG samples were characterized by scanning tunneling and/or scanning electron microscopy (STM and SEM). Upon interaction with NO₂, supported palladium and rhodium remained in the metallic state and, at the same time, exhibited catalytic activity in the oxidation of graphite. The process was accompanied by the destruction of ≥10–15 graphene layers with the penetration of metal particles deep into the carbon support. Rhodium was less active in the oxidation of graphite compared to palladium due to the filling of its surface with NO molecules arising from the dissociation of NO₂. When the samples with deposited platinum were treated in NO₂, the carbon support underwent minimal changes without disturbing its original structure. Platinum retained its metallic state when deposited on the surface of graphite annealed in vacuum and was oxidized to PtO and PtO₂ oxides on the surface activated by etching with argon ions. Based on the results obtained, a mechanism was proposed for the room temperature interaction of M/HOPG systems with NO₂.

Our work is around the heterogeneous catalysts based on phosphate. This is all the more important as Morocco has a significant wealth of world reserves of this mineral. This application of natural phosphate alone or modified, has been successfully generalized to many reactions (Claisen Schmidt condensation, selective hydration of nitriles…). And more precisely, the zirconium phosphate catalyst, its physicochemical parameters and catalytic application in the synthesis of 2-arylquinazolin-4(3H)-ones have been studied in order to opt for the one that offers the most economic, ecological and technical advantages.

The catalytic properties of a copper-aluminum oxide catalyst obtained from double layered hydroxide have been studied in hydrogenation of 1,3,5-trinitrobenzene (TNB) and 2,4,6-trinitrotoluene (TNT) in a flow reactor. The reaction was carried out at temperature of 120°C, total pressure of 30 bar and substrate concentration of 0.10–0.15 M, using methanol as a solvent. 1,3,5-Triaminobenzene (TAB) and 2,4,6-triaminotoluene (TAT) were isolated from the reaction mixture in the form of double salts with sulfuric acid TAB⋅2H₂SO₄ and TAT⋅2H₂SO₄, the yield of which was 92 and 98%, respectively. At an initial trinitroarene concentration of 0.10 M, the hydrolysis of triaminobenzene salts made it possible to synthesize phloroglucinol and methylphloroglucinol in 78 and 91% yields. Increasing the concentration to 0.15 M reduces the yield to 71 and 88%, respectively. According to thermal analysis data, the observed differences in the yields of triaminobenzene salts and polyphenols are explained by the formation of different amounts of resinous by-products on the catalyst surface during hydrogenation of trinitroarene. Hydrogenation of TNT produces less resin, resulting in higher yields of TAT⋅2H₂SO₄ and methyl phloroglucinol. This is probably due to the presence of an electron-donating methyl substituent, which slows down polycondensation of TAT molecules.

The mechanism of the formation of catalytic species in the practically important Mizoroki–Heck reaction, which is in demand in modern fine organic synthesis, has been studied. It has been shown that catalysts based on palladium complexes with N-heterocyclic carbene ligands are transformed into a “ligand-free” form under the conditions of the Mizoroki–Heck reaction. Molecular modeling performed using quantum chemical methods showed that these processes compete with the target reaction at three of the six stages of the catalytic cycle. The presence of catalyst transformation products in the reaction system was confirmed by methods of nuclear magnetic resonance and mass spectrometry. Important mechanistic data have been obtained for the rational design of catalytic systems for cross-coupling reactions.

The effect of natural quaternary ammonium compounds (QAC) of choline (Ch) and its derivatives, acetylcholine (AСh) and L-carnitine (LCh), containing the tetraalkylammonium cation (CH₃)₃RN⁺, on the radical decomposition of hydroperoxides (ROOH) was studied. In mixtures of ACh and Ch with ROOH in chlorobenzene, mixed supramolecular nanoaggregates are formed, and accelerated decomposition of ROOH into radicals takes place; the rates of radical formation measured by the inhibitor method decrease in the series ACh > Ch \( \gg \) LCh. ACh and Ch immobilized on microcrystalline cellulose retain the ability to catalyze the radical decomposition of ROOH and initiate the polymerization of styrene containing ROOH from the surface. LСh adsorbed on cellulose does not affect the decomposition of ROOH and the rate of polymerization. Scanning electron microscopy (SEM) showed that ACh and Ch adsorbed on a silicon plate accelerate the radical decomposition of ROOH and initiate oxidative condensation of egg phosphatidylcholine on the surface of the plate, while adsorbed LCh does not affect the decomposition of ROOH. LCh, unlike ACh and Ch, is an internal salt in which the R₄N⁺ cation is neutralized by its own carboxy anion, i.e., LCh has no external counterion and, probably, for this reason, it differs from ACh and Ch in the mechanism of adsorption and interaction with ROOH.

Ceramometal catalysts CuFeAlO/CuFeAl, obtained from various powdered Cu–Fe–Al precursors differing in stoichiometry and preparation method, were characterized by physicochemical methods and studied in the water gas shift reaction (CO + H₂O ⇌ CO₂ + H₂). The catalysts are a monolith porous composites, in which metal particles are covered with an oxide shell. The sample Cu : Fe : Al = 45 : 22 : 33, synthesized from powder precursor in two stages was shown to be the most stable. At the first stage the mechanochemical melting of Cu and Fe powders was done. The mechanochemical treatment of obtained product and Al powder was performed at the second stage. This procedure provides the most homogeneous distribution of the components in the precursor. Initial and tested at 400°C ceramometal catalysts were characterized with XRD, SEM and XPS methods. It was revealed that the most active at 350°C catalysts after reductive treatment have Cu¹⁺ and Fe³⁺ sites. The least active catalysts are completely reduced to Cu⁰ and partially – to Fe⁰. It was found that the activity at 330–400°C is determined not only by iron, but also by copper active centers on the surface of the catalysts, or their combined action. Two-stage mechanical activation, apparently, leads to a deeper chemical interaction of the components – Fe and Cu, which provides a higher activity of chromium-free CuFeAl ceramic-metal catalysts.