Hydrogen spillover in heterogeneous catalysis

Розанов, В. В.; Крылов, О. В.

doi:10.1070/rc1997v066n02abeh000308

Cited by 132 publications

(83 citation statements)

References 143 publications

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“…29 A negative shift of 0.3 eV for Pd/TiO 2 occurred after Pd was loaded, which should be ascribed to partial reduction of TiO 2 during the H 2 pretreatment. 51 Compared with the Pd/TiO 2 catalyst, a further negative shift of 0.4, 0.5 and 0.7 eV occurred after Na, K, and Cs doping, respectively, which is attributed to electron transfer from the alkali metals to Ti and O of TiO 2 50 or may be partially attributed to further TiO 2 reduction caused by the alkali metal addition 52,53 The O 1s XPS spectra of the catalysts are shown in Fig. 4c.…”

Section: Xps Analysismentioning

confidence: 99%

Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature

Zhang

et al. 2016

Catal. Sci. Technol.

108

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We previously observed that sodium (Na) addition had a dramatic promotion effect on Pd/TiO 2 catalysts for formaldehyde (HCHO) oxidation. In this study, a series of alkali metal (Li, Na, K, Cs) doped Pd/TiO 2 catalysts were prepared and tested for ambient temperature HCHO oxidation. The results showed that the doped alkali metals have a common promotion effect on the performance of the Pd/TiO 2 catalysts for HCHO oxidation under ambient temperature, which followed the order K > Cs > Na > Li. X-ray diffraction (XRD), Brunauer-Emmett-Teller (BET), CO chemisorption, Transmission Electric Microscopy (TEM), temperature-programmed reduction by H 2 (H 2 -TPR), X-ray photoelectron spectroscopy (XPS) and temperature-programmed desorption by O 2 (O 2 -TPD) methods were used to characterize the alkali metal doped catalysts to investigate the mechanism of the alkali metal promotion effect. The results showed that a negatively charged and well-dispersed Pd species was induced and stabilized by alkali metal addition, which facilitates the activation of chemisorbed oxygen, and then enhances the performance of alkali metal doped Pd/TiO 2 catalysts for room temperature HCHO destruction. The K-Pd/TiO 2 catalyst in particular possessed the highest Pd dispersion degree with active sites, attributing to the best activity in ambient temperature HCHO oxidation.

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Section: Xps Analysismentioning

confidence: 99%

Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature

Zhang

et al. 2016

Catal. Sci. Technol.

108

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“…This is associated with the start of the reverse hydrogen spillover (reverse migration of hydrogen from the support to the metal [6]) after pumping off excess gaseous tritium. This, in turn, results in interaction of activated tritium with a water cluster and in formation of a protonated water cluster, [ 3 H + ( 3 H 2 O) n ] (n is the number of water molecules in the cluster).…”

Section: ääääääääääääääääáääääääääääääääääääääääáäääääääääääääääääáäämentioning

confidence: 99%

“…On the other hand, in preparation of tritium water, the catalyst is saturated with activated tritium species (due to hydrogen spillover) [3], and degassing of the catalyst is acccompanied by so-called reverse hydrogen spillover [6]. This term denotes reverse migration of hydrogen from a support to a metal; in the process, a possibility arises for the interaction of tritium cation with molecules of tritium water and substrate adsorbed on the active centers of the catalyst.…”

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confidence: 98%

Optimization of Conditions for Tritium Labeling of Organic Compounds by Isotope Exchange with Tritium Water, Based on the Concepts of Reactions on the Catalyst Surface

2005

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To reveal factors affecting the tritium labeling by isotope exchange with tritium water and to elucidate the reaction mechanism, the concepts of processes involved in heterogeneous catalysis were considered. Conditions were optimized for tritium labeling of deltamethrin, pargiline, trichostatin, ciprofloxacin, and 1,3-O-dibenzylglycerol. Samples with the molar radioactivity of 9.3, 0.5, 1.8, 35.1, and 57.3 Ci mmol !1 , respectively, were prepared.The recently suggested new concept of solid-phase reactions, [capacitor] model [1], allows explanation of the features of tritium labeling of organic compounds. This concept can be briefly presented as follows. The interaction of molecular tritium with a catalyst metal yields activated tritium species ( 3 H*, 3 H + ), and the tritium s electrons are partially donated to the metal conductance band. Atomic tritium recombines to form molecular tritium, and tritium cations and electrons spill over the support (carbon, alumina, silica gel, calcium carbonate, barium sulfate, etc.). In the process, the support surface acquires the properties of a multilayer capacitor. Depending on the experimental conditions, the tritium cations interact with electrons with a certain probability (discharge of adjacent oppositely charged areas) to give atomic tritium, which rapidly recombines and passes into the gas phase; therefore, it does not noticeably react with the organic substrate applied onto the support. When the flow of 3 H + and electrons reaches the substrate, the isotope exchange (by the electrophilic substitution mechanism), hydrogenation, dehalogenation, etc., occur efficiently [2].If the substrate contains groups that can be readily deprotonated, it acquires the positive charge, which impedes its reaction with tritium cations and hence appreciably decreases the degree of labeling, especially in the molecular fragments in the vicinity of the charged fragment [2]. Specifically this factor is responsible for the high stability of the N3CHR3C 6 H 5 , O3CHR3C 6 H 5 bonds, 3NO 2 , =N3OR groups, etc., under the conditions of solid-phase reactions [3].Only at elevated temperatures the contribution of atomic tritium to the formation of the labeled product will become significant. An example of labeling a substrate with atomic tritium as active species is the preparation of labeled sulfobromophthalein at temperatures above 285oC [4].In preparation of labeled compounds in solution, the tritium labeling occurs on active centers of the catalyst rather than on the support surface [5]. In [5], we discussed the mechanisms of tritium labeling by liquid-phase isotope exchange, hydrogenation, and dehalogenation in a gaseous tritium atmosphere.The isotope exchange with tritium water is performed in a solvent, i.e., molecules of compounds can react with tritium water on active centers of a catalyst. On the other hand, in preparation of tritium water, the catalyst is saturated with activated tritium species (due to hydrogen spillover) [3], and degassing of the catalyst is acccompanied by so-called re...

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“…The enhanced mobility of activated hydrogen on inert supports has been discovered. 2 The flow of activated hydrogen species from one phase to another has been called hydrogen spillover. It is hydrogen (tritium) spillover that determines the possibility of solid-phase hydrogenolysis.…”

Section: Introductionmentioning

confidence: 99%

Solid‐phase reactions as approach to the synthesis of organic compounds labelled with tritium

Myasoedov

2007

Labelled Comp Radiopharmac

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The solid-phase method for hydrogenolysis, hydrogenation and isotope exchange reactions is described. Its potential for tritium labelling of organic compounds including lipids, nucleotides, amino acids, peptides and pharmaceuticals is demonstrated. The influence of the reaction conditions on the yield and specific radioactivity of the labelled compounds is considered. It is shown that results can be interpreted by the dependence of tritium spillover reactions on the nature of the initial compound and other factors.

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Hydrogen spillover in heterogeneous catalysis

Cited by 132 publications

References 143 publications

Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature

Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature

Optimization of Conditions for Tritium Labeling of Organic Compounds by Isotope Exchange with Tritium Water, Based on the Concepts of Reactions on the Catalyst Surface

Solid‐phase reactions as approach to the synthesis of organic compounds labelled with tritium

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Hydrogen spillover in heterogeneous catalysis

Cited by 132 publications

References 143 publications

Influence of alkali metals on Pd/TiO2catalysts for catalytic oxidation of formaldehyde at room temperature

Influence of alkali metals on Pd/TiO2catalysts for catalytic oxidation of formaldehyde at room temperature

Optimization of Conditions for Tritium Labeling of Organic Compounds by Isotope Exchange with Tritium Water, Based on the Concepts of Reactions on the Catalyst Surface

Solid‐phase reactions as approach to the synthesis of organic compounds labelled with tritium

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Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature

Influence of alkali metals on Pd/TiO₂catalysts for catalytic oxidation of formaldehyde at room temperature