Interaction of propylene with a V2O5/Al2O3 catalyst

Давыдов, А. А.; Budneva, A. A.

doi:10.1007/bf02063593

Cited by 19 publications

(19 citation statements)

References 2 publications

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“…), and it was proposed that methane interacted with ionic pairs M n+ O 2− of metal oxide surface. 81,82 Different positions of the bands observed for BEA, ZSM-5, and Y zeolites can be accounted for by different topology of the zeolites and thus by different structure of formed molecular complexes of methane and Zn 2+ -sites. Hence, same or similar complex is formed not only on Zn 2+ -modified zeolites (BEA, ZSM-5) but also on the H-BEA zeolite loaded with small zinc oxide clusters.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

“…Such observation can be interpreted in terms of stronger polarization of methane C−H bond when methane interacts with isolated Zn 2+ cationic sites compared to zinc oxide clusters. Indeed, it was found for different metal oxides 82 that the strength of C−H bond polarization, which depends on the strength of surface Lewis M n+ O 2− acid−base sites, affected the intensity of the corresponding IR bands. The stronger the polarization of C−H bonds, the higher the intensity of the IR band.…”

Section: ■ Results and Discussionmentioning

confidence: 99%

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Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

et al. 2017

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Understanding methane activation pathways on Zn-modified high-silica zeolites (ZSM-5, BEA) is of particular importance because of the possibility of methane involvement in coaromatization with higher alkanes on this type of zeolites. Herein, two samples of Zn-modified zeolite BEA containing exclusively either small zinc oxide clusters or isolated Zn 2+ cations have been synthesized and thoroughly characterized by a range of spectroscopic methods ( 1 H MAS NMR, DRIFTS, XPS, EXAFS, HRTEM) to show that only one of the Zn-species, either Zn 2+ cations or ZnO small clusters, exists in the void of zeolite pores. The ability of zinc sites of different nature to promote the activation of methane C−H bond with the zeolite Brønsted acid sites (BAS) has been examined in the reactions of methane H/D hydrogen exchange with BAS and the alkylation of benzene with methane. It has been found that both ZnO and Zn 2+ species promote the reaction of H/D exchange of methane with BAS. The rate of H/D exchange is higher by 2 and 3 orders of magnitude for the zeolite loaded with ZnO or Zn 2+ species, respectively, compared to pure acid-form zeolite H-BEA. So, the promoting effect of Zn 2+ cations is more profound than that of ZnO species for H/D exchange reaction. This implies that the synergistic effect of Zn-sites and BAS for C−H bond activation in methane is significantly higher for Zn 2+ cations compared to small ZnO clusters. It has been revealed, however, that only Zn 2+ cations promote the alkylation of benzene with methane, whereas ZnO species do not. The isolated Zn 2+ cations provide the formation of zinc-methyl species, which are further transformed to zinc-methoxy species. The latter is the key intermediate for the performance of the alkylation reaction. Hence, while both zinc oxide clusters and Zn 2+ cationic species are able to provide a synergistic effect for the activation of C−H bonds of methane displayed by the dramatic acceleration of H/D exchange reaction, only the Zn 2+ cationic species perform methane activation toward the alkylation of benzene with methane. This implies that only the Zn 2+ cations in Zn-modified zeolite can activate methane for the reaction of methane coaromatization with higher alkanes.

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Section: ■ Results and Discussionmentioning

confidence: 99%

Section: ■ Results and Discussionmentioning

confidence: 99%

Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

et al. 2017

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“…In comparison to the carbonate groups already present in the different oxide samples, higher wavenumbers for the υ 4 vibrations and an augmented splitting between υ 4 and υ 1 is observed (compare Table 5). As the ∆υ value for the peak splitting correlates inversely with the strength of the Lewis basic sites, 20,21 the observation of a relatively high splitting suggests only medium Lewis basicity for the O 2anions involved. Because of the experimental conditions chosen, the carbonate groups formed should be located at the surface of the sample.…”

Section: Lanthanum Carbonatementioning

confidence: 99%

Influence of Pretreatment on Lanthanum Nitrate, Carbonate, and Oxide Powders

1996

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Diffuse reflectance FTIR spectra, X-ray diffraction patterns, and BET surface areas of La(NO3)3, La2(CO3)3, and La2O3 have been obtained after various stages of thermal decomposition in the presence and absence of O2. In situ DRIFTS provided information about the surface chemistry taking place during the adsorption of NO and CO2 on the La oxide surfaces obtained. Decomposition of La(NO3)3 under flowing Ar at 773 K resulted in a mixture of La2O3 and a nitrate phase with ionic (noncoordinated) nitrate groups, i.e., those not directly coordinated to a La cation. However, when the decomposition was performed under flowing O2, LaONO3 was the principal compound. NO adsorption on the oxide surface after decomposition enhanced the peak intensity of residual nitrate surface speciesno new peaks appeared. La2(CO3)3 was more stable and was only partly transformed into La2O2CO3 during thermal treatment at 773 K. The commercial La2O3 samples contained mainly hydroxide if exposed to, or stored under, ambient air. The La(OH)3 decomposes when heated to 773 K, but rehydroxylation occurs rapidly if the samples are exposed to ambient air. Both the temperature and the gaseous medium of the calcination pretreatment determine the final state of the material. High temperatures (>1173 K) and a CO2-free medium must be used to guarantee transformation into principally La2O3, which still contains variable amounts of surface or subsurface carbonate groups. However, these high calcination temperatures result in considerable loss of surface area. Bidentate and unidentate carbonates were formed on La2O3 by adsorbing CO2 at either 298 or 773 K, thus revealing the surface sites have medium Lewis basicity. NO adsorption at 298 and 773 K leads to an exchange reaction with carbonate ions to disproportionate NO and form nitrate and nitrite groups, N2 and CO2. These results provide comprehensive references for the preparation and characterization of catalytic La2O3 surfaces.

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“…[1][2][3][4][5] The base strength of alkali-metal ion-exchanged zeolites increases with increasing electropositivity of the exchange cation, and occlusion of alkali-metal oxide clusters in zeolite cages via decomposition of impregnated alkali-metal salts results in a further increase in the basicity of these materials. 1,3,[6][7][8][9] The base sites in alkali-metal-modified zeolites are commonly characterized by IR spectroscopy and/or temperature-programmed desorption of adsorbed probe molecules such as carbon dioxide, 3,[10][11][12][13] pyrrole, [14][15][16] and chloroform. [17][18][19] The nature and strength of an active site are important to understand base catalysis on a molecular level.…”

Section: Introductionmentioning

confidence: 99%

“…Zeolites that have been modified by ion exchange of alkali-metal cations or by decomposition of an occluded alkali-metal salt have emerged as interesting solid bases. They are known to catalyze many reactions, including double-bond isomerization of olefins, side-chain alkylation of aromatics, dehydrogenation of alcohols, and Knoevenagel condensation of aldehydes. − The base strength of alkali-metal ion-exchanged zeolites increases with increasing electropositivity of the exchange cation, and occlusion of alkali-metal oxide clusters in zeolite cages via decomposition of impregnated alkali-metal salts results in a further increase in the basicity of these materials. ,,− The base sites in alkali-metal-modified zeolites are commonly characterized by IR spectroscopy and/or temperature-programmed desorption of adsorbed probe molecules such as carbon dioxide, ,− pyrrole, − and chloroform. − …”

Section: Introductionmentioning

confidence: 99%

UV−Vis Spectroscopy of Iodine Adsorbed on Alkali-Metal-Modified Zeolite Catalysts for Addition of Carbon Dioxide to Ethylene Oxide

et al. 1999

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The basicity of alkali-metal-exchanged (Na, K, Cs) zeolites X and Y was probed by UV−vis diffuse reflectance spectroscopy of adsorbed iodine. The observed blue shift in the visible absorption spectrum of adsorbed iodine, compared to gaseous iodine, correlated well with the negative charge on the framework oxygen atoms calculated from the Sanderson electronegativity equalization principle. The blue shifts associated with iodine adsorbed on classical catalytic supports like silica, alumina, and magnesia suggest that the iodine adsorption technique for probing basicity is applicable to a wide variety of solids. Iodine was also adsorbed on X and Y zeolites containing occluded cesium oxide formed by decomposition of impregnated cesium acetate. However, the iodine appeared to irreversibly react on these strongly basic samples, possibly forming an adsorbed triiodide ion. As a complement to the adsorption studies, the activity of alkali-metal-containing zeolites for the base-catalyzed formation of ethylene carbonate from ethylene oxide and carbon dioxide was investigated. Among the ion-exchanged zeolites, the cesium form of zeolite X exhibited the highest activity for ethylene carbonate formation. The catalytic activity of a zeolite containing occluded cesium was even higher than that of a cesium-exchanged zeolite. The presence of water adsorbed in zeolite pores promoted the rate of ethylene carbonate formation for both cesium-exchanged and cesium-impregnated zeolite X.

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Interaction of propylene with a V2O5/Al2O3 catalyst

Cited by 19 publications

References 2 publications

Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Influence of Pretreatment on Lanthanum Nitrate, Carbonate, and Oxide Powders

UV−Vis Spectroscopy of Iodine Adsorbed on Alkali-Metal-Modified Zeolite Catalysts for Addition of Carbon Dioxide to Ethylene Oxide

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Interaction of propylene with a V2O5/Al2O3 catalyst

Cited by 19 publications

References 2 publications

Different Efficiency of Zn2+ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Different Efficiency of Zn2+ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Influence of Pretreatment on Lanthanum Nitrate, Carbonate, and Oxide Powders

UV−Vis Spectroscopy of Iodine Adsorbed on Alkali-Metal-Modified Zeolite Catalysts for Addition of Carbon Dioxide to Ethylene Oxide

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Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite

Different Efficiency of Zn²⁺ and ZnO Species for Methane Activation on Zn-Modified Zeolite