Pt-CeO2-based composites in environmental catalysis: A review

The Pt–CeO2-based composites have brought about a vivid research interest due to their use in advanced combustion engines, proton-exchange membrane fuel cells, etc. Complementing features of Pt and ceria particles cause numerous applications of such composites in environmental catalysis science and technology. The present review summarizes recent advances in Pt–CeO2 chemistry and discusses the following key aspects: (1) catalyst preparation, including Pt and Ce-MOF-derived precursors, and treatment methods, (2) Pt-related factors: size, including single-atom formulations, and state, (3) CeO2-related factors: morphology, surface defects, and derived features, (4) modification of catalyst composition, including the formation of bimetallic particles, (5) nature and structure of active sites, (6) features of metal–support interaction. The range of covered environmental catalytic applications includes oxidation processes (CO oxidation, VOCs abatement, soot oxidation, combustion of vehicle exhausts, etc.), reduction of nitroaromatics, CO2 utilization (dry reforming of alkanes, CO2 reduction, etc.), and photocatalytic reactions

Effect of Cu modifier on the performance of CrOx/Al2O3 catalysts for isobutane dehydrogenation

The peculiarities of active surface formation and the effect of Cu modifier on the performance of CrOx/Al2O3 catalysts in a fixed-bed isobutane dehydrogenation into isobutylene are considered using a series of model Cu-modified alumina supports (0.7–6.5% wt Cu) and CrOx catalysts on the basis thereof. The samples are characterized using a complex of physical-chemical methods, including low-temperature N2 adsorption, STA, XRF, XRD, UV–vis DR, Raman spectroscopy and H2-TPR. The modification of the alumina-chromia catalysts by a proper amount of copper is shown to enhance the catalyst activity. The catalyst with 2.6% wt Cu shows high conversion and selectivity towards isobutylene. The role of Cu modifier is connected with stabilizing of the active component mostly as monomeric and dimeric Cr(VI) species that can be reduced into the most active mononuclear and dimeric Cr3+ sites

Bimetallic Ag-based catalysts for low-temperature SCR: Quo vadis?

The abatement of nitrogen oxides coming to the atmosphere from diesel engines of automotive vehicles and marine vessels, industrial plants, and other sources is of profound importance. Currently, catalysis-based solutions show growing potential in addressing this challenge. The main requirements that SCR catalysts should meet include enhanced low-temperature activity and selectivity combined with a broad operating window, high resistance to poisons and moisture. While a plethora of SCR catalysts has been proposed by now, recently, a growing number of publications have emphasized the unlocked potential of bimetallic catalyst formulations. Among them, Ag-based systems deserve special attention due to their high performance and relative cheapness. The present review is focused on the recent achievements recorded in the latest 5–10 years on bimetallic Agbased catalysts for low-temperature SCR. Systems, such as Ag-Pt, Ag-Au, Ag-Cu, Ag-Fe, Ag-Mn, are considered and compared with bi-and polymetallic transition metals. The role of catalysts preparation method, Ag loading, metal-support interaction and pre-treatment effects has been pointed out. The outlook of the future research challenges is provided

Influence of method of introduction of Cu- and Zn-based modifiers on the properties of chromia-alumina catalysts

Three methods of introduction of modifiers based on Cu and Zn compounds into the CrOx/Al2O3 catalysts for dehydrogenation of light paraffin hydrocarbons are considered: Introduction from sol, introduction using successive impregnation technique and introduction of modifiers by impregnation along with precursor of chromium oxide. The obtained samples are studied by a complex of physical-chemical methods (XRD, UV-Vis spectroscopy, temperature-programmed reduction with hydrogen (TPR-H2), X-ray fluorescent (XRF) spectrometry, low-temperature N2 sorption). The catalytic properties of the samples are studied in kinetic mode in isobutane dehydrogenation. Cu- and Zn-modifiers are shown to influence on the peculiarities of reduction of Cr6+ and, hence, specify the state of active surface of CrOx/Al2O3 catalysts formed in the reductive reaction medium. Not only do the states of modifiers influence on the initial activity of the catalyst, but also on its activity after oxidative regeneration. Introduction of modifiers by successive impregnation method results in formation of copper and zinc aluminates or defective spinels on the Al2O3 surface. When the active component is introduced, the modified surface of the support promotes formation and stabilization of Cr6+ sites that can undergo reversible reduction–oxidation and provide high activity and selectivity towards formation of isobutylene (>98%)

The structure of an electronic textbook of Kalmyk language: problems and prospects

Article describes the structure of an electronic textbook of Kalmyk language initialized first in the Kalmyk studies by the collective of authors aiming to preserve the Kalmyk language and develop the Kalmyk culture

Synergistic effect of Cu and Zn modifiers on the activity of CrOx/Al2O3 catalysts in isobutane dehydrogenation

In this work, a series of Cu- and/or Zn-modified alumina-supported CrOx catalysts have been synthesized by wetness impregnation method and characterized using the combined techniques, including Raman spectroscopy, UV–vis DR, XRD, XRF, H2-TPR and low-temperature N2 sorption, to reveal the effect of the modifiers on the catalyst performance in a fixed-bed isobutane dehydrogenation into isobutylene. The Zn-based modifier is shown to decrease the reducibility of the supported chromium species and reduce the stability of the redox ones, which results in the decreased catalyst activity in isobutane dehydrogenation. The Cu-based modifier on the contrary facilitates the formation of high amount of redox chromium species that leads to the activity growth. The modification by both Cu- and Zn-based modifiers provides an enhanced catalyst performance caused by the synergistic effect of the modifiers and chromium species. The incorporation of the modifiers into alumina support facilitates the formation of the surface defective spinel phases that prevent the incorporation of chromium into the alumina surface and establish the conditions to form the high amount of the active redox chromium species

Towards the understanding of promoting effects of Re, Cs and Cl promoters for silver catalysts of ethylene epoxidation: A computational study

Promoting effects of Cs, Re oxospecies, and Cl for silver catalysts of ethylene epoxidation are studied computationally using the DFT approach. The promoters are shown to enhance the extent of activation of initial substances, reaction intermediates, and products, while different combinations of promoters are favorable for different stages of the process. The synergistic effect of Cs, Re, and Cl is connected with the adjustment of the substrate location with respect to silver, thus, setting the favorable conditions for rapid transformation of ethylene into ethylene oxide. Re and Cl complement each other to balance and mitigate the effect of the Ag-bound Cs to alter the distribution of electronic density, tuning the electronic states of surface oxygen species by making it more electrophilic, and providing the substrate binding strength that ensures “optimal” substrate residence time and improves the catalyst performance in ethylene epoxidation

Ethylene glycol oxidation over Ag-containing catalysts: A theoretical study

A theoretical interpretation of the mechanism of ethylene glycol oxidation to glyoxal over Ag-containing catalysts is considered. A model system, reflecting the interaction of Ag cluster with process adsorbates and/or intermediates, is proposed. Both partial oxidation of ethylene glycol to glyoxal and CO2 formation routes are reconstructed, and the corresponding reaction profiles are represented. The roles played by the most important reaction intermediates participating in the process under consideration are discussed