The work presents a study and comparison of the catalytic properties of hopcalite catalysts composed of copper-manganese and copper-cobalt-manganese spinel particles in the low-temperature CO oxidation reaction. The cubic spinel structure was formed immediately under reaction conditions through the transformation of hydrothermally prepared crednerite CuMn(Co)O2 particles. Both the initial crednerite-type and the resultant spinel-type particles (Cu, Mn, Co)3O4 exhibited a lamellar morphology and a uniform distribution of elements throughout their bulk and surface. It was found that the modification of the copper-manganese oxide with cobalt resulted in increased particle dispersion and a significant distortion of the crednerite crystal lattice. As a result, this modification reduced the temperature required for the crednerite-to-spinel transformation to 250 degrees C, whereas the unmodified catalyst is transformed after heating to 350-400 degrees C only. Furthermore, it was demonstrated that during the CO oxidation at room temperature, the modified spinel particles (Cu, Mn, Co)3O4 exhibited a specific catalytic activity similar to 3.5 times greater than that of the copper-manganese system. This enhancement is associated with the stabilization of a more oxidized surface state for the modified spinel particles, which may involve an increased contribution of Co3+ and Mn4+ surface species, as well as an enhancement in the overall lattice oxygen mobility.

При разработке катализаторов нового поколения, а также в ходе оптимизации характеристик существующих каталитических систем, важнейшую роль играют фундаментальные исследования, позволяющие установить ключевые параметры, определяющие активность и селективность протекания определенных реакций. В данной работе были проведены исследования нанесенных платино-титановых катализаторов, активных в реакции селективного окисления аммиака. Было рассмотрено влияние модифицирующих добавок: хлорида калия и оксида вольфрама на физико-химические и каталитические свойства системы Pt/TiO2. Структурные методы (порошковая рентгеновская дифракция, просвечивающая электронная микроскопия (ПЭМ)) показали наличие высокодисперсных частиц платины в изученных катализаторах. Исследование методом рентгеновской фотоэлектронной спектроскопии (РФЭС) в режиме ex situ позволило определить зарядовое состояние платины на поверхности модифицированных и немодифицированных катализаторов в зависимости от проведенных окислительно-восстановительных обработок. Было установлено, что модификация образцов оксидом вольфрама стабилизирует металлическое состояние платины, а хлоридом калия - окисленное состояние Pt2+. Корреляция данных о состоянии активного компонента с каталитическими свойствами показала улучшение активности образцов в области температур ниже 180°С при добавлении оксида вольфрама, в то время как введение хлорида калия приводило к повышению селективности в отношении молекулярного азота в области температур ниже 250°С.

The paper presents an investigation into the physicochemical and catalytic properties of CuBO2 oxides with a delafossite/crednerite-type structure, exploring the dependence on the nature of the B3+ cation (Mn3+, Co3+, Cr3+, Fe3+, and Ga3+). The catalytic properties in CO oxidation were examined in conjunction with structural data, surface composition, the distribution of surface metal states, and the reactivity of oxygen. The selection of synthesis conditions was tailored to yield crystallized CuBO2 particles exhibiting either a delafossite or crednerite structure, depending on the nature of the B3+ cation nature. Thermal stability increases in the following order: CuMnO2 < CuCrO2 ≈ CuFeO2 ≈ CuCoO2 < CuGaO2. Heating of all the studied mixed oxides in the CO + O2 mixture to 250 °C did not cause changes in the phase composition and structural characteristics. The highest catalytic activity near room temperature was observed for CuMnO2 and CuCrO2. A correlation was established between the catalytic activity of CuBO2 and the reactivity of surface oxygen, presumably attributed to the pronounced lability of the redox transitions between the Cu1+/Cu2+ and Bn+/Bm+ pairs. The transformation of the delafossite/crednerite into a spinel structure can cause both deactivation (B = Fe and Co) and significant catalytic activation (B = Mn and Cr) in low-temperature CO oxidation.

The present study elucidates new perspectives regarding the Pt-CeO2 system for CO oxidation. The successful deposition of highly dispersed Pt-CeO2 species onto the surface of multiwalled carbon nanotubes (MWCNTs) led to the formation of abnormally active and water-resistant catalysts. The catalysts were investigated by structural (XRD, TEM), spectral (XPS), and kinetic (TPR-CO+O-2, TPR-CO, TPR-H-2) methods. The application of TPR-CO+O-2 revealed the remarkably high activity of all Pt-CeO2/MWCNTs catalysts at temperatures below 0 degrees C. The study of the catalysts at ambient temperature demonstrated high CO conversion in the presence of water vapor at a concentration of 100 ppm CO. The experimental findings suggest that active sites, comprising platinum structures stabilized directly on the surface of MWCNTs, play a pivotal role in the oxidation of CO under humid conditions. A dual-site approach was employed to develop a kinetic model that effectively describes the experimental data. This model provides valuable insights into the mechanism of wet CO oxidation.

Catalysts for the selective oxidation of ammonia to molecular nitrogen are essential for the fight against environmental pollution due to vehicle and industrial emissions. This work reports a study of Pt/TiO 2 -based K-modified catalysts for the selective oxidation of ammonia. The Pt/TiO 2 catalysts are prepared by impregnating a commercial TiO 2 support (Degussa, P25 Aeroxide) by a platinum nitrate precursor followed by depositing small amounts of potassium with variation of the precursor nature (KOH, KNO 3 , KCl). The influence of a promoting additive on the catalysts properties is considered using a complex of physicochemical and kinetic methods such as powder XRD, X-ray photoelectron spectroscopy (XPS), temperature-programmed desorption of NH 3 (NH 3 -TPD), NH 3 +O 2 temperature programmed reaction (NH 3 +O 2 -TPR). According to the XRD data, dispersed platinum particles with a coherent scattering region of no more than 5 nm are formed in the samples. The XPS data indicate that the oxidation state of platinum can be changed by varying the potassium precursor. It is shown that the potassium chloride precursor enhances the selectivity to molecular nitrogen in the temperature range up to 200 °C. The changes in the acidic properties of the sample surfaces are revealed using the NH 3 -TPD data, and the changes are compared with catalytic characteristics of the samples in the reaction of ammonia oxidation.

Ternary oxide of silver, copper and manganese (Ag2CuMnO4) with delafossite-type structure demonstrates excellent catalytic activity in the reaction of CO oxidation at room temperature and even below. To prepare delafossite-based catalyst the hydrothermal approach using metal nitrates in alkaline solution with an excess of peroxodisulphate was applied. X-ray diffraction pattern of Ag2CuMnO4 particles was successfully simulated taking into an account crystallite shape anisotropy, particle size distribution, the presence of stacking faults, and the lattice expansion along c axis. As-prepared Ag2CuMnO4 sample was characterized by the presence of Ag1+-, Cu2+- and Mn4+-like surface species predominantly. In situ XRD data revealed the thermal stability of delafossitetype structure in catalytic CO+O2 mixture up to 500 degrees C, while ex situ XPS showed an evident reorganization of Ag2CuMnO4 surface at markedly lower temperatures (200-250 degrees C). Heating in CO+O2 medium at 150-400 degrees C also resulted in significant catalytic activation of Ag2CuMnO4 owing to the Mn enrichment and optimization of manganese and copper electronic exchange. The low-temperature activity of Ag2CuMnO4 catalyst in CO+O2 reaction was proposed to be mainly provided by redox transitions with the participation of Cu1+/Cu2+ and Mn3+/Mn4+ couples, while the catalytic role of silver species is considered as auxiliary only. The innovation point of this work is related to the investigation of the dynamics of surface and bulk structure transformations in connection with the catalytic activation of delafossite particles for the low-temperature oxidation.

В работе были исследованы композитные катализаторы, представляющие собой Rh-CeOx композиции, нанесенные на поверхность многостенных углеродных нанотрубок (МУНТ). Активные компоненты (Rh, Ce) были нанесены на поверхность МУНТ с сохранением постоянной загрузки родия и варьированием содержания церия в диапазоне соотношений Rhат./Ceат. = 0.085–0.34. Исследование полученных образцов проводилось комбинацией структурных (рентгеновская дифракция, просвечивающая электронная микроскопия (ПЭМ)), спектральных (рентгеновская фотоэлектронная спектроскопия (РФЭС)) и кинетических (температурно-программированная реакция с СО (ТПР-СО) и СО+О2 (ТПР-СО+О2)) методов. Обнаружено, что для всех изученных образцов наблюдается формирование высокодисперсных частиц CeO2 и RhOx. При изменении соотношения Rhат./Ceат. происходит формирование структур, проявляющих каталитическую активность в реакции окисления СО в различных температурных диапазонах. При низких соотношениях Rhат./Ceат. < 0.17 конверсия СО наблюдается при температурах выше 100°С. При увеличении соотношения Rhат./Ceат. в катализаторах Rh-CeO2/МУНТ происходит формирование центров, обладающих каталитической активностью при температурах ниже 0 °С. Исследование композитных катализаторов с высоким соотношением Rhат./Ceат. методами ПЭМВР и ТПР-СО указывает на то, что активными формами могут являться структуры на основе дисперсных окисленных форм родия, модифицированных ионами Ce3+.

In this work, the correlation between structure, composition, surface state, and CO oxidation catalytic activity of the ternary oxide Ag2CuMnO4 was studied. The stepwise surface and structure modification was implemented with the use of pretreatments in different media at various temperatures. It allowed investigating the nature of low-temperature catalytic activity and determining the conditions for the realization of the most efficient route of CO oxidation. The investigation of the interaction of the ternary oxide with carbon monoxide was carried out using TPR-CO, in situ XRD, and ex situ XPS methods. Ex situ XPS was applied to study the evolution of composition and charge state of the ternary oxide components on the surface of particles during the interaction with the reaction CO + O-2 mixture versus the temperature, preventing the contact of the sample with the air. Ex situ XPS data established the presence of prominent charge transfer between copper and manganese within the delafossite structure during the interaction with CO. The results of catalytic measurements revealed that the most active Ag2CuMnO4 state can be achieved by heating in the inert or in the reaction mixture at 250 degrees C. Under these conditions, the enhancement of an interlayer charge transfer occurs at the expense of Cu+ ions accumulation in the linear-coordinated cation layer. The heating above 300 degrees C led to the appearance of tetrahedral Cu+ cations within the "proto-spinel" entities determining the drop in catalytic activity. The data obtained outline the importance of linear and octahedral charge transfer for low-temperature CO oxidation activity.

Composite catalysts consisting of Rh-CeOx structures supported on the surface of multi-walled carbon nanotubes (MWCNTs) are studied. For supported active components (Rh, Ce) the rhodium content is maintained constant on the MWCNT surface and the cerium concentration is varied in the range Rh-at/Ce-at = 0.085-0.34. The obtained samples are investigated by a combination of structural (X-ray diffraction, transmission electron microscopy (TEM)), spectral (X-ray photoelectron spectroscopy (XPS)), and kinetic (temperature-programmed reaction with CO (TPR-CO) and CO+O-2 (TPR-CO+O-2)) techniques. Highly dispersed CeO2 and RhOx particles are found to form in all samples studied. When the Rh-at/Ce-at ratio is changed, structures are formed that exhibit the catalytic activity in the CO oxidation reaction for different temperature ranges. At low Rh-at/Ce-at ratios (< 0.17) the CO conversion is observed at temperatures above 100 degrees C. When the Rh-at/Ce-at ratio increases, centers exhibiting the catalytic activity at temperatures below 0 degrees C are formed in Rh-CeO2/MWCNT catalysts. HR-TEM and TPR-CO studies of composite catalysts with a high Rh-at/Ce-at ratio reveal that structures based on dispersed oxidized rhodium particles modified by Ce3+ ions can be active species.

The application and development of methods using hydrogen as a gas for testing active surface sites is of great interest in the study of oxide catalysts. In this work a systematic study of Pt/CeO2 catalysts, depending on the platinum loading and calcination temperature was carried out using the method of temperature-programmed reduction by hydrogen (TPR-H-2). Experimental TPR-H-2 curves demonstrated a complex structure over a wide temperature range, including the presence of abnormally narrow consumption peaks (ANCP-H-2) at low temperatures. To describe the kinetics, mathematical modeling of H-2 consumption by various platinum active centers has been used, including isolated platinum ions (single atoms) and PtOx clusters of 2D and 3D structures on the surface of ceria nanoparticles. We proposed a criterion that makes it possible to extend the analysis of the TPR-H-2 curves for reducible metal-supported oxide systems and unambiguously establish the action of the autocatalytic mechanism in hydrogen consumption. The kinetics of ANCP-H-2 by cluster PtOx centers with a half-width of several degrees on the base of the autocatalysis mechanism was described on the base of the proposed model. The simulations show that ANCP-H-2 are described by synchronous fast formation of metallic centers that provide a sharp acceleration of H-2 consumption. In general, the obtained results establish the fundamental aspects of the H-2 interaction with heterogeneous catalysts and are of particular interest in the light of various practical applications of hydrogen energy.

Катализаторы селективного окисления аммиака до молекулярного азота играют важную роль в борьбе с загрязнением окружающей среды автомобильными и промышленными выбросами. В работе было проведено исследование катализаторов селективного окисления аммиака на основе Pt/TiO2, модифицированных калием. Катализаторы Pt/TiO2 были получены пропиткой коммерческого носителя TiO2 (Degussa, P25 Aeroxide) нитратным предшественником платины, с последующим нанесением небольших количеств калия с варьированием природы предшественника: КОН, КNO3, KCl. Применение комплекса физико-химических и кинетических методов (порошковая рентгеновская дифракция, рентгеновская фотоэлектронная спектроскопия (РФЭС), температурно-программируемая десорбция NH3 (ТПД-NH3), температурно-программируемая реакция NH3+O2 (ТПР-NH3+O2)) позволило рассмотреть влияние промотирующей добавки на свойства катализаторов. По данным рентгеновской дифракции для образцов наблюдалось образование дисперсных частиц платины с размером области когерентного рассеяния не более 5 нм. Данные РФЭС указывают на изменение степени окисления платины при варьировании предшественника калия. Было показано, что применение хлоридного предшественника калия способствует повышению селективности по молекулярному азоту в области температур до 200°С. Данные ТПД-NH3 позволили проследить изменение кислотных свойств поверхности образцов и провести сопоставление с их каталитическими характеристиками в реакции окисления аммиака.

Composite catalysts consisting of Rh–CeOx structures supported on the surface of multi-walled carbon nanotubes (MWCNTs) are studied. For supported active components (Rh, Ce) the rhodium content is maintained constant on the MWCNT surface and the cerium concentration is varied in the range Rhat/Ceat = 0.085-0.34. The obtained samples are investigated by a combination of structural (X-ray diffraction, transmission electron microscopy (TEM)), spectral (X-ray photoelectron spectroscopy (XPS)), and kinetic (temperature-programmed reaction with CO (TPR-CO) and CO+O2 (TPR-CO+O2)) techniques. Highly dispersed CeO2 and RhOx particles are found to form in all samples studied. When the Rhat/Ceat ratio is changed, structures are formed that exhibit the catalytic activity in the CO oxidation reaction for different temperature ranges. At low Rhat/Ceat ratios (< 0.17) the CO conversion is observed at temperatures above 100 °C. When the Rhat/Ceat ratio increases, centers exhibiting the catalytic activity at temperatures below 0 °C are formed in Rh–CeO2/MWCNT catalysts. HR-TEM and TPR-CO studies of composite catalysts with a high Rhat/Ceat ratio reveal that structures based on dispersed oxidized rhodium particles modified by Ce3+ ions can be active species.

This review analyzes the literature data and the results of studies of the Pt/CeO2-based catalysts that are capable of providing the low-temperature CO oxidation (LTO CO). The review summarizes the catalytic characteristics and the main properties of Pt/CeO2-based catalysts necessary for the low-temperature oxidation at T<50 degrees C. Analysis of the literature data on the use of physical methods of investigation and their correlation with the activity of Pt/CeO2 catalysts allowed us to conclude that the main active forms of platinum are small metallic clusters, single atoms Pt2+-SA and oxide clusters PtOx interacting with ceria nanoparticles. It has been established that the most active forms are PtOx clusters, which provide a high reaction rate in the temperature range from -50 to +50 degrees C. Forms of ionic Pt2+ with different coordination with oxygen ensure the activity of catalysts starting at temperatures above 100 degrees C. Finally, small metallic clusters occupy an intermediate position, providing activity above 0 degrees C, but their instability and gradual transition to the oxidized state Pt2+/PtOx are noted. At the conclusion of the review, the results of mathematical modeling demonstrate the correct kinetics description of the low-temperature CO oxidation based on the Mars-van Krevelen and associative mechanisms.

The activity and selectivity of catalytic systems are influenced by many important factors, such as the composition of the surface, the size and structure of the active sites, as well as the oxidation state of the active components. In this study, we investigated the nature of the active components in Pt/TiO2 catalysts for selective ammonia oxidation upon their modification with copper. Analysis using X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) revealed that an increase in copper content led to a significant dispersion of platinum particles due to the formation of subnanoscale Pt(Cu)O x species. Application of temperature-programmed reduction (TPR-H2) and X-ray photoelectron spectroscopy (XPS) techniques provided valuable data on the redox properties of the catalysts. The introduction of copper resulted in a notable increase in the fraction of oxidized platinum. Once reduced, platinum in the composition of the Pt-Cu/TiO2 catalysts was easily reoxidized upon subsequent exposure to oxygen already at room temperature. The Pt-Cu/TiO2 catalysts comprised oxidized copper species, which demonstrated more labile redox behavior at lower temperatures compared to the Cu/TiO2 catalyst. The facilitated redox transitions of the active components contributed to the enhanced selectivity of the Pt-Cu/TiO2 samples toward N2 by affecting the reaction mechanism. The obtained results provide new insights into key aspects governing the effective oxidation of slip ammonia at low temperatures.

Методами РФЭС и ТПД проведено детальное исследование адсорбции атомарного кислорода на поверхности поликристаллического золота. Исследование показало, что начальные этапы воздействия атомарного кислорода приводили к формированию слоя хемосорбированного атомарного кислорода в диапазоне покрытия Q = 0,0 - 0,5 МС. Увеличение воздействия атомарного кислорода привело к образованию двумерного оксида золота. При максимальном насыщении кислородом расчетная толщина оксидного слоя составляла 3 Å и соответствовала стехиометрии, близкой к AuO2. ТПД-анализ показал, что термическая стабильность адсорбированного кислорода составила 510К для хемосорбированного слоя и 525К для двумерного оксида золота. Структура двумерного оксида золота определялась как один слой атомов золота и два слоя кислорода – адсорбированные на поверхности и внутри подповерхностного слоя. Реакционная способность адсорбированного кислорода была протестирована посредством взаимодействия СО и Н2 при комнатной температуре, и было обнаружено, что все формы кислорода активны. Установлено, что реакционная способность по отношению к СО выше на 2 порядка, чем к Н2, что указывает на роль форм кислорода в механизме PROX.

In this work, for the first time, the experimental catalytic kinetics of the CO oxidation reaction on plat-inum-ceria catalysts was simulated in a wide temperature range -50-450 degrees C. On the basis of the exper-iments performed, a substantiation of the catalytic action of two types of Pt-containing active centers in the form of isolated [Pt2.-O4] ions and PtOx clusters is presented. The relative content of these platinum forms on the ceria surface is controlled by the loading of platinum. Using the catalysts with a low content of platinum, where the active centers are isolated [Pt2.-O4] ions, a satisfactory simulation of CO conver-sion depending on temperature was carried out based on the concepts of the Mars-van Krevelen (MvK) mechanism. It was established that these centers provide the catalysts activity in the temperature range above 100 degrees C. To simulate the reaction kinetics in the temperature range below 100 degrees C, the Pt-O-Pt active centers based on PtOx cluster forms were considered. The PtOx cluster forms made it possible to consider both the MvK mechanism and temperature-dependent associative Low-T mechanism. The introduction into the kinetic scheme of stages simulating the implementation of both the Low-T and the MvK mech-anisms allowed us to perform complete quantitative modeling of the experimental data over the entire temperature range of the reaction from -50 degrees C to 450 degrees C. (c) 2022 Elsevier Ltd. All rights reserved.

CO molecules can be efficiently oxidized over Pt/CeO2 catalysts, but the stability and reactivity of differ-ent states of Pt in the catalysts are still unclear. Here we combine experimental and computational meth-ods to characterize Pt/CeO2 catalysts subjected to reductive and oxidative pre-treatments and exposed CO oxidation reaction conditions. Particles of metallic Pt, known to be catalytically active at elevated tem-perature, are shown to be precursors for the formation, under operando conditions, of more stable PtOx particles that enable CO oxidation below room temperature. These PtOx particles are similarly stable to - but more active than - atomically dispersed Pt2+ species. The results and approaches presented this study illustrate the complex response of catalytic materials to reaction conditions and pave the way for future efforts to improve Pt/CeO2 and similar catalysts using dedicated pre-treatment strategies.(c) 2023 The Author(s). Published by Elsevier Inc. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).

The local structure of the active sites is one of the key aspects of establishing the nature of the catalytic activity of the systems. In this work, a detailed structural investigation of the Rh-CeO2 catalysts prepared by the co-precipitation method was carried out. The application of a variety of physicochemical methods such as XRD, Raman spectroscopy, XPS, TEM, TPR-H2, and XAS revealed the presence of highly dispersed Rh3+ species in the catalysts: Rh3+ single ions and RhOx clusters. The substitution of Ce4+ ions by Rh3+ species, which provided a strong distortion of the CeO2 lattice, is shown. XAS data ensured the refinement of the Rh local structure. It was shown that single Rh3+ sites located next to each other can merge the formation of RhOx clusters with Rh local environment close to the one in Rh2O3 and CeRh2O5 oxides. The distortion of the CeO2 lattice around single and cluster rhodium species had a beneficial effect on the catalytic activity of the samples in low-temperature CO oxidation (LTO-CO). TEM, XAS, and in situ XRD data allowed establishing the structural transformations of the catalysts under Red-Ox treatments. The reduction treatment led to Rhn metallic cluster formation localized on defects of the reduced CeO2-δ. The reduced sample demonstrated efficient CO conversion at 0 °C. However, this system was not stable: its contact with air led to ceria reoxidation and partial reoxidation of Rh to highly dispersed Rh3+ species at room temperature, while heating in an oxidizing atmosphere resulted in the complete reoxidation of metallic rhodium species. The results of the work shed light on the structural aspects of the reversibility of the Rh-CeO2 catalysts based on the highly dispersed Rh3+ species under treatment in the reaction conditions.

The powders of Rh and CeO 2 are synthesized by pulsed laser ablation in liquid. The Rh–CeO 2 model catalysts are prepared by the calcination of these powders in a wide temperature range from 450 °C to 1000 °C. The formation of individual and mixed (rhodium- and cerium-containing) phases with increasing temperature of catalyst calcination is studied by powder XRD and Raman spectroscopy. The redox properties of prepared catalysts are tested in a temperature-programmed reaction of CO reduction; their catalytic properties are studied on the example of CO oxidation. It is shown that the catalysts remain stable during catalytic tests due to the formation of a nano-heterophase system consisting of rhodium oxide (Rh 2 O 3 ) and cerium oxide (CeO 2 ) nanoparticles. The discovered high stability is most likely explained by the formation of the Rh 3+ –CeO 2 species with the localization of Rh 3+ ions in subsurface CeO 2 layers due to the contacts between rhodium oxide and cerium oxide nanoparticles. Introducing Rh 3+ ions into Ce 4+ positions of the CeO 2 lattice distorts the cerium oxide structure and leads to the formation of active oxygen species interacting with CO at low temperatures. The catalysts are shown to preserve high activity in the reaction of low-temperature CO oxidation even after the calcination at 1000 °C.

A mixed oxide of silver and nickel AgNiO2 was obtained via co-precipitation in alkaline medium. This oxide demonstrates room temperature activity in the reaction of ethylene epoxidation with a high selectivity (up to 70%). Using the PDF method, it was found that the initial structure of AgNiO2 contains stacking faults and silver vacancies, which cause the nonstoichiometry of the oxide (Ag/Ni < 1). It has been established that on the initial surface of AgNiO2 oxide, silver state can be considered as an intermediate between Ag2O and Ag0 (i.e. Agδ+-like), while nickel is characterized by signs of a deeply oxidized state (Ni3+-like). The interaction of AgNiO2 with C2H4 at room temperature leads to the simultaneous removal of two oxygen species with Eb(O 1s) = 529.0 eV and 530.5 eV considered as nucleophilic and electrophilic oxygen states, respectively. Nucleophilic oxygen was attributed to the lattice oxygen (Ag-O-Ni), while the electrophilic species with epoxidation activity was associated with the weakly bound oxygen stabilized on the surface. According to the TPR-C2H4 data, a large number of weakly bound oxygen species were found on the pristine AgNiO2 surface. The removal of such species at room temperature didn't result in noticeable structural transformation of delafossite. As the temperature of ethylene oxidation over AgNiO2 increased, the appearance of Ag0 particles was first observed below 200 °C followed by the complete destruction of the delafossite structure at higher temperatures.