A comparative study of the interaction of palladium supported on the surface of highly oriented pyrolytic graphite (Pd/HOPG) with oxygen and nitrogen dioxide was carried out using X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The samples were prepared by vacuum deposition of metallic Pd onto HOPG; the size of the resulting particles was ≤5 nm. The samples were treated in oxygen at room temperature or 150°C and a pressure of 20 mbar. The interaction with NO2 was carried out at room temperature and a pressure of 10–6 mbar. For the two oxidants used, O2 and NO2, fundamental differences in their effects on Pd/HOPG were found. At room temperature, the treatment in O2 was limited by the formation of some amount of oxygen-containing compounds CxOy on the surface of the carbon support. After increasing the temperature to 150°C, a portion of palladium was converted into a PdO oxide. When NO2 was used as an oxidizing reagent, intense oxidative destruction of graphite occurred to a depth of 10–15 graphene layers. Palladium remained in a metallic state, but its particles penetrated deep into the carbon support, which led to significant screening of its lines in the X-ray photoelectron spectrum and the disappearance of particles in SEM images. A possible mechanism for the interaction of Pd/HOPG with O2 and NO2 has been proposed, which allowed us to explain the different behaviors of these oxidizing molecules.

In this work, we used X-ray photoelectron spectroscopy (XPS) to perform a comparative study of the interaction of NO2 with two samples of highly oriented pyrolytic graphite (HOPG), on the surfaces of which rhodium was preliminarily deposited by evaporation in a vacuum, at room temperature and a pressure of 10–5 mbar. Before metal deposition, one of the HOPG samples was annealed in a vacuum at 600°C, and the other was bombarded with argon ions followed by exposure to air at room temperature for 1 h in order to introduce strongly bound oxygen atoms into the surface composition. After the deposition of rhodium onto the two HOPG samples, two model catalysts designated as Rh/C and Rh/C(A)–O were prepared. It was found that the interaction of NO2 with Rh/C led to the oxidation of graphite with the destruction of the surface layer. The Rh particles remained in a metallic state, but they were introduced into the near-surface layer of the carbon support. On the contrary, when the Rh/C(A)–O sample was treated with NO2, the deposited rhodium was partially converted into Rh2O3, while the graphite was oxidized to an insignificant degree and retained its original structure. The role of surface oxygen in the stabilization of graphite with respect to oxidation in NO2 was discussed.

In this work, using the method of X-ray photoelectron spectroscopy (XPS), a comparative study of the nature of the interaction of NO₂ at room temperature and a pressure of 10⁻⁵ mbar with two samples of highly oriented pyrolytic graphite (HOPG), on the surface of which rhodium was preliminarily deposited by vacuum deposition, was carried out. Before metal deposition, one of the HOPG samples was annealed in vacuum at 600°C, and the other was subjected to bombardment with argon ions, followed by exposure to air at room temperature for an hour in order to introduce strongly bound oxygen atoms into the surface composition. After deposition of rhodium on two samples of HOPG prepared, two model catalysts were obtained, designated as Rh/C and Rh/C(A)-O. It was found that the interaction of NO₂ with Rh/C led to the oxidation of graphite with the destruction of the surface layer. The Rh particles remained in the metallic state, but at the same time they were introduced into the near-surface layer of the carbon support. On the contrary, when the Rh/C(A)-O sample was treated with NO₂, the deposited rhodium was partially converted into RH₂O₃, while the graphite was oxidized to an insignificant degree and retained its original structure. The role of surface oxygen in the stabilization of graphite with respect to oxidation to NO₂ was discussed.

Samples of model single-site catalysts based on iridium and rhodium were synthesized by immobilizing the complexes [Ir(COD)(IMes)Cl] and [Rh(COD)(IMes)Cl] (where COD is 1,5-cyclooctadiene and IMes is 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene) on silica, the surface of which was modified with a linker containing a diphenylphosphine group (Ph2P). The supports were silicon plates with a flat surface coated with a layer of natural oxide 1–3 nm thick (Si–SiO2(nat)) or with a specially grown SiO2 film (∼300 nm) (Si–SiO2(ox)). The states of chemical elements in the modified silicon plates and samples of model catalysts were determined by XPS. Based on the results obtained, the nature of the coordination of the immobilized complexes was assumed. Samples of the catalysts were tested in the reaction of gas-phase hydrogenation of propene with parahydrogen.

In this work, X-ray photoelectron spectroscopy (XPS) was used to study the effect of preliminary oxidative treatment of a carbon support surface on the results of NO2 interaction with model systems prepared by palladium deposition onto highly oriented pyrolytic graphite (HOPG). It was found that, in Pd/HOPG samples with the atomic ratios [O]/[C] ≤ 0.0035, the carbon support was oxidized with the destruction of its structure to a depth of 10–15 graphene layers. In this case, the palladium particles remained in a metallic state, and they penetrated into the near-surface layer of the support due to the deep oxidation of adjacent carbon atoms. At the atomic ratio [O]/[C] ≈ 0.01–0.02, the result of the interaction changed dramatically. In this case, the support remained stable, and the palladium particles were oxidized to form an oxide. This finding explained the high stability of supported palladium catalysts prepared on Sibunit carbon supports in oxidative catalysis reactions.

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, and Rh) at a pressure of 10‑6–10–4 mbar. Particular attention was focused on establishing the chemical states of the supported metal particles and carbon support using X-ray photoelectron spectroscopy (XPS). Before treatment in NO2, the M/HOPG samples were characterized by scanning tunneling and/or scanning electron microscopy (STM and SEM, respectively). Upon interaction with NO2, supported palladium and rhodium remained in metallic states 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 a vacuum, and it 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.

The interaction of NO2 with a carbon material from the Sibunit family with palladium metal particles supported on its surface was studied by X-ray photoelectron spectroscopy (XPS) at a pressure of 10–6 mbar in a temperature range from room temperature to 300°C. Two Pd/Sibunit samples, one of which was prepared by chemical deposition of palladium (Pd/C-HC sample) and the other, by vacuum evaporation of the metal onto the support (Pd/C-VE sample), were studied. Both of the samples showed similar behaviors in the interaction with NO2. Over the entire temperature range, the C1s spectrum of the samples contained a single peak with a binding energy of 284.4 eV from carbon atoms in the sp2-hybrid state, which indicated a weak effect of NO2 on Sibunit. At temperatures from room temperature to 150°C, the state of palladium supported onto the surface of Sibunit also did not change, but palladium was partially oxidized with the formation of PdO in a range from 200 to 300°C.

The comprehensive study of the electronic density distribution of CuCr 0.99 Ln 0.01 S 2 (Ln = La, Ce) solid solutions was carried out using both X-ray photoelectron and emission spectroscopy. It was found that cationic substitution of chromium with lanthanum or cerium atoms does not significantly affect the atomic charges of the matrix elements (Cu, Cr, S) in the lanthanide-doped solid solutions. The copper atoms in the composition of CuCrS 2 -matrix and the lanthanide-doped solid solutions were found to be in the monovalent state. The chromium and lanthanide atoms were found to be in the trivalent state. This fact indicates the isovalent cationic substitution character. The sulfur atoms were found to be in the divalent state. The near-surface layers contain the additional oxidation forms of sulfur (S 0 , S 4+ , S 6+ ) and copper (Cu 2+ ) atoms. The detailed analysis of the valence band structure using DFT calculations has shown that partial DOS distribution character of the matrix elements is preserved after the cationic substitution. The experimental valence band spectra structure of CuCrS 2 -matrix and CuCr 0.99 Ln 0.01 S 2 is determined by the occupied copper d -states contribution. The contribution of the lanthanide states in the valence band structure is lower in comparison with those for the matrix elements. The major contribution of the lanthanide states was found to be mainly localized near the conduction band bottom.

A comprehensive study of the electronic structure of trinuclear molybdenum complexes (NH4)2[Mo3S13] and [Mo3S7(dtc)3]Br with cluster core {Mo3S7} and [Mo3S4(tu)8H2O]Cl4 complexes with cluster core {Mo3S4} is conducted by X-ray emission spectroscopy (XES), X-ray photoelectron spectroscopy (XPS), X-ray absorption near edge structure (XANES) spectroscopy, and quantum chemistry methods. Data were obtained on the partial atomic composition of the highest occupied molecular orbitals and unoccupied molecular orbitals and the nature of atomic interactions within cluster cores.

Методом РСА изучено строение биядерного тиоцианатного комплекса ниобия(IV) — (Bu4N)4[Nb2(μ2-S2)2(NCS)8]·H2O (1·H2O). Соединение 1·H2O кристаллизуется в ромбической сингонии (пространственная группа Pbca) с параметрами элементарной ячейки a = 23.2139(4) Å, b = 25.2962(4) Å, с = 32.5478(6) Å, V = 19112.8(6) Å3, R = 0.0592. Методами рентгеновской спектроскопии изучена электронная структура комплексов (Bu4N)4[Nb2(μ2-S2)2(NCS)8] и (Bu4N)4[Nb2(μ2-Se2)2(NCS)8], проведено сравнение с полимерными халькогалогенидами Nb2S4Br4 и Nb2Se4Br4. Методом РФЭС показано, что эффективные заряды на атомах ядра {Nb2(μ-Q2)2}4+ (Q = S, Se) не изменяются при переходе от Br– к NCS– лигандам. Методами РЭС и XANES изучена структура HOMO и LUMO для (Bu4N)4[Nb2(μ2-S2)2(NCS)8] и (Bu4N)4[Nb2(μ2-Se2)2(NCS)8]. Установлено, что наибольшие вклады состояний S 3p лигандов NCS– в занятые молекулярные орбитали находятся вблизи верхней границы валентной зоны, тогда как вклады от дихалькогенидных мостиковых лигандов имеют более равномерное распределение. В случае зоны проводимости вклады состояний S 3p лигандов NCS– расположены в более глубокой области, а вклады от дихалькогенидных мостиковых лигандов — вблизи нижней границы зоны проводимости. Взаимодействие состояний Nb 4d и S 3p/Se 4p дихалькогенидных мостиков для HOMO имеет разрыхляющий характер, для всех остальных занятых молекулярных орбиталей — связующий, а для всех свободных молекулярных орбиталей — разрыхляющий.

The structure of a binuclear niobium(IV) thiocyanate complex (Bu 4 N) 4 [Nb 2 (μ 2 -S 2 ) 2 (NCS) 8 ]·H 2 O ( 1 ·H 2 O) is studied by X-ray crystallography. Compound 1 ·H 2 O crystallizes in the orthorhombic crystal system (space group Pbca ) with unit cell parameters a = 23.2139(4) Å, b = 25.2962(4) Å, с = 32.5478(6) Å, V = 19112.8(6) Å 3 , R = 0.0592. The electronic structures of (Bu 4 N) 4 [Nb 2 (μ 2 -S 2 ) 2 (NCS) 8 ] and (Bu 4 N) 4 [Nb 2 (μ 2 -Se 2 ) 2 (NCS) 8 ] complexes are investigated by X-ray spectroscopy techniques and compared with the structures of polymeric chalcogenides Nb 2 S 4 Br 4 and Nb 2 Se 4 Br 4 . By XPS it is shown that effective charges on atoms of the {Nb 2 (μ- Q 2 ) 2 } 4+ ( Q = S, Se) core do not change when passing from Br – to NCS – ligands. The HOMO and LUMO structures of (Bu 4 N) 4 [Nb 2 (μ 2 -S 2 ) 2 (NCS) 8 ] and (Bu 4 N) 4 [Nb 2 (μ 2 -Se 2 ) 2 (NCS) 8 ] are analyzed by XPS and XANES techniques. The largest contributions of S 3 p states of NCS – ligands to the occupied molecular orbitals are found to be near the upper boundary of the valence band while the contributions from dichalcogenide bridging ligands have a more uniform distribution. For the conduction band, the contributions of S 3 p states of NCS – ligands are located deeper whereas the contributions from dichalcogenide bridging ligands are near the lower boundary of the conduction band. The interaction of Nb 4 d and S 3 p /Se 4 p states of dichalcogenide bridges for the HOMO has an antibonding character, which is bonding for all the other occupied molecular orbitals and antibonding for all unoccupied molecular orbitals.

Samples of rhodium nanoparticles supported on the surface of highly oriented pyrolytic graphite (HOPG) are prepared by vacuum deposition; their interaction with nitrogen dioxide is studied by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). In the initial state, metallic rhodium particles with a size of about 2–5 nm are combined into aggregates localized on the steps and terraces, apparently, in the region of localization of structural defects. After treatment in NO2 at room temperature and pressures of 10−6 and 10−5 mbar, carbon oxidation accompanied by the degradation of the structure of 12–15 graphene layers on the HOPG surface is observed. Under these conditions, rhodium remains in the metallic state, and the Rh particles are encapsulated with carbon. The results are compared with data on the interaction of NO2 with Pt and Pd nanoparticles supported on the HOPG surface.

Методами рентгеновской эмиссионной спектроскопии (РЭС), рентгеновской фотоэлектронной спектроскопии (РФЭС), рентгеновской спектроскопии поглощения (XANES) и квантовой химии проведено детальное исследование особенностей электронной структуры трехъядерных комплексов молибдена (NH4)2[Mo3S13] и [Mo3S7(dtc)3]Br с кластерным ядром {Mo3S7}, а также [Mo3S4(tu)8H2O]Cl4 с кластерным ядром {Mo3S4}. Получены данные о парциальном атомном составе высших занятых и свободных молекулярных орбиталей и характере взаимодействий между атомами внутри кластерного ядра.

Expressions are obtained for the IMVV/I3d ratio of the AgMVV Auger line intensity to the Ag3d photoemission line intensity in XPS spectra (AlKα radiation, hν = 1486.6 eV) of Au-Ag bimetallic particles located on the flat surface of the support. Bimetallic hemispherical particles with non-uniform distribution of metals (silver core covered with a gold shell) are considered. The particles are characterized by normal size distribution (with respect to the core radius R) with a maximum at Rmax = 3.5 nm and the standard deviation σ = 0.5 nm, 1.0 nm, and 2.0 nm. The bimetallic system is analyzed in the conditions of R-independence: in one case, the shell thickness δ = const(R); in the other case, the atomic ratio of gold to silver γ = const(R). As the Au-shell is formed around the Ag-core and y increases, the IMVV/I3d ratio is shown to decrease significantly due to more effective screening by the shell of AgMVV Auger electrons as compared to that of Ag3d photoelectrons. The IMVV/I3d ratio as a function of γ weakly depends on σ and on the choice of conditions δ = const(R) or γ = const(R). When an alloy with a uniform spatial distribution of gold and silver atoms over the particle volume is formed, the IMVV/I3d ratio also decreases with increasing γ, though to a much smaller extent. The derived expressions can be used in XPS studies to consider the formation of supported bimetallic particles in model planar systems and the changes occurring with the particles as a result of heat-treatment in the reaction medium.

A sample of palladium nanoparticles with an average size of ~5 nm on the surface of highly oriented pyrolytic graphite (HOPG) was prepared by vacuum deposition. With the use of X-ray photoelectron spectroscopy (XPS), it was found that the interaction of the resulting Pd/HOPG sample with nitrogen dioxide at room temperature and a pressure of 10–6 mbar led to the oxidation of graphite. In this case, palladium particles retained their metallic state. A comparison with the behavior of a palladium sample supported onto HOPG activated by ion etching under similar conditions showed that structural defects on the graphite surface did not play a decisive role in the oxidation of graphene layers. A comparison with the results obtained upon the interaction of NO2 with Pt nanoparticles supported on the HOPG surface was made.

Получены выражения для отношения интенсивности Оже-линии AgMVV к интенсивности фотоэмиссионной линии Ag3d, IMVV/I3d в спектрах РФЭС (излучение AlKα, hν = 1486.6 эВ) биметаллических частиц Au—Ag, расположенных на плоской поверхности носителя. Рассмотрены биметаллические частицы полусферической формы с неоднородным распределением металлов, при котором ядро из атомов серебра покрыто оболочкой из атомов золота. Частицы характеризуются нормальным распределением по размерам (по радиусу ядра R) с максимумом при Rmax = 3.5 нм и с шириной σ = 0.5 нм, 1.0 нм и 2.0 нм. Проведен анализ биметаллической системы в условиях независимости от R: в одном случае — толщины оболочки δ = const(R) и в другом случае — атомного отношения золота к серебру γ = const(R). Показано, что по мере формирования вокруг Ag-ядра Au-оболочки с ростом γ происходит существенное уменьшение отношения IMVV/I3d за счет более эффективной экранировки оболочкой AgMVV Оже-электронов по сравнению с Ag3d фотоэлектронами. зависимость IMVV/I3d от γ слабо связана с σ и выбором условия δ = const(R) или γ = const(R). При образовании сплава с однородным пространственным распределением атомов золота и серебра по объему частицы отношение IMVV/I3d также уменьшается с ростом γ, но в значительно меньшей степени. Полученные выражения могут быть использованы при исследовании методом РФЭС процесса формирования нанесенных биметаллических частиц в модельных планарных системах и изменений, происходящих с частицами при их термической обработке в реакционной среде.

The interaction of palladium nanoparticles (average size, ∼3 nm) deposited on the surface of highly oriented pyrolytic graphite (HOPG) with nitrogen dioxide at room temperature and a pressure of 10–6 or 10–5 mbar was studied by X-ray photoelectron spectroscopy (XPS). It was shown that the structure of several surface graphene layers was destroyed under these conditions due to the oxidation of carbon at the interface between Pd and HOPG. The reaction proceeded with the participation of oxygen atoms, which were formed as a result of the dissociation of NO2 molecules on the palladium surface. Palladium particles retained their metallic nature, but they penetrated deep into graphite in this case.

Возможность получения новых данных стандартными методами электронной спектроскопии и квантовой химии показана на примере интеркалата C2FBr0.15 и серебряной фольги. Особенности протяженных рентгеновских фотоэлектронных спектров интерпретированы электронными переходами в валентной зоне аналогичных элементарных ячеек. Анализ экспериментальных и расчетных спектров выявил два состояния внедренного Br2 — молекулярное и цепочечное. Взаимодействие Ag и NO2 при 300—520 K ограничено образованием окисленного состояния в приповерхностном слое толщиной ~6 Å, при этом в спектрах Ag3d и Ag MNN доминирует металлическое состояние серебра. Геометрические параметры, состояние атомов и характер связей между ними согласуются с полученными ранее результатами.

The possibility to obtain novel data by standard electron spectroscopy and quantum chemical techniques is exemplified by C2FBr0.15 intercalate and silver foil. The features of extended X-ray photoelectron spectra are interpreted by electronic transitions in the valence band of similar unit cells. The analysis of experimental and calculated spectra reveals two states of intercalated Br2: molecular and chain-like. The interaction of Ag with NO2 at 300–520 K is limited by the formation of an oxidized state in the near-surface layer with a thickness of ∼6 A, with the metallic state of silver dominating in the Ag3d И Ag MNN spectra. Geometric parameters, states of atoms, and the character of bonds between them are consistent with the previously obtained results.